Showing 1–50 of 485 results for author: Oh, S

Beyond the Diffusion Coefficient: Propagators and Memory in Cosmic Ray Transport

Authors: Naixin Liang, S. Peng Oh

Abstract: Cosmic ray (CR) transport is usually modeled with a single diffusion coefficient, but this description captures only the growth of the variance and not the full transport process. Distinct transport mechanisms can share the same effective diffusion coefficient while producing different particle distributions and approaches to the diffusive limit. This limitation is especially relevant in realistic… ▽ More Cosmic ray (CR) transport is usually modeled with a single diffusion coefficient, but this description captures only the growth of the variance and not the full transport process. Distinct transport mechanisms can share the same effective diffusion coefficient while producing different particle distributions and approaches to the diffusive limit. This limitation is especially relevant in realistic multiphase, structured, and time-dependent media, and is also reflected in observed environmental variations in CR transport near pulsar wind nebulae, supernova remnants, and molecular clouds. Particle-tracing studies also show clear departures from standard diffusion, including both superdiffusion and subdiffusion. We therefore develop a propagator-based framework centered on $P(x,t)$, the probability distribution of particle positions, or equivalently its Fourier-Laplace transform $P(k,s)$. This object is compact and statistically complete, and naturally exposes memory: the CR flux can depend on earlier gradients when unresolved trapping or phase changes are coarse-grained away. Using the Montroll-Weiss formalism, we show how to measure $P(k,s)$ directly from trajectories, how to recover the associated memory kernel, and how to represent broad kernels efficiently with a Prony expansion. Applied to a multiphase medium, the framework shows that slow regions can regulate escape without dominating the total residence-time budget. We also introduce an accelerated Monte Carlo method for coarse-grained transport, and show that if trapping structures evolve while particles are still sampling them, the static long-time limit need not be reached. This paper provides the foundation for future observational applications, particle-tracing measurements, and CR-MHD closures. △ Less

Submitted 13 April, 2026; originally announced April 2026.

Probing the Cosmic Web with Fast Radio Bursts. I. Scattering

Authors: Sharon Lapiner, Nir Mandelker, Paz Beniamini, S. Peng Oh

Abstract: We study the formation of multiphase gas in the post-accretion-shock regions of cosmic sheets, filaments, and the circumgalactic medium (CGM) of haloes, i.e., cosmic web objects (CWOs). Local instabilities in the hot medium result in fragmentation and cooling, eventually forming small-scale overdensities with temperatures of $\sim 10^{4}{\,\rm K}$ in pressure equilibrium with the hot environment.… ▽ More We study the formation of multiphase gas in the post-accretion-shock regions of cosmic sheets, filaments, and the circumgalactic medium (CGM) of haloes, i.e., cosmic web objects (CWOs). Local instabilities in the hot medium result in fragmentation and cooling, eventually forming small-scale overdensities with temperatures of $\sim 10^{4}{\,\rm K}$ in pressure equilibrium with the hot environment. Such dense, ionised inhomogeneities can affect the propagation of radio waves from fast radio bursts (FRBs), thereby offering us a way to probe their presence and properties in CWOs through scattering signatures in the observed FRB flux. We find that high-$z$ filaments \& sheets have a negligible contribution to the total observed scattering. The high rates of FRBs expected even at high redshifts may still allow detection from high-temperature filaments along rare sightlines, and we suggest other methods for such systems in a companion paper. Our model further predicts that if turbulent cloudlets exist in the CGM of intervening massive haloes with a volume-filling fraction of $f_{\rm v}\gtrsim 10^{-3}$, they are expected to cause considerable cumulative scattering along an average sightline, resulting in a significant correlation between the total scattering time and source redshifts. The lack of such a correlation in current observations may imply that the cool gas in the CGM has substantial non-thermal pressure, reducing its density, or significant damping of small-scale density fluctuations. Forthcoming localised FRB samples can map these constraints into bounds on volume-filling fractions, densities, cloud sizes, and the strength of turbulence. △ Less

Submitted 23 March, 2026; originally announced March 2026.

Comments: 20 pages + 4 pages in the appendix

AVID: A Near-Major Post-Merger of Late-Type Dwarfs beneath a Regularly Rotating HI Disk (VCC 693)

Authors: Fujia Li, Hong-Xin Zhang, Elias Brinks, Se-Heon Oh, Rory Smith, Zesen Lin, Weibin Sun, Yu-Zhu Sun, Tie Li, Minsu Kim, Jaebeom Kim, Lijun Chen, Lanyue Zhang, Patrick Côté, Alessandro Boselli, Pierre-Alain Duc, Laura Ferrarese, Matteo Fossati, Stephen Gwyn, Xu Kong, Sanjaya Paudel, Eric W. Peng, Thomas H. Puzia, Rubén Sánchez-Janssen, Matthew Taylor , et al. (1 additional authors not shown)

Abstract: On the periphery of galaxy clusters, moderately high galaxy densities and velocity dispersions favour interactions and mergers that influence galaxy evolution prior to cluster infall. Observational studies of this phase in dwarfs remain rare. We present a high-resolution study of the merger remnant VCC 693 in the outskirts of Virgo cluster, using observations from the Atomic gas in Virgo Interacti… ▽ More On the periphery of galaxy clusters, moderately high galaxy densities and velocity dispersions favour interactions and mergers that influence galaxy evolution prior to cluster infall. Observational studies of this phase in dwarfs remain rare. We present a high-resolution study of the merger remnant VCC 693 in the outskirts of Virgo cluster, using observations from the Atomic gas in Virgo Interacting Dwarf galaxies (AVID) project. We explore the origin of VCC 693 and the consequences of the merger on its star formation and structure through a joint analysis of VLA and FAST HI emission line observations, together with complementary optical imaging and spectroscopy. We employ hydrodynamical simulations to help interpret the observations. Our analysis favours a near-major merger between two dwarfs with a stellar mass ratio of 3:1-4:1, with one likely gas-poor progenitor (i.e., a damp merger). The optical appearance of VCC 693 is dominated by complex tidal structures throughout the system, whereas the HI gas has settled to a regular rotating disk. Compared with similar-mass dwarfs, the central star formation and gas-phase metallicity are moderately enhanced. The global star formation rate, HI gas content, and HI-to-optical size ratio of VCC 693 are broadly consistent with those of typical dwarfs of similar mass, albeit somewhat lower. Decomposition of the HI rotation curve into baryonic and dark matter indicates a high halo concentration, suggesting post-merger relaxation into a more centrally peaked configuration. Together with two recent studies of AVID post-merger systems, these results support the view that even major dwarf mergers can produce remnants with overall stellar structures indistinguishable from ordinary dwarfs, and that the environmental effects in cluster outskirts can promote damp or mixed mergers, constituting an integral part of galactic pre-processing. △ Less

Submitted 25 February, 2026; originally announced February 2026.

Comments: 19 pages (excluding appendices), 16 figures (excluding appendices), Accepted for publication in Astronomy & Astrophysics

Journal ref: A&A 708, A233 (2026)

Large-scale and local environmental drivers of quenching: tracing H$α$ concentration in X-ray and optical galaxy groups

Authors: Stefania Barsanti, Di Wang, Matthew Colless, Ang Liu, Esra Bulbul, Matt S. Owers, Scott M. Croom, Benedetta Vulcani, Julia J. Bryant, Yifan Mai, Sree Oh, Andrei Ristea, Sarah M. Sweet, Jesse van de Sande

Abstract: To explore the environmental mechanisms causing quenching in nearby star-forming galaxies, we study the variation with local and large-scale environments of a star formation concentration index, C-index $\equiv\log{(r_{50,{\rm H}α}/r_{50,\rm cont}})$, that traces the spatially-resolved distribution of H$α$ emission. Our analysis combines (i) GAMA spectroscopic redshift survey data to optically sel… ▽ More To explore the environmental mechanisms causing quenching in nearby star-forming galaxies, we study the variation with local and large-scale environments of a star formation concentration index, C-index $\equiv\log{(r_{50,{\rm H}α}/r_{50,\rm cont}})$, that traces the spatially-resolved distribution of H$α$ emission. Our analysis combines (i) GAMA spectroscopic redshift survey data to optically select galaxy groups and reconstruct the cosmic web, (ii) eROSITA data to identify X-ray-emitting groups, and (iii) SAMI Galaxy Survey data to characterise spatially-resolved star formation. We find that galaxies in X-ray+optical groups exhibit the lowest median C-index and the highest fraction of centrally-concentrated star-forming galaxies relative to optical groups and the field (independently of group or stellar mass). Star-forming galaxies in more X-ray luminous groups at fixed dynamical mass show more concentrated star formation. At large scales, nodes show the lowest median C-index and the highest fraction of centrally-concentrated star-forming galaxies relative to filaments and voids, which have similar C-index distributions. C-index correlates most strongly with the distance to the closest node, leaving no significant role for other local or large-scale environment metrics. Finally, regular star-forming galaxies tend to have spins aligned parallel to filaments, consistent with smooth gas accretion, while centrally-concentrated galaxies tend have spins aligned perpendicular to filaments, likely driven by mergers and associated with bulge growth. These results suggest that multi-scale environmental processes, i.e. locally and at large-scale, act to concentrate star formation toward galaxy centres, via gas-related mechanisms in nodes and ram-pressure stripping in X-ray+optical groups. △ Less

Submitted 16 February, 2026; originally announced February 2026.

Comments: 20 pages, 19 figures. Submitted to MNRAS. Comments from referee addressed

Jet-torus interaction revealed by sub-parsec SO absorption in NGC 1052

Authors: Satoko Sawada-Satoh, Seiji Kameno, Nozomu Kawakatsu, Do-Young Byun, Se-Jin Oh, Sang-Sung Lee, Duk-Gyoo Roh, Chungsik Oh, Jae-Hwan Yeom, Dong-Kyu Jung, Hyo- Ryoung Kim, Young-Sik Kim, Sanghyun Kim

Abstract: We report the first λ2-mm very long baseline interferometry (VLBI) observations of the radio galaxy NGC 1052, conducted with the Korean VLBI Network (KVN) using a wide-band recording mode. Leveraging the wide bandwidth covering a velocity range at 2300 km/s, we successfully detect broad (> 700 km/s) multi-component SO J_N = 3_3 - 2_2 absorption against the sub-parsec-scale continuum structure. The… ▽ More We report the first λ2-mm very long baseline interferometry (VLBI) observations of the radio galaxy NGC 1052, conducted with the Korean VLBI Network (KVN) using a wide-band recording mode. Leveraging the wide bandwidth covering a velocity range at 2300 km/s, we successfully detect broad (> 700 km/s) multi-component SO J_N = 3_3 - 2_2 absorption against the sub-parsec-scale continuum structure. The absorption profile consists of both redshifted and blueshifted components, including a newly identified blueshifted feature at -412 km/s relative to the systemic velocity. Significant SO absorption is confined to the central components, with no substantial detection toward the outer jet components. This constrains the location of SO gas to a compact region smaller than 0.45 pc in the sub-parsec vicinity of the supermassive black hole (SMBH). Our results support the scenario in which SO molecules are evaporated through shock heating caused by jet-torus interaction. The SO gas clumps are likely driven outward by the jet, with some returning toward the SMBH as inflowing material. Comparison with 321 GHz H2O masers reveals partial similarities in spatial distribution and radial velocity, suggesting that the jet-torus interaction may also trigger the excitation of H2O masers. △ Less

Submitted 2 February, 2026; v1 submitted 6 January, 2026; originally announced January 2026.

Comments: 8 pages, 5 figures, accepted for publication in PASJ

Particle Acceleration in Magnetized Shear-Driven Turbulence

Authors: Mingxuan Liu, Mateusz Ruszkowski, Ellen Zweibel, Xiaochen Sun, Damiano Caprioli, Naixin Liang, Siang Peng Oh, Anatoly Spitkovsky

Abstract: Shear flows, ubiquitous in space and astrophysical plasmas, can accelerate particles through turbulence excited by the Kelvin-Helmholtz instability. We present the first numerical study of particle acceleration in non-relativistic, magnetized, and purely shear-driven turbulence that includes full particle backreaction. Using two-dimensional MHD-PIC simulations with an initially uniform flow-aligne… ▽ More Shear flows, ubiquitous in space and astrophysical plasmas, can accelerate particles through turbulence excited by the Kelvin-Helmholtz instability. We present the first numerical study of particle acceleration in non-relativistic, magnetized, and purely shear-driven turbulence that includes full particle backreaction. Using two-dimensional MHD-PIC simulations with an initially uniform flow-aligned magnetic field and external stirring force, we demonstrate that sustained particle acceleration requires continuously driven turbulence, whereas freely decaying turbulence rapidly depletes its energy reservoirs and halts the acceleration. The acceleration mechanism operates through the systematic distortion of gyro-orbits by turbulent electric fields: acceleration phases extend the particle trajectory along the electric force, increasing the energy gain, while deceleration phases shorten the trajectory, reducing the energy loss. This asymmetry produces net energy gain despite stochastic fluctuations, with the mean energy change scaling quadratically with shear velocity, characteristic of second-order Fermi acceleration. Initially monoenergetic particles develop substantial non-thermal tails after the turbulence onset. For particles repeatedly crossing shear layers, their energization follows geometric Brownian motion with weak systematic drift, yielding a log-normal distribution. High-energy particles exhibit pitch-angle anisotropy, becoming preferentially perpendicular to the flow-aligned magnetic field as their gyroradii exceed the turbulent layer width. These results establish shear-driven turbulence as a viable particle acceleration mechanism, providing a general model for particle energization in shear flows. △ Less

Submitted 14 December, 2025; originally announced December 2025.

