Table of contents for issue 2, volume 990, The Astrophysical Journal

Fast blue optical transients (FBOTs) are luminous, rapidly evolving events with blue spectra, possibly powered by newborn magnetars and linked to fast radio bursts (FRBs). Given this potential connection, we conducted deep radio observations of two nearby FBOTs (AT2018cow and CSS161010) using the Five-hundred-meter Aperture Spherical radio Telescope, but detected no FRB-like signals. Our observations establish the most stringent upper limits on millisecond radio transients from FBOTs, reaching ∼10 mJy flux density. Assuming a log-normal luminosity function analogous to the repeating FRB 121102, we constrain the burst rate from potential magnetars in FBOTs to < 0.01 hr⁻¹. The short ejecta escape timescale (∼2.6 yr) compared to our observation epochs (4−6 yr post-explosion) suggests that nondetection may not be attributed to FBOT’s ejecta absorption. These findings impose useful constraints on the FRB activity emanating from newborn magnetars within FBOTs. They indicate that if there is a burst phase, it is either characterized by weaker bursts, occurs less frequently compared to those in known repeating FRB sources, or takes place beyond the time frame of our current observations. To gain deeper insights into the birth-related activity of magnetars, it is of importance to conduct timely and sustained FRB searches in FBOTs that emerge in the future.

Dust-obscured galaxies (DOGs) with extremely red optical-to-infrared colors are often associated with intense starburst and active galactic nucleus (AGN) activity. Studying DOGs can provide insights into the processes that drive the growth of galaxies and their central supermassive black holes. However, the general DOG population is heterogeneous, spanning a wide range of evolutionary stages, and has X-ray obscuring column densities (N_H) covering low to high levels. In this work, we focus on seven high Eddington ratio DOGs () to examine their X-ray obscuration properties using new and archival X-ray observations. We confirm that these systems are generally heavily obscured, with six out of seven having N_H ≳ 10²³ cm⁻² and three out of seven having N_H ≳ 10²⁴ cm⁻². Based on the observed similarity with the rare Hot DOG population, we argue that both high-λ_Edd DOGs and Hot DOGs likely trace the postmerger phase, during which AGNs are enshrouded by large columns of dust-rich material.

We developed a one-dimensional magnetohydrodynamic (MHD) simulation code to investigate the long-term evolution of protoplanetary disks with low computational cost. In this simulation code, the physical processes necessary for protostellar formation and protoplanetary disk evolution, such as magnetic braking, nonideal MHD effects, and angular momentum transport due to viscosity, are implemented. Using this simulation code, we performed the simulations of the long-term evolution of protoplanetary disks starting from the molecular cloud. Our simulation results suggest that the disk size and mass are a few tens of astronomical units and ∼0.01 M_⊙ at 10⁵ yr after protostellar formation. These values were relatively consistent with observations. The disk evolves through magnetic braking, and its radial profiles are consistent with the analytical solutions of previous studies. Our simulation code will be an important tool for studying the long-term evolution of protoplanetary disks.

We investigate the formation history of intrahalo light (IHL) using the high-resolution (∼1 kpc), large-scale (∼1 Gpc) cosmological hydrodynamical simulation Horizon Run 5 (HR5). IHL particles are identified by carefully considering both their binding energies and positions with respect to the tidal radii of individual galaxies. By analyzing more than 1200 galaxy groups and clusters with ≳10¹³M_⊙ and tracing their individual IHL particles back in time, we classify the origin of each IHL particle at each epoch, based on the status of the originating galaxy, into one of three categories: brightest halo galaxy (BHG) formation/merger, satellite galaxy stripping, and preprocessing. Our study reveals that IHL production through BHG formation/merger is the predominant production channel, contributing over 60% of the total IHL mass across all redshifts. The second most significant IHL production channel is preprocessing, providing more than 20% in the final HR5 snapshot. Stripping is negligible at z > 4 but becomes gradually more important as the halos mature at z < 4. Finally, we verify that the IHL production through the disruption of dwarf galaxies and in situ formation is negligible, contributing less than ∼3% and ∼0.5% to the total IHL production, respectively.

Much of the dynamics of the ambient solar wind (SW) manifests at mesoscales—scales larger than kinetic but smaller than global structures. Mesoscale structures often form at the Sun, survive to 1 au, and are geoeffective. Identifying their origins, release, and acceleration mechanisms is critical to advancing heliophysics. We investigate a 6 day interval (2022 March 4 00:00:00 UT–2022 March 9 23:59:59 UT) in which Solar Orbiter (SO) was radially aligned with Earth. We characterize mesoscale structures observed in SO Heavy Ion Sensor (HIS) Fe/O and O⁷⁺/O⁶⁺ in situ measurements, and confirm their survival to L1. A subset of these structures are periodic, suggesting that they formed at the Sun. We use the ADAPT-WSA model to connect in situ measurements to their remotely observed sources at the Sun. We characterize the SW sources using model-determined proxies for SW formation (e.g., the S-web). We compare Fe/O observed at SO/HIS, with S/O abundances derived by the Spectral Imaging of the Coronal Environment (SO/SPICE), at the WSA-determined SW sources. We find (1) SO and ACE/Wind observe similar many-hour structures, linking mesoscale structures from their source to two well-separated locations in situ for the first time. (2) Observed periodicities are consistent with those observed in prior studies of mesoscale structures throughout the inner heliosphere. (3) SW originating from only one of the four SPICE rasters can be interpreted as plasma originating from open fields. The SW from the other three require a different interpretation, and we suggest interchange reconnection as the most natural solution.

The circumgalactic medium (CGM) is a reservoir of metals and star-forming fuel. Most baryons in the Universe are in the CGM or the intergalactic medium (IGM). The baryon cycle—how mass and metals reach the CGM from the inner regions of the galaxy and how gas from the CGM replenishes star-forming activity in the inner regions—is an essential question in galaxy evolution. In this paper, we study the flow of mass and metals in a stacked sample of 2770 isolated halos from the IllustrisTNG100 cosmological hydrodynamic simulation. The mean gas flow as a function of radius and angle is similar across a large galactic mass range when accounting for different feedback modes. Although both star formation and black holes cause powerful outflows, the flows from star formation are more angularly restricted. Black hole feedback dominates mass flow throughout the halo, while star formation feedback mainly affects the inner region. When scaling by virial radius (R_v), large dynamical changes occur at 0.2R_v for most halos, suggesting a characteristic size for the inner galaxy. Despite kinetic-mode feedback from black holes being the primary quenching mechanism in IllustrisTNG, a small population of high-mass kinetic-mode disks are able to form stars.

The past few years have seen the emergence of a wide array of novel techniques for analyzing high-precision data from upcoming galaxy surveys, which aim to extend the statistical analysis of galaxy clustering data beyond the linear regime and the canonical two-point (2pt) statistics. We test and benchmark some of these new techniques in a community data challenge named “Beyond-2pt,” initiated during the Aspen 2022 Summer Program “Large-Scale Structure Cosmology beyond 2-Point Statistics,” whose first round of results we present here. The challenge data set consists of high-precision mock galaxy catalogs for clustering in real space, in redshift space, and on a light cone. Participants in the challenge have developed end-to-end pipelines to analyze mock catalogs and extract unknown (“masked”) cosmological parameters of the underlying ΛCDM models with their methods. The methods represented are density-split clustering, nearest neighbor statistics, BACCO power spectrum emulator, void statistics, LEFTfield field-level inference using effective field theory (EFT), and joint power spectrum and bispectrum analyses using both EFT and simulation-based inference. In this work, we review the results of the challenge, focusing on problems solved, lessons learned, and future research needed to perfect the emerging beyond-2pt approaches. The unbiased parameter recovery demonstrated in this challenge by multiple statistics and the associated modeling and inference frameworks supports the credibility of cosmology constraints from these methods. The challenge data set is publicly available, and we welcome future submissions from methods that are not yet represented.

Type III radio bursts are signatures of the fluxes of near-relativistic electrons ejected during solar flares. These bursts are frequently observed by spacecraft such as the Parker Solar Probe. It has been traditionally believed that these electron beams generate Langmuir waves through the two-stream instability, which are then converted into electromagnetic waves. In this study, we revise that model, by examining how the electron distribution becomes truncated due to the “time-of-flight” effect, as the beam travels through a randomly inhomogeneous and gently varying solar wind plasma. Rather than the two-stream instability, this truncation destabilizes the distribution and leads to the generation of Langmuir waves via a linear instability; we confine our analysis to this linear regime and do not take into account the backreaction of the generated Langmuir waves on the electron distribution, which is nonlinear. The instability grows until slower electrons arrive and dampen the waves. Our qualitative analysis shows that the resulting wave intensity growth and decay closely match the intensity–time profile of observed type III radio bursts at the fundamental frequency, supporting this modified theory.

A major open issue concerning the active Sun is the effectiveness with which magnetic reconnection accelerates electrons in flares. A paper published by Nature in 2022 used microwave observations to conclude that the Sun is an almost ideal accelerator, energizing nearly all electrons within a coronal volume to nonthermal energies. Shortly thereafter, a paper published in Astrophysical Journal Letters used hard X-ray measurements of the same event to reach the contradictory conclusion that less than 1% of the available electrons were accelerated. Here we address this controversy by using spatially resolved observations of hard X-ray emission and a spectral inversion method to determine the evolution of the electron spectrum throughout a set of flares. We use the spatial variation of the electron spectrum to deduce the density of the medium where electrons propagate and, from this and the total intensity of the flare, the ratio of accelerated to ambient electron densities. Results show that this ratio never exceeds 1% or so in all the events analyzed.

Luminous infrared galaxies (LIRGs) and ultraluminous infrared galaxies (ULIRGs) in the local Universe are highly centrally concentrated in the mid-infrared (MIR) and substantially more likely than non-(U)LIRGs to be involved in mergers. At higher redshifts, images of radio emission, cold dust, and molecular gas have suggested that (U)LIRGs at cosmic noon and even earlier may be relatively less concentrated than their z ∼ 0 counterparts. Prior to the launch of the James Webb Space Telescope (JWST), quantifying the extent of obscured star formation in (U)LIRGs at z ∼ 1 was not possible due to the low spatial resolution of previous instruments in the MIR. With JWST’s Mid-Infrared Instrument (MIRI), it is now possible. We use MIRI imaging to identify a sample of 24 LIRGs at 0.5 ≤ z ≤ 1.22 in the Systematic Mid-Infrared Legacy Extragalactic Survey and find that they are generally less centrally concentrated than their z ∼ 0 counterparts. Compared to high-mass star-forming galaxies that are not LIRGs, we find little evidence that LIRGs are more likely to be morphologically disturbed at rest-frame UV, optical, and near-infrared wavelengths at z ∼ 1. This also differs from the local counterparts where strong disturbances and major mergers are closely associated with LIRGs. These results support suggestions that smaller disturbances and perhaps even internal processes can trigger the collapse of gas clouds outside of galactic cores and cause very high levels of extended star formation at z ≳ 1.

Understanding stars and their evolution is a key goal of astronomical research and has long been a focus of human interest. In recent years, theorists have paid much attention to the final interior processes within massive stars, as they can be essential for revealing neutrino-driven supernova mechanisms and other potential transients of massive star collapse. However, it is challenging to observe directly the last hours of a massive star before explosion, since it is the supernova event that triggers the start of intense observational study. Here, we report evidence for a final phase of stellar activity known as a “shell merger,” an intense shell burning in which the O-burning shell swallows its outer C-/Ne-burning shell, deep within the progenitor’s interior moments before the supernova explosion. In the violent convective layer created by the shell merger, Ne, which is abundant in the stellar O-rich layer, is burned as it is pulled inward, and Si, which is synthesized inside, is transported outward. The remnant still preserves some traces of such Ne-rich downflows and Si-rich upflows in the O-rich layer, suggesting that inhomogeneous shell-merger mixing began just hours (≲10⁴ s) before its gravitational collapse. Our results provide the first observational evidence that the final stellar burning process rapidly alters the internal structure, leaving a pre-supernova asymmetry. This breaking of spherical symmetry facilitates the explosion of massive stars and influences various supernova and remnant characteristics, including explosion asymmetries and the neutron star’s kick and spin.

A star destroyed by the tidal field of a supermassive black hole (SMBH) in a tidal disruption event (TDE) gives rise to a luminous flare. TDEs are being detected at an ever-increasing rate, motivating the need for accurate models of their lightcurves. The “maximum gravity” (MG) model posits that a star is completely destroyed when the tidal field of the SMBH exceeds the maximum self-gravitational field within the star, , and predicts the peak fallback rate and the time to peak t_peak. Here we perform hydrodynamical simulations of the complete disruption of 24 stars with masses ranging from 0.2 to 5.0 M_⊙, at different stages of their main sequence evolution, to test the predictions of this model. We find excellent agreement between the MG model predictions and our simulations for stars near the zero-age main sequence, while the predictions are less accurate (but still within ∼35%–50% of the simulation results) for highly evolved stars. We also generalize the MG model to incorporate the Paczyński–Wiita potential to assess the impact of strong-gravity effects, which are especially important for deep encounters that are required to completely destroy evolved and centrally concentrated stars, and find good agreement with recent works that include relativistic gravity. Our results demonstrate that this model provides accurate constraints on the peak timescale of TDE lightcurves and their correlation with black hole mass.

In astrophysical simulations, nuclear reacting flows pose computational challenges due to the stiffness of reaction networks. We introduce neural network-based surrogate models using the DeePODE framework to enhance simulation efficiency while maintaining accuracy and robustness. Our method replaces conventional stiff ordinary differential equation (ODE) solvers with deep learning models trained through evolutionary Monte Carlo sampling from zero-dimensional simulation data, ensuring generalization across varied thermonuclear and hydrodynamic conditions. Tested on 3-species and 13-species reaction networks, the models achieve ≲1% accuracy relative to semi-implicit numerical solutions and deliver a ∼2.6× speedup on CPUs. A temperature-thresholded deployment strategy ensures stability in extreme conditions, sustaining neural network utilization above 75% in multidimensional simulations. These data-driven surrogates effectively mitigate stiffness constraints, offering a scalable approach for high-fidelity modeling of astrophysical nuclear reacting flows.

High-resolution spectroscopy (HRS) of exoplanet atmospheres has successfully detected many chemical species and is quickly moving toward detailed characterization of the chemical abundances and dynamics. HRS is highly sensitive to the line shape and position; thus, it can detect three-dimensional (3D) effects such as winds, rotation, and spatial variation of atmospheric conditions. At the same time, retrieval frameworks are increasingly deployed to constrain chemical abundances, pressure–temperature (P–T) structures, orbital parameters, and rotational broadening. To explore the multidimensional parameter space, we need computationally fast models, which are consequently mostly one-dimensional (1D). However, this approach risks introducing interpretation bias since the planet’s true nature is 3D. We investigate the robustness of this methodology at high spectral resolution by running 1D retrievals on simulated observations in emission within an observational framework using 3D global circulation models of the quintessential HJ WASP-76 b. We find that the retrieval broadly recovers conditions present in the atmosphere, but that the retrieved P–T and chemical profiles are not a homogeneous average of all spatial and phase-dependent information. Instead, they are most sensitive to spatial regions with large thermal gradients, which do not necessarily coincide with the strongest emitting regions. Our results further suggest that the choice of parameterization for the P–T and chemical profiles, as well as Doppler offsets among opacity sources, impact the retrieval results. These factors should be carefully considered in future retrieval analyses.

We report new spectroscopic and interferometric observations of the Pleiades binary star Atlas, which played an important role nearly 3 decades ago in settling the debate over the distance to the cluster from ground-based and space-based determinations. We use the new measurements, together with other published and archival astrometric observations, to improve the determination of the 291 day orbit and the distance to Atlas (136.2 ± 1.4 pc). We also derive the main properties of the components, including their absolute masses (5.04 ± 0.17 M_⊙ and 3.64 ± 0.12 M_⊙), sizes, effective temperatures, projected rotational velocities, and chemical compositions. We find that the more evolved primary star is rotationally distorted, and we are able to estimate its oblateness and the approximate orientation of its spin axis from the interferometric observations. The spin axis may well be aligned with the orbital axis. Models of stellar evolution from the Modules for Experiments in Stellar Astrophysics (or MESA) that account for rotation provide a good match to all of the primary’s global properties, and point to an initial angular rotation rate on the zero-age main sequence of about 55% of the breakup velocity. The current location of the star in the Hertzsprung–Russell diagram is near the very end of the hydrogen-burning main sequence, at an age of about 105 Myr, according to these models. Our spectroscopic analysis of the more slowly rotating secondary indicates that it is a helium-weak star, with other chemical anomalies.

We report the first comprehensive census of the satellite dwarf galaxies around NGC 55 (2.1 Mpc) as a part of the DECam Local Volume Exploration DEEP (DELVE-DEEP) survey. NGC 55 is one of four isolated, Magellanic analogs in the Local Volume around which DELVE-DEEP aims to identify faint dwarfs and other substructures. We employ two complementary detection methods: one targets fully resolved dwarf galaxies by identifying them as stellar overdensities, while the other focuses on semiresolved dwarf galaxies, detecting them through shredded unresolved light components. As shown through extensive tests with injected galaxies, our search is sensitive to candidates down to M_V ≲ −6.6 and surface brightness μ ≲ 28.5 mag arcsec², and ∼80% complete down to M_V ≲ −7.8. We do not report any new confirmed satellites beyond two previously known systems, ESO 294–010 and NGC 55-dw1. We construct the satellite luminosity function of NGC 55 and find it to be consistent with the predictions from cosmological simulations. As one of the first complete luminosity functions for a Magellanic analog, our results provide a glimpse of the constraints on low-mass-host satellite populations that will be further explored by upcoming surveys, such as the Vera C. Rubin Observatory’s Legacy Survey of Space and Time.

A tracer sample in a gravitational potential, starting from a generic initial condition, phase-mixes toward a stationary state. This evolution is accompanied by an entropy increase, and the final state is characterized by a distribution function (DF) that depends only on integrals of motion (Jeans’ theorem). We present a method to constrain a gravitational potential assuming a stationary (phase mixed) sample by minimizing the entropy that the sample would have if it were allowed to phase-mix in trial potentials. This method avoids modeling the DF and is applicable to any sets of integrals. We provide expressions for the entropy of DFs depending on energy, f(E), energy and angular momentum, f(E, L), or three actions, f(J), and investigate the bias and statistical uncertainties in their estimates. We show that the method correctly recovers the parameters for spherical and axisymmetric potentials. We also present a methodology to characterize the posterior probability distribution of the parameters with an approximate Bayesian computation, indicating a pathway for application to observational data. Using 10⁴ tracers with 10%(20%) uncertainties in the 6D coordinates, we recover the flattening parameter q of an axisymmetric potential with σ_q/q ∼ 5%(10%). The python module for the entropy estimators, tropygal, is made publicly available.

Gamma-ray bursts are expected to be generated by structured jets, whose profiles significantly impact their afterglow emission. Previously, we developed a numerical code jetsimpy, to model the afterglow of jets with arbitrary angular profiles. In this study, we extend the code to incorporate a stratified radial profile, enabling it to model jets with arbitrary axisymmetric two-dimensional structures. The radial profile leads to the formation of a reverse shock. We modeled the shock system using an energy conservation prescription, which differs from the pressure balance approach. This leads to remarkably different predictions for reverse shock emission. In particular, we find that the reverse shock emission in the thin shell case is significantly overestimated in analytic models. We also explore the off-axis reverse shock emission from structured jets, where the cores belong to thick shell cases and the wings belong to thin shell cases. We have confirmed the prediction that off-axis observers may see a thin-to-thick transition, but we find that the light curve morphology is hard to distinguish from pure thin or thick shell cases. A radial profile also introduces hydrodynamic energy injection. As such, our code can naturally apply to refreshed shock cases, where the modeling of kilonova afterglows is demonstrated as an example. To validate our method, we fit the optical flash of GRB 990123, showing good agreement with the data. The upgraded jetsimpy provides unprecedented flexibility in modeling the afterglow emission of jets with various profiles, including those derived from general relativistic magnetohydrodynamic simulations.