Comments: 19 pages, 17 figures. Submitted to ApJ

The Non-universal Pseudo Phase-Space Density Profiles of Symphony Host Halos

Authors: Bocheng Feng, Ethan O. Nadler, S. Peng Oh, Suoqing Ji

Abstract: Cosmological N-body simulations have long suggested that the pseudo phase-space density (PPSD), $ρ/σ^3$, of cold dark matter haloes follows the universal relation $ρ/σ^3 \propto r^χ$, with $χ\approx -1.875$, as predicted by spherical secondary-infall similarity solutions. This power law appears to hold despite the fact that neither the density $ρ(r)$ nor velocity dispersion $σ(r)$ follow universal… ▽ More Cosmological N-body simulations have long suggested that the pseudo phase-space density (PPSD), $ρ/σ^3$, of cold dark matter haloes follows the universal relation $ρ/σ^3 \propto r^χ$, with $χ\approx -1.875$, as predicted by spherical secondary-infall similarity solutions. This power law appears to hold despite the fact that neither the density $ρ(r)$ nor velocity dispersion $σ(r)$ follow universal power law relations individually, even at fixed mass. We analyze 246 host haloes from the \textit{Symphony} suite of high-resolution cosmological zoom-in simulations, to consistently measure PPSD profiles across host masses from $10^{11}$ to $10^{15} M_\odot$. We find that the PPSD systematically deviates from a power law, and that haloes with larger deviations from Jeans equilibrium systematically develop steeper average PPSD slopes. This result suggests that the PPSD is not universal; instead, it is linked to a halo's degree of dynamical equilibrium, which is ultimately set by halo formation history. As a result, we show that secondary halo properties such as concentration and accretion rate inherit significant correlations with the PPSD slope. Moreover, our hosts' PPSD profiles are remarkably consistent with predictions from one-dimensional self-similar fluid collapse models, indicating that three-dimensional structure, velocity anisotropy, and filamentary accretion all play negligible roles in shaping the PPSD. Thus, we argue that the PPSD is shaped by mass assembly alone, and that its non-universality reflects the diversity of halo growth histories. △ Less

Submitted 14 April, 2026; v1 submitted 24 November, 2025; originally announced November 2025.

Comments: 17 pages, 17 figures, 1 table; Accepted for publication in MNRAS. This version matches the accepted manuscript. Volume 546, Issue 4, March 2026

Journal ref: Mon. Not. R. Astron. Soc. 546, stag215 (2026)

Star Formation Histories and Stellar Dynamics in the Central Galaxies of RX J0820.9+0752, A1835, and PKS 0745-191

Authors: Marie-Joëlle Gingras, B. R. McNamara, Alison L. Coil, Serena Perrotta, Fabrizio Brighenti, H. R. Russell, S. Peng Oh, Wenmeng Ning

Abstract: We present Keck Cosmic Web Imager observations of stellar populations in three galaxies at the centers of cooling flow clusters. All three host rich molecular gas reservoirs and show prominent Balmer absorption from $30-100$ Myr-old stars consistent with long lasting star formation. Two systems, A1835 and PKS 0745-191, have extended young stellar populations in their centers with recent star forma… ▽ More We present Keck Cosmic Web Imager observations of stellar populations in three galaxies at the centers of cooling flow clusters. All three host rich molecular gas reservoirs and show prominent Balmer absorption from $30-100$ Myr-old stars consistent with long lasting star formation. Two systems, A1835 and PKS 0745-191, have extended young stellar populations in their centers with recent star formation rates of 100 M$_{\odot}$ yr$^{-1}$ and 8 M$_{\odot}$ yr$^{-1}$, respectively. In A1835 we uncover a massive blueshifted clump of young stars moving at high speed with respect to the gas and central galaxy. We suggest this feature is a young population that formed in a gaseous outflow that has detached from its natal gas and is falling back toward the galaxy. This result, combined with a companion study (arXiv:2404.02212) tracing nebular emission which presumably cooled from the hot X-ray atmosphere, indicates that star formation is proceeding in a dynamically complex environment resulting from the central galaxy's motion with respect to the cooling clouds and motion induced by feedback from the central radio jets. In RX J0820.9+0752 intermediate age stars are found in a filament outside of the nucleus with no discernible star formation at the center of the galaxy. All projected galaxies are composed of old stellar populations with deep D4000 breaks and are devoid of detectable warm gas. While in some instances they may be interacting gravitationally with the central galaxy, they cannot have donated the upward of $10^{10}$ M$_{\odot}$ of molecular gas found in these systems. △ Less

Submitted 3 November, 2025; originally announced November 2025.

Comments: 21 pages, 14 figures, submitted to ApJ

Modeling Emission-Line Surface Brightness in a Multiphase Galactic Wind: An O VI Case Study

Authors: Zirui Chen, Zixuan Peng, Kate H. R. Rubin, Timothy M. Heckman, Matthew J. Hayes, Yakov Faerman, Crystal L. Martin, S. Peng Oh, Drummond B. Fielding

Abstract: We present a fast and robust analytic framework for predicting surface brightness (SB) of emission lines in galactic winds as a function of radius up to $\sim 100$ kpc out in the circum-galactic medium. We model multiphase structure in galactic winds by capturing emission from both the volume-filling hot phase (T $\sim 10^{6-7}$ K) and turbulent radiative mixing layers that host intermediate tempe… ▽ More We present a fast and robust analytic framework for predicting surface brightness (SB) of emission lines in galactic winds as a function of radius up to $\sim 100$ kpc out in the circum-galactic medium. We model multiphase structure in galactic winds by capturing emission from both the volume-filling hot phase (T $\sim 10^{6-7}$ K) and turbulent radiative mixing layers that host intermediate temperature gas at the boundaries of cold clouds (T $\sim 10^4$ K). Our multiphase framework makes significantly different predictions of emission signatures compared to traditional single-phase models and explains the paucity of OVI SB measurements in the literature. After accounting for ram pressure equilibrium between the cold clouds and hot wind in supersonic outflows, non-equilibrium ionization effects, and energy budgets other than mechanical energy from core-collapse supernovae, our OVI SB predictions qualitatively match observational results. Our framework provides constraints on the optimal galactic wind properties that facilitate OVI emission observations, including star formation rate surface density, hot phase mass loading factor, and thermalization efficiency factor. These constraints are consistent with existing observations and can help inform future target selections. △ Less

Submitted 27 March, 2026; v1 submitted 2 October, 2025; originally announced October 2025.

Comments: 19 pages, 15 figures. Accepted for publication in MNRAS, 27 March 2026. Zirui Chen and Zixuan Peng are co-first authors who made equal contributions to this work

Hector Galaxy Survey: Data Processing, Quality Control and Early Science

Authors: S. Oh, M. L. P. Gunawardhana, S. M. Croom, G. Quattropani, S. Tuntipong, J. J. Bryant, P. Corcho- Caballero, P. K. Das, O. Çakır, J. H. Lee, A. Ristea, S. Barsanti, M. Pak, S. M. Sweet, T. J. Woodrow, T. Rutherford, Y. Mai, M. S. Owers, M. Colless, L. S. J. Stuart, H. R. M. Zovaro, S. P. Vaughan, J. van de Sande, T. Farrell, M. Beom , et al. (30 additional authors not shown)

Abstract: The Hector Galaxy Survey is a new optical integral field spectroscopy (IFS) survey currently using the AAT to observe up to 15,000 galaxies at low redshift ($z < 0.1$). The Hector instrument employs 21 optical fibre bundles feeding into two double-beam spectrographs to enable wide-field multi-object IFS observations of galaxies. To efficiently process the survey data, we adopt the data reduction p… ▽ More The Hector Galaxy Survey is a new optical integral field spectroscopy (IFS) survey currently using the AAT to observe up to 15,000 galaxies at low redshift ($z < 0.1$). The Hector instrument employs 21 optical fibre bundles feeding into two double-beam spectrographs to enable wide-field multi-object IFS observations of galaxies. To efficiently process the survey data, we adopt the data reduction pipeline developed for the SAMI Galaxy Survey, with significant updates to accommodate Hector's dual-spectrograph system. These enhancements address key differences in spectral resolution and other instrumental characteristics relative to SAMI, and are specifically optimised for Hector's unique configuration. We introduce a two-dimensional arc fitting approach that reduces the RMS velocity scatter by a factor of 1.2--3.4 compared to fitting arc lines independently for each fibre. The pipeline also incorporates detailed modelling of chromatic optical distortion in the wide-field corrector, to account for wavelength-dependent spatial shifts across the focal plane. We assess data quality through a series of validation tests, including wavelength solution accuracy, spectral resolution, throughput characterisation, astrometric precision, sky subtraction residuals, and flux calibration stability (4\% systematic offset when compared to Legacy Survey fluxes). We demonstrate that Hector delivers high-fidelity, science-ready datasets, supporting robust measurements of galaxy kinematics, stellar populations, and emission-line properties, and provide examples. Additionally, we address systematic uncertainties identified during the data processing and propose future improvements to enhance the precision and reliability of upcoming data releases. This work establishes a robust data reduction framework for Hector, delivering high-quality data products that support a broad range of extragalactic studies. △ Less

Submitted 30 September, 2025; originally announced September 2025.

Comments: 26 pages, 24 figures, accepted for publication in PASA

$\textit{Eppur Si Muove}$: Self-Sustained Streaming Motions in Multi-Phase MHD

Authors: Chaoran Wang, S. Peng Oh, Yan-Fei Jiang, Ish Kaul

Abstract: Radiative cooling can drive dynamics in multi-phase gas. A dramatic example is hydrodynamic `shattering', the violent, pressure-driven fragmentation of a cooling cloud which falls drastically out of pressure balance with its surroundings. We run MHD simulations to understand how shattering is influenced by magnetic fields. In MHD, clouds do not `shatter' chaotically. Instead, after initial fragmen… ▽ More Radiative cooling can drive dynamics in multi-phase gas. A dramatic example is hydrodynamic `shattering', the violent, pressure-driven fragmentation of a cooling cloud which falls drastically out of pressure balance with its surroundings. We run MHD simulations to understand how shattering is influenced by magnetic fields. In MHD, clouds do not `shatter' chaotically. Instead, after initial fragmentation, both hot and cold phases coherently `stream' in long-lived, field-aligned, self-sustaining gas flows, at high speed ($\sim 100 \, {\rm km \, s^{-1}}$). MHD thermal instability also produces such flows. They are due to the anisotropic nature of MHD pressure support, which only operates perpendicular to B-fields. Thus, even when $P_{\rm B} + P_{\rm gas} \approx$const, pressure balance only holds perpendicular to B-fields. Field-aligned gas pressure variations are unopposed, and results in gas velocities $v \sim (2 ΔP/ρ)^{1/2}$ from Bernoulli's principle. Strikingly, gas in adjacent flux tubes $\textit{counter-stream}$ in opposite directions. We show this arises from a cooling-induced, MHD version of the thin shell instability. Magnetic tension is important both in enabling corrugational instability and modifying its non-linear evolution. Even in high $β$ hot gas, streaming can arise, since magnetic pressure support grows as gas cools and compresses. Thermal conduction increases the sizes and velocities of streaming cloudlets, but does not qualitatively modify dynamics. These results are relevant to the counter-streaming gas flows observed in solar coronal rain, as well as multi-phase gas cooling and condensation in the ISM, CGM and ICM. △ Less

Submitted 30 June, 2025; originally announced July 2025.

Comments: 29 Pages, 29 Figures, Submitted to MNRAS. Comments welcome!

Unveiling the nature and fate of the almost-dark cloud AGC 226178 through HI mapping

Authors: Yu-Zhu Sun, Hong-Xin Zhang, Elias Brinks, Rory Smith, Fujia Li, Minsu Kim, Se-Heon Oh, Zesen Lin, Jaebeom Kim, Weibin Sun, Tie Li, Patrick Côté, Alessandro Boselli, Lijun Chen, Pierre-Alain Duc, Sanjaya Paudel, Matthew A. Taylor, Kaixiang Wang, Enci Wang, Lanyue Zhang, Yinghe Zhao

Abstract: The origin of extragalactic, almost dark HI clouds with extreme gas-to-stellar mass ratios remains poorly understood. We investigate the nature and fate of the "almost dark" cloud AGC 226178, projected within the Virgo cluster, with an HI-to-stellar mass ratio of ~1000. We present deep single-dish HI mapping from the Five-hundred-meter Aperture Spherical Telescope (FAST), complemented by high-reso… ▽ More The origin of extragalactic, almost dark HI clouds with extreme gas-to-stellar mass ratios remains poorly understood. We investigate the nature and fate of the "almost dark" cloud AGC 226178, projected within the Virgo cluster, with an HI-to-stellar mass ratio of ~1000. We present deep single-dish HI mapping from the Five-hundred-meter Aperture Spherical Telescope (FAST), complemented by high-resolution interferometric data from the Very Large Array (VLA), as part of the Atomic gas in Virgo Interacting Dwarf galaxies (AVID) project. These observations provide the highest-quality HI analysis to date of such a cloud, combining resolution and sensitivity. FAST data reveal a short, low-velocity tail toward the dwarf galaxy VCC 2034, previously proposed as a possible origin for AGC 226178. However, VCC 2034 shows a line-of-sight asymmetric HI feature and cometary morphology indicating a stripping event unrelated to AGC 226178. VLA data reveal a velocity gradient across AGC 226178 and a clumpy internal structure. The velocity dispersion exceeds the thermal linewidth, implying turbulence or unresolved motions. The cloud cannot be gravitationally bound by atomic gas alone. The resolved HI clumps follow standard HI mass-star formation rate and mass-size relations, with those forming stars reaching surface densities above the threshold for self-shielding. We conclude that AGC 226178 is a free-floating HI cloud of unknown origin. The system appears to be in the process of disintegration. It is likely located well outside the Virgo cluster, as the preservation of its extended HI morphology within the cluster environment would otherwise require a substantial reservoir of unseen molecular gas with a mass exceeding that of the observed HI content. While confinement pressure from the hot intracluster medium may aid its stability, it is unlikely to be the dominant factor preventing its disruption. △ Less

Submitted 31 July, 2025; v1 submitted 29 June, 2025; originally announced June 2025.