We present observations of the nearby extremely metal-poor galaxy I Zw 18 using the Keck Cosmic Web Imager (KCWI) and the JWST Mid-InfraRed Instrument (MIRI) Integral Field Spectrographs. From optical and mid-IR oxygen emission lines, we measured direct-method abundances for three ionic states of oxygen, including O³⁺/H⁺. In contrast to previous studies of I Zw 18 the high spatial resolution afforded by KCWI and MIRI/MRS revealed chemical inhomogeneities on 60 pc scales in the form of metal-poor pockets and metal-enriched gas. These are located outside I Zw 18’s star-forming complexes having possibly been dispersed beyond these regions via stellar feedback effects. We found that metallicities derived using a single low-ionization density tracer, and T_e([O ii]) derived from a temperature relationship commonly used in high-z galaxy studies, exhibited the largest scatter and underestimated the metallicity compared to those derived using multi-ion densities and estimated T_e([N ii]). Finally, we compared O³⁺/H⁺ abundances from a theoretical ionization correction factor (ICF) against observed values and found that the oxygen ICF underestimates the O³⁺/H⁺ abundance by a factor of 2, indicating that either additional ionizing sources are needed or standard stellar population models are unable to produce the requisite ionizing flux.

We present a new framework to incorporate feedback from massive interacting binaries in simulations of star cluster formation. Our new feedback model adds binary stellar evolution to the cluster formation code Torch, and couples it in Amuse to the preexisting modules for collisional stellar dynamics, magnetohydrodynamics, and mechanical and radiative feedback. Our model accounts for the effects of mass transfer on the stars’ mass-loss rates, their radiation spectra, and the timing of core-collapse supernovae. It also injects mass lost through nonconservative mass transfer and CE ejection into the interstellar medium (ISM). We demonstrate the use of our feedback model through simulations of isolated binaries in a gaseous medium, and of embedded clusters of massive binaries. Feedback from interacting binaries efficiently couples with the surrounding ISM. It increases the size of H ii regions, increases the kinetic and thermal energy of the gas, and increases the pressure within H ii regions compared to models that use single star stellar evolution. Those differences arise from the ionizing radiation, which increases by 3 orders of magnitude, resulting in H ii regions that expand due to thermal pressure rather than radiation pressure. The effects of stellar dynamics and the gravitational potential of the background gas cause the evolution of individual binaries to deviate from the predictions made by secular evolution, impacting the subsequent feedback from the binary. We conclude that massive interacting binaries are an important source of feedback in cluster-forming regions, and must be considered when studying the emerging timescales of young star clusters.

We present initial results from a planned 10 yr survey of Ca II H and K emission, using observations made with the Astrophysical Research Consortium 3.5 m Telescope at Apache Point Observatory. The primary goal of the survey is to investigate activity cycles in low-mass stars. The sample includes stars chosen from the legacy Mount Wilson Observatory (MWO) survey carried out by Olin Wilson more than 50 yr ago, together with newly identified planet-hosting stars and a select sample of early to mid M dwarfs. This paper presents the first 4 yr of data, comprising 1040 observations of 271 stars, with a specific focus on K and M stars. We identify a subsample of 153 stars for continuing observations over the full 10 yr survey. Early results indicate that our data are consistent with the MWO cycle periods over a time span of more than 50 yr; that there is a bifurcation in activity in the late K range with separate populations of low- and high-activity stars at lower masses; and that M dwarf planet hosts tend to be mainly found in the population of low-activity stars, even in the unbiased (by activity) TESS sample, potentially indicating a link between activity and planet formation. We have also found indications of possible cyclic variability in some of the lower-mass stars in the sample. Our ultimate goal is to link the activity cycle and rotation periods in a robust sample of stars spanning the FGKM spectral types and to investigate the implications for the underlying magnetic dynamo.

Understanding the impact of dust on the spectral energy distributions (SEDs) of galaxies is crucial for inferring their physical properties and for studying the nature and evolution of interstellar dust. In this study, we analyze dust attenuation curves of ∼6400 galaxies (M_⋆ ∼ 10⁹–10^11.5M_⊙) at z = 0.07 from the IllustrisTNG50 & TNG100 simulations. Using radiative transfer post-processing, we generate synthetic attenuation curves and fit them with a versatile parametric model that encompasses both known extinction and attenuation curves (e.g., Calzetti, MW, SMC, and LMC) and more exotic forms. We present the distributions of the best-fitting parameters—UV slope (c₁), optical-to-near-IR (NIR) slope (c₂), far-UV (FUV) slope (c₃), 2175 Å bump strength (c₄), and normalization (A_V)—accounting for scatter from orientation effects. Key correlations emerge between A_V and the star formation rate surface density Σ_SFR, as well as the UV slope c₁. Furthermore, the UV and FUV slopes (c₁, c₃) and the visual attenuation and bump strength (A_V, c₄) exhibit robust internal correlations (anticorrelation in the latter case). The optical-to-NIR slope exhibits minimal variations. Using these insights from simulations, we provide a set of scaling relations that predict a galaxy’s median (averaged over line of sight) dust attenuation curve based solely on its Σ_SFR and/or A_V. These predictions agree well with observed attenuation curves from the GALEX–Sloan Digital Sky Survey–Wide-field Infrared Survey Explorer Legacy Catalog, although there are minor differences in bump strength. This study delivers the most comprehensive library of synthetic attenuation curves for local galaxies, and provides a foundation for physically motivated priors for SED fitting and galaxy inference studies, such as those performed as part of the Learning the Universe Collaboration.

This study statistically compares ion properties between the thermal core and total ion populations in the Martian magnetosheath, based on observations collected by the Mars Atmosphere and Volatile EvolutioN (or MAVEN) spacecraft from 2015 to 2023. Ion moments for the core population are derived by fitting measured three-dimensional ion velocity distributions with bi-Maxwellian functions, whereas those for the total population are obtained by directly computing weighted sums over the distributions. The core population accounts for a median of approximately 80% of the total number density and dominates the bulk flow of the total population. In contrast, the total population exhibits significantly higher temperature, thermal pressure, and plasma beta, primarily due to the presence of suprathermal ions. Both populations exhibit greater temperature anisotropies downstream of quasi-perpendicular shocks compared to quasi-parallel shocks, consistent with stronger shock compression and a greater contribution from gyrating reflected ions under quasi-perpendicular conditions. Notably, the core population consistently exhibits significantly higher temperature anisotropy than the total population under both shock geometries, suggesting the presence of additional perpendicular heating mechanisms acting on the core population beyond shock compression. One plausible mechanism is stochastic energization by kinetic Alfvén waves. Overall, this systematic comparison of ion parameters between the core and total populations provides new insights into the thermodynamic structure and governing processes of the Martian magnetosheath.

We studied the propagation of blobs, which are a subset of density mesoscale structures observed in the solar corona. The detection of blobs in white-light data was performed during Solar Cycle 23. Blobs are tracers of the solar wind and an important source of its variability. We analyzed the deprojected blob radial elongation and kinematics as they evolved in the inner heliosphere using a dynamical “drag-force” model. We characterized 13 blob-like structures detected by Large Angle Spectrometric Coronagraph and SECCHI coronagraphs aboard Solar and Heliospheric Observatory and Solar TErrestrial RElations Observatory, respectively. We applied, for the first time, analysis techniques that were typically used for coronal mass ejections to these compact plasma blobs that seem to propagate “passively” with the solar wind. This is the first time that the mass of blobs has been reported, with a mean value of 3.32 ± 0.19 × 10¹²g. In addition, blobs show a mean radial expansion rate of 1.10 ± 0.96 × 10⁻¹R_⊙ hr⁻¹. We assumed that the blob movement is governed by a force that is active at a heliocentric distance ∼5 R_⊙, “dragging” blobs near the Sun outward until they reached a mean final velocity of 427 ± 55 km s⁻¹ at ∼15 R_⊙. According to the physical parameters involved in this “drag-force” model, the best estimate of the dynamic viscosity of the ambient solar wind is 1.27 ± 0.98 × 10⁻⁴ g cm⁻¹ s⁻¹. This is also the first time that this crucial parameter for aerodynamical studies has been reported close to the Sun.

The orbital regime of a terrestrial planet plays a significant role in shaping its atmospheric dynamics, climate, and hence potential habitability. The orbit is also likely to play a role in shaping the response of a planetary atmosphere to the influx of material from an icy cometary impact. To investigate this response, we model the impact of an icy cometary body with an Earth-analog exoplanet (i.e., an Earth-like planet orbiting a Sun-like star with a diurnal cycle) using a cometary impact and breakup model coupled with the 3D Earth system model WACCM6/CESM2. To quantify the role that the atmospheric dynamics play in setting the response to a cometary impact, we compare our results with a previous study investigating an impact with a tidally locked terrestrial exoplanet. We find that the circulation regime of the planet plays a key role in shaping the response of the atmosphere to an icy cometary impact. The weak multicelled circulation structure that forms on Earth-like planets is efficient at mixing material horizontally but not vertically, limiting the transport of water from the deep breakup site to higher altitudes. In turn, this limits the rate of water photodissociation at low pressures, reducing the magnitude of postimpact changes to composition. It also reduces the potential observability of an impact due to weakened cloud ice formation, and hence scattering, at low pressures. Despite this, small changes to the overall composition of the planet persist to a quasi steady state, reinforcing the idea that ongoing bombardment may help to shape the composition/habitability of terrestrial worlds.

Galactic high-velocity clouds (HVCs) are known to be complex, multiphase systems consisting of neutral and/or ionized gas moving at high velocities relative to the rotation of the disk. In this work, we investigate Milky Way–like galaxies from the TNG50 simulation to characterize the properties, morphology, and accretion rates of the warm and hot ionized material comoving with neutral HVCs visible in H i. We find that the ionized gas forms an envelope around the neutral material, and in most cases (73% of the HVCs), it is prolate in morphology. We also find that the ionized mass is ∼6 times greater than the neutral mass, which leads to significantly more accretion being possible from the ionized gas () than the neutral gas (), consistent with estimates made from observations of our own Galaxy. We investigate the accretion rates from both phases of HVCs around 47 Milky Way–like galaxies, finding that scales with and both scale with the star formation rate of the galaxy. Finally, we find that, on average, could account for 81% of the galactic star formation rate (assuming the material can sufficiently cool and condense), while can only balance 11%. Thus, the diffuse, ionized, high-velocity circumgalactic medium plays a defining role in the evolution and growth of galaxies at low redshift.

This paper examines the evolution of cosmic filaments across redshifts 1, 0.5, and 0 using the IllustrisTNG100-1 magnetohydrodynamical simulation. To achieve this, we introduce GrAviPaSt, a simple, efficient, and parameter-free filament identification method that leverages gravitational potential, an A*-like pathfinding algorithm, and spanning trees. Applying this method to galaxy distributions at different redshifts allows us to analyze various filament properties, including their length, thickness, mass density contrast, and radial profile. Additionally, we investigate dynamic characteristics such as the mean distance of filament galaxies from the skeleton, their weighted mean velocity, and velocity trends normalized by their positions within the filaments. Our findings reveal the evolution of cosmic filaments from redshift 1–0, highlighting key differences across classifications. In particular, we examine the mass density contrast radial profile of filaments connecting two galaxy groups and those linking two galaxy clusters, identifying distinct differences in profile shape between these categories. Furthermore, in the context of weighted mean velocity, we analyze cosmic filaments exhibiting either negative or positive weighted mean velocity, demonstrating their differing evolutionary trends in terms of the mean distance of filament galaxies from the skeleton.

We present new results from the ASTRID simulation from z = 3 to z = 0.5, covering the epoch of cosmic noon. The galaxy stellar mass function, as well as the black hole mass and luminosity functions in ASTRID, exhibit good agreement with recent observational constraints. We study the M_BH–M_*scaling relation and its connections to active galactic nucleus (AGN) luminosity, galaxy color, and star formation rate, demonstrating that AGN feedback plays a crucial role in the quenching of massive galaxies (M_* > 10^10.5M_⊙). Although AGN feedback ultimately suppresses star formation through quenching, AGN-host galaxies can still exhibit statistically higher star formation rates than inactive ones, reflecting a positive correlation driven by their shared dependence on a common cold gas reservoir. The fraction of quiescent galaxies in ASTRID increases with both galaxy mass and redshift evolution, aligning well with observational trends. We find that different quenching mechanisms can leave distinct morphological imprints on quenched galaxies. Massive, compact quiescent galaxies typically experience shorter quenching timescales, have younger central regions, and host overmassive black holes. This is usually due to a compaction-like quenching mechanism that funnels gas into the galactic center, leading to starbursts and triggering AGN kinetic feedback. In contrast, quiescent galaxies with more diffuse morphologies generally experience “inside-out” quenching, which is characterized by older central regions compared to the outskirts. These galaxies typically experience longer quenching timescales due to quenching processes operating on a larger halo scale, which gradually deplete the galactic star-forming gas. Data of the ASTRID simulation down to z = 0.5 is available at https://astrid.psc.edu.

This case study focuses on the pre-eruptive conditions of active regions that produced either low-energy flares accompanied by major CMEs (AR 12371 and AR 11692) or major X-class flares also associated with significant CMEs (AR 12673, AR 12158, AR 11520, AR 11429, and AR 13664). The study examines the evolution of 10 morphological parameters that serve as indicators of pre-eruptive conditions—not only at the photosphere but also in higher layers of the solar atmosphere. We found that active regions with a greater number of parameters exceeding their threshold values at higher altitudes tend to exhibit a higher eruptive potential. Specifically, in active regions associated with X-class flares and fast CMEs, at least 8 out of 10 parameters exceeded their thresholds at elevated layers, whereas in the 2 active regions linked to M-class flares and fast CMEs, fewer than 7 parameters did so. These results suggest that assessing the height-dependent behavior of pre-eruptive proxy parameters could significantly improve the identification and prediction of eruptive active regions. Future studies should extend this approach to a larger data set to better determine the maximum atmospheric height at which the predictive thresholds of different parameters are met, thereby enhancing the accuracy of solar eruption prediction.

This study introduces PI-AstroDeconv, a physics-informed semi-supervised learning method specifically designed for removing beam effects in astronomical telescope observation systems. The method utilizes an encoder–decoder network architecture and combines the telescope’s point-spread function or beam as prior information, while integrating Fast Fourier Transform–accelerated convolution techniques into the deep learning network. This enables the effective removal of beam effects from astronomical observation images. PI-AstroDeconv can handle multiple point-spread functions or beams, tolerate imprecise measurements to some extent, and significantly improve the efficiency and accuracy of image deconvolution. Therefore, this architecture is particularly suitable for astronomical data processing that does not rely on annotated data. To validate the reliability of the architecture, we used the Square Kilometre Array Science Data Challenge 3a data sets and compared it with the CLEAN deconvolution method at the 21 cm power spectrum level. The results demonstrate that our algorithm not only restores details and reduces blurriness in celestial images at the pixel level, but also more accurately recovers the true neutral hydrogen power spectrum at the power spectrum level.

Star-forming galaxies on the main sequence (MS) are often regarded as a uniform population characterized by similar global star formation properties. However, there exists a diversity in galaxy morphologies at a fixed stellar mass and star formation rate. In this study, using spatially resolved properties from the MaNGA final data release, we classify MS galaxies into late type (MS-late) and early type (MS-early). In addition, we further divide the MS-early galaxies into two distinct subgroups based on their internal star formation and stellar mass distributions within the galaxies. The first group—“MS-early_SF”—shows centrally concentrated star formation without prominent stellar bulges and resides preferentially in dense environments, suggesting environmentally driven evolution. The second group—“MS-early_stellar”—exhibits significant stellar bulges with suppressed central star formation, maintains disk-like star formation patterns, and inhabits environments similar to those of late-type galaxies, indicating evolution through internal secular processes. Our findings demonstrate that spatially resolved observations play critical roles in revealing the diverse evolutionary pathways hidden within galaxies that share similar global properties.

Tidal synchronization plays a fundamental role in the evolution of binary star systems. However, key details such as the timescale of synchronization, efficiency of tidal dissipation, rotation period, and dependence on stellar mass are not well constrained. We present a catalog of rotation periods, orbital periods, and eccentricities from eclipsing binaries (EBs) that can be used to study the role of tides in the rotational evolution of low-mass dwarf (FGKM spectral type) binaries. This study presents the largest catalog of EB orbital and rotational periods (P_orb and P_rot) measured from the Transiting Exoplanet Satellite Survey (TESS). We first classify 4584 light curves from the TESS EB catalog according to out-of-eclipse stellar variability type: starspot modulation, ellipsoidal variability, nonperiodic variability, and “other” variability (e.g., pulsations). We then manually validate each light curve’s classification, resulting in a sample of 1039 candidates with 584 high-confidence EBs that exhibit detectable starspot modulation. From there, we measure and compare the rotation period of each starspot-modulated EB using three methods: a Lomb–Scargle periodogram, autocorrelation function, and phase dispersion minimization. We find that our period distributions are consistent with previous work that used a sample of 816 starspot EBs from Kepler to identify two populations: a synchronous population (with P_orb ≈ P_rot), and a subsynchronous population (with 8P_orb ≈ 7P_rot). Using Bayesian model comparison, we find that a bimodal distribution is a significantly better fit than a unimodal distribution for the Kepler and TESS samples, both individually or combined, confirming that the subsynchronous population is statistically significant.

We study the formation of stars with varying amounts of heavy elements synthesized by the rapid neutron-capture process (r-process) based on our detailed cosmological zoom-in simulation of a Milky Way–like galaxy with an N-body/smoothed particle hydrodynamics code, asura. Most stars with no overabundance in r-process elements, as well as the strongly r-process-enhanced (RPE) r-II stars ([Eu/Fe] > +0.7), are formed in dwarf galaxies accreted by the Milky Way within the 6 Gyr after the Big Bang. In contrast, over half of the moderately enhanced r-I stars (+0.3 < [Eu/Fe] ≤ +0.7) are formed in the main in situ disk after 6 Gyr. Our results suggest that the fraction of r-I and r-II stars formed in disrupted dwarf galaxies is larger the higher their [Eu/Fe] is. Accordingly, the most strongly enhanced r-III stars ([Eu/Fe] > +2.0) are formed in accreted components. These results suggest that non-r-process-enhanced stars and r-II stars are mainly formed in low-mass dwarf galaxies that hosted either none or a single neutron star merger, while the r-I stars tend to form in the well-mixed in situ disk. We compare our findings with high-resolution spectroscopic observations of RPE metal-poor stars in the halo and dwarf galaxies, including those collected by the R-Process Alliance. We conclude that observed [Eu/Fe] and [Eu/Mg] ratios can be employed in chemical tagging of the Milky Way’s accretion history.

Active galactic nuclei (AGN) are known to drive ionized gas into their host galaxies, which may affect the evolution of both the central supermassive black holes and their hosts. In the case of NGC 3516, a nearby Seyfert 1 galaxy, these AGN winds have historically proven difficult to disentangle from galactic rotation. Using long-slit spectroscopy at multiple position angles from Hubble Space Telescope’s Space Telescope Imaging Spectrograph and Apache Point Observatory’s Kitt Peak Ohio State Multi-Object Spectrograph, we separate these kinematic components by fitting multiple Gaussians to the Hα, [N II], Hβ, and [O III] emission lines along the slits. We present a biconical outflow model that agrees well with the observed kinematics of the outflowing gas in the narrow-line region (NLR). Our results indicate that the structure of the [O III] emission is explained by dusty gas spirals in the galactic disk that are illuminated by the ionizing bicone, which is viewed along one edge, resulting in the complex nuclear kinematics. Our view into the bicone edge is consistent with the multiple, deep components of ionized absorption lines seen in UV and X-ray spectra of NGC 3516. The observed turnover in the velocity of the NLR clouds matches that from a simple dynamical model of radiative acceleration by the AGN and gravitational deceleration by the AGN and galaxy, indicating they are the principal forces at work on the gas clouds. Finally, the model launch radii indicate that the outflowing clouds originate primarily from the inner dusty spirals near the AGN.

Recent observations suggest that the extended stellar halos of low-redshift massive galaxies are tightly connected to the assembly of their dark matter halos. In this paper, we use the Illustris, IllustrisTNG100, and IllustrisTNG300 simulations to compare how different stellar aperture masses trace halo mass. For massive central galaxies (M_⋆ ≥ 10^11.2 M_⊙), we find that a 2D outskirt stellar mass measured between 50 and 100 kpc (M_⋆,[50,100]) consistently outperforms other aperture-based stellar masses. We further show that M_⋆,[50,100] correlates better with halo mass than the total mass of accreted stars (the ex situ mass), which suggests that not all accreted stars connect to halo assembly equally. While the galaxy formation recipes differ between Illustris and IllustrisTNG100, the two simulations yield consistent ex situ outskirt fractions for massive galaxies (∼70% in M_⋆,[50,100]). These results demonstrate the potential of using the outskirt stellar mass to deepen our understanding of the galaxy–halo connection in massive dark matter halos and to trace dark matter halos better.