Comments: 18 pages, 14 figures. Accepted for Publication in A&A

Journal ref: A&A 701, A73 (2025)

AVID: Formation and evolution of a coalesced major merger of late-type dwarf galaxies (VCC 479) on the outskirts of the Virgo cluster

Authors: Weibin Sun, Hong-Xin Zhang, Rory Smith, Elias Brinks, Patrick Côté, Se-Heon Oh, Zesen Lin, Alessandro Boselli, Laura Ferrarese, Fujia Li, Yuzhu Sun, Lijun Chen, Lanyue Zhang, Minsu Kim, Jaebeom Kim, Tie Li, Bojun Tao, Matt Taylor, Pierre-Alain Duc, Ruben Sánchez-Janssén, Yinghe Zhao, Sanjaya Paudel, Eric W. Peng, Kaixiang Wang, Stephen Gwyn , et al. (2 additional authors not shown)

Abstract: Dwarf-dwarf galaxy mergers are among the least explored aspects of dwarf galaxy pre-processing as they fall into clusters. We present the first case study of a coalesced late-type dwarf major merger (VCC 479; stellar mass $\sim\,8\,\times\,10^7\,\rm M_\odot$) that has undergone significant environmental influence, with the aim of exploring dwarf galaxy evolution under the combined effects of galax… ▽ More Dwarf-dwarf galaxy mergers are among the least explored aspects of dwarf galaxy pre-processing as they fall into clusters. We present the first case study of a coalesced late-type dwarf major merger (VCC 479; stellar mass $\sim\,8\,\times\,10^7\,\rm M_\odot$) that has undergone significant environmental influence, with the aim of exploring dwarf galaxy evolution under the combined effects of galaxy interactions and environmental processes, and understanding its relevance to the diversity of dwarf galaxies in cluster environments. Our analysis is based on VLA and FAST HI emission line mapping from the Atomic gas in Virgo Interacting Dwarf galaxies (AVID) survey. We also perform idealized hydrodynamical simulations of dwarf-dwarf mergers to help interpret the observations. We identify symmetric stellar shell structures in VCC 479, indicative of a coalesced major merger of dwarf galaxies. The galaxy features a central starburst, initiated $\sim$600 Myr ago, embedded within an exponential disk quenched $\sim$1 Gyr ago. The starburst contributes only 2.9$\pm$0.5\% of the total stellar mass, and VCC 479's global star formation rate is 0.3 dex lower than typical dwarfs of similar mass. The galaxy is highly HI deficient, with most HI gas concentrated within the central 1 kpc and little extended HI envelope. The misalignment of the HI velocity field with the stellar body is best explained by merger-triggered gas inflow, as seen in our simulations. Our analysis is consistent with a scenario that the majority of HI gas of the progenitor galaxies was removed by the cluster environment prior to the final coalescence. The merger concentrates the remaining gas toward the galaxy center, triggering a central starburst. The combined effect of environment stripping and galaxy merger has transformed VCC 479 into a blue-core dwarf undergoing morphological transition from a late-type to an early-type galaxy. △ Less

Submitted 6 July, 2025; v1 submitted 18 June, 2025; originally announced June 2025.

Comments: 18 pages, 15 figures. Accepted for Publication in A&A

Journal ref: A&A 700, A113 (2025)

Spatially Resolved Star Formation Rate and Dust Attenuation of Nearby Galaxies from CALIFA, GALEX, and WISE Data

Authors: Jong Chul Lee, Joon Hyeop Lee, Hyunjin Jeong, Mina Pak, Sree Oh

Abstract: We study star formation rate (SFR) indicators and dust attenuation of 74 nearby star-forming galaxies on kiloparsec scales, based on GALEX far-ultraviolet (FUV) and WISE mid-infrared (MIR) images with CALIFA optical integral field spectroscopic data. We obtain hybrid SFR indicators by combining the observed FUV and MIR luminosities and calibrate them using the dust-corrected H$α$ luminosity as a r… ▽ More We study star formation rate (SFR) indicators and dust attenuation of 74 nearby star-forming galaxies on kiloparsec scales, based on GALEX far-ultraviolet (FUV) and WISE mid-infrared (MIR) images with CALIFA optical integral field spectroscopic data. We obtain hybrid SFR indicators by combining the observed FUV and MIR luminosities and calibrate them using the dust-corrected H$α$ luminosity as a reference SFR. The simple linear combination appears to follow well the reference SFR, but the calibration residual shows a significant dependence on the specific SFR (sSFR), which can be removed by employing the combination coefficient or conversion offset that varies with the sSFR. In the plane of gas versus stellar attenuation, the median trend line's slope ($\approx$ stellar-to-gas attenuation ratio) changes from 0.44 to 1.0 with increasing attenuation. The differential attenuation, defined as the deviation of stellar attenuation from the median trend line, is strongly correlated with the SFR surface density and sSFR, compatible with the two-component dust model. The differential attenuation seems to be affected by both local and global factors. △ Less

Submitted 28 April, 2025; originally announced April 2025.

Comments: 18 pages, 13 figures, To appear in ApJ

The (Limited) Effect of Viscosity in Multiphase Turbulent Mixing

Authors: Tirso Marin-Gilabert, Max Gronke, S. Peng Oh

Abstract: Multiphase gas can be found in many astrophysical environments, such as galactic outflows, stellar wind bubbles, and the circumgalactic medium, where the interplay between turbulence, cooling, and viscosity can significantly influence gas dynamics and star formation processes. We investigate the role of viscosity in modulating turbulence and radiative cooling in turbulent radiative mixing layers (… ▽ More Multiphase gas can be found in many astrophysical environments, such as galactic outflows, stellar wind bubbles, and the circumgalactic medium, where the interplay between turbulence, cooling, and viscosity can significantly influence gas dynamics and star formation processes. We investigate the role of viscosity in modulating turbulence and radiative cooling in turbulent radiative mixing layers (TRMLs). In particular, we aim to determine how different amounts of viscosity affect the Kelvin-Helmholtz instability (KHI), turbulence evolution, and the efficiency of gas mixing and cooling. Using idealized 2D numerical setups, we compute the critical viscosity required to suppress the KHI in shear flows characterized by different density contrasts and Mach numbers. These results are then used in a 3D shear layer setup to explore the impact of viscosity on cooling efficiency and turbulence across different cooling regimes. We find that the critical viscosity follows the expected dependence on overdensity and Mach number. Our viscous TRMLs simulations show different behaviors in the weak and strong cooling regimes. In the weak cooling regime, viscosity has a strong impact, resulting in laminar flows and breaking previously established inviscid relations between cooling and turbulence (albeit leaving the total luminosity unaffected). However, in the strong cooling regime, when cooling timescales are shorter than viscous timescales, key scaling relations in TRMLs remain largely intact. In this regime -- which must hold for gas to remain multiphase -- radiative losses dominate, and the system effectively behaves as non-viscous regardless of the actual level of viscosity. Our findings have direct implications for both the interpretation of observational diagnostics and the development of subgrid models in large-scale simulations. △ Less

Submitted 21 April, 2025; originally announced April 2025.

Comments: 18 pages, 20 figures, submitted to Astronomy and Astrophysics

JADES NIRSpec Spectroscopy of GN-z11: Evidence for Wolf-Rayet contribution to stellar populations at 430 Myr after Big Bang?

Authors: Madusha L. P. Gunawardhana, Jarle Brinchmann, Scott Croom, Andrew Bunker, Julia Bryant, Sree Oh

Abstract: We investigate the unusual emission line luminosity ratios observed in the JADES NIRSpec spectroscopy of GN-z11, which reveal exceptionally strong emission lines and a significant detection of the rarely observed N III] $\lambda1748-1753$Å multiplet. These features suggest an elevated N/O abundance, challenging existing models of stellar populations and nebular emission. To assess whether Wolf-Ray… ▽ More We investigate the unusual emission line luminosity ratios observed in the JADES NIRSpec spectroscopy of GN-z11, which reveal exceptionally strong emission lines and a significant detection of the rarely observed N III] $\lambda1748-1753$Å multiplet. These features suggest an elevated N/O abundance, challenging existing models of stellar populations and nebular emission. To assess whether Wolf-Rayet (WR) stars can account for the observed line ratios, we construct a suite of stellar and nebular models incorporating high-resolution stellar spectral libraries, enabling a more accurate treatment of WR evolution and its influence on the ionising radiation field. We find that the inclusion of WR stars is essential for reproducing the observed position of GN-z11 in the C III]/He II versus C III]/C iv diagnostic plane, resolving discrepancies from previous studies. The model-derived metallicity (0.07$\lesssim$Z/Z$_{\odot}\lesssim$0.15), ionisation parameter ($\log\,U$$\approx$-2) and stellar ages are consistent with the literature estimates. However, our models under-predict the N III/O III] ratio, suggesting that WR stars alone cannot fully explain the nitrogen enrichment. This suggests that additional mechanisms, such as rapid chemical enrichment in a young, metal-poor environment, may be necessary to explain the nitrogen excess. While our models successfully reproduce most observed line ratios, further refinements to the models are needed to fully characterise the stellar populations and the enrichment processes of high-redshift galaxies like GN-z11. △ Less

Submitted 16 April, 2025; originally announced April 2025.

Comments: 21 pages, 14 figures, Submitted to MNRAS

Near-Infrared Spectroscopy with IGRINS-2 for Studying Multiple Stellar Populations in Globular Clusters

Authors: Dongwook Lim, Young-Wook Lee, Sol Yun, Young Sun Lee, Sang-Hyun Chun, Heeyoung Oh, Jae-Joon Lee, Chan Park, Sanghyuk Kim, Ueejeong Jeong, Hye-In Lee, Woojin Park, Youngsam Yu, Yunjong Kim, Moo-Young Chun, Jae Sok Oh, Sungho Lee, Jeong-Gyun Jang, Bi-Ho Jang, Hyeon Cheol Seong, Hyun-Jeong Kim, Cynthia B. Brooks, Gregory N. Mace, Hanshin Lee, John M. Good , et al. (31 additional authors not shown)

Abstract: Recent advancements in near-infrared (NIR) spectroscopy have opened new opportunities for studying multiple stellar populations in globular clusters (GCs), particularly for newly discovered clusters in the inner Milky Way. While optical spectroscopy has traditionally played a primary role in detailed chemical abundance studies of GCs, the increasing discovery of GCs in highly reddened environments… ▽ More Recent advancements in near-infrared (NIR) spectroscopy have opened new opportunities for studying multiple stellar populations in globular clusters (GCs), particularly for newly discovered clusters in the inner Milky Way. While optical spectroscopy has traditionally played a primary role in detailed chemical abundance studies of GCs, the increasing discovery of GCs in highly reddened environments underscores the need for robust NIR spectroscopic methods. To evaluate the utility of high-resolution NIR spectroscopy for studying multiple stellar populations, we observed six stars in M5, a well-studied halo GC, using the recently commissioned IGRINS-2 spectrograph on the Gemini-North telescope. Our chemical abundance measurements in the NIR wavelength range show good agreement with those derived from high-resolution optical spectroscopy, with minor systematic offsets in elements such as Na and Mg. In addition, the measured chemical abundance ratios clearly reproduce the distinctive patterns of multiple stellar populations, including the Na-O anti-correlation. The ability of NIR spectroscopy to measure C, N, and O abundances with high precision further enhances its utility for studying chemical properties of stars and GCs. Our findings demonstrate that IGRINS-2 and similar instruments have significant potential to advance our understanding of GC formation, stellar chemical evolution, and the evolutionary history of the Milky Way. △ Less

Submitted 3 April, 2025; originally announced April 2025.

Comments: 12 pages, 7 figures, accepted for publication in JKAS

Journal ref: Journal of The Korean Astronomical Society (2025) Vol.58 No.1 pp.81-92

Velocity Structure Correlations between the Nebular, Molecular, and Atmospheric Gases in the Cores of Four Cool Core Clusters

Authors: Muzi Li, B. R. McNamara, Alison L. Coil, Marie-Joelle Gingras, Fabrizio Brighenti, H. R. Russell, Prathamesh D. Tamhaneh, S. Peng Oh, Serena Perrotta

Abstract: We investigate the velocity structure of nebular gas in the central galaxies of four clusters: Abell 1835, PKS 0745-191, Abell 262, and RXJ0820.9+0752, using data from the Keck Cosmic Web Imager (KCWI). Velocity structure functions (VSFs) of the [OII] emission line are compared to VSFs of molecular clouds observed with the Atacama Large Millimeter/submillimeter Array (ALMA). Apart from Abell 262 w… ▽ More We investigate the velocity structure of nebular gas in the central galaxies of four clusters: Abell 1835, PKS 0745-191, Abell 262, and RXJ0820.9+0752, using data from the Keck Cosmic Web Imager (KCWI). Velocity structure functions (VSFs) of the [OII] emission line are compared to VSFs of molecular clouds observed with the Atacama Large Millimeter/submillimeter Array (ALMA). Apart from Abell 262 where the gas is located in a circumnuclear disk, the nebular gas in the remaining galaxies lies in off-nuclear filamentary structures with VSFs steeper than the Kolmogorov slope. This steepening may be plausibly attributed to gravity although other factors, such as magnetic stresses and bulk motion,} may be significant. The VSFs of CO and [OII] emission are similar in RXJ0820 and Abell 262, indicating close coupling of the nebular and molecular gases. In contrast, the nebular and molecular gases are differentiated on most scales in PKS 0745 and Abell 1835. This discrepancy is likely due to the radio-AGN churning the gas. We compare the scale-dependent velocity amplitudes of the hot atmospheres constrained by X-ray surface brightness fluctuation analysis using Chandra observations to the nebular VSFs. The large-scale consistency in Abell 1835 and RXJ0820 is consistent with condensation from the hot atmospheres. {We explore substantial systematic biases, including projection effects, windowing, and smoothing effects when comparing VSFs using different telescopes and instruments. △ Less

Submitted 18 March, 2025; originally announced March 2025.

Comments: 25 pages; 12 figures; Accepted by ApJ in March 2025, DOI: 10.3847/1538-4357/adc102

An Early Look at the Performance of IGRINS-2 at Gemini-North with Application to the ultrahot Jupiter, WASP-33 b

Authors: Yeon-Ho Choi, Ueejeong Jeong, Jae-Joon Lee, Hyun-Jeong Kim, Heeyoung Oh, Chan Park, Changwoo Kye, Luke Finnerty, Micheal R. Line, Krishna Kanumalla, Jorge A. Sanchez, Peter C. B. Smith, Sanghyuk Kim, Hye-In Lee, Woojin Park, Youngsam Yu, Yunjong Kim, Moo-Young Chun, Jae Sok Oh, Sungho Lee, Jeong-Gyun Jang, Bi-Ho Jang, Hyeon Cheol Seong, Cynthia B. Brooks, Gregory N. Mace , et al. (34 additional authors not shown)

Abstract: Ground-based high-resolution spectroscopy enables precise molecular detections and velocity-resolved atmospheric dynamics, offering a distinct advantage over low-resolution methods for exoplanetary atmospheric studies. IGRINS-2, the successor to IGRINS, features improved throughput and enhanced sensitivity to carbon monoxide by shifting its $\textit{K}$-band coverage by 36 nm to longer wavelengths… ▽ More Ground-based high-resolution spectroscopy enables precise molecular detections and velocity-resolved atmospheric dynamics, offering a distinct advantage over low-resolution methods for exoplanetary atmospheric studies. IGRINS-2, the successor to IGRINS, features improved throughput and enhanced sensitivity to carbon monoxide by shifting its $\textit{K}$-band coverage by 36 nm to longer wavelengths. IGRINS is a near-infrared high-resolution spectrograph mounted at McDonald, Lowell, and Gemini-South observatories. Our order-drop test shows this added range improves the CO cross-correlation signal-to-noise ratio (SNR) by 2$-$3%, confirming a measurable but modest sensitivity gain. To evaluate its performance, we attempt to investigate the atmospheric characteristics of WASP-33 b. Observations were conducted on 2024 January 7 for a total of 2.43 hours; This includes 1.46 hours in the pre-eclipse phase to capture the planet's thermal emission spectrum. We successfully detect clear cross-correlation signals from molecular species in the dayside atmosphere of WASP-33 b with a combined SNR of 7.4. More specifically, we capture CO, H$_{2}$O, and OH with SNRs of 6.3, 4.7, and 4.2, respectively. These results are consistent with previous studies and demonstrate that IGRINS-2 is well-suited for detailed investigation of exoplanetary atmospheres. We anticipate that future observations with IGRINS-2 will further advance our understanding of exoplanetary atmospheres. △ Less

Submitted 20 June, 2025; v1 submitted 16 March, 2025; originally announced March 2025.

Comments: 11 pages, 6 figures, 1 table, revised and resubmitted to AJ

Journal ref: AJ 170, 238 (2025)

Square Kilometre Array Science Data Challenge 3a: foreground removal for an EoR experiment

Authors: A. Bonaldi, P. Hartley, R. Braun, S. Purser, A. Acharya, K. Ahn, M. Aparicio Resco, O. Bait, M. Bianco, A. Chakraborty, E. Chapman, S. Chatterjee, K. Chege, H. Chen, X. Chen, Z. Chen, L. Conaboy, M. Cruz, L. Darriba, M. De Santis, P. Denzel, K. Diao, J. Feron, C. Finlay, B. Gehlot , et al. (159 additional authors not shown)

Abstract: We present and analyse the results of the Science data challenge 3a (SDC3a, https://sdc3.skao.int/challenges/foregrounds), an EoR foreground-removal community-wide exercise organised by the Square Kilometre Array Observatory (SKAO). The challenge ran for 8 months, from March to October 2023. Participants were provided with realistic simulations of SKA-Low data between 106 MHz and 196 MHz, includin… ▽ More We present and analyse the results of the Science data challenge 3a (SDC3a, https://sdc3.skao.int/challenges/foregrounds), an EoR foreground-removal community-wide exercise organised by the Square Kilometre Array Observatory (SKAO). The challenge ran for 8 months, from March to October 2023. Participants were provided with realistic simulations of SKA-Low data between 106 MHz and 196 MHz, including foreground contamination from extragalactic as well as Galactic emission, instrumental and systematic effects. They were asked to deliver cylindrical power spectra of the EoR signal, cleaned from all corruptions, and the corresponding confidence levels. Here we describe the approaches taken by the 17 teams that completed the challenge, and we assess their performance using different metrics. The challenge results provide a positive outlook on the capabilities of current foreground-mitigation approaches to recover the faint EoR signal from SKA-Low observations. The median error committed in the EoR power spectrum recovery is below the true signal for seven teams, although in some cases there are some significant outliers. The smallest residual overall is $4.2_{-4.2}^{+20} \times 10^{-4}\,\rm{K}^2h^{-3}$cMpc$^{3}$ across all considered scales and frequencies. The estimation of confidence levels provided by the teams is overall less accurate, with the true error being typically under-estimated, sometimes very significantly. The most accurate error bars account for $60 \pm 20$\% of the true errors committed. The challenge results provide a means for all teams to understand and improve their performance. This challenge indicates that the comparison between independent pipelines could be a powerful tool to assess residual biases and improve error estimation. △ Less

Submitted 14 March, 2025; originally announced March 2025.

Comments: 29 pages, 10 figures, submitted to MNRAS

Extraction of HI gas with bulk motions in the disk of galaxies

Authors: Se-Heon Oh, Jing Wang

Abstract: We propose a new method for extracting bulk motion gases in the disk of a galaxy from HI data cubes, offering improvements over classical techniques like moment analysis and line profile fitting. Our approach decomposes the line-of-sight velocity profiles into multiple Gaussian components, which are then classified into (underlying and dominant) bulk and non-bulk motion gases based on criteria suc… ▽ More We propose a new method for extracting bulk motion gases in the disk of a galaxy from HI data cubes, offering improvements over classical techniques like moment analysis and line profile fitting. Our approach decomposes the line-of-sight velocity profiles into multiple Gaussian components, which are then classified into (underlying and dominant) bulk and non-bulk motion gases based on criteria such as HI surface density, velocity dispersion, kinetic energy, and rotation velocity. A 2D tilted-ring analysis is employed to refine the kinematical parametres of the galaxy disk, ensuring robust extraction of the bulk motion gases. We demonstrate the effectiveness of this method using the HI data cubes of NGC 4559 from the WSRT-HALOGAS survey, distinguishing between bulk and non-bulk gas components. From this, we find that approximately 50% of the HI gas in NGC 4559 is classified as non-bulk, possibly linked to processes such as stellar feedback. This work provides a robust framework for analysing HI kinematics of galaxies from high sensitivity HI observations of galaxies like MeerKAT-MHONGOOSE and FAST-FEASTS and allows us to best exploit the kinematic information of the complex gas dynamics within galaxy disks. △ Less

Submitted 14 March, 2025; originally announced March 2025.

Comments: 14 pages, 9 figures, accepted for publication in MNRAS

Lévy Flights and Leaky Boxes: Anomalous Diffusion of Cosmic Rays

Authors: Naixin Liang, Siang Peng Oh

Abstract: In classical diffusion, particle step-sizes have a Gaussian distribution. However, in superdiffusion, they have power-law tails, with transport dominated by rare, long Lévy flights. Similarly, if the time interval between scattering events has power-law tails, subdiffusion occurs. Both forms of anomalous diffusion are seen in cosmic ray (CR) particle tracking simulations in turbulent magnetic fiel… ▽ More In classical diffusion, particle step-sizes have a Gaussian distribution. However, in superdiffusion, they have power-law tails, with transport dominated by rare, long Lévy flights. Similarly, if the time interval between scattering events has power-law tails, subdiffusion occurs. Both forms of anomalous diffusion are seen in cosmic ray (CR) particle tracking simulations in turbulent magnetic fields. They also likely occur if CRs are scattered by discrete intermittent structures. Anomalous diffusion mimics a scale-dependent diffusion coefficient, with potentially wide-ranging consequences. However, the finite size of galaxies implies an upper bound on step-sizes before CRs escape. This truncation results in eventual convergence to Gaussian statistics by the central limit theorem. Using Monte-Carlo simulations, we show that this occurs in both standard finite-thickness halo models, or when CR diffusion transitions to advection or streaming-dominated regimes. While optically thick intermittent structures produce power-law trapping times and thus subdiffusion, gaussianization also eventually occurs on timescales longer than the maximum trapping time. Anomalous diffusion is a transient, and converges to standard diffusion on the (usually short) timescale of particle escape, either from confining structures (subdiffusion), or the system as a whole (superdiffusion). Thus, standard assumptions of classical diffusion are physically justified in most applications, despite growing simulation evidence for anomalous diffusion. However, if escape times are long, this is no longer true. For instance, anomalous diffusion in the CGM or ICM would change CR pressure profiles. Finally, we show the standard diagnostic for anomalous diffusion, $\langle d^2 \rangle \propto t^α$ with $α\neq 1$, is not justified for truncated Lévy flights, and propose an alternative robust measure. △ Less

Submitted 13 March, 2025; originally announced March 2025.

Journal ref: Mon Not R Astron Soc (2025) 1911-1934

The SAMI Galaxy Survey: large-scale environment affects galaxy spin amplitudes and the formation of slow rotators

Authors: Stefania Barsanti, Scott M. Croom, Matthew Colless, Joss Bland-Hawthorn, Sarah Brough, Julia J. Bryant, Nuria Lorente, Sree Oh, Giulia Santucci, Sarah Sweet, Jesse van de Sande, Charlotte Welker

Abstract: We explore the impact of the large-scale 3D density field, as defined by deep, wide-field galaxy surveys, on stellar spin ($λ_{\rm R_e}$) and the distributions of fast and slow rotators. We use the GAMA spectroscopic redshift survey to reconstruct the cosmic web and obtain spatially-resolved stellar kinematics from the SAMI Galaxy Survey. Among various local and large-scale environment metrics, th… ▽ More We explore the impact of the large-scale 3D density field, as defined by deep, wide-field galaxy surveys, on stellar spin ($λ_{\rm R_e}$) and the distributions of fast and slow rotators. We use the GAMA spectroscopic redshift survey to reconstruct the cosmic web and obtain spatially-resolved stellar kinematics from the SAMI Galaxy Survey. Among various local and large-scale environment metrics, the distance to the closest filament ($D_{\rm fil}$) correlates most significantly with $λ_{\rm R_e}$, but it is secondary to the more dominant roles played by stellar age and mass. Fast rotators tend to have increasing $λ_{\rm R_e}$ going from nodes to filaments to voids, independently of mass. Slow rotators and mass-matched fast rotators are found to have significantly different distributions of large-scale environment metrics but consistent distributions of local environment metrics. About 95% of slow rotators have $D_{\rm fil}\leq2$Mpc, while covering broader ranges (similar to fast rotators) in distance to nodes and voids, local galaxy density, halo mass, and position with respect to the halo. At fixed mass, the fraction of slow rotators, $f_{\rm SR}$, increases for smaller $D_{\rm fil}$, especially for massive galaxies. While controlling for age or mass, only galaxies very close to filaments and nodes show a significant impact of local environment on $f_{\rm SR}$. Our results demonstrate that the cosmic web leaves an imprint on galactic spin amplitudes, and that pre-processing by mergers occurring within filaments is likely to be an important physical mechanism for the formation of slow rotators before they reach nodes. △ Less

Submitted 12 March, 2025; originally announced March 2025.

Comments: Accepted for publication on MNRAS; 16 pages, 16 figures

10 Years of Archival High-Resolution NIR Spectra: The Raw and Reduced IGRINS Spectral Archive (RRISA)

Authors: Erica Sawczynec, Kyle F. Kaplan, Gregory N. Mace, Jae-Joon Lee, Daniel T. Jaffe, Chan Park, In-Soo Yuk, Moo-Young Chun, Soojong Pak, Narae Hwang, Ueejeong Jeong, Hwihyun Kim, Hyun-Jeong Kim, Kang-Min Kim, Sanghyuk Kim, Huynh Anh N. Le, Hye-In Lee, Sungho Lee, Heeyoung Oh, Jae Sok Oh, Byeong-Gon Park, Woojin Park, Young-Sam Yu

Abstract: The Immersion GRating INfrared Spectrometer (IGRINS) is a compact, high-resolution (R~45,000) near-infrared spectrograph spanning 1.45 to 2.45 um in a single exposure. We introduce the Raw and Reduced IGRINS Spectral Archive (RRISA), which provides public data access for all non-proprietary IGRINS data taken at McDonald Observatory's Harlan J. Smith Telescope, the Lowell Discovery Telescope (forme… ▽ More The Immersion GRating INfrared Spectrometer (IGRINS) is a compact, high-resolution (R~45,000) near-infrared spectrograph spanning 1.45 to 2.45 um in a single exposure. We introduce the Raw and Reduced IGRINS Spectral Archive (RRISA), which provides public data access for all non-proprietary IGRINS data taken at McDonald Observatory's Harlan J. Smith Telescope, the Lowell Discovery Telescope (formerly Discovery Channel Telescope), and Gemini South. RRISA provides access to raw files, reduced data products, and cross-matched IGRINS targets with the SIMBAD, 2MASS, Gaia DR3, APOGEE2 DR17, and PASTEL catalogs. We also introduce version 3 of the IGRINS data reduction pipeline, IGRINS PLP v3, which implements an improved cosmic ray correction, pattern noise removal, and a new flexure correction that reduces telluric residuals. RRISA and supporting information can be found at http://igrinscontact.github.io. △ Less

Submitted 7 March, 2025; originally announced March 2025.