In the theory of energetic particle transport, the spatial variation of large-scale magnetic fields gives rise to a so-called adiabatic focusing term in the pitch-angle-dependent transport equation. This focusing term leads to the effect of convection, but it also alters the parallel spatial diffusion coefficient. Over the past few decades researchers have tried to derive analytical forms for the parallel diffusion coefficient as a function of the focusing length. Two different results have been derived contradicting each other. In the current paper we revisit this problem and provide the final solution. We combine previously developed numerical methods such as the subspace approach, allowing us to compute the parallel diffusion coefficient as a function of the focusing length with very high precision within a very short computational time. Most importantly, we derive an exact formula for the diffusion coefficient by employing analytical theory. The new formula agrees perfectly with the numerically obtained results proofing its validity.

Type Ia supernovae (SNe Ia) are powered by the radioactive decay of isotopes such as ⁵⁶Ni and ⁵⁶Co, making their γ-ray spectra useful probes of the explosion mechanism and ejecta structure. Accurate interpretation of γ-ray observables, including line ratios and continuum fluxes, requires a detailed understanding of the microphysical processes that shape the spectra. One such process is positronium formation during electron–positron annihilation, which can redistribute flux from the 511 keV line into the surrounding continuum. To assess the impact of positronium on the emergent spectra, we developed a new open-source module, tardis-He, for time-dependent three-dimensional γ-ray transport, integrated into the radiative transfer code tardis. The code simulates γ-ray spectra and light curves from one-dimensional supernova ejecta models and allows for flexible incorporation of decay chains and opacity treatments. Using tardis-He, we explore the effect of positronium formation by varying the positronium fraction from 0% to 100%, and assuming an extreme case where 75% of positronium decays result in three-photon emission. We find that full positronium formation can reduce the 511 keV line flux by ≈70% and modestly enhance energy deposition by up to 2% at around 100 days postexplosion, compared to models without positronium. These results demonstrate that, while the effect is not dominant, positronium formation introduces measurable changes to γ-ray observables. Future observations with missions such as the Compton Spectrometer and Imager may offer constraints on positronium formation in SNe Ia and help refine models of their radioactive energy transport.

In this work, we apply a soft-sphere discrete element method (SSDEM) within the PKDGRAV N-body integrator to investigate the formation of planetesimal systems through the gravitational collapse of clouds of superparticles. Previously published numerical models have demonstrated that the gravitational collapse of pebble clouds is an efficient pathway to produce binary planetesimal systems. However, such investigations were limited by their use of a perfect-merger and inflated-radii superparticle approach, which inhibits any analysis of planetesimal shapes and spin states, precludes the formation of the tightest binary orbits, and produces significantly underdense planetesimals. The SSDEM enables superparticles to rest upon each other through mutual surface penetration and by simulating contact physics. Superparticles do not need to be inflated, and collisions are not treated as perfect mergers; we can thus track the evolution of planetesimal shapes, spins, and tight binary orbits. We demonstrate that the SSDEM is an excellent method to model the collapse process, and is capable of producing many binary planetesimal systems from a single cloud. The most massive systems often exhibit low-inclination (i ≲ 15°) and moderately eccentric (e ≲ 0.40) orbits within a tight range of semimajor axes normalized by their Hill radii (a/R_Hill ∼ 0.02–0.15). Conversely, less massive planetesimal systems display a wider range of eccentricities and inclinations and maintain a wider range of a/R_Hill (0.15 to ≥0.50). These results confirm the findings of previously published perfect-merging models while also producing novel results about planetesimal spin and shape properties. Newly formed planetesimals exhibit 10 hr rotation periods on average and can be characterized by a wide variety of shapes (spherical, oblate, top-shaped, flattened, egg-shaped, or prolate), with the most massive planetesimals primarily forming as spheres and oblate spheroids.

We present the properties of a nuclear star cluster (NSC) in the low-surface-brightness galaxy AGC 223218. The disk of the galaxy can be modeled using two Sérsic components with distinct central positions: one representing the inner bright disk and the other corresponding to the extended outer disk. We estimate the stellar masses of the NSC and the host galaxy using two methods: spectral energy distribution (SED) fitting and mass-to-light versus color relations (MLCRs). The stellar mass ratio of the NSC to AGC 223218 is 0.094 based on the SED method and 0.072 using MLCRs. The NSC presents a younger stellar population and a lower [Fe/H] value than the host, as determined from Sloan Digital Sky Survey (SDSS) and LAMOST spectra analysis using pPXF fitting. AGC 223218 is located at the boundary between the Seyfert and star-forming regions in the [S II]-Baldwin–Phillips–Terlevich (BPT) diagram, whereas in the [N II]-BPT diagram, it falls in the track of star-forming SDSS galaxies. This suggests the presence of strong shocks in AGC 223218. We propose that the NSC in AGC 223218 may have formed as a result of a merger event. Furthermore, the observed X-ray luminosity of AGC 223218 with eROSITA is 2 orders of magnitude higher than the expected X-ray luminosity from X-ray binaries, suggesting the presence of an intermediate-mass black hole (IMBH) in the NSC. To account for the observed X-ray luminosity, we estimate the IMBH accretion rate to be approximately 0.001.

We studied 28 red giant branch stars in the mildly metal-rich globular cluster M5 ([Fe/H] = −1.29) using archival high-resolution spectra from the Keck Observatory archive to better understand the r-process in globular clusters. Previous studies (M15, M92, and NGC 2298) have shown r-process dispersion in varying amounts, hinting at the source of the r-process in those clusters. We extend these dispersion studies to the more metal-rich cluster M5 by studying the rare-earth peak, specifically the elements Ba, Nd, and Eu. We separately analyze the different stellar generations, as traced by the abundance of Na and O. Based on the Nd and Eu abundances, we report a tenuous detection of r-process dispersion that is dependent on the generation and element. Based on a log-likelihood dispersion study accounting for measurement errors, Nd has an intrinsic first-generation abundance spread of and a 2σ upper limit on the second-generation spread of σ_2G(Nd) < 0.28. The upper limits on the Eu intrinsic spread are σ_1G(Eu) < 0.34 and σ_2G(Eu) < 0.16. A potential dispersion implies the cluster gas was inhomogeneously polluted, either due to an event concurrent with the formation of the cluster or due to clouds of disparate composition that coalesced to form the cluster.

We present a comparative test of four widely used full spectral fitting codes, with the aim of answering the question: How robust is the retrieval of the stellar initial mass function (IMF) and other stellar properties of galaxies? We used Absorption Line Fitter (ALF), Python Stellar Absorption Feature Fitting (PyStaff), Starlight, and Penalized PiXel-Fitting (pPXF) to fit a set of optical+near-IR spectroscopic data from the Magellan telescope of the two brightest galaxies in the Fornax cluster, NGC 1399 and NGC 1404. By fitting the same data set with the same models, we can compare the radial trends (out to ∼1 R_e) of IMF slope, age, metallicity, and 19 elemental abundances when allowed with the four codes. To further test the robustness of our analysis, we carried out parallel simulations by creating inputs with different star formation history (SFH) complexity. The results from simulations show that codes such as ALF and PyStaff, which both assume a simple stellar population (SSP), return greater precision and accuracy only when the underlying population is a pure SSP; however, in cases where the SFH is more complex, these codes return erroneous results. Although codes like Starlight and pPXF, which retrieve the best-fit SFH without prior assumptions, tend to produce results with greater scatter and bias, they are generally more reliable in identifying secondary components. Our analysis on the two targets shows that ALF and PyStaff, which assume an SSP, give results pointing to a single old age, a decreasing metallicity with radius, and a flat super-Salpeter IMF. In contrast, Starlight and pPXF suggest the presence of a secondary component with different metallicity and IMF characteristics.

We test the use of the Mg ii resonant lines for measurement of the magnetic field at the top of the chromosphere of polar coronal holes (CHs). The Hanle effect in the core of Mg II k enables access to a regime of field strengths where the Zeeman effect has little diagnostic value (especially at the solar poles, where most of the field is transverse to the line of sight). Synthetic Stokes spectra computed from a radiation magnetohydrodynamic simulation of a CH emulating a high viewing angle are inverted with the HanleRT Tenerife Inversion Code, which accounts for the physical processes that lead to scattering-induced polarization and its modification due to the magnetic field and other symmetry-breaking mechanisms. We find that, while degeneracies in the atmospheric model lead to poor inferences of the thermodynamical properties, the magnetic inferences are highly consistent with the model values. The mean magnetic field strength in the simulation cube is typically retrieved with a relative error of δB ∼ 20% and an absolute error of ΔB ∼ 2 G at the top of the chromosphere. This opens up an avenue for promising chromospheric constraints for magnetic extrapolation models that ingest photospheric magnetograms, whose biases and uncertainties are troublesome to the reconstruction of the heliospheric magnetic field.

The James Webb Space Telescope (JWST) has opened a window on many new puzzles in the early Universe, including a population of high-redshift star clusters with extremely high stellar surface density, suggesting unique star formation conditions in the Universe’s early evolution. We study the formation and evolution of these first star clusters and galaxies using an AREPO cosmological simulation box designed to resolve the intricate environments of the smallest halos hosting Population III star clusters at z ≥ 12. Our approach, which prioritizes baryonic structure identification through a friends-of-friends algorithm, provides new insights into early star cluster formation and delivers predictions directly relevant to observations. We investigate the dynamical properties of these first star clusters and use numerical and analytical methods to understand the populations of virialized and nonvirialized systems. Our findings indicate that high-z star clusters in a feedback-free regime can achieve extreme surface densities, consistent with the systems detected by JWST. These results imply that JWST may have the opportunity to uncover stellar systems at high redshift whose dynamical state preserves evidence of the hierarchical structure formation process.

Luminous and ultraluminous IR galaxies are critical for investigating feedback mechanisms due to a combination of intense star formation episodes and active galactic nuclei (AGN), particularly in the context of complex galaxy interactions. We conduct a detailed analysis of the II ZW 096 merging system using the Multi-Unit Spectroscopic Explorer on the Very Large Telescope, combining high-resolution narrow-field mode and large-area wide-field mode observations. We mapped the morphology, kinematics, and ionizing radiation of the system’s gas by fitting atomic emission lines and the optical continuum. We identify three or more distinct galaxies within II ZW 096, revealing rotational patterns and complex interactions consistent with a collapsing small galaxy group. The kinematics and ionization structures suggest high star formation rates and shock-driven processes, which align with this proposed scenario. Focusing on the D1 compact region, which contributes 40%–70% of the system’s IR emission, and combining information from archival multiwavelength observations, we find strong evidence of a heavily obscured AGN powering it. Our analysis of the internal structure, interactions, and merger state of II ZW 096 offers novel insights into the galaxy evolution processes in this dynamic and highly chaotic system.

The accretion disks that power active galactic nuclei (AGN) are thought to house populations of stars and compact objects; after forming binaries these compact objects may merge, begetting gravitational waves (GWs) such as those detected by LIGO and VIRGO. We present a comprehensive study of the early evolution of binaries within AGN disks as their orbits are influenced by the surrounding gas, focusing on eccentric and unequal-mass binaries. Nearly equal-mass binaries behave similarly to their equal-mass counterparts: Prograde binaries inspiral, albeit somewhat slowly, and have their eccentricities damped; retrograde binaries inspiral ∼2–3 times faster than their prograde counterparts, and those with near-equal masses are driven quickly toward near-unity eccentricities. However, the primaries in retrograde binaries with mass ratios of m₂/m₁ ≲ 0.4 experience significantly weaker headwinds and retain substantial accretion disks that help damp binary eccentricities, slowing binary inspirals. Additionally, we find that while accretion drives prograde binaries toward equal masses thanks to the exchange of material between the primary and secondary accretion disks, retrograde binaries are driven slowly toward more extreme mass ratios. Prograde binaries, and generally those with low mass ratios, likely accrete for multiple e-folding timescales before merger. On the other hand, high-mass-ratio retrograde binaries may merge before accreting substantially, potentially approaching merger with detectable eccentricity. Future ground-based GW observatories, with their broader frequency coverage, should be particularly useful for studying these populations.

An understanding of how turbulent energy is partitioned between ions and electrons in weakly collisional plasmas is crucial for modeling many astrophysical systems. Using theory and simulations of a four-dimensional reduced model of low-beta gyrokinetics (the “Kinetic Reduced Electron Heating Model”), we investigate the dependence of collisionless heating processes on plasma beta and imbalance (normalized cross-helicity). These parameters are important because they control the helicity barrier, the formation of which divides the parameter space into two distinct regimes with remarkably different properties. In the first, at lower beta and/or imbalance, the absence of a helicity barrier allows the cascade of injected power to proceed to small (perpendicular) scales, but its slow cascade rate makes it susceptible to significant electron Landau damping, in some cases leading to a marked steepening of the magnetic spectra on scales above the ion Larmor radius. In the second, at higher beta and/or imbalance, the helicity barrier halts the cascade, confining electron Landau damping to scales above the steep “transition-range” spectral break, resulting in dominant ion heating. We formulate quantitative models of these processes that compare well to simulations in each regime, and combine them with results of previous studies to construct a simple formula for the electron–ion heating ratio as a function of beta and imbalance. This model predicts a “winner takes all” picture of low-beta plasma heating, where a small change in the fluctuations' properties at large scales (the imbalance) can cause a sudden switch between electron and ion heating.

We present a new pipeline utilizing machine learning for classifying short-duration features in raw time-ordered data (TOD) of cosmic microwave background survey observations. The pipeline, specifically designed for the Atacama Cosmology Telescope, works in conjunction with the previous TOD preprocessing techniques that employ statistical thresholding to indiscriminately remove all large spikes in the data, whether they are due to noise features, cosmic rays, or true astrophysical sources, in a process called “data cuts.” This has the undesirable effect of excising real astrophysical sources, including transients, from the data. The classification pipeline demonstrated in this work uses the output from these data cuts and is able to differentiate between electronic noise, cosmic rays, and point sources, enabling the removal of undesired signals while retaining true astrophysical signals during TOD preprocessing. We achieve an overall accuracy of 90% in categorizing data spikes of different origin and, importantly, 94% for identifying those caused by astrophysical sources. Our pipeline also measures the amplitude of any detected source seen more than once and produces a subminute-to-minute light curve, providing information on its short-timescale variability. This automated pipeline for source detection and amplitude estimation will be particularly useful for upcoming surveys with large data volumes, such as the Simons Observatory.

Bars are one of the most prominent galactic structures. The classical swing-amplification theory can qualitatively describe the spontaneous bar instability of stellar disks. Still, it cannot quantify the bar formation process or explain why some disk galaxies do not have a bar. Recent studies found that the bar formation timescale depends exponentially on the disk mass fraction of the host galaxy (dubbed as “Fujii relation”), but they only explored a limited parameter space, where the physical effects of Toomre Q (local disk stability parameter) and disk scale height of the host galaxies are not fully explored. In this work, we check the robustness of the Fujii relation in a higher-dimensional parameter space of disk mass fraction, Toomre Q, and scale height. We find that the Fujii relation holds for disk galaxies with physically reasonable Toomre Q and scale height. Furthermore, the bar formation timescale also approximately linearly depends on both Toomre Q and scale height, with a more prolonged bar formation in a hotter or thicker disk. We propose an empirical relation to combine the dependency of the bar formation timescale on the three parameters. Based on the empirical relation and recent observations, we estimate that the bar formation timescale in pure stellar disks ranges from to Gyr or even significantly beyond the Hubble timescale in some extreme cases.

Cataclysmic variables (CVs) are close interacting binaries in which a white dwarf accretes materials from a low-mass main-sequence companion. CVs can experience nova eruptions due to low mass transfer rates. In the standard theory of CV evolution, the ejected materials during nova eruptions are assumed to leave the system in the form of fast, isotropic, optically thick winds, which predicts that novae only result in positive variation (expansion) of the orbital period (i.e., positive ΔP). In addition, the angular momentum losses (magnetic braking and gravitational radiation) only predict a steady long-term decay in the orbital period of CVs, i.e., is negative. Interestingly, an observation lasting over 30 yr reveals positive and negative values for both ΔP and in CVs, strongly conflicting with the standard evolutionary patterns. However, it cannot be excluded that these observations originate from short-term phenomena caused by nova eruptions because of a short timescale of observations. In this paper, we model the effect of instantaneous nova eruptions on the evolution of CVs, considering three mechanisms associated with mass loss in nova eruptions, including fast wind, the Frank jet, and binary-driven mass loss. By assuming that the observed ΔP and are dominated by short-term phenomena, our results show that the binary-driven mass loss can explain almost all of the observations of normal CVs. However, the Frank jet may be needed for some long-period CVs with evolved companions.

We report on our finding of an excess of neutrinos at the location of the pulsar wind nebula (PWN) G63.7+1.1. By analyzing the IceCube track-like neutrino data for a group of 14 PWNe, which are selected as targets because of their reported association with molecular clouds, G63.7+1.1 is found to be the only one detected with neutrino emission, and the post-trail significance for the detection is 3.2σ. Previously, this PWN was estimated to have an age of ≳8 kyr, contain a candidate pulsar detected in X-rays, and have a distance of ∼6 kpc. More importantly, and related to the PWN’s possible neutrino emission, surrounding molecular materials are seen to interact with the PWN. On the basis of these properties, we examine the proton–proton interactions as the process for the neutrino production. The PWN (or the pulsar) can provide sufficient energy to power the required high-energy (HE) protons. This possibly first neutrino-emitting case in our Galaxy, with problems or other possibilities to be solved or examined, may reveal to us that PWNe are the significant Galactic HE neutrino sources.

Cosmic-ray (CR) feedback plays a vital role in shaping the formation and evolution of galaxies through their interaction with magnetohydrodynamic waves. In the CR self-confinement scenario, the waves are generated by the CR gyroresonant instabilities via CR streaming or CR pressure anisotropy and saturate by balancing wave damping. The resulting effective particle scattering rate by the waves, ν_eff, critically sets the coupling between the CRs and background gas, but the efficiency of CR feedback is yet poorly constrained. We employ 1D kinetic simulations under the magnetohydrodynamic-particle-in-cell framework with the adaptive δf method to quantify ν_eff for the saturated state of the CR pressure anisotropy instability with ion-neutral friction. We drive CR pressure anisotropy by expanding/compressing the box, mimicking the background evolution of magnetic field strength, and the CR pressure anisotropy eventually reaches a quasi-steady state by balancing quasi-linear diffusion. At the saturated state, we measure ν_eff and the CR pressure anisotropy level, establishing a calibrated scaling relation with environmental parameters. The scaling relation is consistent with quasi-linear theory and can be incorporated to CR fluid models, in either the single-fluid or p-by-p treatments. Our results serve as a basis for accurately calibrating the subgrid physics in macroscopic studies of CR feedback and transport.

Solar active regions are believed to provide significant information on the mutual conversion of the poloidal and toroidal components of the global magnetic field. However, the multiscale periodic variations, in particular the quasi-biennial oscillations (QBOs), of solar active regions are not fully understood. In the present study, the flux, area, and number of solar active regions, as well as the sunspot number data in the period from 1996 May to 2023 November, are studied in detail. The multiscale periodic components in the above four data sets are investigated by the techniques of ensemble empirical mode decomposition and cross-correlation analysis. The main results are as follows. (1) The four data sets exhibit similar periodic components, including the 11 yr Schwabe cycle, the QBOs, and a Rieger-type period. (2) The multiscale periodicity of solar active regions shows different physical characteristics. Under different periodic scales, the highest correlation is between active region flux and area, indicating that active region flux and area better reflect the evolution of active regions. (3) By superimposing the QBOs on the 11 yr Schwabe cycle, the Gnevyshev gap phenomenon was clearly observed, implying that the Gnevyshev gap may be caused by the modulation of the 11 yr Schwabe cycle. (4) The active region flux in both hemispheres shows similar periodic components to the full disk, but the periodic variations are uneven between the northern and southern hemispheres. The results of our analysis could be beneficial for the understanding of the spatiotemporal distribution of solar active regions, and could also provide statistical constraints on solar dynamo theories.

We present evidence of a negative eccentricity gradient in the debris disk of the nearby A-type main-sequence star, Fomalhaut. Fitting to the high-resolution, archival ALMA 1.32 mm continuum data for Fomalhaut (with a synthesized angular resolution of 076 × 055; 4–6 au), we present a model that describes the bulk properties of the disk (semimajor axis, width, and geometry) and its asymmetric morphology. The best-fit model incorporates a forced eccentricity gradient that varies with semimajor axis, , a generalized form of the parametric models of E. M. Lynch & J. B. Lovell, with n_pow = −1.75 ± 0.16. We show that this model is statistically preferred to models with constant forced and free eccentricities. In comparison to disk models with constant forced eccentricities, negative eccentricity gradient models broaden disk widths at pericenter versus apocenter, and increase disk surface densities at apocenter versus pericenter, both of which are seen in the Fomalhaut disk, and which we collectively term “Eccentric Velocity Divergence.” We propose single-planet architectures consistent with the model and investigate the stability of the disk over 440 Myr to planet–disk interactions via N-body modeling. We find that Fomalhaut’s ring eccentricity plausibly formed during the protoplanetary disk stage, with subsequent planet–disk interactions responsible for carving the disk morphology.

We present a multiepoch spectroscopic study of the broad absorption line (BAL) quasar J115636.82+085628.9 (z_em = 2.1077), based on five spectra spanning nearly two decades in the observer’s frame. This source exhibits remarkable variability in both low-ionization (LoBAL: Al iii and Mg ii) and high-ionization (HiBAL: C iv and Si iv) absorption features. For the first time, we detect the emergence and subsequent disappearance of LoBAL troughs at high velocities (∼20,000 km s⁻¹), coinciding with the strengthening and weakening of the corresponding HiBAL absorption. The C iv BAL profile extends from ∼6700 km s⁻¹ to a conservative upper limit of 30,000 km s⁻¹ and is composed of narrow, variable absorption features embedded within a broad, smooth envelope. Both C iv and Si iv BAL troughs exhibit dramatic equivalent width (EW) changes—among the most extreme reported to date. Notably, these EW variations are strongly anticorrelated with continuum flux changes inferred from optical photometric light curves. We interpret this variability as the result of a new absorbing flow transiting into our line of sight, increasing the shielding of a more distant, preexisting outflow and giving rise to transient LoBAL absorption. This scenario supports a unified picture in which LoBAL and HiBAL features arise from similar outflow structures, with observed differences governed primarily by line-of-sight column densities consistent with previous findings.

The detection of gravitational waves has brought to light a population of binary black holes that merge within a Hubble time. Multiple formation channels can contribute to this population, making it difficult to definitively associate particular population features with underlying stellar physics. Black hole spins are considered an important discriminator between various channels, but they are less well measured than masses, making conclusive astrophysical statements using spins difficult thus far. In this paper, we consider the distribution of the effective inspiral spin χ_eff—a quantity much better measured than individual component spins. We show that non-Gaussian features like skewness, asymmetry about zero, and multimodality can naturally arise in the χ_eff distribution when multiple channels contribute to the population. Searching for such features, we find signs of skewness and asymmetry already in the current catalogs, but no statistically significant signs of bimodality. These features provide robust evidence for the presence of a subpopulation with spins preferentially aligned to the binary’s orbital angular momentum; and we conservatively estimate the fraction of this subpopulation to be at least 12%–17% (at 90% credibility). Our models do not find a sharp excess of nonspinning systems and instead find that at least ∼20% of the binaries have some degree of negative χ_eff. The data also suggest that, if preferentially aligned mergers form a significant fraction of the population, they must have small spins.

We present and analyze the extensive optical broadband photometry of the Type II SN 2023ixf up to 1 yr after explosion. We find that, when compared to two preexisting model grids, the bolometric light curve is consistent with drastically different combinations of progenitor and explosion properties. This may be an effect of known degeneracies in Type IIP light-curve models. We independently compute a large grid of MESA+STELLA single-star progenitor and light-curve models with various zero-age main-sequence masses, mass-loss efficiencies, and convective efficiencies. Using the observed progenitor variability as an additional constraint, we select stellar models consistent with the pulsation period and explode them according to previously established scaling laws to match plateau properties. Our hydrodynamic modeling indicates that SN 2023ixf is most consistent with a moderate-energy ( erg) explosion of an initially high-mass red supergiant progenitor (≳16.5 M_⊙) that lost a significant amount of mass in its prior evolution, leaving a low-mass hydrogen envelope (≲3 M_⊙) at the time of explosion, with a radius ≳950 R_⊙ and a synthesized ⁵⁶Ni mass of ≈0.068 M_⊙. We posit that previous mass transfer in a binary system may have stripped the envelope of SN 2023ixf’s progenitor. The analysis method with pulsation period presented in this work offers a way to break degeneracies in light-curve modeling in the future, particularly with the upcoming Vera C. Rubin Observatory Legacy Survey of Space and Time, when a record of progenitor variability will be more common.

The rates and properties of tidal disruption events (TDEs) provide valuable insights into their host galaxy central stellar densities and the demographics of their central supermassive black holes. TDEs have been observed only at low redshifts (z ≲ 1), due to the difficulty in conducting deep time-domain surveys. In this work, we present the discovery of a high-redshift TDE candidate, HZTDE-1, in the COSMOS-Web survey with JWST’s NIRCam, using a novel selection technique based on color and morphology. We outline a methodology for identifying high-z TDEs in deep infrared imaging surveys, leveraging the unique spectral energy distributions and morphologies of these transients. While focused on TDEs, this methodology could also be applied to find other UV-bright transients, such as superluminous supernovae (SLSNe). We apply this technique to COSMOS-Web in filters F115W, F150W, F277W, and F444W, and identify HZTDE-1, a transient point source relative to archival UltraVISTA infrared observations. If we assume it is a TDE, we estimate a photometric redshift of . HZTDE-1 cannot be explained by reasonable supernova or active galactic nuclei models. However, an SLSN at z ≳ 3 can also plausibly explain this transient and would be the highest-redshift SLSN yet known. If confirmed with follow-up observations, HZTDE-1 would represent the highest-redshift TDE discovery to date, and suggest an enhancement of the TDE rate in the high-redshift Universe. Our method, which can be applied to future deep surveys with the JWST and Nancy Grace Roman Space Telescope, offers a pathway to identify TDEs at z > 4 and probe black hole demographics at early cosmic times.

The radical hydrocarbon molecule C₂H is widely detected in various stages of star and planet formation, and has emerged as a useful tracer of high-C/O gas within the photochemically active surface layers of mature (Class II) protoplanetary disks. However, the chemistry and evolution of C₂H within younger (Class 0/I) protostars remains much more poorly understood. Here, using data observed as part of the PEACHES survey along with new Atacama Large Millimeter/submillimeter Array Atacama Compact Array observations, we investigate the C₂H emission toward an unbiased sample of 35 Class 0/I low-mass protostars in Perseus. With this large sample, we identify a clear association between C₂H emission and the protostellar outflow cavity walls, and a consistent spatial anticorrelation between C₂H and SO emission. Together, these trends confirm that C₂H is tracing photochemically active, O-poor gas in these younger sources. We fitted the C₂H spectra with a simple LTE model to yield column density maps, and find values ranging from 10¹⁴ to 10¹⁵ cm⁻² in these sources. We also looked for trends in the C₂H emission morphology as a function of various protostellar evolutionary metrics, but find no clear patterns; the C₂H emission remains spatially extended in most sources, independent of age. This indicates that the transition to the compact C₂H emission observed on the surfaces of Class II disks must happen rapidly, sometime just after the embedded stage.

We present the largest catalog to date of triply ionized carbon (C iv) absorbers detected in quasar spectra from the Dark Energy Spectroscopic Instrument. Using an automated matched-kernel convolution method with adaptive signal-to-noise thresholds, we identify 101,487 C iv systems in the redshift range 1.4 < z < 4.5 from 300,637 quasar spectra. Completeness is estimated via Monte Carlo simulations, and the catalog is 50% complete at EW_{C IV} ≥ 0.4 Å. The differential equivalent width frequency distribution declines exponentially and shows weak redshift evolution. The absorber incidence per unit comoving path increases by a factor of 2–5 from z ≈ 4.5 to z ≈ 1.4, with stronger redshift evolution for strong systems. Using column densities derived from the apparent optical depth method, we constrain the cosmic mass density of C iv, Ω_{C IV}, which increases by a factor of ∼3.8 from (0.82 ± 0.05) × 10⁻⁸ at z ≈ 4.5 to (3.16 ± 0.2) × 10⁻⁸ at z ≈ 1.4. From Ω_{C IV}, we estimate a lower limit on intergalactic medium metallicity at z ∼ 2.3, with a smooth decline at higher redshifts. These trends trace the cosmic star formation history and He ii photoheating rate, suggesting a link between C iv enrichment, star formation, and UV background over ∼3 Gyr. The catalog also provides a critical resource for future studies connecting circumgalactic metals to galaxy evolution, especially near cosmic noon.

We present analysis of one of the most extreme quasar outflows found to date in our survey of extremely high-velocity outflows (EHVOs). J164653.72+243942.2 (z_em ∼ 3.04) shows variable C ivλλ1548,1551 absorption at speeds larger than 0.1c, accompanied by Si iv, N v, and Lyα, and disappearing absorption at lower speeds. We perform absorption measurements using the apparent optical depth method and SimBAL. We find the absorption to be very broad (Δv ∼  35,100 km s⁻¹ in the first epoch and 13,000 km s⁻¹ in the second one) and fast (v_max ∼  –50,200 km s⁻¹ and −49,000 km s⁻¹, respectively). We measure large column densities ( 21.6 (cm⁻²)) and are able to place distance estimates for the EHVO (5 ≲ R ≲ 28 pc) and the lower-velocity outflow (7 ≲ R ≲ 540 pc). We estimate a mass outflow rate for the EHVO to be and a kinetic luminosity of in both epochs. The lower-velocity component has a mass outflow rate and a kinetic luminosity of . We find that J164653.72+243942.2 is not an outlier among EHVO quasars in regard to its physical properties. While its column density is lower than typical BAL values, its higher outflow velocities drive most of the mass outflow rate and kinetic luminosity. These results emphasize the crucial role of EHVOs in powering quasar feedback, and failing to account for these outflows likely leads to underestimating the feedback impact on galaxies.

Fast radio bursts (FRBs) are extremely energetic radio transients, typically classified as repeat or nonrepeat, but their origins remain uncertain. In this work, we focus on the timing characteristics of the pulses in 536 FRBs observed by CHIME with improved pulse-finding and fitting algorithms. The results show that the fitted mean of rise time, decay time, FWHM, and minimum variable timescale distributions for the repeat FRBs are larger. Furthermore, the Kolmogorov–Smirnov test reveals significant differences (>5σ) for some parameters between repeat and nonrepeat FRBs, implying that the former may have more stable and longer-lived sources (e.g., magnetars). However, we do not find significant differences in waiting times, which may be a limitation of the sample. We also investigate the relationship between these parameters, identifying some correlations, e.g., a negative power-law correlation between pulse amplitude and FWHM. Our findings suggest that the repeat and nonrepeat FRBs originate from different progenitors, environments, and/or emission mechanisms. Interestingly, both of their observations do not contradict that they originate from within the magnetosphere of a magnetar.

The accretion disks of active galactic nuclei (AGN) are widely considered the ideal environments for binary black hole mergers and the only plausible sites for their electromagnetic counterparts. M. J. Graham et al. (2023) identified seven AGN flares that are potentially associated with gravitational wave (GW) events detected by the LIGO–Virgo–KAGRA Collaboration during the third observing run. In this article, utilizing an additional three years of Zwicky Transient Facility public data after their discovery, we conduct an updated analysis and find that only three flares can be identified. By implementing a joint analysis of optical and GW data through a Bayesian framework, we find two flares exhibit a strong correlation with GW events, with no secondary flares observed in their host AGN up to 2024 October 31. Combining these two most robust associations, we derive a Hubble constant measurement of and incorporating the multimessenger event GW170817 improves the precision to . Both results are consistent with existing measurements reported in the literature.

We explore the physical environment of the Galactic mid-infrared (MIR) bubble [HKS2019] E71 (hereafter E71) through a multiwavelength approach. E71 is located at the edge of a filamentary structure, as traced in Herschel images (250–500 μm), Herschel column density map, and molecular maps in the velocity range [−20, −14] km s⁻¹. It hosts a stellar cluster (radius ∼ 1.26 pc, distance ∼1.81 ± 0.15 kpc) associated with radio continuum emission, including a centrally positioned B1.5-type massive star (hereafter “m2”), along with an enhanced population of evolved low-mass stars and young stellar objects. MIR images and molecular line maps reveal a photodissociation region surrounding “m2,” exhibiting an arc-like structure along the edges of E71. Regularly spaced molecular and dust condensations are identified along this structure. The position–velocity map of ¹²CO (1–0) emission suggests an expansion of molecular gas concentrated at the periphery of E71. Near-infrared spectroscopic observations with TANSPEC confirm the presence of the accretion process in a massive young stellar object (MYSO) located near the edge of the bubble. High-resolution uGMRT radio continuum maps uncover substructures in the ionized emission, both toward the MYSO and the center of E71. These findings support that “m2” has shaped an arc-like morphology through its feedback processes. The pressure exerted by “m2” and the velocity structure of the ^12/13CO (1–0) emission suggest that the stellar feedback has likely driven out molecular material, leading to the formation of the expanding E71 bubble. Our overall investigation infers that the “collect and collapse” process might be a possible mechanism that can describe the ongoing star formation activities around the E71 bubble.

Gravitational waves (GWs) can convert into electromagnetic waves in the presence of a magnetic field via the Gertsenshtein–Zeldovich effect. The characteristics of the magnetic field substantially affect this conversion probability. This paper confirms that strong magnetic fields in neutron stars significantly enhance the conversion probability, facilitating detectable radio signatures of very high-frequency (VHF, ) GWs. We theoretically identify two distinct signatures using single-dish telescopes (FAST, TMRT, QTT, GBT) and interferometers (SKA1/2-MID): transient signals from burst-like GW sources and persistent signals from cosmological background GW sources. These signatures are mapped to graviton spectral lines derived from quantum field theory by incorporating spin-2 and mass constraints, resulting in smooth, featureless profiles that are critical for distinguishing GW signals from astrophysical foregrounds. FAST attains a characteristic strain bound of h_c < 10⁻²³, approaching 10⁻²⁴ in the frequency range of 1–3 GHz with a 6 hr observation period. This performance exceeds the 5σ detection thresholds for GWs originating from primordial black holes and nears the limits set by Big Bang nucleosynthesis. Additionally, projections for SKA2-MID indicate even greater sensitivity. Detecting such GWs would improve our comprehension of cosmological models, refine the parameter spaces for primordial black holes, and function as a test for quantum field theory. This approach addresses significant deficiencies in VHF GW research, improving detection sensitivity and facilitating the advancement of next-generation radio telescopes such as FASTA and Square Kilometre Array, which feature larger fields of view and enhanced gain.

The radiation physics of bright prompt optical emission of gamma-ray bursts (GRBs) remains a puzzle. Assuming that the GRB ejecta is structured, we investigated this issue by characterizing the ejecta as an ultrarelativistic uniform jet core surrounded by a mild-relativistic cocoon. The mixed jet-cocoon (MJC) region can accelerate particles through the shear acceleration mechanism. Parameterizing the radial velocity profile of the MJC region with an exponential function and assuming a uniform magnetic field configuration, we show that the synchrotron radiation of the shear-accelerated electrons can produce a bright optical flash. Emission of the self-synchrotron Compton process of the electron population can result in an X-ray excess and an extra MeV–GeV gamma-ray flash relative to the Band function component in the keV–MeV band, which is attributed to the synchrotron radiation of the shock-accelerated electrons in the jet core. Our model reasonably represents the extremely bright optical flash and spectral characteristics of GRBs 990123, 080319B, and 130427A. The inferred magnetic field strength of the MJC region is above 10⁵ G, potentially suggesting that the jets of these GRBs are highly magnetized.

Supercritical accretion onto compact objects is expected to drive optically thick winds, resulting in observed X-ray emission as a function of viewing angle. However, their optical emission, either from the outer accretion disk or companion surface, tends to be nearly isotropic. Based on a sample of luminous and very soft X-ray sources that are argued to be supercritical accretion systems viewed close to edge-on, we identify the optical counterparts for some of them and compare the optical properties with those of ultraluminous X-ray sources, which are supposed to be supercritical accretion systems viewed close to face-on. The optical luminosity is found in a wide range, with the absolute visual magnitude ranging from dimmer than −1.2 in some sources to about −7 in one case. Most sources show a power-law-like spectrum, while four of them display a blackbody shape. One of them shows an optical spectrum resembling a B-type main sequence, suggesting that it may be a Be white dwarf system. Strong variability in flux at timescales as short as 10 days are revealed, indicating that some of these sources are powered by accretion onto compact objects. These suggest that the luminous and very soft X-ray sources in nearby galaxies have a diverse population, and some of them are indeed consistent with emission from supercritical accretion, with consistent optical magnitudes and colors. Future optical spectroscopic observations are needed to further constrain their natures.

Using 148 out-axis gamma-ray bursts (GRBs), we build their spectrum–energy relations of peak energy versus isotropic energy, peak energy versus peak luminosity, and peak energy versus jet-calibrated energy, which are corrected for a structured jet model. These relations are found to depend on the observer’s viewing angle as long as the observer is within the jet cone. After converting the out-axis energy relations to the in-axis situations, we find that the corresponding in-axis energy relations are universally steeper, of which all of them can be roughly interpreted by the synchrotron radiation mechanism as shown in Xu et al. Meanwhile, we notice that the in-axis means of isotropic energies are about 1 order of magnitude larger than the out-axis means for both short and long bursts except the supernova-associated GRBs. Furthermore, we apply all the newly found energy relations to construct the Hubble diagrams of out/in-axis bursts. It is found that the in-axis Hubble diagrams are better cosmological indicators.

The discovery of supermassive black holes (SMBHs) at high redshifts has intensified efforts to understand their early formation and rapid growth during the cosmic dawn. Using a semi-analytical cosmological framework, we investigate the role of tidal disruption events (TDEs) involving Population III (Pop III) stars in driving the growth of heavy-seed black holes (10⁴−10⁶M_⊙). Our results indicate that Pop III TDEs significantly accelerate the growth of relatively lighter massive black holes (∼10⁴−10⁵M_⊙), allowing them to increase their mass by roughly an order of magnitude within the first 10 Myr. Cosmological evolution modeling further supports such Pop-III-TDE-driven growth scenarios being consistent with the formation pathways of observed luminous high-redshift quasars originating from seed black holes at 10 < z < 15. We also discuss future observational probes of these early-stage growth processes that future facilities, including space-based gravitational-wave observatories and infrared telescopes like JWST, could potentially conduct. These findings provide a clear observational framework to test the critical role of Pop III star interactions in the rapid buildup of SMBHs during the earliest epochs.

Kinetic simulations excel at capturing microscale plasma physics phenomena with high accuracy, but their computational demands make them impractical for modeling large-scale space and astrophysical systems. In this context, we build a surrogate model, using Deep Operator Networks (DeepONets), based upon the Vlasov–Poisson simulation data to model the dynamical evolution of plasmas, focusing on the Landau damping process—a fundamental kinetic phenomenon in space and astrophysical plasmas. The trained DeepONets are able to capture the evolution of electric field energy in both linear and nonlinear regimes under various conditions. Extensive validation highlights DeepONets’ robust performance in reproducing complex plasma behaviors with high accuracy, paving the way for large-scale modeling of space and astrophysical plasmas.

In this work, we study how the abundance and dynamics of populations of disrupting satellite galaxies change systematically as a function of host galaxy properties. We apply a theoretical model of the phase-mixing process to classify intact satellite galaxies and stellar streamlike and shell-like debris in ∼1500 Milky Way–mass systems generated by a semi-analytic galaxy formation code, SatGen. In particular, we test the effect of host galaxy halo mass, disk mass, ratio of disk scale height to length, and stellar feedback model on disrupting satellite populations. We find that the counts of tidal debris are consistent across all host galaxy models, within a given host mass range, and that all models can have streamlike debris on low-energy orbits, consistent with that observed around the Milky Way. However, we find a preference for streamlike debris on lower-energy orbits in models with a thicker (lower-density) host disk or on higher-energy orbits in models with a more massive host disk. Importantly, we observe significant halo-to-halo variance across all models. These results highlight the importance of simulating and observing large samples of Milky Way–mass galaxies and accounting for variations in host properties when using disrupting satellites in studies of near-field cosmology.