Comments: Accepted for publication in PASP. 18 pages, 3 figures, 6 tables

Microphysics of Circumgalactic Turbulence Probed by Fast Radio Bursts and Quasars

Authors: S. K. Ocker, M. Chen, S. P. Oh, P. Sharma

Abstract: The circumgalactic medium (CGM) is poorly constrained at the sub-parsec scales relevant to turbulent energy dissipation and regulation of multi-phase structure. Fast radio bursts (FRBs) are sensitive to small-scale plasma density fluctuations, which can induce multipath propagation (scattering). The amount of scattering depends on the density fluctuation spectrum, including its amplitude… ▽ More The circumgalactic medium (CGM) is poorly constrained at the sub-parsec scales relevant to turbulent energy dissipation and regulation of multi-phase structure. Fast radio bursts (FRBs) are sensitive to small-scale plasma density fluctuations, which can induce multipath propagation (scattering). The amount of scattering depends on the density fluctuation spectrum, including its amplitude $C_{\rm n}^2$, spectral index $β$, and dissipation scale $l_{\rm i}$. We use quasar observations of CGM turbulence at $\gtrsim$ pc scales to infer $C_{\rm n}^2$, finding it to be $10^{-16}\lesssim C_{\rm n}^2\lesssim 10^{-9}$ m$^{-20/3}$ for hot ($T>10^6$ K) gas and $10^{-8}\lesssim C_{\rm n}^2\lesssim 10^{-4}$ m$^{-20/3}$ for cool ($10^4\lesssim T\lesssim 10^5$ K) gas, depending on the gas sound speed and density. These values of $C_{\rm n}^2$ are much smaller than those inferred in the interstellar medium at similar physical scales. The resulting scattering delays from the hot CGM are negligible ($\ll1$ $μ$s at 1 GHz), but are more detectable from the cool gas as either radio pulse broadening or scintillation, depending on the observing frequency and sightline geometry. Joint quasar-FRB observations of individual galaxies can yield lower limits on $l_{\rm i}$, even if the CGM is not a significant scattering site. An initial comparison between quasar and FRB observations (albeit for different systems) suggests $l_{\rm i}\gtrsim750$ km in $\sim10^4$ K gas in order for the quasar and FRB constraints to be consistent. If a foreground CGM is completely ruled out as a source of scattering along an FRB sightline then $l_{\rm i}$ may be comparable to the smallest cloud sizes ($\lesssim$ pc) inferred from photoionization modeling of quasar absorption lines. △ Less

Submitted 5 June, 2025; v1 submitted 4 March, 2025; originally announced March 2025.

Comments: 21 pages, 9 figures, accepted for publication in ApJ

Tales of Tension: Magnetized Infalling Clouds and Cold Streams in the CGM

Authors: Ish Kaul, Brent Tan, S. Peng Oh, Nir Mandelker

Abstract: The observed star formation and wind outflow rates in galaxies suggest cold gas must be continually replenished via infalling clouds or streams. Previous studies have highlighted the importance of cooling-induced condensation on such gas, which enables survival, mass growth, and a drag force which typically exceeds hydrodynamic drag. However, the combined effects of magnetic fields, cooling, and i… ▽ More The observed star formation and wind outflow rates in galaxies suggest cold gas must be continually replenished via infalling clouds or streams. Previous studies have highlighted the importance of cooling-induced condensation on such gas, which enables survival, mass growth, and a drag force which typically exceeds hydrodynamic drag. However, the combined effects of magnetic fields, cooling, and infall remains unexplored. We conduct 3D magnetohydrodynamic (MHD) simulations of radiatively cooling infalling clouds and streams in uniform and stratified backgrounds. For infalling clouds, magnetic fields aligned with gravity do not impact cloud growth or dynamics significantly, although we see enhanced survival for stronger fields. By contrast, even weak transverse magnetic fields significantly slow cloud infall via magnetic drag, due to the development of strong draped fields which develop at peak infall velocity, before the cloud decelerates. Besides enhancing survival, long, slow infall increases total cloud mass growth compared to the hydrodynamic case, even if reduced turbulent mixing lowers the rate of mass growth. Streams often result in qualitatively different behavior. Mass growth and hence accretion drag are generally much lower in hydrodynamic streams. Unlike in clouds, aligned magnetic fields suppress mixing and thus both mass growth or loss. Transverse fields do apply magnetic drag and allow streams to grow, when the streams have a well-defined 'head' pushing through the surrounding medium. Overall, regardless of the efficacy of drag forces, streams are surprisingly robust in realistic potentials, as the destruction time when falling supersonically exceeds the infall time. We develop analytic models which reproduce cloud/stream trajectories. △ Less

Submitted 24 February, 2025; originally announced February 2025.

Comments: 36 pages, 22 figures

FEASTS Combined with Interferometry. III. The Low Column Density HI Around M51 and Possibility of Turbulent-mixing Gas Accretion

Authors: Xuchen Lin, Jing Wang, Lister Staveley-Smith, Suoqing Ji, Dong Yang, Xinkai Chen, Fabian Walter, Hsiao-Wen Chen, Luis C. Ho, Peng Jiang, Nir Mandelker, Se-Heon Oh, Bo Peng, Céline Péroux, Zhijie Qu, Q. Daniel Wang

Abstract: With a new joint-deconvolution pipeline, we combine the single-dish and interferometric atomic hydrogen (HI) data of M51 observed by the Five-hundred-meter Aperture Spherical radio Telescope (FAST) (FEASTS program) and the Very Large Array (VLA) (THINGS). The product data cube has a typical line width of $13\,\text{km}\,\text{s}^{-1}$ and a $2σ$ line-of-sight (LOS) sensitivity of HI column density… ▽ More With a new joint-deconvolution pipeline, we combine the single-dish and interferometric atomic hydrogen (HI) data of M51 observed by the Five-hundred-meter Aperture Spherical radio Telescope (FAST) (FEASTS program) and the Very Large Array (VLA) (THINGS). The product data cube has a typical line width of $13\,\text{km}\,\text{s}^{-1}$ and a $2σ$ line-of-sight (LOS) sensitivity of HI column density $N_\text{HI}\sim3.2\times10^{18}\,\text{cm}^{-2}$ at a spatial resolution of ${\sim}18''$ (${\sim}0.7\,\text{kpc}$). Among the HI-detected LOSs extending to ${\sim}50\,\text{kpc}$, ${\sim}89\%$ consist of diffuse HI only, which is missed by previous VLA observations. The distribution of dense HI is reproduced by previous hydrodynamical simulations of this system, but the diffuse component is not, likely due to unresolved physics related to the interaction between the circumgalactic and interstellar media. With simple models, we find that these low-$N_\text{HI}$ structures could survive the background ultraviolet photoionization, but are susceptible to the thermal evaporation. We find a positive correlation between LOS velocity dispersion ($σ_v$) and $N_\text{HI}$ with a logarithmic index of ${\sim}0.5$. Based on existing turbulent mixing layer (TML) theories and simulations, we propose a scenario of hot gas cooling and accreting onto the disk through a TML, which could reproduce the observed power index of ${\sim}0.5$. We estimate the related cooling and accretion rates to be roughly one-third to two-thirds of the star-formation rate. A typical column density of diffuse HI (${\sim}10^{19}\,\text{cm}^{-2}$) can be accreted within $300\,\text{Myr}$, the interaction time scale previously estimated for the system. Such a gas accretion channel has been overlooked before, and may be important for gas-rich interacting systems and for high redshift galaxy evolution. △ Less

Submitted 24 April, 2025; v1 submitted 14 February, 2025; originally announced February 2025.

Comments: 16 pages of main text, 7 pages of appendices, 27 pages in total; 18 figures, 1 table; minor typesetting correction and fix the figure issue of HTML version. Data are publicly available at https://github.com/FEASTS/LVgal/wiki

Journal ref: ApJ 982 (2025) 151

Precision Analysis of $\mathrm{^{12}C / ^{13}C}$ Ratios in Orion IRc2 Acetylene Isotopologues via $χ^2$ Fitting

Authors: Minkyu Lee, Jubin Park, Sehoon Oh, Myung-Ki Cheoun, Se Young Park

Abstract: We present a detailed analysis of acetylene (C$_2$H$_2$) and its isotopologues in the Orion IRc2 region, focusing on the determination of $^{12}$C/$^{13}$C isotopic ratios using high-resolution infrared spectra from SOFIA. By employing a robust $χ^2$ fitting method, we simultaneously determined temperature and column density, achieving a $^{12}$C/$^{13}$C ratio of $18.72^{+1.54}_{-1.46}$ for the b… ▽ More We present a detailed analysis of acetylene (C$_2$H$_2$) and its isotopologues in the Orion IRc2 region, focusing on the determination of $^{12}$C/$^{13}$C isotopic ratios using high-resolution infrared spectra from SOFIA. By employing a robust $χ^2$ fitting method, we simultaneously determined temperature and column density, achieving a $^{12}$C/$^{13}$C ratio of $18.72^{+1.54}_{-1.46}$ for the blue clump and $15.07^{+1.61}_{-1.60}$ for the red clump. These results revealed significant discrepancies with the traditional rotational diagram method, which overestimated the ratios by 12.1% and 23.9%, respectively. Our $χ^2$ approach also reduced uncertainties by up to 75%, providing more precise and reliable isotopic ratios. Additionally, we extended the analysis to isotopologues not covered in HITRAN, calculating vibrational and rotational constants through quantum chemical calculations. This allowed us to model subtle isotopic shifts induced by $^{13}$C and deuterium substitution, enabling accurate isotopologue detection in astrophysical environments. The Python package (TOPSEGI) developed in this study facilitates efficient $χ^2$ fitting and isotopic ratio analysis, making it a valuable tool for future high-resolution observations. This work highlights the critical role of advanced spectral models and fitting techniques in understanding isotopic fractionation and the chemical evolution of interstellar matter. △ Less

Submitted 26 February, 2025; v1 submitted 27 January, 2025; originally announced January 2025.

Journal ref: A&A 700, A238 (2025)

Exploring lenticular galaxy formation in field environments using NewHorizon: evidence for counter-rotating gas accretion as a formation channel

Authors: Seongbong Han, J. K. Jang, Emanuele Contini, Yohan Dubois, Seyoung Jeon, Sugata Kaviraj, Taysun Kimm, Katarina Kraljic, Sree Oh, Sebastien Peirani, Christophe Pichon, Sukyoung K. Yi

Abstract: The formation pathways of lenticular galaxies (S0s) in field environments remain a matter of debate. We utilize the cosmological hydrodynamic simulation, NewHorizon, to investigate the issue. We select two massive star-formation quenched S0s as our main sample. By closely tracing their physical and morphological evolution, we identify two primary formation channels: mergers and counter-rotating ga… ▽ More The formation pathways of lenticular galaxies (S0s) in field environments remain a matter of debate. We utilize the cosmological hydrodynamic simulation, NewHorizon, to investigate the issue. We select two massive star-formation quenched S0s as our main sample. By closely tracing their physical and morphological evolution, we identify two primary formation channels: mergers and counter-rotating gas accretion. The former induces central gas inflow due to gravitational and hydrodynamic torques, triggering active central star formation which quickly depletes the gas of the galaxy. Counter-rotating gas accretion overall has a similar outcome but more exclusively through hydrodynamic collisions between the pre-existing and newly-accreted gas. Both channels lead to S0 morphology, with gas angular momentum cancellation being a crucial mechanism. These formation pathways quench star formation on a short timescale (< Gyr) compared to the timescales of environmental effects. We also discuss how counter-rotating gas accretion may explain the origin of S0s with ongoing star formation and the frequently observed gas-star misaligned kinematics in S0s. △ Less

Submitted 8 November, 2024; originally announced November 2024.

Comments: 19 pages, 16 figures, Accepted for publication in ApJ, Oct 27 2024

WALLABY Pilot Survey: Star Formation Enhancement and Suppression in Gas-rich Galaxy Pairs

Authors: Qifeng Huang, Jing Wang, Xuchen Lin, Se-Heon Oh, Xinkai Chen, Barbara Catinella, Nathan Deg, Helga Dénes, Bi-Qing For, Baerbel Koribalski, Karen Lee-Waddell, Jonghwan Rhee, Austin Shen, Li Shao, Kristine Spekkens, Lister Staveley-Smith, Tobias Westmeier, O. Ivy Wong, Albert Bosma

Abstract: Galaxy interactions can significantly affect the star formation in galaxies, but it remains a challenge to achieve a consensus on the star formation rate (SFR) enhancement in galaxy pairs. Here, we investigate the SFR enhancement of gas-rich galaxy pairs detected by the Widefield ASKAP L-band Legacy All-sky Blind surveY (WALLABY). We construct a sample of 278 paired galaxies spanning a stellar mas… ▽ More Galaxy interactions can significantly affect the star formation in galaxies, but it remains a challenge to achieve a consensus on the star formation rate (SFR) enhancement in galaxy pairs. Here, we investigate the SFR enhancement of gas-rich galaxy pairs detected by the Widefield ASKAP L-band Legacy All-sky Blind surveY (WALLABY). We construct a sample of 278 paired galaxies spanning a stellar mass ($M_\ast$) range from $10^{7.6}$ to $10^{11.2}M_\odot$. We obtain individual masses of atomic hydrogen (HI) for these paired galaxies, using a novel deblending algorithm for HI data cubes. Quantifying the interaction stages and strengths with parameters motivated by first principles, we find that at fixed stellar and HI mass, the alteration in SFR of galaxy pairs starts when their dark matter halos encounter. For galaxies with stellar mass lower than $10^9M_\odot$, their SFRs show tentative suppression of 1.4 sigma after the halo encounter, and then become enhanced when their HI disks overlap, regardless of mass ratios. In contrast, the SFRs of galaxies with $M_\ast > 10^9M_\odot$ increase monotonically toward smaller projected distances and radial velocity offsets. When a close companion is present, a pronounced SFR enhancement is found for the most HI-poor high-mass galaxies in our sample. Collecting the observational evidence, we provide a coherent picture of the evolution of galaxy pairs, and discuss how the tidal effects and hydrodynamic processes shape the SFR enhancement. Our results provide a coherent picture of gas-rich galaxy interactions and impose constraints on the underlying physical processes. △ Less

Submitted 29 October, 2024; originally announced October 2024.

Comments: 25 pages, 15 figures, accepted for publication in ApJ

Effects of Cloud Geometry and Metallicity on Shattering and Coagulation of Cold Gas, and Implications for Cold Streams Penetrating Virial Shocks

Authors: Zhiyuan Yao, Nir Mandelker, S. Peng Oh, Han Aung, Avishai Dekel

Abstract: Theory and observations reveal that the circumgalactic medium (CGM) and the cosmic web at high redshifts are multiphase, with small clouds of cold gas embedded in a hot, diffuse medium. A proposed mechanism is `shattering' of large, thermally unstable clouds into tiny cloudlets of size lshatter~min(cs*tcool). We study these processes using idealized numerical simulations of thermally unstable gas… ▽ More Theory and observations reveal that the circumgalactic medium (CGM) and the cosmic web at high redshifts are multiphase, with small clouds of cold gas embedded in a hot, diffuse medium. A proposed mechanism is `shattering' of large, thermally unstable clouds into tiny cloudlets of size lshatter~min(cs*tcool). We study these processes using idealized numerical simulations of thermally unstable gas clouds. We expand upon previous works by exploring the effects of cloud geometry (spheres, streams, and sheets), metallicity, and the inclusion of an ionizing UV background. We find that `shattering' is triggered by clouds losing sonic contact and rapidly imploding, leading to a reflected shock which causes the cloud to re-expand and induces Richtmyer-Meshkov instabilities at its interface. After fragmentation the cloudlets experience a drag force from the surrounding hot gas, leading to recoagulation into larger clouds. We distinguish between `fast' and `slow' coagulation regimes, showing that sheets are always in the `fast' coagulation regime while streams and spheres have a maximum overdensity for rapid coagulation. The critical overdensity for spheres is smaller than for streams, such that the coagulation efficiency increases from spheres to streams to sheets. Surprisingly, lshatter does not appear to be a characteristic clump size even if it is well resolved. Rather, fragmentation continues until the grid scale with a mass distribution of N(>m)~m^{-1}. We apply our results to the case of cold streams feeding massive (Mv>10^{12}Msun) high-z (z>2) galaxies from the cosmic web, finding that streams are likely to shatter upon entering the CGM through the virial shock. This could explain the large clumping factors and covering fractions of cold gas in the CGM around such galaxies, and may be related to galaxy quenching by preventing cold streams from reaching the central galaxy. [abridged] △ Less

Submitted 8 November, 2024; v1 submitted 16 October, 2024; originally announced October 2024.

Comments: 36 pages, 20 figures, submitted to MNRAS. Comments are welcome!

Variations in the Inferred Cosmic-Ray Spectral Index as Measured by Neutron Monitors in Antarctica

Authors: Pradiphat Muangha, David Ruffolo, Alejandro Sáiz, Chanoknan Banglieng, Paul Evenson, Surujhdeo Seunarine, Suyeon Oh, Jongil Jung, Marc Duldig, John Humble

Abstract: A technique has recently been developed for tracking short-term spectral variations in Galactic cosmic rays (GCRs) using data from a single neutron monitor (NM), by collecting histograms of the time delay between successive neutron counts and extracting the leader fraction $L$ as a proxy of the spectral index. Here we analyze $L$ from four Antarctic NMs during 2015 March to 2023 September. We have… ▽ More A technique has recently been developed for tracking short-term spectral variations in Galactic cosmic rays (GCRs) using data from a single neutron monitor (NM), by collecting histograms of the time delay between successive neutron counts and extracting the leader fraction $L$ as a proxy of the spectral index. Here we analyze $L$ from four Antarctic NMs during 2015 March to 2023 September. We have calibrated $L$ from the South Pole NM with respect to a daily spectral index determined from published data of GCR proton fluxes during 2015--2019 from the Alpha Magnetic Spectrometer (AMS-02) aboard the International Space Station. Our results demonstrate a robust correlation between the leader fraction and the spectral index fit over the rigidity range 2.97--16.6 GV for AMS-02 data, with uncertainty 0.018 in the daily spectral index as inferred from $L$. In addition to the 11-year solar activity cycle, a wavelet analysis confirms a 27-day periodicity in the GCR flux and spectral index corresponding to solar rotation, especially near sunspot minimum, while the flux occasionally exhibited a strong harmonic at 13.5 days, and that the magnetic field component along a nominal Parker spiral (i.e., the magnetic sector structure) is a strong determinant of such spectral and flux variations, with the solar wind speed exerting an additional, nearly rigidity-independent influence on flux variations. Our investigation affirms the capability of ground-based NM stations to accurately and continuously monitor cosmic ray spectral variations in the long-term future. △ Less

Submitted 25 August, 2024; originally announced August 2024.

Comments: 17 pages, 10 figures

Swift-BAT GUANO follow-up of gravitational-wave triggers in the third LIGO-Virgo-KAGRA observing run

Authors: Gayathri Raman, Samuele Ronchini, James Delaunay, Aaron Tohuvavohu, Jamie A. Kennea, Tyler Parsotan, Elena Ambrosi, Maria Grazia Bernardini, Sergio Campana, Giancarlo Cusumano, Antonino D'Ai, Paolo D'Avanzo, Valerio D'Elia, Massimiliano De Pasquale, Simone Dichiara, Phil Evans, Dieter Hartmann, Paul Kuin, Andrea Melandri, Paul O'Brien, Julian P. Osborne, Kim Page, David M. Palmer, Boris Sbarufatti, Gianpiero Tagliaferri , et al. (1797 additional authors not shown)

Abstract: We present results from a search for X-ray/gamma-ray counterparts of gravitational-wave (GW) candidates from the third observing run (O3) of the LIGO-Virgo-KAGRA (LVK) network using the Swift Burst Alert Telescope (Swift-BAT). The search includes 636 GW candidates received in low latency, 86 of which have been confirmed by the offline analysis and included in the third cumulative Gravitational-Wav… ▽ More We present results from a search for X-ray/gamma-ray counterparts of gravitational-wave (GW) candidates from the third observing run (O3) of the LIGO-Virgo-KAGRA (LVK) network using the Swift Burst Alert Telescope (Swift-BAT). The search includes 636 GW candidates received in low latency, 86 of which have been confirmed by the offline analysis and included in the third cumulative Gravitational-Wave Transient Catalogs (GWTC-3). Targeted searches were carried out on the entire GW sample using the maximum--likelihood NITRATES pipeline on the BAT data made available via the GUANO infrastructure. We do not detect any significant electromagnetic emission that is temporally and spatially coincident with any of the GW candidates. We report flux upper limits in the 15-350 keV band as a function of sky position for all the catalog candidates. For GW candidates where the Swift-BAT false alarm rate is less than 10$^{-3}$ Hz, we compute the GW--BAT joint false alarm rate. Finally, the derived Swift-BAT upper limits are used to infer constraints on the putative electromagnetic emission associated with binary black hole mergers. △ Less

Submitted 27 March, 2025; v1 submitted 13 July, 2024; originally announced July 2024.

Comments: Update to version accepted for publication in ApJ. 50 pages, 10 figures, 4 tables

Journal ref: ApJ, Volume 980, 2025, 207

Supernova Pointing Capabilities of DUNE

Authors: DUNE Collaboration, A. Abed Abud, B. Abi, R. Acciarri, M. A. Acero, M. R. Adames, G. Adamov, M. Adamowski, D. Adams, M. Adinolfi, C. Adriano, A. Aduszkiewicz, J. Aguilar, B. Aimard, F. Akbar, K. Allison, S. Alonso Monsalve, M. Alrashed, A. Alton, R. Alvarez, T. Alves, H. Amar, P. Amedo, J. Anderson, D. A. Andrade , et al. (1340 additional authors not shown)

Abstract: The determination of the direction of a stellar core collapse via its neutrino emission is crucial for the identification of the progenitor for a multimessenger follow-up. A highly effective method of reconstructing supernova directions within the Deep Underground Neutrino Experiment (DUNE) is introduced. The supernova neutrino pointing resolution is studied by simulating and reconstructing electr… ▽ More The determination of the direction of a stellar core collapse via its neutrino emission is crucial for the identification of the progenitor for a multimessenger follow-up. A highly effective method of reconstructing supernova directions within the Deep Underground Neutrino Experiment (DUNE) is introduced. The supernova neutrino pointing resolution is studied by simulating and reconstructing electron-neutrino charged-current absorption on 40Ar and elastic scattering of neutrinos on electrons. Procedures to reconstruct individual interactions, including a newly developed technique called ``brems flipping'', as well as the burst direction from an ensemble of interactions are described. Performance of the burst direction reconstruction is evaluated for supernovae happening at a distance of 10 kpc for a specific supernova burst flux model. The pointing resolution is found to be 3.4 degrees at 68% coverage for a perfect interaction-channel classification and a fiducial mass of 40 kton, and 6.6 degrees for a 10 kton fiducial mass respectively. Assuming a 4% rate of charged-current interactions being misidentified as elastic scattering, DUNE's burst pointing resolution is found to be 4.3 degrees (8.7 degrees) at 68% coverage. △ Less

Submitted 24 December, 2025; v1 submitted 14 July, 2024; originally announced July 2024.

Comments: 26 pages, 17 figures

Report number: FERMILAB-PUB-24-0319-LBNF

Journal ref: Phys. Rev. D 111, 092006 (Published 12 May, 2025)

Impact of Internal Dust Correction on the Stellar Populations of Galaxies Estimated Using the Full Spectrum Fitting

Authors: Joon Hyeop Lee, Hyunjin Jeong, Jiwon Chung, Mina Pak, Sree Oh

Abstract: Full spectrum fitting is a powerful tool for estimating the stellar populations of galaxies, but the fitting results are often significantly influenced by internal dust attenuation. For understanding how the choice of the internal dust correction method affects the detailed stellar populations estimated from the full spectrum fitting, we analyze the Sydney-Australian Astronomical Observatory Multi… ▽ More Full spectrum fitting is a powerful tool for estimating the stellar populations of galaxies, but the fitting results are often significantly influenced by internal dust attenuation. For understanding how the choice of the internal dust correction method affects the detailed stellar populations estimated from the full spectrum fitting, we analyze the Sydney-Australian Astronomical Observatory Multi-object Integral field spectrograph (SAMI) galaxy survey data using the Penalized PiXel-Fitting (PPXF) package. Three choices are compared: (Choice-1) using the PPXF reddening option, (Choice-2) using the multiplicative Legendre polynomial, and (Choice-3) using none of them (no dust correction). In any case, the total mean stellar populations show reasonable mass-age and mass-metallicity relations (MTR and MZR), although the correlations appear to be strongest for Choice-1 (MTR) and Choice-2 (MZR). When we compare the age-divided mean stellar populations, the MZR of young (< 10^9.5 yr ~ 3.2 Gyr) stellar components in Choice-2 is consistent with the gas-phase MZR, whereas those in the other two choices hardly are. On the other hand, the MTR of old (>= 10^9.5 yr) stellar components in Choice-1 seems to be more reasonable than that in Choice-2, because the old stellar components in low-mass galaxies tend to be relatively younger than those in massive galaxies. Based on the results, we provide empirical guidelines for choosing the optimal options for dust correction. △ Less

Submitted 19 June, 2024; originally announced June 2024.

Comments: 10 pages, 8 figures, accepted for publication in Journal of the Korean Astronomical Society

The SAMI Galaxy Survey: impact of star formation and AGN feedback processes on the ionized gas velocity dispersion

Authors: Sree Oh, Matthew Colless, Stefania Barsanti, Henry R. M. Zovaro, Scott M. Croom, Sukyoung K. Yi, Andrei Ristea, Jesse van de Sande, Francesco D'Eugenio, Joss Bland-Hawthorn, Julia J. Bryant, Sarah Casura, Hyunjin Jeong, Sarah M. Sweet, Tayyaba Zafar

Abstract: We investigate the influence of star formation and instantaneous AGN feedback processes on the ionized gas velocity dispersion in a sample of 1285 emission-line galaxies with stellar masses $\log\,(M_*/M_{\odot}) \geq 9$ from the integral-field spectroscopy SAMI Galaxy Survey. We fit both narrow and broad emission line components using aperture spectra integrated within one effective radius, while… ▽ More We investigate the influence of star formation and instantaneous AGN feedback processes on the ionized gas velocity dispersion in a sample of 1285 emission-line galaxies with stellar masses $\log\,(M_*/M_{\odot}) \geq 9$ from the integral-field spectroscopy SAMI Galaxy Survey. We fit both narrow and broad emission line components using aperture spectra integrated within one effective radius, while ensuring the elimination of velocity differences between the spectra of individual spaxels. Our analysis reveals that 386 (30%) galaxies can be adequately described using a single emission component while 356 (28%) galaxies require two (broad and narrow) components. Galaxies characterized by high mass, elevated star formation rate surface density, or type-2 AGN-like emissions tend to feature an additional broad emission-line component, leading to their classification as double-component galaxies. We explore the correlations between $M_*$ and gas velocity dispersions, highlighting that the prominence of the broad component significantly contributes to elevating the gas velocity dispersion. Galaxies displaying AGN-like emission based on optical definitions show enhanced gas velocity dispersions. In star-forming galaxies, both stellar mass and star-formation rate surface density substantially contribute to the velocity dispersion of the narrow component. Increased star-forming activity appears to elevate the velocity dispersion of the narrow component. The broad component exhibits a weaker dependence on stellar mass and is primarily driven by galactic outflows. We suggest that strong star forming activity leads to the formation of a broad emission-line component, but the impact on inflating gas velocity dispersion is moderate. On the other hand, AGN-driven outflows appear to be a more important contributor to the elevated velocity dispersion of the ionized gas. △ Less

Submitted 31 May, 2024; originally announced May 2024.