We present the results of astrochemical modeling of complex organic molecules (COMs) in the ice and gas of the prestellar core L1544 with the recently updated MONACO rate equation-based model. The model includes, in particular, nondiffusive processes, new laboratory verified chemical routes for acetaldehyde and methane ice formation, and variations of H and H₂ desorption energies depending on the surface coverage by H₂ molecules. For the first time, we simultaneously reproduce the abundances of several oxygen-bearing COMs in the gas-phase, the approximate location of the peak of methanol emission, as well as the abundance of methanol in the icy mantles of L1544. Radical–radical reactions on the grain surface between species such as CH₃, CH₃O, and HCO efficiently proceed nondiffusively. COMs are delivered to the gas-phase via chemical desorption amplified by the loops of H-addition/abstraction surface reactions. However, gas-phase chemical reactions as well provide a noticeable input to the formation of COMs in the gas, but not to the COMs solid-state abundances. This particularly applies for CH₃CHO and CH₃OCH₃. The simulated abundances of COMs in the ice are in the range 1%–2% (for methyl formate ice) or ∼0.1% (for CH₃CHO and CH₃OCH₃) with respect to the abundance of H₂O ice. We stress a similarity between the simulated abundances of icy COMs in L1544 and the abundances of COMs in the gas-phase of hot cores/corinos. We compare our nondiffusive model with the diffusive model and provide constraints for the species’ diffusion-to-desorption energy ratios.

MeerKAT observations of the recently discovered, extremely low mass galaxy Pavo have revealed a neutral gas (H i) reservoir that was undetected in archival H i single dish data. We measure Pavo’s H i mass as , making it the lowest mass H i reservoir currently known in an isolated galaxy (with a robust distance measurement). Despite Pavo’s extreme isolation, with no known neighbor within over 700 kpc, its H i reservoir is highly disturbed. It does not show clear signs of rotation, and its center of mass is offset from the stellar body center by 320 pc, while its peak is offset by 82 pc (both in projection). Despite this disturbed morphology, Pavo still appears to be consistent with the H i size–mass relation, although it is not possible to accurately determine a suitable inclination correction. Such disturbed, offset, and disorganized H i reservoirs are predicted by simulations of low-mass, star-forming dwarfs in which supernova-driven outflows efficiently disrupt the interstellar medium after a star formation (SF) event. It is likely that we are witnessing Pavo in precisely this period, tens to a few hundred Myr after a SF episode, when internal feedback has disrupted its gas reservoir.

The dynamics of star-forming gas can be affected by many physical processes, such as turbulence, gravity, supernova explosions, and magnetic fields. In this paper, we investigate several nearby star-forming regions (Orion, Upper Sco, Taurus, and Perseus) for kinematic imprints of these influences on the newly formed stars. Using Gaia DR3 astrometry and APOGEE DR17 radial velocities, we compute first-order velocity structure functions (VSFs) of young stars in galactic Cartesian coordinates in both 6D (3D positions and 3D velocities) and 4D (3D positions and each 1D velocity) to identify signatures of turbulence and anisotropic motion. We also construct 3D and 1D radial velocity profiles to identify coherent expansion trends, and compare stellar proper motions to plane-of-sky magnetic field orientations in Taurus and Perseus. We find that the VSFs are mildly anisotropic, with slightly different amplitudes, slopes, or features in different directions in several groups, but in general, they are all consistent with Larson’s Relation at intermediate length scales, especially in less compact groups. In several cases, the VSFs exhibit features suggestive of local energy injection from supernovae. Radial velocity profiles reveal clear anisotropic expansion in multiple groups, with the most extreme cases corresponding to those with the most anisotropic VSFs. In Perseus, we find that the motions of young stars are preferentially perpendicular to the local magnetic field. We find multiple, overlapping causes in each group for the observed kinematics. Our findings support that young stars remember more than just the turbulent state of their natal clouds.

The active suppression of star formation in galaxies is critical for preventing the growth of overly massive systems and explaining the formation of present-day elliptical galaxies. We present a high-resolution, spatially resolved, multiwavelength study of two z ∼ 0.7 massive post-starburst galaxies, SDSS J1448+1010 and SDSS J2258+2313, from the Studying Quenching in Intermediate-z Galaxies: Gas, anguar momentum, and Evolution (SQuIGGE) survey, providing new insights into the role of mergers in driving quenching. Atacama Large Millimeter/submillimeter Array CO(2–1) observations show that both galaxies removed ∼50% of their molecular gas into extended tidal tails, spanning up to 65 kpc, following recent mergers. Hubble Space Telescope Wide Field Camera 3 imaging and grism spectroscopy show that while SDSS J1448+1010 exhibits Hα emission in its northern tidal tail consistent with ongoing star formation, SDSS J2258+2313 lacks detectable star-forming activity outside the central galaxy. Very Large Array 6 GHz continuum data reveal compact radio emission in SDSS J2258+2313, while SDSS J1448+1010 hosts small radio jets indicative of active galactic nucleus activity. Both galaxies retain substantial molecular gas reservoirs in their central regions, which appear more turbulent than “normal” star-forming galaxies, likely contributing to the observed low star formation rates in the hosts. Despite the similarities in their cold gas content and tidal features, the galaxies are distinct from each other in their star formation, gas–star alignment, and radio morphology, highlighting the complexity of tidal gas removal as a quenching mechanism at intermediate redshifts.

Type IIn supernovae (SNe) resembling SN 2009ip (09ip-like SNe) originate from the interaction between circumstellar material (CSM) and the ejecta. This subclass not only shares similar observational properties around the maximum but is also commonly characterized by a long-duration precursor before its maximum. Investigating the observed properties of the precursor provides constraints on the mass-loss history of the progenitor. We present observational data of SN 2023vbg, an 09ip-like type IIn SN that displayed unique observational properties compared to other 09ip-like SNe. SN 2023vbg showed a long-duration precursor at M_g ∼ −14 mag lasting for ∼100 days, followed by a bright bump at M_g ∼ −17 mag at 12–25 days before the maximum. The luminosity of the precursor is similar to those of other 09ip-like SNe, but the bright bump has not been observed in other cases. After reaching the peak luminosity, the light curve exhibited a relative smooth decline. While the Hα profile displays two velocity components (∼500 and 3000 km s⁻¹), a broad component observed in other 09ip-like SNe was not seen, but it may emerge later. We suggest that these properties are explained by the difference in the CSM structure as compared to other 09ip-like SNe; SN 2023vbg had an inner denser CSM component, as well as generally smooth CSM density distribution in a more extended scale than in the others. Such diversity of CSM likely reflects the diversity of pre-SN outbursts, which in turn may mirror the range of evolutionary pathways in the final stages of the progenitors.

Extended emission line nebulae around galaxies or active galactic nuclei (AGNs) provide a unique window to investigate the galactic ecosystem through the circumgalactic medium (CGM). Using Subaru Hyper Suprime-Cam narrowband imaging and spectroscopic follow-up, we serendipitously discover “Oxyster”—a large ionized nebula next to an interacting starburst galaxy at z = 0.924. The nebula is traced by extended [O ii] λλ3726, 3729 (∼30 kpc) and [O iii] λ5007 (∼20 kpc) emission lines. On the nebula luminosity–size plane, Oxyster surpasses the extended narrow-line regions around low-z AGNs, resembling a higher-z analog of “Hanny’s Voorwerp.” However, its uniformly low [O iii]/[O ii] ratio (O32) sets it apart from typical AGN light echoes. For the host galaxy, Hubble Space Telescope and JWST images reveal a disturbed red disk galaxy with a single blue spiral “arm.” Spectral energy distribution fitting suggests the (2–6) × 10¹⁰M_⊙ host galaxy sits above the star-forming main sequence with an ongoing starburst, especially in the “arm,” and has <5% luminosity contribution from AGNs, consistent with X-ray nondetection and the radio continuum. Standard photoionization and shock models struggle to explain simultaneously Oxyster’s emission line luminosities, low O32 ratio, and the nondetection of the Hβ line. A plausible explanation could involve the combination of a recent (<10⁸ yr) starburst and a low-luminosity AGN (L_bol ∼ 1 × 10⁴² erg s⁻¹). While Oxyster’s nature awaits future investigation, its discovery highlights the potential of ground-based narrowband imaging to uncover extended emission line nebulae around non-AGN systems, opening new avenues for studying the CGM of normal galaxies in the early Universe.

Faraday rotation measure (RM) synthesis is a well-known approach originated in B. J. Burn and later developed by M. A. Brentjens & A. G. de Bruyn for studying magnetic fields. This work presents a complementary approach—the polarization frequency analysis (PFA)—allowing for the properties of the turbulent magnetic field, which are difficult to include in B. J. Burn’s original approach. Based on synthetic polarization observation of magnetohydrodynamic turbulence simulation data, we study the influence of the coupling effect between density and magnetic field on synchrotron polarization dispersion. By applying the PFA to different simulated interstellar turbulence environments, we find that the PFA technique can reveal the scaling slope of the turbulent magnetic field in the case of a weak coupling effect and can also reflect the scaling slope of the RM in the case of a strong coupling effect. Since it avoids the influence of Faraday depolarization, the PFA technique is a promising way to uncover turbulence properties using observational data from the Low-Frequency Array for Radio Astronomy and the Square Kilometre Array.

Recent LHAASO observations hint at potential spectral hardening around 20 TeV in M87’s very high energy emission, suggesting a possible new radiation component. In this work, we construct averaged multiwavelength spectral energy distributions by combining data from Chandra and Swift-UVOT/XRT covering the same period as the LHAASO detection to investigate the origin of this feature. We test several radiation mechanisms, including the pp interaction, proton synchrotron emission, photomeson process, and two-zone leptonic model. We find that only the pion decay gamma rays in pp interactions can interpret this feature in the framework of the one-zone model. With analytical analysis, we prove that proton synchrotron emission cannot generate a hard spectrum above 0.17 TeV. The photomeson model requires an emission zone compressed near the Schwarzschild radius of the central supermassive black hole, incompatible with broadband optical-GeV spectral constraints. In addition, the two-zone leptonic model also emerges as a viable alternative.

We compare halo mass estimates from three galaxy group catalogs (redMaPPer, Yang21, and Zou21) with those derived from gravitational lensing measurements. Each catalog employs distinct methodologies, including mass–richness relations, abundance matching, and luminosity-based calibration. A linear correlation is observed between catalog-estimated and lensing-derived masses. The redMaPPer catalog shows the best agreement, especially for lower-redshift groups, with minor deviations in higher-redshift bins. Yang21 is the only catalog containing low mass groups, which gives a reasonably good mass estimation, except for the lowest mass bin. Cross-matched groups between redMaPPer and Yang21 reveal the former catalog provides more accurate mass estimation, while the Yang21 makes underestimation of halo mass for those sharing the central galaxy with redMaPPer and overestimation of halo mass for those with different center determination with redMaPPer and for the unique Yang21 groups. These findings emphasize the importance of redshift-dependent calibration and refined group definitions for accurate mass estimation.

High rates of stable mass transfer likely occur for some binary star systems, but the resulting flow of mass and angular momentum (AM) is unclear. We perform hydrodynamical simulations of a polytropic donor star and a point-mass secondary to determine the mass, AM, and velocity of gas that leaves the system, and the dependence on binary parameters such as mass ratio. The simulations use an adiabatic equation of state and do not include radiative cooling or irradiation of the outflow. Mass transfer is initiated by injecting heat into the stellar envelope, causing it to gradually inflate and overflow its Roche lobe. The transferred mass flows into an accretion disk, but soon begins to escape through the outer Lagrange point (L2), with a lesser amount escaping through the L3 point. This creates an equatorially concentrated circumbinary outflow with an opening angle of 10°–30° with a wind-like density profile ρ ∝ r⁻². We find that the ratios of the specific AM of the outflowing gas over that of the L2 point are approximately {0.95, 0.9, 0.8, 0.65} for mass ratios q = {0.25, 0.5, 1, 2} (accretor/donor). The asymptotic radial velocity of the outflowing gas, in units of the binary orbital velocity, is approximately 0.1–0.2 for the same mass ratios, except for q = 0.25, where it might be higher. This outflow, if ultimately unbound from the binary, may be a source of circumstellar material that interacts with ejecta from a subsequent supernova or stellar merger.

Star formation is a fundamental, yet poorly understood, process of the Universe. It is important to study how star formation occurs in different galactic environments. Thus, here, in the first of a series of papers, we introduce the Low-metallicity Star Formation (LZ-STAR) survey of the Sh2-284 (hereafter S284) region, which, at Z ∼  0.3–0.5Z_⊙, is one of the lowest-metallicity star-forming regions of our Galaxy. LZ-STAR is a multifacility survey, including observations with JWST, the Atacama Large Millimeter/submillimeter Array (ALMA), Hubble Space Telescope, Chandra, and Gemini. As a starting point, we report JWST and ALMA observations of one of the most massive protostars in the region, S284p1. The observations of shock-excited molecular hydrogen reveal a symmetric, bipolar outflow originating from the protostar, spanning several parsecs, and fully covered by the JWST field of view and ALMA observations of CO(2–1) emission. These allow us to infer that the protostar has maintained a relatively stable orientation of disk accretion over its formation history. The JWST near-infrared continuum observations detect a centrally illuminated bipolar outflow cavity around the protostar, as well as a surrounding cluster of low-mass young stars. We develop new radiative transfer models of massive protostars designed for the low metallicity of S284. Fitting these models to the protostar’s spectral energy distribution implies a current protostellar mass of ∼10 M_⊙ has formed from an initial ∼100 M_⊙ core over the last ∼3 × 10⁵ yr. Overall, these results indicate that massive stars can form in an ordered manner in low-metallicity, protocluster environments.

The existence of billion-solar-mass black holes hosted in luminous quasars within the first gigayear of cosmic history poses a challenge to our understanding of supermassive black hole (SMBH) growth. The problem is further exacerbated by the very short quasar lifetimes of t_Q ≲ 10⁶ yr, as derived from the extent of their proximity zone (PZ) sizes observed in the quasars’ rest-UV spectra. However, the quasar lifetime estimates based on the extents of the PZs may be underestimated, as time-variable obscuration effects might have limited the quasars’ emission along our sightline in the past. In this work, we present independent quasar lifetime measurements for six quasars at z ∼ 6 leveraging the extended nebular emission perpendicular to our line of sight. We use observations from the Very Large Telescope/Multi-Unit Spectroscopic Explorer to search for extended Lyα emission in the circumgalactic medium around quasars with small PZs and estimate their lifetimes as the light travel time between the SMBH and the outer edge of the nebula. We find agreement between the independent lifetime estimates. For one object we find a proximate absorption system prematurely truncating the extent of the quasar’s PZ, which thus results in an expected discrepancy between the lifetime estimates. Our results provide further evidence that the quasars’ current accretion episode has only recently begun, challenging our models of SMBH growth.

Fast radio bursts (FRBs) are brief, high-energy bursts of radio waves from extragalactic sources, and their origin remains an open question. In this paper, we perform a comprehensive analysis of the FRB population using the first CHIME/FRB catalog, focusing on their energy and redshift distributions, with careful consideration of selection effects. We investigate a range of models, including the Schechter function and the broken power-law function for the energy distribution, and several redshift evolution models, such as the star formation history (SFH) model, as well as models incorporating time delays relative to the SFH or additional redshift evolution factors. Our results indicate that the energy distribution of FRBs is best described by the Schechter function, with a power-law index of and a characteristic cutoff energy of erg. Furthermore, we find no evidence for redshift evolution in the energy distribution of FRBs. As for their redshift distribution, our analysis shows that it follows the cosmic SFH, without requiring additional delayed components or redshift evolution factors, suggesting that most FRBs likely originate from young stellar populations. Simultaneously, we infer a local volumetric rate of for E > 10³⁹ erg. These results, robust against CHIME observational biases, may provide new insights into the underlying properties of the FRB population.

We consider if outflowing winds that are detected via narrow absorption lines (NALs) with FWHM of <500 km s⁻¹ (i.e., NAL outflows) in quasar spectra contribute to feedback. As our sample, we choose 11 NAL systems in eight optically luminous quasars from the NAL survey of T. Misawa et al. (2007a), based on the following selection criteria: (i) they exhibit “partial coverage” suggesting quasar origin (i.e., intrinsic NALs), (ii) they have at least one low-ionization absorption line (C ii and/or Si ii), and (iii) the Lyα absorption line is covered by available spectra. The results depend critically on this selection method, which has caveats and uncertainties associated with it, as we discuss in a dedicated section of this paper. Using the column density ratio of the excited and ground states of C ii and Si ii, we place upper limits on the electron density as n_e < 0.2–18 cm⁻³ and lower limits on their radial distance from the flux source R as greater than several hundreds of kpc. We also calculate lower limits on the mass outflow rate and kinetic luminosity of 1.9–5.5 and –49.8, respectively. Taking the NAL selection and these results at face value, the inferred feedback efficiency can be comparable to or even larger than those of broad absorption line and other outflow classes, and large enough to generate significant active galactic nucleus feedback. However, the question of the connection of quasar-driven outflows to NAL absorbers at large distances from the central engine remains open and should be addressed by future theoretical work.

Nucleosynthetic isotope anomalies have been documented within the solar protoplanetary disk for several isotopes, including ⁴⁸Ca, ⁵⁰Ti, ⁵⁴Cr, ⁹⁴Mo, and ⁹⁶Zr. However, the existence of isotopic heterogeneities for short-lived radionuclides such as ²⁶Al remains debated. Here, we investigate potential heterogeneity in the ²⁶Al distribution by examining nucleosynthetic ⁵⁰Ti and ²⁶Al–²⁶Mg isotope systematics in high-temperature early solar system solids—Ca-Al-rich inclusions (CAIs) and hibonites from CM chondrites—and comparing these with presolar grain data. We present high-precision titanium isotope measurements for 13 CAIs, comprising 11 ²⁶Al-rich “normal”-type and two ²⁶Al-poor fractionation and unidentified nuclear effect (FUN)-type CAIs. Our data, combined with previously published results, reveal a fundamental decoupling between significant nucleosynthetic ⁵⁰Ti anomalies and high abundances of ²⁶Al, a pattern also present in presolar grains. We propose that this mutual exclusivity of ⁵⁰Ti and ²⁶Al observed in CAIs and CM hibonites is inherited directly from protosolar molecular cloud material. Specifically, this isotopic signature reflects the mixing of newly formed, ²⁶Al-rich molecular cloud material with older, Galactically inherited ²⁶Al-poor dust characterized by large nucleosynthetic ⁵⁰Ti variability. Consequently, solids exhibiting substantial ⁵⁰Ti anomalies (²⁶Al-poor FUN-type CAIs and CM hibonites) predominantly inherited older, ²⁶Al-poor presolar dust, whereas those with minimal ⁵⁰Ti anomalies and abundant ²⁶Al (²⁶Al-rich normal CAIs and CM hibonites) incorporated more of the younger, ²⁶Al-rich component. This inherited isotopic signature provides a consistent explanation for disk-scale nucleosynthetic heterogeneity in bulk meteorites, challenging the widely accepted notion that the canonical ²⁶Al/²⁷Al ratio of 5.25 × 10⁻⁵ in ²⁶Al-rich CAIs represents the solar system average.

Using measurements from the Alpha Magnetic Spectrometer (AMS-02) aboard the International Space Station, we have examined the long-term variations in galactic cosmic ray (GCR) proton fluxes in 2011–2018. The AMS-02 data allow for the study of time profiles and the rigidity dependence of the long-term variations observed directly in space in a wide rigidity range from 1 to 100 GV. We have investigated the rigidity dependence of the amplitude of the long-term GCR variations described by the power-law fitting over the solar cycle. For a physical interpretation, we have considered the relationship between long-term GCR variations and heliospheric magnetic field turbulence using power spectral density frequency exponents. The apparent solar cycle variability can be seen in the time profile of the spectral index γ of the power-law rigidity spectrum of long-term GCR variations for 2006–2018 during solar cycle 24. The spectral index γ shows a tendency to be higher for the solar maximum phase compared to the solar minimum phase. Furthermore, we find evidence of the energy-dependent rigidity spectrum of the long-term GCR variations observed by AMS-02. We reveal the soft rigidity spectrum of the GCR isotropic intensity variations for the solar maximum and the hard rigidity spectrum for the solar minimum owing to the essential temporal rearrangements of the structure in the heliospheric magnetic field turbulence from the maxima to minima epoch of solar activity. The long-term GCR variations by AMS-02 show the softening of the spectra toward higher energies.

We explore constraints on the size of cool gas clouds in the circumgalactic medium (CGM) obtainable from the presence, or lack thereof, of refractive scattering in fast radio bursts (FRBs). Our refractive analysis sets the most conservative bounds on parsec-scale CGM clumpiness as it does not make assumptions about the turbulent density cascade. We find that the bulk of low-redshift cool CGM gas, constrained to have densities of n_e ≲ 10⁻² cm⁻³, likely cannot produce two refractive images and, hence, scattering. It is only for extremely small cloud sizes ≲ 0.1 pc (about 100 times smaller than the so-called shattering scale) that such densities could result in detectable scattering. Dense n_e ≳ 0.1 cm⁻³ gas with shattering-scale cloud sizes is more likely to inhabit the inner several kiloparsecs of the low-redshift CGM; such clouds would result in multiple refractive images and large scattering times ≳ 1−10 ms, but a small fraction of FRB sight lines are likely to be affected. We argue that such large scattering times from an intervening CGM would be a signature of subparsec clouds, even if diffractive scattering from turbulence contributes to the overall scattering. At redshift z ∼ 3, we estimate ∼0.1% of FRBs to intersect massive protoclusters, which may be the most likely place to see scattering owing to their ubiquitous n_e ≈ 1 cm⁻³ cold gas. While much of our discussion assumes a single cloud size, we show similar results hold for a CGM cloud-size distribution motivated by hydrodynamic simulations.

Although shock waves have been well documented in fundamental-mode RRab stars, their existence in first-overtone pulsator stars, RRc stars, has remained uncertain. Building upon the spectroscopic frameworks established by M. Chadid et al., we present the first direct detection of multistructured shock phenomena in RRc stars. Using high-resolution phase-resolved spectroscopy, we identify unambiguous shock signatures, including Hα emission, line-doubling, and large-scale variations in radial velocity and line broadening.Our analysis reveals a structured sequence of distinct shock fronts: the main outward shock, Sh_He+H, the ballistic shock, Sh_Ball, and a gravitational collapse shock, Sh_Gravity. These phenomena produce measurable dynamical and spectroscopic effects at both photospheric and higher atmospheric layers. We find that RRc stars sustain hypersonic shock regimes despite the absence of He I or He II emission typically used in RRab classification schemes. This discrepancy is attributed to the compact and low-opacity nature of RRc atmospheres, which promotes rapid shock dissipation. These discoveries challenge conventional models of RRc atmospheres and update the classification scheme. We propose an extension to existing classification frameworks to accommodate the unique shock dynamics of RRc stars. These results challenge the long-standing assumption that first-overtone RR Lyrae pulsators lack strong shocks and demonstrate that RRc stars exhibit complex, multiphase atmospheric dynamics. Altogether, our findings reshape the current understanding of RRc atmospheric dynamics.

Understanding the location and evolution of the cool dense prominence in relation to the large-scale structure of coronal mass ejections (CMEs) is critical to distinguish between different CME initiation mechanisms and to further deepen our understanding of CME evolution through the heliosphere. Combining remote observations of extreme-ultraviolet images and white-light coronagraphs and heliospheric imagers (HIs) obtained from the Solar Dynamics Observatory, Solar and Heliospheric Observatory, STEREO-A, and Solar Orbiter, we present an analysis of the continuous tracking from the corona to interplanetary space of the substructures of a CME associated with a prominence that erupted on 2022 September 23. The prominence is found to remain bright and compact during the CME propagation for more than three days. We investigate the kinematic evolution of the CME substructures as the CME propagated to around 0.5 au. We find that for the first 0.28 au, both the CME front and prominence propagated coherently, indicating that the prominence was tied to the CME magnetic structure. Beyond 0.28 au, the CME bright front was seen to be distorted. However, the prominence continued to propagate at a nearly constant velocity up to at least 0.5 au. STEREO-A/HI images further show a dark ridge-like feature trailing the CME that passed over the prominence, and the prominence appeared tilted. We deduce that the prominence propagated independently of the CME at larger distances from the Sun. Overall, this study shows that both previously proposed hypotheses—namely, that the prominence is tied to or propagates independently of the CME—are valid but within different distance ranges.

Escape velocity has long been used to constrain the mass of the dark matter (DM) halo in the Milky Way (MW). Here, we present a study of the escape velocity curve using a sample of high-velocity K giants with full 6D phase-space information and of relatively good quality, selected from LAMOST DR8 and cross-matched with Gaia DR3. To expand the high-velocity stars to larger distances, we used radius-dependent criteria of total velocity, i.e., v_GC > 300 km s⁻¹ for the solar neighborhood and for the outer region. We also selected halo stars based on v_ϕ − [Fe/H] information to ensure that the sample is isotropic. We modeled the velocity distribution with traditional power-law models to determine the escape velocity in each radial bin. For the first time, we have directly measured a relatively continuous escape velocity curve that can extend to Galactocentric radii of ∼50 kpc, finding a decline in agreement with previous studies. The escape velocity at the solar position yielded by our measurements is . Combined with the local circular velocity, we estimated the mass of the MW assuming a Navarro–Frenk–White DM profile, which resulted in a total mass of , with a concentration of . The small uncertainty implies that including the escape velocities beyond the solar neighborhood can result in a more precise mass estimate. Our derived MW mass is consistent with some recent studies using the escape velocity as well as other tracers, which may support a lower mass of the DM halo than in the past.

We present a comprehensive analysis of the HL Tau dust disk by modeling its intensity profiles across six wavelengths (0.45–7.9 mm) with a resolution of 005 (∼7 au). Using a Markov Chain Monte Carlo (MCMC) approach, we constrain key dust properties, including temperature, surface density, maximum grain size, composition, filling factor, and size distribution. The full fitting, with all parameters free, shows a preference for organics-rich dust with a low filling factor in the outer region (r ≳ 40 au), where the spectral index is ∼3.7, but amorphous-carbon-rich dust also reasonably reproduces the observed intensity profiles. Considering the scattering polarization observed at 0.87 mm, compact, amorphous-carbon-rich dust is unlikely and moderately porous dust is favored. Beyond 40 au, the maximum dust size is likely ∼100 μm if dust is compact or amorphous-carbon rich. However, if the dust is moderately porous and organics-rich, both the predicted dust surface density and dust size can be sufficiently large for the pebble accretion rate to reach ∼10 M_⊕ Myr⁻¹ in most regions, suggesting that pebble accretion could be a key mechanism for forming planets in the disk. In contrast, if the dust is amorphous-carbon-rich, forming a giant planet core via pebble accretion is unlikely due to the combined effects of low dust surface density and small dust size required to match the observed emission, suggesting other mechanisms, such as disk fragmentation due to gravitational instability, may be responsible for planet formation in the HL Tau disk.

We analyze bars formed in N-body simulations to investigate two key aspects of stellar kinematic structure of barred galaxies: the angular distributions of the radial and azimuthal components of stellar velocities, and the impact of bars on rotation curves. We find that stars on bar-supporting x₁-like orbits exhibit characteristic sawtooth-like radial velocity patterns and archlike tangential velocity patterns as a function of azimuth. In contrast, stars on box and disk orbits show little azimuthal variation, effectively smoothing the overall velocity distribution. When averaged over all orbital families, the resulting kinematics are broadly consistent with the bisymmetric model of Sellwood and Spekkens, with the amplitudes of bar-induced velocity perturbations increasing with bar strength. In addition, bars amplify the radial pressure gradient associated with enhanced random stellar motions, leading to a noticeable reduction in the mean rotational velocity. This effect becomes more pronounced with increasing bar strength, resulting in a shallower rotation curve within the bar region. We discuss our results in the context of the kinematic properties of observed barred galaxies.

We analyze a wide set of historical magnetar burst observations detected with five different instruments, calibrating these to the energy range of Fermi-GBM observations for consistency. We find a striking correlation between a magnetar’s characteristic age and both its typical burst energy and its burst activity level. Arguing that this bursting behavior also correlates with true age, we interpret it as the result of a reducing high-stress volume of the crust in an aging magnetar: Previous giant flares cause relaxation of large regions of its crust and inhibit burst clustering, while the reducing burst energy reflects the progressively shallower region of the crust where Hall drift can build stresses effectively, as the field decays through the range ∼10¹²–10¹³ G. Low-energy bursts from very young magnetars may represent failures of weak regions of the crust that have only recently solidified.

Line-resolved X-ray spectra of outflows from X-ray binaries are interesting since they provide quantifiable measures of the accreted material onto the compact object (black hole or neutron star), which can not be observed directly in the accretion disk. One such measurement that has been largely overlooked is that of the elemental abundances, which potentially provide insights into the origin of the ejected material. Using the Chandra/HETG grating spectrometer we measure and present elemental abundances in four low-mass X-ray binaries. We compare two measurement methods. One is by fitting line series of individual ions and reconstructing the absorption measure distribution (AMD), and the other is a global fit with one or two individual ionization components. All outflows feature a steep AMD strongly favoring high ionization degrees. The present abundances are consistent with previous works suggesting the abundances in the outflows are nonsolar. We find a tentative trend of increasing abundances with atomic number, which fits some core-collapse supernova models, but there is no exact match to a specific one.

Super-Earths and sub-Neptunes are the most common exoplanets, with a “radius valley” suggesting that super-Earths may form by shedding sub-Neptunes’ gaseous envelopes. Exoplanets that lie closer to the super-Earth side of the valley are more likely to have lost a significant fraction of their original H/He envelopes and become enriched in heavier elements, with CO₂ gaining in abundance. It remains unclear which types of haze would form in such atmospheres, potentially significantly affecting spectroscopic observations. To investigate this, we performed laboratory simulations of two CO₂-rich gas mixtures (with 2000 times solar metallicity at 300 and 500 K). We found that under plasma irradiation organic hazes were produced at both temperatures, with a higher haze production rate at 300 K, probably because condensation occurs more readily at lower temperature. Gas-phase analysis demonstrates the formation of various hydrocarbons, oxygen- and nitrogen-containing species, including reactive gas precursors like C₂H₄, CH₂O, and HCN, for haze formation. The compositional analysis of the haze particles reveals various functional groups and molecular formulas in both samples. The 500 K haze sample has larger average molecular sizes, a higher degree of unsaturation with more double or triple bonds present, and higher nitrogen content incorporated as N–H and C=N bonds, indicating different haze formation pathways. These findings not only improve the haze formation theories in CO₂-rich exoplanet atmospheres but also offer important implications for the interpretation of future observational data.

We present Hubble Space Telescope (HST) far-UV spectra and light curves of the magnetic cataclysmic variable (CV) LAMOST J024048.51+195226.9 (J0240), the second known CV propeller. The five consecutive HST orbits span a full 7.34 hr binary orbital period. We detect a 24.939 ± 0.006 s far-UV modulation, confirming that J0240 contains the fastest spinning white dwarf (WD) in a CV. A high N v/C iv emission line ratio is considered an indicator of a recent episode of thermal-timescale mass transfer. The observed ratio in J0240 is higher than seen in typical magnetic CVs, but far less than observed in the only other confirmed propeller, AE Aquarii (AE Aqr). We also find that J0240 is significantly less luminous than AE Aqr during both low- and high-flux states. Around orbital phase 0.5, the Si iv emission line displays a P-Cygni absorption profile, likely related to the gas accelerated in the propeller. We derive new mass-dependent limits for the surface temperature of the WD of T ≤ 11,000–15,000 K. This temperature is low enough to allow for WD core crystallization, which may be linked to magnetism in WDs, particularly those in CVs.

In cold molecular clouds, UV photolysis of icy grain mantles generates radicals that lead to new molecule formation. When radical diffusion is limited by low temperatures, oxygen atom addition and insertion reactions, enabled by photolysis of common ice components such as H₂O, CO₂, CO, and O₃, offer an alternative route to chemical complexity through the production of metastable, highly reactive O(¹D) atoms. We examine the reactivity of these oxygen atoms generated by UV photolysis of O₃ with methyl cyanide (CH₃CN). These studies are conducted in an ultra-high vacuum chamber at cryogenic and low-pressure conditions equipped with in situ infrared spectroscopy to monitor destruction and product formation in real time. We conclude that oxygen atoms rapidly insert into CH₃CN to produce primarily methyl isocyanate (CH₃NCO) in matrix-free ices. Over the range from 10 to 40 K, we observe no temperature dependence to either CH₃CN destruction or CH₃NCO production. When placing CH₃CN:O₃ in H₂O and CO₂ ice matrices, we find that CH₃NCO formation remains robust, but that the yield likely decreases due to competing reaction pathways. In the case of the H₂O ice, we also observe a shift in product branching ratios toward alternative pathways such as the formation of hydroxyacetonitrile (HOCH₂CN). Overall, our results demonstrate that oxygen atom reactivity provides an important channel for generating chemical complexity from nitriles on cold grains where radical mobility is limited.

The reflection effect is here incorporated within an earlier analytic binary system light- and velocity-curve model that includes a circumstellar equipotential disk. The modeled disk is semitransparent, to explore the attenuation and reemission of irradiance within the disk, as well as the irradiance of the companion star. The reflection functions defined in R. E. Wilson ensure efficient computation and allow multiple reflection. A capsule summary of the general binary system potential problem provides a foundation for close binary morphological ideas. Chief among these ideas is that many or perhaps most postnovae may be of the double contact morphological type. The location of an outer-disk null point of effective gravity accurately quantifies a limit on disk size. The disk should not extend beyond the outer null point, as the local material would then be unbound to the disk. The disk’s inner extent is set by another null point. The inner and outer null locations are computed at each solution iteration, thus obviating any need for the arbitrary cutoffs seen in other postnova disk models. Remarkably, impersonal light-curve solutions find the disk edge quite close to the outer null point for U Scorpii (U Sco). Other reflection-related topics include irradiation heating and measurement of disk interior density and temperature. Analyses find white dwarf masses about 3%–6% lower than in nongravitating disk models that implicitly include disk mass as part of the white dwarf. The results from CI Aquilae and U Sco analyses are tabulated and prospects for further progress are outlined.

We used the NSF Jansky Very Large Array at a frequency ν = 22 GHz to study the nearest billion-solar-mass black hole (BH), in the early-type galaxy NGC 3115 at a distance of 9.7 Mpc. We localize a faint continuum nucleus, with flux density S_{22 GHz} = 48.2 ± 6.4 μJy, to a FWHM diameter d_{22 GHz} < 59 mas (2.8 pc). We find no evidence for adjacent emission within a stagnation region of radius R_sta ∼ 360 mas (17 pc) identified in a recent hydrodynamic simulation tailored to NGC 3115. Within that region, the simulated gas flow developed into an advection-dominated accretion flow (ADAF). The nucleus’ luminosity density L_{22 GHz} = 5.4 × 10¹⁷ W Hz⁻¹ is about 60 times that of Sagittarius A^⋆. The nucleus’ spectral index (S_ν ∝ ν^α) indicates optically thin synchrotron emission. The spectral energy distribution of the nucleus peaks near ν_peak = 9 GHz. Modeling this radio peak as an ADAF implies a BH mass M_ADAF = (1.2 ± 0.2) × 10⁹M_⊙, consistent with previous estimates of (1–2) × 10⁹M_⊙ from stellar or hot-gas dynamics. Also, the Eddington-scaled accretion rate for NGC 3115, , is about 4–8 times lower than recent estimates for Sagittarius A^⋆.

We use archival data from the Diffuse Infrared Background Experiment (DIRBE) to map the polycyclic aromatic hydrocarbon (PAH) 3.3 μm emission feature and analyze its correlation with anomalous microwave emission (AME) in 98 compact sources identified by the Planck collaboration. We find that while far-IR thermal dust emission continues to be a better tracer of AME in most of the considered regions, 17% of the AME sources are better correlated with emission from small PAHs as traced by DIRBE. Furthermore, of the 27 sources that were identified as highly significant AME detections in the Planck analysis, 37% prefer PAHs as an AME tracer. Further work is required to understand to what extent local interstellar conditions are affecting PAH emission mechanisms and to reveal the underlying carriers of AME.

We report the first detection of circular polarization in 4.7 GHz excited OH masers in star-forming regions made using full Stokes measurements with the Green Bank 100 m telescope. The Zeeman shift between the two circular components provides a measure of the magnetic field pervading these maser spots. Three different methods are used to determine the shift in velocity between the RCP and LCP components. We find fields with B ∼ 100 mG using archival molecular parameters that have limited precision and uncertain values. Reservations of using 1.7 and 6.0 GHz OH masers to estimate magnetic fields in star-forming regions are discussed.

Knowledge of the X-ray properties of the hot-gas halos of early-type galaxies (ETGs) has significantly advanced in the past years, for large and homogeneously investigated samples. We compare these results with the X-ray properties of an exploratory set of gas evolution models in realistic ETGs, produced with our high-resolution 2D hydrodynamical code MACER that includes active galactic nucleus feedback and accretion from a circumgalactic medium. The model X-ray emission and absorption are integrated along the line of sight, to obtain maps of the surface brightness Σ_X and temperature T_X. The X-ray diagnostics considered are the luminosity and average temperature for the whole galaxy (L_X and 〈T_X〉) and within five optical effective radii (L_X,5 and 〈T_X,5〉) and the circularized profiles Σ_X(R) and T_X(R). The values for L_X, L_X,5, 〈T_X〉, and 〈T_X,5〉 compare very well with those observed. The Σ_X(R) and T_X(R) also present qualitative similarities with those of the representative galaxy NGC 5129 and those of ETGs with the most commonly observed shape for T_X(R): Σ_X(R) matches the observed profile over many optical effective radii R_e, and T_X(R) reproduces the characteristic bump that peaks at R = (1 ÷ 3)R_e. Inside the peak position, T_X(R) declines toward the center, but the explored models are systematically hotter by ≃30%; possible explanations for this discrepancy are discussed. Interestingly, Σ_X(R) and T_X(R) as large as those observed outside R ≃ R_e are reproduced only with significant accretion from a circumgalactic medium, highlighting its importance.

Studying the emergence of magnetic fields is essential for understanding the physical mechanisms behind various phenomena in the solar atmosphere. Most importantly, the emerging fields offer valuable insights into how energy and mass are transferred to the upper solar atmosphere. As a result, they have garnered significant attention from both observational and theoretical perspectives. In this article, we present two models of quiet-Sun-like magnetic fields generated by the Bifrost code. We compare these models with observations from the Swedish 1 m Solar Telescope (SST) and the Interface Region Imaging Spectrograph (IRIS). By tracking the magnetic features in both the SST and Bifrost data, we determine the similarities and differences between the fields identified in the models and those observed. We conduct a quantitative comparison of various properties, such as flux content, flux densities, horizontal and line-of-sight velocities, lifetimes, sizes, and surface interactions. Additionally, we identify and analyze the properties of the largest emerging bipoles in the SST and Bifrost data. Our findings indicate that the magnetic bipoles in the Bifrost simulations are generally stronger than those observed with the SST. However, a qualitative comparison of the chromospheric and transition region responses to the emerging fields in the Bifrost models, SST, and IRIS observations shows similar heating processes occurring above and around the emerging fields. Finally, we outline our plans for future work aimed at studying the emergence of magnetic fields in the quiet Sun, with a particular focus on the chromosphere and upper atmospheric layers.

We aim to improve cluster lens modeling and source reconstruction by utilizing the full information in giant, caustic-crossing arcs lensed by galaxy clusters. Lens models are generally constrained using image positions and assuming point sources, but spatially extended giant arcs provide more constraints; however, they require a more complex model that accounts for the structure of the extended source. We seek to determine whether improvements to the lens model and reconstructed source merit the difficulty of handling the extra constraints. We choose the spatially extended z = 0.725 giant arc in the z = 0.375 Abell 370 galaxy cluster field for our study. We present (1) a series of pixel-based source reconstructions (PBSRs) for cluster mass models exploring the range of uncertainties in our fiducial model, (2) a similar analysis done using a prototype Python de-lensing code for cluster mass models from each of the Hubble Frontier Fields (HFF) modeling teams, (3) an optimized model with PBSR, and (4) and an investigation of how our optimized model affects the cluster mass model locally and globally in the highest-magnification regions. We find that our optimized model (1) is able to correct resolution-limited assumptions in cluster model inputs local to the arc, (2) has significantly smaller arc model residuals than results from the standard HFF models, and (3) affects the critical curves and therefore the information derived from highest-magnification zones most significantly in regions local to the arc.