Comments: 17 pages, 11 figures

JWST Lensed quasar dark matter survey II: Strongest gravitational lensing limit on the dark matter free streaming length to date

Authors: Ryan E. Keeley, Anna M. Nierenberg, Daniel Gilman, Charles Gannon, Simon Birrer, Tommaso Treu, Andrew J. Benson, Xiaolong Du, K. N. Abazajian, T. Anguita, V. N. Bennert, S. G. Djorgovski, K. K. Gupta, S. F. Hoenig, A. Kusenko, C. Lemon, M. Malkan, V. Motta, L. A. Moustakas, M. S. H. Oh, D. Sluse, D. Stern, R. H. Wechsler

Abstract: This is the second in a series of papers in which we use JWST MIRI multiband imaging to measure the warm dust emission in a sample of 31 multiply imaged quasars, to be used as a probe of the particle nature of dark matter. We present measurements of the relative magnifications of the strongly lensed warm dust emission in a sample of 9 systems. The warm dust region is compact and sensitive to pertu… ▽ More This is the second in a series of papers in which we use JWST MIRI multiband imaging to measure the warm dust emission in a sample of 31 multiply imaged quasars, to be used as a probe of the particle nature of dark matter. We present measurements of the relative magnifications of the strongly lensed warm dust emission in a sample of 9 systems. The warm dust region is compact and sensitive to perturbations by populations of halos down to masses $\sim 10^6$ M$_{\odot}$. Using these warm dust flux-ratio measurements in combination with 5 previous narrow-line flux-ratio measurements, we constrain the halo mass function. In our model, we allow for complex deflector macromodels with flexible third and fourth-order multipole deviations from ellipticity, and we introduce an improved model of the tidal evolution of subhalos. We constrain a WDM model and find an upper limit on the half-mode mass of $10^{7.6} M_\odot$ at posterior odds of 10:1. This corresponds to a lower limit on a thermally produced dark matter particle mass of 6.1 keV. This is the strongest gravitational lensing constraint to date, and comparable to those from independent probes such as the Ly$α$ forest and Milky Way satellite galaxies. △ Less

Submitted 2 May, 2024; originally announced May 2024.

Joint Semi-Analytic Multipole Priors from Galaxy Isophotes and Constraints from Lensed Arcs

Authors: Maverick S. H. Oh, Anna Nierenberg, Daniel Gilman, Simon Birrer

Abstract: Flux-ratio anomalies in quadruply imaged quasars are sensitive to the imprint of low-mass dark-matter haloes. The reliability of detection depends on the robustness of the smooth mass model. Optical surveys show that massive early-type galaxies similar to galaxy-scale gravitational lenses depart from perfect ellipticity, exhibiting $m=3$ and $m=4$ multipole distortions. We construct the semi-analy… ▽ More Flux-ratio anomalies in quadruply imaged quasars are sensitive to the imprint of low-mass dark-matter haloes. The reliability of detection depends on the robustness of the smooth mass model. Optical surveys show that massive early-type galaxies similar to galaxy-scale gravitational lenses depart from perfect ellipticity, exhibiting $m=3$ and $m=4$ multipole distortions. We construct the semi-analytic, five-dimensional joint population prior for the $m=3$ and $m=4$ amplitude and orientation as well as the axis ratio of the deflector, calibrated on the sample of 840 SDSS E/S0 galaxies. The parameters are fitted via hierarchical Bayesian modeling, minimizing a joint Jensen-Shannon divergence between model and data. We use this prior to model the mass distribution of mock lenses with HST quality data with different multipole amplitudes. We find that we robustly measure the true multipole amplitudes and orientations. Compared to fits that use only the four point-image positions, adding the lensed host-galaxy arcs tightens the 68 % credible regions of multipole parameters by factors of 3-12 and reduces the predicted flux-ratio uncertainties by a mean factor of ~6. This analysis does not include substructure or a complex source, and thus can be considered an upper limit on the expected improvement. The combination of arc information and realistic multipole priors therefore yields an order-of-magnitude improvement in smooth mass model precision, paving the way for more robust measurements of dark-matter substructure. △ Less

Submitted 17 June, 2025; v1 submitted 25 April, 2024; originally announced April 2024.

Comments: v1: 23 pages, 8 figures. v2: 23 pages, 8 figures. v3: 29 pages, 9 figures. Substantial revision presenting a joint semi-analytic prior for multipole parameters

Discovery of a dormant 33 solar-mass black hole in pre-release Gaia astrometry

Authors: Gaia Collaboration, P. Panuzzo, T. Mazeh, F. Arenou, B. Holl, E. Caffau, A. Jorissen, C. Babusiaux, P. Gavras, J. Sahlmann, U. Bastian, Ł. Wyrzykowski, L. Eyer, N. Leclerc, N. Bauchet, A. Bombrun, N. Mowlavi, G. M. Seabroke, D. Teyssier, E. Balbinot, A. Helmi, A. G. A. Brown, A. Vallenari, T. Prusti, J. H. J. de Bruijne , et al. (390 additional authors not shown)

Abstract: Gravitational waves from black-hole merging events have revealed a population of extra-galactic BHs residing in short-period binaries with masses that are higher than expected based on most stellar evolution models - and also higher than known stellar-origin black holes in our Galaxy. It has been proposed that those high-mass BHs are the remnants of massive metal-poor stars. Gaia astrometry is exp… ▽ More Gravitational waves from black-hole merging events have revealed a population of extra-galactic BHs residing in short-period binaries with masses that are higher than expected based on most stellar evolution models - and also higher than known stellar-origin black holes in our Galaxy. It has been proposed that those high-mass BHs are the remnants of massive metal-poor stars. Gaia astrometry is expected to uncover many Galactic wide-binary systems containing dormant BHs, which may not have been detected before. The study of this population will provide new information on the BH-mass distribution in binaries and shed light on their formation mechanisms and progenitors. As part of the validation efforts in preparation for the fourth Gaia data release (DR4), we analysed the preliminary astrometric binary solutions, obtained by the Gaia Non-Single Star pipeline, to verify their significance and to minimise false-detection rates in high-mass-function orbital solutions. The astrometric binary solution of one source, Gaia BH3, implies the presence of a 32.70 \pm 0.82 M\odot BH in a binary system with a period of 11.6 yr. Gaia radial velocities independently validate the astrometric orbit. Broad-band photometric and spectroscopic data show that the visible component is an old, very metal-poor giant of the Galactic halo, at a distance of 590 pc. The BH in the Gaia BH3 system is more massive than any other Galactic stellar-origin BH known thus far. The low metallicity of the star companion supports the scenario that metal-poor massive stars are progenitors of the high-mass BHs detected by gravitational-wave telescopes. The Galactic orbit of the system and its metallicity indicate that it might belong to the Sequoia halo substructure. Alternatively, and more plausibly, it could belong to the ED-2 stream, which likely originated from a globular cluster that had been disrupted by the Milky Way. △ Less

Submitted 19 April, 2024; v1 submitted 16 April, 2024; originally announced April 2024.

Comments: 23 pages, accepted fro publication in A&A Letters. New version with small fixes

Complex Velocity Structure of Nebular Gas in Active Galaxies Centred in Cooling X-ray Atmospheres

Authors: Marie-Joëlle Gingras, Alison L. Coil, B. R. McNamara, Serena Perrotta, Fabrizio Brighenti, H. R. Russell, Muzi Li, S. Peng Oh, Wenmeng Ning

Abstract: [OII] emission maps obtained with the Keck Cosmic Web Imager (KCWI) are presented for four galaxies centered in cooling X-ray cluster atmospheres. Nebular emission extending tens of kpc is found in systems covering a broad range of atmospheric cooling rates, cluster masses, and dynamical states. Abell 262's central galaxy hosts a kpc-scale disk. The nebular gas in RXJ0820.9+0752 is offset and reds… ▽ More [OII] emission maps obtained with the Keck Cosmic Web Imager (KCWI) are presented for four galaxies centered in cooling X-ray cluster atmospheres. Nebular emission extending tens of kpc is found in systems covering a broad range of atmospheric cooling rates, cluster masses, and dynamical states. Abell 262's central galaxy hosts a kpc-scale disk. The nebular gas in RXJ0820.9+0752 is offset and redshifted with respect to the central galaxy by $10-20$ kpc and 150 km s$^{-1}$, respectively. The nebular gases in PKS 0745-191 and Abell 1835 are being churned to higher velocity dispersion by X-ray bubbles and jets. The churned gas is enveloped by larger scale, lower velocity dispersion (quiescent) nebular emission. The mean line-of-sight speeds of the churned gas, quiescent gas, and the central galaxy each differ by up to $\sim 150$ km s$^{-1}$; nebular speeds upward of $800$ km s$^{-1}$ are found. Gases with outwardly-rising speeds upward of several hundred km s$^{-1}$ are consistent with being advected behind and being lifted by the rising bubbles. The peculiar motion between the galaxy, nebular gas, and perhaps the hot atmosphere from which it presumably condensed is affecting the bubble dynamics, and may strongly affect thermally unstable cooling, the dispersal of jet energy, and the angular momentum of gas accreting onto the galaxies and their nuclear black holes. △ Less

Submitted 30 September, 2024; v1 submitted 2 April, 2024; originally announced April 2024.

Comments: 36 pages, 26 figures, Accepted for publication in ApJ

MHONGOOSE -- A MeerKAT Nearby Galaxy HI Survey

Authors: W. J. G. de Blok, J. Healy, F. M. Maccagni, D. J. Pisano, A. Bosma, J. English, T. Jarrett, A. Marasco, G. R. Meurer, S. Veronese, F. Bigiel, L. Chemin, F. Fraternali, B. W. Holwerda, P. Kamphuis, H. R. Klöckner, D. Kleiner, A. K. Leroy, M. Mogotsi, K. A. Oman, E. Schinnerer, L. Verdes-Montenegro, T. Westmeier, O. I. Wong, N. Zabel , et al. (35 additional authors not shown)

Abstract: The MHONGOOSE (MeerKAT HI Observations of Nearby Galactic Objects: Observing Southern Emitters) survey maps the distribution and kinematics of the neutral atomic hydrogen (HI) gas in and around 30 nearby star-forming spiral and dwarf galaxies to extremely low HI column densities. The HI column density sensitivity (3 sigma over 16 km/s) ranges from ~ 5 x 10^{17} cm^{-2} at 90'' resolution to ~4 x 1… ▽ More The MHONGOOSE (MeerKAT HI Observations of Nearby Galactic Objects: Observing Southern Emitters) survey maps the distribution and kinematics of the neutral atomic hydrogen (HI) gas in and around 30 nearby star-forming spiral and dwarf galaxies to extremely low HI column densities. The HI column density sensitivity (3 sigma over 16 km/s) ranges from ~ 5 x 10^{17} cm^{-2} at 90'' resolution to ~4 x 10^{19} cm^{-2} at the highest resolution of 7''. The HI mass sensitivity (3 sigma over 50 km/s) is ~5.5 X 10^5 M_sun at a distance of 10 Mpc (the median distance of the sample galaxies). The velocity resolution of the data is 1.4 km/s. One of the main science goals of the survey is the detection of cold, accreting gas in the outskirts of the sample galaxies. The sample was selected to cover a range in HI masses, from 10^7 M_sun to almost 10^{11} M_sun, to optimally sample possible accretion scenarios and environments. The distance to the sample galaxies ranges from 3 to 23 Mpc. In this paper, we present the sample selection, survey design, and observation and reduction procedures. We compare the integrated HI fluxes based on the MeerKAT data with those derived from single-dish measurement and find good agreement, indicating that our MeerKAT observations are recovering all flux. We present HI moment maps of the entire sample based on the first ten percent of the survey data, and find that a comparison of the zeroth- and second-moment values shows a clear separation between the physical properties of the HI in areas with star formation and areas without, related to the formation of a cold neutral medium. Finally, we give an overview of the HI-detected companion and satellite galaxies in the 30 fields, five of which have not previously been catalogued. We find a clear relation between the number of companion galaxies and the mass of the main target galaxy. △ Less

Submitted 6 June, 2024; v1 submitted 2 April, 2024; originally announced April 2024.

Comments: Accepted for publication in Astronomy & Astrophysics

Journal ref: A&A 688, A109 (2024)

Turbocharging constraints on dark matter substructure through a synthesis of strong lensing flux ratios and extended lensed arcs

Authors: Daniel Gilman, Simon Birrer, Anna Nierenberg, Maverick S. H. Oh

Abstract: Strong gravitational lensing provides a purely gravitational means to infer properties of dark matter halos and thereby constrain the particle nature of dark matter. Strong lenses sometimes appear as four lensed images of a background quasar accompanied by spatially-resolved emission from the quasar host galaxy encircling the main deflector (lensed arcs). We present methodology to simultaneously r… ▽ More Strong gravitational lensing provides a purely gravitational means to infer properties of dark matter halos and thereby constrain the particle nature of dark matter. Strong lenses sometimes appear as four lensed images of a background quasar accompanied by spatially-resolved emission from the quasar host galaxy encircling the main deflector (lensed arcs). We present methodology to simultaneously reconstruct lensed arcs and relative image magnifications (flux ratios) in the presence of full populations of subhalos and line-of-sight halos. To this end, we develop a new approach for multi-plane ray tracing that accelerates lens mass and source light reconstruction by factors of $\sim 100-1000$. Using simulated data, we show that simultaneous reconstruction of lensed arcs and flux ratios isolates small-scale perturbations to flux ratios by dark matter substructure from uncertainties associated with the main deflector mass profile on larger angular scales. Relative to analyses that use only image positions and flux ratios to constrain the lens model, incorporating arcs strengthens likelihood ratios penalizing warm dark matter (WDM) with a suppression scale $m_{\rm{hm}} / M_{\odot}$ in the range $\left[10^7 - 10^{7.5}\right]$, $\left[10^{7.5} - 10^{8}\right]$, $\left[10^8 - 10^{8.5}\right]$, $\left[10^{8.5} - 10^{9}\right]$ by factors of $1.3$, $2.5$, $5.6$, and $13.1$, respectively, for a cold dark matter (CDM) ground truth. The $95\%$ exclusion limit improves by 0.5 dex in $\log_{10} m_{\rm{hm}}$. The enhanced sensitivity to low-mass halos enabled by these methods pushes the observational frontier of substructure lensing to the threshold of galaxy formation, enabling stringent tests of any theory that alters the properties of dark matter halos. △ Less

Submitted 19 August, 2024; v1 submitted 5 March, 2024; originally announced March 2024.