We investigate the redshift evolution of intrinsic alignments (IAs) of the shapes of galaxies and subhalos with the large-scale structures of the Universe using the cosmological hydrodynamic simulation, Horizon Run 5. To this end, early-type galaxies are selected from the simulated galaxy catalogs based on stellar mass and kinematic morphology. The shapes of galaxies and subhalos are computed using the reduced inertia tensor derived from mass-weighted particle positions. We find that the misalignment between galaxies and their corresponding dark matter subhalos decreases over time. We further analyze the two-point correlation between galaxy or subhalo shapes and the large-scale density field traced by their spatial distribution, and quantify the amplitude using the nonlinear alignment model across a wide redshift range from z  =  0.625 to z  =  2.5. We find that the IA amplitude, A_NLA, of galaxies remains largely constant with redshift, whereas that of dark matter subhalos exhibits moderate redshift evolution, with a power-law slope that deviates from zero at a significance level exceeding 3σ. Additionally, A_NLA is found to depend on both the stellar mass and kinematic morphology of galaxies. Notably, our results are broadly consistent with existing observational constraints. Our findings are in good agreement with previous results of other cosmological simulations.

Tidal disruption events (TDEs) occur when stars pass close enough to supermassive black holes to be torn apart by tidal forces. Traditionally, these events are studied with computationally intensive hydrodynamical simulations. In this paper, we present a fast, physically motivated two-stage model for TDEs. In the first stage, we model the star’s tidal deformation using linear stellar perturbation theory, treating the star as a collection of driven harmonic oscillators. When the tidal energy exceeds a fraction γ of the star’s gravitational binding energy (with ), we transition to the second stage, where we model the disrupted material as free particles. The parameter γ is determined with a one-time calibration to the critical impact parameter obtained in hydrodynamical simulations. This method enables fast computation of the energy distribution dM/dE and fallback rate dM/dT while offering physical insight into the disruption process. We apply our model to MESA-generated profiles of middle-age main-sequence stars. Our code is available on GitHub (https://github.com/ZihanZhou26/PerTDE).

The dynamical stability of differentially rotating neutron stars, including hypermassive neutron stars, is of paramount importance in understanding the fate of the postmerger remnant of binary neutron stars mergers and the formation of a black hole during core-collapse supernovae. We study systematically the dynamical stability of differentially rotating neutron stars within a broad range of masses, rotation rates, and degrees of differential rotation, modeled as polytropes with Γ = 2. We pay particular attention to quasi-toroidal configurations that are outside the parameter space region explored in previous works. We estimate the limits of the region of stability against quasi-radial perturbations by performing an extensive set of numerical simulations. We find that some of the stability criteria proposed in the past are not sufficient or necessary to determine stability if differential rotation is present, and propose a new, more general criterion. We show that there is a large parameter space that allows for quasi-toroidal configurations that will not collapse immediately to a black hole and that can sustain masses up to ∼2.5 times the maximum mass of a nonrotating neutron star.

We determine magnetic fields from the photosphere to the upper chromosphere combining data from the Hinode satellite and the CLASP2.1 sounding rocket experiment. CLASP2.1 provided polarization profiles of the Mg iih and k lines, as well as of the Mn i lines around 2800 Å, across various magnetic structures in an active region, containing a plage, a pore, and the edges of a sunspot penumbra. By applying the weak-field approximation to the circular polarization profiles of these spectral lines, we obtain a longitudinal magnetic field map at three different heights in the chromosphere (lower, middle, and upper). This is complemented by data from Hinode (photospheric magnetic field), the Interface Region Imaging Spectrograph, and the Solar Dynamics Observatory (high spatial resolution observations of the chromosphere and corona). We quantify the height expansion of the plage magnetic fields and find that the magnetic fields expand significantly in the middle chromosphere, shaping the moss observed above in the transition region and corona. We identified an area with polarity reversal at the upper chromosphere around the edge of the pore, suggesting the presence of a magnetic discontinuity in the upper chromosphere. Transient and recurrent jetlike events are observed in this region, likely driven by magnetic reconnection. Around the penumbral edge, we find large-scale magnetic fields corresponding to the superpenumbral fibrils seen in the upper chromosphere. In the superpenumbral fibrils, we find Zeeman-induced linear polarization signals, suggesting the presence of a significantly inclined magnetic field, as strong as 1000 G in the upper chromosphere.

We present the Virtual Research Assistant (VRA) of the ATLAS sky survey, which performs preliminary eyeballing on our clean transient data stream. The VRA uses histogram-based gradient-boosted decision tree classifiers trained on real data to score incoming alerts on two axes: “Real” and “Galactic.” The alerts are then ranked using a geometric distance such that the most “real” and “extragalactic” receive high scores; the scores are updated when new lightcurve data is obtained on subsequent visits. To assess the quality of the training we use the recall at rank K, which is more informative to our science goal than general metrics (e.g., accuracy, F1-scores). We also establish benchmarks for our metric based on the pre-VRA eyeballing strategy, to ensure our models provide notable improvements before being added to the ATLAS pipeline. Then, policies are defined on the ranked list to select the most promising alerts for humans to eyeball and to automatically remove bogus alerts. In production the VRA method has resulted in a reduction in eyeballing workload by 85% with a loss of follow-up opportunity <0.08%. It also allows us to automatically trigger follow-up observations with the Lesedi telescope, paving the way toward automated methods that will be required in the era of LSST. Finally, this is a demonstration that feature-based methods remain extremely relevant in our field, being trainable on only a few thousand samples and highly interpretable; they also offer a direct way to inject expertise into models through feature engineering.

By assuming the inverse square law of solar wind plasma density as representative of other stars, it is shown that just outside a star, the outward deflection of a passing radio signal at ν ≈ 1 GHz (which is capable of penetrating the plasma) is about 5 times larger than the gravitational inward deflection by the star, and the ensuing lens equation, which takes both effects into account is a cubic polynomial with three roots and a new strong lensing caustic. The geometric optics approach is valid for a radio source size ≲1 pc. Microlensing magnification of a steady background source occurs typically over a timescale of milliseconds, resulting in ≈80 fast radio bursts (FRBs) per day over the whole sky, which can only perturb the isotropy of FRB distribution at the several percent level. Moreover, repeating FRBs could be triggered by the periodic interception of the line of sight of the background source by members of a binary system. The temporal signatures of such FRBs are consistent with the power spectrum of solar wind density fluctuations on corresponding scales, except that the mean density of the wind is a few times higher than the solar value.

The evolutionary history of the Milky Way disk is imprinted in the ages, positions, and chemical compositions of individual stars. In this study, we derive the intrinsic density distribution of different stellar populations using the final data release of the Apache Point Observatory Galactic Evolution Experiment (APOGEE) survey. A total of 203,197 red giant branch stars are used to sort the stellar disk (R ≤ 20 kpc) into subpopulations of metallicity (Δ[M/H]  = 0.1 dex), age (), and α-element abundances ([α/M]). We fit the present-day structural parameters and density distribution of each stellar subpopulation after correcting for the survey selection function. The low-α disk is characterized by longer scale lengths and shorter scale heights, and is best fit by a broken exponential radial profile for each population. The high-α disk is characterized by shorter scale lengths and larger scale heights, and is generally well-approximated by a single exponential radial profile. These results are applied to produce new estimates of the integrated properties of the Milky Way from early times to the present day. We measure the total stellar mass of the disk to be M_⊙, and the average mass-weighted scale length is R_d = 2.37 ± 0.2 kpc. The Milky Way’s present-day color of (g − r) = 0.72 ± 0.02 is consistent with the classification of a red spiral galaxy, although it has only been in the “green valley” region of the galaxy color–mass diagram for the last ∼3 Gyr.

For three decades, adaptive optic surveys have revealed an excess of T Tauri binaries across a = 10–100 au in nearby star-forming regions compared to the field population of main-sequence (MS) stars. Such an excess requires that most stars are born in dense clusters and subjected to significant dynamical processing that disrupts such binaries across intermediate separations. However, we demonstrate that the apparent excess is due to an observational selection bias. Close binaries within a < 100 au clear out their dusty circumstellar disks on faster timescales compared to wide binaries and single stars. A magnitude-limited sample is therefore biased toward close binaries that have preferentially cleared out their obscuring disks. We reexamine the separation distribution of pre-MS binaries in low-density Taurus, moderately dense Upper Scorpius (Upper Sco), and the extremely dense Orion Nebula Cluster (ONC). By limiting the samples to primary spectral type/mass instead of magnitude, the artificial excess across a = 10–100 au disappears in all three environments. Across wider separations a = 100–4000 au, Taurus exhibits an excess of companions (mostly tertiaries), the ONC displays a deficit, and Upper Sco matches the field MS population. The field derives from an amalgam of all three environments, where Upper Sco corresponds to the average birth environment of solar-type stars. The total binary fraction within a < 10,000 au in Taurus is only 52% ± 7%, substantially lower than the 100% inferred from the biased observations and only slightly higher than the field MS value of 45%. N-body interactions preferentially disrupt outer tertiaries with only marginal dynamical processing of the inner binaries, especially those within a < 100 au.

Starspots are ubiquitous in young, low-mass stars, yet their impact on the spectral classification and fundamental parameter inference of pre-main-sequence stars (PMS) has been largely overlooked. In this study, we demonstrate that cool starspots systematically distort spectral morphology and bias the effective temperatures, surface gravities, and luminosities derived for nonaccreting weak-lined T Tauri stars (WTTSs). Using a sample of 56 WTTSs with high-resolution, broadband X-Shooter spectra, we perform two-temperature spectral fits that explicitly account for spot coverages and temperature contrasts. These composite models consistently outperform traditional single-temperature fits, particularly in the 3350–4000 K regime, where spot contributions dominate the red-optical and near-IR flux. Moreover, we propose that surface gravity discrepancies between optical and IR measurements are a natural consequence of spot-dominated emission in PMS stars. We find that single-temperature models can overestimate effective temperatures by up to 700 K and underestimate by 1–2 dex. Using spot-corrected effective temperatures, we derive masses and ages from traditional, magnetic, and spotted evolutionary models, finding that spot corrections systematically raise inferred masses by up to 80% and stellar ages by up to 0.5 dex. These discrepancies are strongest for stars in the 0.3–0.8 M_⊙ range. Using starspots as a proxy for magnetic topology, we find evidence that a shift from largely axisymmetric to nonaxisymmetric magnetic fields dominated by small-scale structures coincides with the formation of a radiative core during PMS evolution, effectively distinguishing between the convective and interface dynamo regimes.

In 2023 November, the Fermi Large Area Telescope detected a γ-ray flare from the high-redshift blazar GB6 B1428+4217 (z = 4.715). We initiated a multiwavelength follow-up campaign involving Swift, NuSTAR, the Sierra Nevada and Perkins Observatories, and the Effelsberg 100 m radio telescope. This source, also known as 5BZQ J1430+4204, has shown an anomalous soft X-ray spectrum in previous observations, including possible ionized absorption features or signatures of bulk Comptonization of thermal electrons, which are also detected during the flaring episode. Simultaneous optical data revealed a polarization fraction of ∼8% in the R band, confirming that synchrotron emission dominated over thermal emission from the accretion disk. The hard X-ray flux was enhanced during the flare. Modeling of the broadband spectral energy distribution suggests that the high-energy component is dominated by Compton scattering by external seed photons from the accretion disk. The origin of the flare is consistent with the injection of a hard-spectrum electron population in the emission region. With a γ-ray luminosity among the top 5% of flaring events, GB6 B1428+4217 exemplifies a prototypical MeV blazar. Its Compton-dominated spectral energy distribution and extreme luminosity are in line with expectations from the blazar sequence. High-redshift flares like this are critical for understanding jet physics in the early Universe and may improve detection prospects with future missions such as the Compton Spectrometer and Imager.

Chemical abundance measurements from stars in the Milky Way to the intragalactic medium in the Perseus Cluster have challenged the spherical explosion models. Models in the literature cannot closely match the observed element ratios, where Si, S are overproduced and Ar, Ca are underproduced. In this article, we explore the impact of the model parameters during the evolution of massive stars on the final explosive nucleosynthesis. We investigate the effects of a parameterized model of the convective process, including the mixing length parameter and the semiconvection parameter, on the production of Si-group elements. We search for the value pair that can reduce the discrepancy in the models. We conclude that a mixing length parameter of 2.2 and a semiconvection parameter of 0.03 are required to fit these criteria. Using this updated value pair, we compute a sequence of massive star models from M_ZAMS = 15–40 M_⊙. The high-resolution data from future observations, such as XRISM, will provide further details on less constrained processes in stellar evolution and supernova explosions. Future comparison with supernova models of various progenitor metallicity will further shed light on the supernova population and their relative rates on cosmological scales.

The potential habitability of tidally locked planets orbiting M stars remains uncertain. However, recent observations with JWST and numerous theoretical studies investigating atmospheric evolution over time suggest that thick atmospheres (>1 bar) with abundant surface water are increasingly unlikely. A significant challenge to habitability for tidally locked systems is the prevention of atmospheric collapse. For tenuous atmospheres, this challenge is even more extreme, since low-pressure atmospheres cannot transport heat effectively from the day- to nightside. Previous studies find that collapse is likely for CO₂ atmospheres with surface pressures less than 100 mbar for planets in the habitable zone of Trappist-1, which would significantly reduce the likelihood for long-term habitability in that system. In this study, we find that modest levels of atmospheric mineral dust mitigate this collapse for a tenuous 7.05 mbar atmosphere on a small Mars-sized planet. Dust heating modifies the vertical and zonal thermal gradients and wind sheers. Due to the rapid planetary rotation (1 yr = 6 sols), this change is reflected in the magnitude of rotational components of the global circulation, including the equatorial jet and midlatitude eddies. We find that heat transport by these components is increased in dusty simulations, and atmospheric collapse on the permanent nightside is prevented. This dust-dominated climate is consistent with a planetary atmosphere evolving towards low pressure and high aridity with time. Our findings therefore provide an alternative target to Earth-like climates around M stars and reopens the possibility of habitability in M star systems.

Photodissociation regions (PDRs) are key to understanding the feedback processes that shape interstellar matter in galaxies. One important type of PDR is the interface between H ii regions and molecular clouds, where far-ultraviolet radiation from massive stars heats gas and dissociates molecules. Photochemical models predict that as metallicity decreases, the C/CO transition occurs at greater depths in the PDR compared to the H/H₂ transition, increasing the extent of CO-dark H₂ gas in low-metallicity environments. This prediction has been difficult to test outside the Milky Way due to the lack of high-spatial-resolution observations tracing H₂ and CO. This study examines a low-metallicity PDR in the N13 region of the Small Magellanic Cloud (SMC), where we spatially resolve the ionization front, the H₂ dissociation front, and the C/CO transition using ¹²CO J = 2−1, 3−2, and [C I] 1–0 observations from the Atacama Large Millimeter/submillimeter Array and near-infrared spectroscopy of the H₂ 2.12 1–0 S(1) vibrational line, and H recombination lines from the James Webb Space Telescope. Our analysis shows that the separation between the H/H₂ and C/CO boundaries is approximately 0.043 ± 0.013(stat.) ± 0.0036(syst.) pc (equivalent to at the SMC’s distance of 62 kpc), defining the spatial extent of the CO-dark H₂ region. Compared to our plane-parallel PDR models, we find that a constant-pressure model matches the observed structure better than a constant-density one. Overall, we find that the PDR model does well at predicting the extent of the CO-dark H₂ layer in N13. This study represents the first resolved benchmark for low-metallicity PDRs.

The dynamics of stellar mass black holes (sBHs) embedded in active galactic nuclei (AGNs) could produce highly eccentric orbits near the central supermassive black hole, leading to repeated close encounters that emit gravitational waves in the Laser Interferometer Gravitational-Wave Observatory (LIGO) frequency band. Many works have focused on the mergers of sBHs in the disk that produce gravitational waves; however, sBHs in hyperbolic orbits also emit gravitational-wave bremsstrahlung that can be detected by ground-based interferometers like LIGO. In this work, we analyze the scattering of sBHs in an AGN disk as they migrate inside the disk, focusing on gravitational-wave bremsstrahlung emission. We determine how the gravitational-wave emission depends on the different parameters of the scattering experiments, such as the mass of the supermassive black hole and the sBH migration rate and mass ratio. We find that scattering with detectable gravitational-wave bremsstrahlung is more frequent around lower-mass supermassive black holes (∼10⁵⁻⁶M_⊙). We then conduct a suite of Monte Carlo simulations and estimate the rate for ground-based gravitational-wave detections to be in the range of 0.08–1194 Gpc⁻³ yr⁻¹, depending on migration forces and detection thresholds, with large uncertainties accounting for variations in possible AGN environments. The expected rate for our Fiducial parameters is 3.2 Gpc⁻³ yr⁻¹. Finally, we provide first-principle gravitational-wave templates produced by the encounters.

We here quantify the gravitational-wave (GW) phase shift appearing in the waveform of eccentric binary black hole (BBH) mergers formed dynamically in 3-body systems. For this, we have developed a novel numerical method where we construct a reference binary, by evolving the post-Newtonian () evolution equations backwards from a point near merger without the inclusion of the third object, that can be compared to the perturbed binary that evolves under the influence from the third BH. From this, we quantify how the interplay between dynamical tides, -effects, and the time-dependent Doppler shift of the eccentric GW source results in unique observable GW phase shifts that can be used to probe the dynamical assembly mechanism of individual GW sources. We further find an analytical expression for the GW phase shift, which has a universal functional form that only depends on the time-evolving BBH eccentricity. The normalization scales with the BH masses and initial separation, which can be linked to the underlying astrophysical environment. GW phase shifts from a chaotic 3-body BH scattering taking place in a cluster, and from a BBH inspiraling in a disk migration trap near a supermassive BH, are also shown for illustration.

Inaccuracy in our knowledge of the transport properties of relevant mixtures under planetary interior conditions is a roadblock in predicting the observable properties of planets in our solar system and beyond. In this work, we investigate methane–hydrogen mixtures using data sets obtained from density functional theory calculations for the electronic structure, combined with molecular dynamics simulations for the ions for a wide range of pressure and temperature. Hydrogen concentration significantly affects the equation of state (EOS) but has little influence on transport properties. We provide an analytical expression to model thermal EOS and transport properties as a function of hydrogen content, with the maximum deviation observed at low P–T conditions. These insights are particularly relevant to improve the planetary models and enhance our ability to predict the properties of “ice” giants and beyond.

We report the detection of GeV gamma-ray emission likely associated with supernova remnant (SNR) G335.2+0.1 and the finding of a molecular cloud (∼20′– in angular size) that is very likely in physical contact with the SNR and responsible for the gamma-ray emission. Using the 16.8 yr Fermi-LAT data, an extended emission, with a significance of 13.5σ and a radius 024 in 0.2–500 GeV in the uniform-disk model, was found to the adjacent east of the SNR. With archival Mopra CO-line data, a large molecular clump at local-standard-of-rest velocity ∼−48 to −43 km s⁻¹ was revealed, appearing coincident with the gamma-ray source. The SNR was found located in a cavity encircled by a “C”-shaped ring-like molecular shell at −45 to −43 km s⁻¹. This morphological agreement, together with the position-velocity diagrams made along lines cutting across the cavity, suggests that the SNR was evolving in the expanding molecular bubble created by the stellar wind of the progenitor with a mass ≳15 M_⊙. The giant molecular cloud, visible at around −46 km s⁻¹, and the associated SNR are thus estimated to lie at a kinematic distance of 3.1 kpc, with the H i absorption taken into account. We suggest that the SNR has entered the radiative phase after the blastwave recently struck the cavity wall. With the evolutionary scenario of the SNR, we demonstrate that the gamma-ray emission reported here can be naturally interpreted by the hadronic interaction between the accelerated protons escaped from the SNR shock and the eastern large molecular clump.

We present the analysis results of flux and spectral variability of the blazar OP 313 across intra-night to short-term timescales using BVRI photometric data, gathered over 25 nights from 2024 November to 2025 May, using two optical telescopes in Aryabhatta Research Institute of Observational Sciences, India. The source was in an outburst state during this period. We searched for intraday variability (IDV), using two powerful statistical tests: the power-enhanced F-test and the nested ANOVA test. The source displayed IDV in the R band for five of the 10 nights, yielding a duty cycle of 34%. During the entire monitoring of the source, it showed variations of over two mag in all B, V, R, and I data bands. We obtained a variability timescale for a variable light curve, giving us an upper limit for the size of the emission region. We generated optical spectral energy distributions of the blazar for these 25 nights, fitted a power law of form (F) and found the weighted mean spectral index to be 1.471 ± 0.004. An analysis of the color–magnitude diagram shows that, contrary to the redder-when-brighter trend typically observed in FSRQs, this source exhibits a bluer-when-brighter trend on short-term variability timescales—a behavior more commonly associated with BL Lac objects. We explore potential physical mechanisms responsible for the observed spectral variability.

The dynamics of the origin of gamma-ray emissions in gamma-ray bursts (GRBs) remains an enigma. Through a joint analysis of GRB 180427A, observed by the Fermi Gamma-ray Space Telescope and AstroSat’s Cadmium Zinc Telluride Imager, we identify emissions from two distinct regions with varying polarization properties. Time-resolved polarization analysis reveals a synchronous evolution of the polarization angle (PA) and fraction with two emission pulses, peaking with a delay of 5.09 ± 0.29 s. Spectral analysis indicates that the first pulse is characterized by a stronger blackbody component, while the second pulse exhibits a more prominent nonthermal spectrum (power law with an exponential cutoff). Using a bottom-to-top approach through simulations, we decouple the polarization properties of the individual spectral components, revealing polarization fractions (PFs) of 25%–40% for the blackbody spectrum and 30%–60% for the nonthermal spectrum. At a redshift of z ∼ 0.22, the blackbody emission originates from the jet photosphere at ∼a few 10¹¹ cm, whereas the nonthermal emission arises from an optically thin region at a few 10¹³ cm. The changing dominance of these emissions explains the observed PA shift of 60° ± 22°. The spectral cutoff at 1 MeV suggests pair opacity due to the jet’s relatively lower bulk Lorentz factor (Γ∼ a few tens). The high PF and hard low-energy spectral slopes (α > −0.5) imply a top-hat jet structure observed off-axis, near the jet’s edge. This off-axis viewing introduces anisotropy in the observed radiation within the viewing cone (1/Γ), accounting for the observed polarization.

We present the first optical-UV spectral systematic analysis of 30 Type 1 active galactic nuclei selected in the far-infrared and X-ray in the Lockman-SpReSO Survey. The sample of faint objects (m_B = 19.6–21.8) covers a large redshift range of 0.33 >z > 4.97 with a high signal-to-noise ratio (∼21 on average). A detailed spectral analysis based on the quasar main-sequence phenomenology prescription was applied to deblend the principal optical-UV emitting regions. Our sample spans a bolometric luminosity range of 44.85 < logL_bol < 47.87, absolute B-magnitude of 20.46 >M_B > –26.14, BH mass of 7.59 < logM_BH < 9.80, and Eddington ratio of –1.70 < logR_Edd < 0.56. The analysis shows that 18 high-z objects correspond to Population (Pop) B, whereas three low-z fall in Pop A2, B1, and B1+. The remaining eight are candidates to be Pop B and one Pop A object. None of them is an extreme accretor. We looked for tendencies in our sample and compared them with other samples with different selection criteria. Evidence for winds was explored using the C ivλ1549 line half-height centroid c_(1/2), finding wind velocities between 941 and −1587 km s⁻¹. This result is consistent with samples with similar ranges of z and M_B. The Baldwin effect showed a slope of –0.23 ± 0.03 dex consistent with previous studies. Spectra from 12 objects in our sample were found in the Sloan Digital Sky Survey Data Release 17 database. We applied the same methodology to compare them to our spectra, finding no evidence of variability.

Active galactic nuclei (AGNs) are a promising source of the binary black hole mergers observed in gravitational waves with LIGO-Virgo-Kagra (LVK). Constraining the AGN channel allows us to limit AGN parameter space (disk density, size, average lifetime) and nuclear star cluster (NSC) parameter space. Constraints on AGNs and NSCs have implications for Λ cold dark matter models of AGN feedback and models of AGN-driven supermassive black hole merger and growth. Here we present several qualitative studies of the AGN channel using new public, open-source, fast, reproducible code McFACTS (https://github.com/mcfacts/mcfacts): Monte Carlo for AGN channel Testing and Simulation. We demonstrate several important features for testing the AGN channel, including: (i) growth to large-mass intermediate-mass black hole is helped by the presence of migration traps or swamps, (ii) flat BH initial mass functions highlight hierarchical merger features in the mass spectrum, (iii) the (q, χ_eff) anticorrelation is a strong test of the bias to prograde mergers in the AGN channel, (iv) spheroid encounters can drive a fraction of mergers with high in-plane spin components (χ_p), (v) a high rate of extreme mass ratio inspirals are driven by an initial population of embedded retrograde BH, and (vi) both LVK and LISA are powerful probes of models of AGN disks and their embedded populations.

We analyze photometry, spectra, and variability of over 100 faint X-ray sources in the globular cluster Terzan 5, using 737 ks of Chandra data. X-ray colors and spectral fitting allow for clear separation of foreground sources (with less extinction than the cluster), quiescent low-mass X-ray binaries (qLMXBs), and sources with harder spectra. We identify 22 candidate qLMXBs, over twice that found in any other cluster. This is consistent with Terzan 5’s stellar interaction rate, the highest among Galactic globular clusters. We do not see qLMXBs dominated by thermal emission below L_X ∼ 10³² erg s⁻¹, though qLMXBs with stronger nonthermal emission could be missed. We find that more than 50% of the qLMXB sources have a neutron star thermal component contributing over 80% of the total luminosity. We report an unusual spectral feature around 1.75 keV in the combined spectrum of Ter 5 X-3. The concentration of the qLMXBs within the cluster is consistent with that of a population of mass 1.46 ± 0.14 M_⊙. We identify secure X-ray counterparts to millisecond pulsars Terzan 5 ar and Terzan 5 at, using positional coincidence and orbital X-ray light curves matching those expected for spider pulsars.

Type-I thermonuclear bursts (TNBs) from neutron star low-mass X-ray binaries (NS LMXBs) originate on the neutron star’s surface from the unstable burning of the accreted material. On the other hand, kHz quasiperiodic oscillations (QPOs) are thought to originate in the innermost regions of the inspiralling accretion disk. Type-I TNBs are expected to impact the inner accretion flow, and consequently the kHz QPOs, due to the intense radiation pressure. In this work, we systematically study the evolution of the upper and the lower kHz QPOs immediately before and after a type-I TNB on 4U 1636−536 using AstroSat observations in the 3–20 keV band. The analysis of the power density spectra shows the presence of kHz QPOs within 200 s before the onset of the type-I burst. However, we have not detected any prominent signature of the same within 100–200 s after the burst. The kHz QPOs then reemerge after ≈200 s. The fractional rms variation in the 3–20 keV band drops by ≈5%–6%, supporting the nonexistence of kHz QPOs in the 200 s postburst zone. The timescale of 200 s coincides with the viscous timescale, highlighting a scenario where the inner disk is temporarily disrupted by the intense radiation from the type-I TNB. The kHz QPO then reestablishes as the inner disk is restored.

Galactic outflows shape galaxy evolution, but their mass, energy, and momentum transfer remain uncertain. High-resolution spectroscopy can help, but systematic discrepancies hinder model interpretation. In this study, we evaluate the performance of semianalytical line transfer (SALT) and empirical partial covering models (PCMs) to recover the properties of outflows in the FIRE-2 simulation suite from synthetic Si II lines (1190 Å, 1193 Å, 1260 Å, 1304 Å, 1527 Å). When applicable, we assess each model’s ability to recover mass, energy, and momentum outflow rates, as well as radial density and velocity profiles, column densities, and flow geometries. We find that the PCM underestimates column densities by 1.3 dex on average in the range with dispersion 1.3 dex. We attribute this bias to instrumental smoothing. Since the PCM underestimates column densities, it also underestimates flow rates, though its predictions are independent of radius, with a dispersion of 0.55 dex. We detect no bias in the SALT estimates of the column density with dispersion 1.3 dex. When the velocity and density field obey power laws, SALT can constrain the mass, momentum, and energy outflow rates to 0.36(0.63), 0.56(0.56), and 0.97(0.80) dex at 0.15(0.30)R_vir, respectively. However, certain profiles in FIRE-2 fall outside the SALT framework, where the model breaks down. We find that SALT effectively tracks the flow geometry, capturing the temporal evolution of the photon escape fraction that is out of phase with the star formation rate, fully consistent with hydrodynamic simulations. We advocate for integral field unit spectroscopy to better constrain flow properties.

We present Atacama Large Millimeter/submillimeter Array Total Power CO(1–0) mapping of Stephan’s Quintet (SQ), a prototypical compact galaxy group, with a uniform noise level at a spatial scale of ∼25 kpc. These observations provide the first complete view of molecular gas across the whole system. Molecular gas is found to spread over a wide area (∼120 × 80 kpc), mainly over the two main member galaxies (NGC 7318B and 7319), but also in the shocked ridges between these galaxies, the tidal tail, and also in intergalactic regions north of the tail. The total CO(1–0) luminosity is (2.47 ± 0.12) × 10⁹ K km s⁻¹ pc², corresponding to a molecular gas mass of (1.07 ± 0.05) × 10¹⁰M_⊙ assuming the Galactic CO-to-H₂ conversion factor. The global star formation efficiency of SQ is estimated at 0.29–0.70 Gyr⁻¹, comparable to or lower than that of nearby star-forming galaxies. Molecular gas spans a velocity range of ∼1300 km s⁻¹, which can be divided into three components (low, mid, and high). The low- and mid-velocity components, linked to NGC 7318B and the ridge, show relatively active star formation, whereas the high-velocity component, associated with NGC 7319, shows suppressed star formation. Our mapping reveals molecular gas extending ∼100 kpc in projection along the inner tail and north of it, containing (1.64 ± 0.08) × 10⁹M_⊙ (15% of total) with low velocity dispersion (∼20 km s⁻¹) and ongoing star formation. While previous studies suggested in situ molecular gas formation in the tail, our data suggest an additional contribution from gas stripped from NGC 7319.

Modeling the broadband emission of blazars has become increasingly challenging with the advent of multimessenger observations. Building upon previous successes in applying convolutional neural networks (CNNs) to leptonic emission scenarios, we present an efficient CNN-based approach for modeling blazar emission under proton synchrotron and hybrid lepto-hadronic frameworks. Our CNN is trained on extensive numerical simulations generated by SOPRANO, which span a comprehensive parameter space accounting for the injection and all significant cooling processes of electrons and protons. The trained CNN captures complex interactions involving both primary and secondary particles, effectively reproducing electromagnetic and neutrino emissions. This allows for rapid and thorough exploration of the parameter space characteristic of hadronic and hybrid emission scenarios. The effectiveness of the trained CNN is demonstrated through fitting the spectral energy distributions of two prominent blazars, TXS 0506+059 and PKS 0735+178, both associated with IceCube neutrino detections. The modeling is conducted under assumptions of constant neutrino flux across distinct energy ranges, as well as by adopting a fitting that incorporates the expected neutrino event count through a Poisson likelihood method. The trained CNN is integrated into the Markarian Multiwavelength Data Center (www.mmdc.am), offering a robust tool for the astrophysical community to explore blazar jet physics within a hadronic framework.

The question of whether a dynamo can be triggered by gravitational collapse is of great interest, especially for the early Universe. Here, we employ supercomoving coordinates to study the magnetic field amplification from decaying turbulence during gravitational collapse. We perform 3D simulations and show that for large magnetic Reynolds numbers, there can be exponential growth of the comoving magnetic field with conformal time before the decay of turbulence impedes further amplification. The collapse dynamics only affect the nonlinear feedback from the Lorentz force, which diminishes more rapidly for shorter collapse times, allowing nearly kinematic continued growth. We confirm that helical turbulence is more efficient in driving dynamo action than nonhelical turbulence, but this difference decreases for larger collapse times. We also show that for nearly irrotational flows, dynamo amplification is still possible, but it is always associated with a growth of vorticity—even if it still remains very small. In nonmagnetic runs, the growth of vorticity is associated with viscosity and grows with the Mach number. In the presence of magnetic fields, vorticity emerges from the curl of the Lorentz force. During a limited time interval, an exponential growth of the comoving magnetic field with conformal time is interpreted as clear evidence of dynamo action.

A subset of low-mass giants (<2.2 M_⊙) exhibit anomalous lithium enhancement behavior, which is still an open topic. Given that more massive giants retain more surface lithium, increasing mass by accreting circumstellar matter could be a channel to enriching lithium. We evaluate this process in the current work. Using the Modules for Experiments in Stellar Astrophysics, we construct a model of matter accretion, including mass loss, that evolves a star from the main-sequence turnoff to the red giant branch tip. The mean accretion rate is estimated from the upper limit of the accreted mass and the evolutionary time of the star during this period, and a grid of accretion rates is constructed. We separately consider their effects on the lithium enhancement of giants, both in terms of the mass and the composition of accretion. Accreting matter with higher lithium abundances has a promoting effect on the lithium enhancement of giants. The accreted matter with excess lithium alleviates the dilution of lithium in the convective envelope during the first dredge-up. The added mass results in lower temperatures at the bottom of the convective envelope, which likewise weaken the depletion of surface lithium. The weak accretion of circumstellar matter is a possible route to lithium enhancement for giants, and it predicts an upper limit on the lithium abundance of ∼2.5 dex. However, the mass increment it requires poses a potential challenge to real astrophysical environments. Such accretion suppresses lithium dilution and depletion of the star during the first dredge-up, thus exhibiting lithium enhancement behavior.

We use the TNG-Cluster simulation to investigate how stellar mass and star formation rate (SFR) incompleteness affect the identification of density peaks within galaxy protoclusters at different redshifts. Our analysis focuses on a sample of 352 protoclusters, defined as the progenitor populations of galaxies that reside within the virialized region of z = 0 clusters with . For comparison, we define our “baseline” protocluster population as galaxies with M_⋆ > 10^8.5M_⊙ at any redshift. We find that M_⋆-limited (M_⋆ > 10^9.5M_⊙) and SFR-limited (SFR > 10 M_⊙ yr⁻¹) subpopulations recover the baseline highest galaxy density peak in roughly ∼60% of cases within an accuracy of 1.0 pMpc (corresponding to an angular scale of ) at z > 2. This recovery fraction drops to ∼40%−50% when restricting to galaxies with M_⋆ > 10^10.0M_⊙. We find that the baseline highest galaxy density peaks typically coincide with the highest dark matter and stellar mass density peaks, with separations less than 0.5 pMpc in ∼60%−75% of cases at z > 2. This agreement drops to ∼45%−50% when restricting to galaxies with M_⋆ > 10^10.0M_⊙. These results indicate that identifying the densest regions of protoclusters—i.e., the core—is highly sensitive to stellar mass and SFR completeness limits. Nevertheless, at z > 2, we find that the baseline highest galaxy density peaks are generally sites of enhanced star formation and accelerated mass growth relative to the remainder of the protocluster, consistent with some observational studies.

Understanding turbulence within the intracluster medium of galaxy clusters is pivotal for comprehending their evolution and dynamics. Employing 3D magnetohydrodynamic simulations of galaxy cluster mergers, we examine the statistical properties of gas density, magnetic fields, and velocity, particularly emphasizing the central regions spanning 400 kpc. The simulations are designed to resemble massive cool-core clusters such as Perseus, while varying the initial plasma β values (100, 200, and 500). Our findings indicate that while the statistical histogram distributions of gas density and velocity appear similar across different β scenarios, their spatial distributions and morphological patterns exhibit noticeable differences. Through the application of the second-order structure function, we identified a scaling relation in velocity fluctuations, characterized by a slope of 1/2 and predominantly dominated by solenoidal components. Furthermore, our analysis reveals a pronounced anisotropy in both velocity and magnetic field fluctuations, with more significant fluctuations along the direction perpendicular to the magnetic fields. This anisotropy is scale-dependent, becoming more pronounced at smaller scales, and exhibits a decreasing trend in scenarios where the magnetic field is relatively weak, particularly at β = 500. This suggests that the anisotropic nature of these fluctuations is predominantly regulated by the magnetic fields. Additionally, we test the efficacy of the synchrotron intensity gradient (SIG) method for tracing magnetic fields in these environments. The SIG shows a global agreement with the magnetic field across all three β scenarios, confirming the SIG’s insensitivity to the medium’s magnetization level.

The evolution of warped disks is governed by internal, oscillatory shear flows driven by their distorted geometry. However, these flows are known to be vigorously unstable to hydrodynamic parametric instability. In many warped systems, this might coexist and compete with the magnetorotational instability (MRI). The interplay of these phenomena and their combined impact on the internal flows has not been studied. To this end, we perform three-dimensional, magnetohydrodynamic unstratified shearing box simulations with an oscillatory radial forcing function to mimic the effects of a warped disk. In the hydrodynamic study, we find that the parametric instability manifests as strong, vertical “elevator” flows that resist the sloshing motion. Above a critical forcing amplitude, these also emerge in our magnetized runs and dominate the vertical stress, although they are partially weakened by the MRI, and hence the system equilibrates with larger radial sloshing flows. Below this critical forcing, the MRI effectively quenches the parametric instability. In all cases, we find that the internal stresses are anisotropic in character and better described by a viscoelastic relationship with the shearing flows. Unfortunately, these important effects are typically unresolved in global simulations of warped disks and are simplified in analytically tractable models. The incorporation of such complex, warp-amplitude-dependent, viscoelastic stresses will sensitively regulate the laminar flow response and inevitably modify the detailed spatio-temporal evolution of warped systems.

Direct collapse of pristine gas in early galaxies is a promising pathway for forming supermassive black holes (SMBHs) powering active galactic nuclei at the Epoch of Reionization (EoR). This seeding mechanism requires suppression of molecular hydrogen (H₂) cooling during primordial star formation via intense far-ultraviolet radiation from nearby starburst galaxies clustered in overdense regions. However, nondetection of 21 cm signals from the EoR reported by the Hydrogen Epoch of Reionization Array (HERA) experiment suggests that such galaxies may also emit X-rays more efficiently than in the local Universe, promoting H₂ production and thereby potentially quenching massive black hole (BH) seed formation. In this study, we examine the thermal and chemical evolution of collapsing gas in dark matter halos using a semi-analytic model incorporating observationally calibrated X-ray intensities. We find that strong X-ray irradiation, as suggested by HERA, significantly suppresses direct collapse and leads most halos to experience H₂ cooling. Nevertheless, massive BH seeds with M_BH ≳ 10⁴M_⊙ still form by z ≃ 15, particularly in regions with baryonic streaming motion, and their abundance reaches ∼ 10⁻⁴ Mpc⁻³, sufficient to explain the SMBHs identified by James Webb Space Telescope spectroscopy at 3 < z < 6. While the formation of highly overmassive BHs with masses comparable to their host galaxies is prohibited by X-ray ionization, our model predicts that BH-to-stellar mass ratios of ≃0.01–0.1 were already established at seeding.

Outflows are key indicators of ongoing star formation. We report the discovery of an unanchored forked stream within the propagating path of an extremely young protostellar outflow in the 70 μm-dark clump G34.74-0.12, based on Atacama Large Millimeter/submillimeter Array (ALMA) 1.3 mm observations with an angular resolution of 16 (∼5000 au). This outflow originates from a 9.7 M_⊙ core, exhibits a fork-shaped stream structure in its redshifted lobe, which is traced by CO (2–1), SiO (5–4), and H₂CO (3_0,3–2_0,2). It has a momentum of 13 M_⊙ km s⁻¹, an energy of 107 M_⊙ km² s⁻², and a dynamical timescale of ∼10⁴ yr. Significantly, the enhanced relative abundances of SiO, H₂CO, and CH₃OH with respect to CO, along with the increased temperature at the forked point, indicate a collisional origin. The forked point does not coincide with any dust continuum core >0.1 M_⊙. Moreover, CO (2–1) emission also traces three other outflows in this region, characterized by their masses (0.40, 0.02, and 0.15 M_⊙) and momenta (5.2, 0.2, and 1.8 M_⊙ km s⁻¹), as part of the ALMA Survey of 70 μm dark High-mass clumps in Early Stages project. All the newly discovered morphological and kinematic features associated with these extremely young protostellar outflows (with timescales of 10³–10⁴ yr) suggest that the initial stages of star formation are more complicated than previously understood.