Comments: matches MNRAS accepted version

Ultralight vector dark matter search using data from the KAGRA O3GK run

Authors: The LIGO Scientific Collaboration, the Virgo Collaboration, the KAGRA Collaboration, A. G. Abac, R. Abbott, H. Abe, I. Abouelfettouh, F. Acernese, K. Ackley, C. Adamcewicz, S. Adhicary, N. Adhikari, R. X. Adhikari, V. K. Adkins, V. B. Adya, C. Affeldt, D. Agarwal, M. Agathos, O. D. Aguiar, I. Aguilar, L. Aiello, A. Ain, P. Ajith, T. Akutsu, S. Albanesi , et al. (1778 additional authors not shown)

Abstract: Among the various candidates for dark matter (DM), ultralight vector DM can be probed by laser interferometric gravitational wave detectors through the measurement of oscillating length changes in the arm cavities. In this context, KAGRA has a unique feature due to differing compositions of its mirrors, enhancing the signal of vector DM in the length change in the auxiliary channels. Here we prese… ▽ More Among the various candidates for dark matter (DM), ultralight vector DM can be probed by laser interferometric gravitational wave detectors through the measurement of oscillating length changes in the arm cavities. In this context, KAGRA has a unique feature due to differing compositions of its mirrors, enhancing the signal of vector DM in the length change in the auxiliary channels. Here we present the result of a search for $U(1)_{B-L}$ gauge boson DM using the KAGRA data from auxiliary length channels during the first joint observation run together with GEO600. By applying our search pipeline, which takes into account the stochastic nature of ultralight DM, upper bounds on the coupling strength between the $U(1)_{B-L}$ gauge boson and ordinary matter are obtained for a range of DM masses. While our constraints are less stringent than those derived from previous experiments, this study demonstrates the applicability of our method to the lower-mass vector DM search, which is made difficult in this measurement by the short observation time compared to the auto-correlation time scale of DM. △ Less

Submitted 5 March, 2024; originally announced March 2024.

Comments: 20 pages, 5 figures

Report number: LIGO-P2300250

Real-time portable muography with Hankuk Atmospheric-muon Wide Landscaping : HAWL

Authors: J. Seo, N. Carlin, D. F. F. S. Cavalcante, J. S. Chung, L. E. Franca, C. Ha, J. Kim, J. Y. Kim, H. Kimku, B. C. Koh, Y. J. Lee, B. B. Manzato, S. W. Oh, R. L. C. Pitta, S. J. Won

Abstract: Cosmic ray muons prove valuable across various fields, from particle physics experiments to non-invasive tomography, thanks to their high flux and exceptional penetrating capability. Utilizing a scintillator detector, one can effectively study the topography of mountains situated above tunnels and underground spaces. The Hankuk Atmospheric-muon Wide Landscaping (HAWL) project successfully charts t… ▽ More Cosmic ray muons prove valuable across various fields, from particle physics experiments to non-invasive tomography, thanks to their high flux and exceptional penetrating capability. Utilizing a scintillator detector, one can effectively study the topography of mountains situated above tunnels and underground spaces. The Hankuk Atmospheric-muon Wide Landscaping (HAWL) project successfully charts the mountainous region of eastern Korea by measuring cosmic ray muons with a detector in motion. The real-time muon flux measurement shows a tunnel length accuracy of 6.0 %, with a detectable overburden range spanning from 8 to 400 meter-water-equivalent depth. This is the first real-time portable muon tomography. △ Less

Submitted 4 August, 2024; v1 submitted 4 March, 2024; originally announced March 2024.

Comments: 10pages, 12 figures

The SAMI Galaxy Survey: Using Tidal Streams and Shells to Trace the Dynamical Evolution of Massive Galaxies

Authors: Tomas H. Rutherford, Jesse van de Sande, Scott M. Croom, Lucas M. Valenzuela, Rhea-Silvia Remus, Francesco D'Eugenio, Sam P. Vaughan, Henry R. M. Zovaro, Sarah Casura, Stefania Barsanti, Joss Bland-Hawthorn, Sarah Brough, Julia J. Bryant, Michael Goodwin, Nuria Lorente, Sree Oh, Andrei Ristea

Abstract: Slow rotator galaxies are distinct amongst galaxy populations, with simulations suggesting that a mix of minor and major mergers are responsible for their formation. A promising path to resolve outstanding questions on the type of merger responsible, is by investigating deep imaging of massive galaxies for signs of potential merger remnants. We utilise deep imaging from the Subaru-Hyper Suprime Ca… ▽ More Slow rotator galaxies are distinct amongst galaxy populations, with simulations suggesting that a mix of minor and major mergers are responsible for their formation. A promising path to resolve outstanding questions on the type of merger responsible, is by investigating deep imaging of massive galaxies for signs of potential merger remnants. We utilise deep imaging from the Subaru-Hyper Suprime Cam Wide data to search for tidal features in massive ($\log_{10}(M_*/M_{\odot}) > 10$) early-type galaxies (ETGs) in the SAMI Galaxy Survey. We perform a visual check for tidal features on images where the galaxy has been subtracted using a Multi-Gauss Expansion (MGE) model. We find that $31\pm 2$ percent of our sample show tidal features. When comparing galaxies with and without features, we find that the distributions in stellar mass, light-weighted mean stellar population age and H$α$ equivalent width are significantly different, whereas spin ($λ_{R_e}$), ellipticity and bulge to total ratio have similar distributions. When splitting our sample in age, we find that galaxies below the median age (10.8 Gyr) show a correlation between the presence of shells and lower $λ_{R_e}$, as expected from simulations. We also find these younger galaxies which are classified as having "strong" shells have lower $λ_{R_e}$. However, simulations suggest that merger features become undetectable within $\sim 2-4$ Gyr post-merger. This implies that the relationship between tidal features and merger history disappears for galaxies with older stellar ages, i.e. those that are more likely to have merged long ago. △ Less

Submitted 5 February, 2024; originally announced February 2024.

Comments: Accepted for publication in MNRAS. 22 pages, 14 figures

High-resolution spectroscopic study of extremely metal-poor stars in the Large Magellanic Cloud

Authors: W. S. Oh, T. Nordlander, G. S. Da Costa, M. S. Bessell, A. D. Mackey

Abstract: We present detailed abundance results based on UVES high dispersion spectra for 7 very and extremely metal-poor stars in the Large Magellanic Cloud. We confirm that all 7 stars, two of which have [Fe/H] $\leq$ --3.0, are the most metal-poor stars discovered so far in the Magellanic Clouds. The element abundance ratios are generally consistent with Milky Way halo stars of similar [Fe/H] values. We… ▽ More We present detailed abundance results based on UVES high dispersion spectra for 7 very and extremely metal-poor stars in the Large Magellanic Cloud. We confirm that all 7 stars, two of which have [Fe/H] $\leq$ --3.0, are the most metal-poor stars discovered so far in the Magellanic Clouds. The element abundance ratios are generally consistent with Milky Way halo stars of similar [Fe/H] values. We find that 2 of the more metal-rich stars in our sample are enhanced in r-process elements. This result contrasts with the literature, where all nine metal-poor LMC stars with higher [Fe/H] values than our sample were found to be rich in r-process elements. The absence of r-process enrichment in stars with lower [Fe/H] values is consistent with a minimum delay timescale of $\sim$100 Myr for the neutron star binary merger process to generate substantial r-process enhancements in the LMC. We find that the occurrence rate of r-process enhancement (r-I or r-II) in our sample of very and extremely metal-poor stars is statistically indistinguishable from that found in the Milky Way's halo, although including stars from the literature sample hints at a larger r-II frequency the LMC. Overall, our results shed light on the earliest epochs of star formation in the LMC that may be applicable to other galaxies of LMC-like mass. △ Less

Submitted 5 January, 2024; v1 submitted 20 December, 2023; originally announced December 2023.

The SAMI Galaxy Survey: $Σ_{\rm SFR}$ drives the presence of complex emission line profiles in star-forming galaxies

Authors: Henry R. M. Zovaro, J. Trevor Mendel, Brent Groves, Lisa J. Kewley, Matthew Colless, Andrei Ristea, Luca Cortese, Sree Oh, Francesco D'Eugenio, Scott M. Croom, Ángel R. López-Sánchez, Jesse van de Sande, Sarah Brough, Anne M. Medling, Joss Bland-Hawthorn, Julia J. Bryant

Abstract: Galactic fountains driven by star formation result in a variety of kinematic structures such as ionised winds and thick gas disks, both of which manifest as complex emission line profiles that can be parametrised by multiple Gaussian components. We use integral field spectroscopy (IFS) from the SAMI Galaxy Survey to spectrally resolve these features, traced by broad H$α$ components, and distinguis… ▽ More Galactic fountains driven by star formation result in a variety of kinematic structures such as ionised winds and thick gas disks, both of which manifest as complex emission line profiles that can be parametrised by multiple Gaussian components. We use integral field spectroscopy (IFS) from the SAMI Galaxy Survey to spectrally resolve these features, traced by broad H$α$ components, and distinguish them from the star-forming thin disk, traced by narrow components, in 3068 galaxies in the local Universe. Using a matched sample analysis technique, we demonstrate that the presence of complex emission line profiles in star-forming galaxies is most strongly correlated with the global star formation rate (SFR) surface density of the host galaxy measured within $1R_{\rm e}$ ($Σ_{{\rm SFR},R_{\rm e}}$), even when controlling for both observational biases, including inclination, amplitude-to-noise and angular scale, and sample biases in parameters such as stellar mass and SFR. Leveraging the spatially resolved nature of the dataset, we determine that the presence of complex emission line profiles within individual spaxels is driven not only by the local $Σ_{\rm SFR}$, but by the $Σ_{{\rm SFR},R_{\rm e}}$ of the host galaxy. We also parametrise the clumpiness of the SFR within individual galaxies, and find that $Σ_{{\rm SFR},R_{\rm e}}$ is a stronger predictor of the presence of complex emission line profiles than clumpiness. We conclude that, with a careful treatment of observational effects, it is possible to identify structures traced by complex emission line profiles, including winds and thick ionised gas disks, at the spatial and spectral resolution of SAMI using the Gaussian decomposition technique. △ Less

Submitted 6 December, 2023; originally announced December 2023.

Comments: 21 pages, 17 figures, accepted for publication in MNRAS

A superconducting tensor detector for mid-frequency gravitational waves: its multi-channel nature and main astrophysical targets

Authors: Yeong-Bok Bae, Chan Park, Edwin J. Son, Sang-Hyeon Ahn, Minjoong Jeong, Gungwon Kang, Chunglee Kim, Dong Lak Kim, Jaewan Kim, Whansun Kim, Hyung Mok Lee, Yong-Ho Lee, Ronald S. Norton, John J. Oh, Sang Hoon Oh, Ho Jung Paik

Abstract: Mid-frequency band gravitational-wave detectors will be complementary for the existing Earth-based detectors (sensitive above 10 Hz or so) and the future space-based detectors such as LISA, which will be sensitive below around 10 mHz. A ground-based superconducting omnidirectional gravitational radiation observatory (SOGRO) has recently been proposed along with several design variations for the fr… ▽ More Mid-frequency band gravitational-wave detectors will be complementary for the existing Earth-based detectors (sensitive above 10 Hz or so) and the future space-based detectors such as LISA, which will be sensitive below around 10 mHz. A ground-based superconducting omnidirectional gravitational radiation observatory (SOGRO) has recently been proposed along with several design variations for the frequency band of 0.1 to 10 Hz. For three conceptual designs of SOGRO (e.g., pSOGRO, SOGRO and aSOGRO), we examine their multi-channel natures, sensitivities and science cases. One of the key characteristics of the SOGRO concept is its six detection channels. The response functions of each channel are calculated for all possible gravitational wave polarizations including scalar and vector modes. Combining these response functions, we also confirm the omnidirectional nature of SOGRO. Hence, even a single SOGRO detector will be able to determine the position of a source and polarizations of gravitational waves, if detected. Taking into account SOGRO's sensitivity and technical requirements, two main targets are most plausible: gravitational waves from compact binaries and stochastic backgrounds. Based on assumptions we consider in this work, detection rates for intermediate-mass binary black holes (in the mass range of hundreds up to $10^{4}$ $M_\odot$) are expected to be $0.0014-2.5 \,\, {\rm yr}^{-1}$. In order to detect stochastic gravitational wave background, multiple detectors are required. Two aSOGRO detector networks may be able to put limits on the stochastic background beyond the indirect limit from cosmological observations. △ Less

Submitted 29 November, 2023; originally announced November 2023.

Comments: 35 pages, 8 figures, 4 tables

The Survival and Entrainment of Molecules and Dust in Galactic Winds

Authors: Zirui Chen, S. Peng Oh

Abstract: Recent years have seen excellent progress in modeling the entrainment of T $\sim$ $10^4$K atomic gas in galactic winds. However, the entrainment of cool, dusty T $\sim$ 10-100K molecular gas, which is also observed outflowing at high velocity, is much less understood. Such gas, which can be $10^5$ times denser than the hot wind, appears extremely difficult to entrain. We run 3D wind-tunnel simulat… ▽ More Recent years have seen excellent progress in modeling the entrainment of T $\sim$ $10^4$K atomic gas in galactic winds. However, the entrainment of cool, dusty T $\sim$ 10-100K molecular gas, which is also observed outflowing at high velocity, is much less understood. Such gas, which can be $10^5$ times denser than the hot wind, appears extremely difficult to entrain. We run 3D wind-tunnel simulations with photoionization self-shielding and evolve thermal dust sputtering and growth. Unlike almost all such simulations to date, we do not enforce any artificial temperature floor. We find efficient molecular gas formation and entrainment, as well as dust survival and growth through accretion. Key to this success is the formation of large amounts of 10^4K atomic gas via mixing, which acts as a protective "bubble wrap" and reduces the cloud overdensity to $\sim$ 100. This can be understood from the ratio of the mixing to cooling time. Before entrainment, when shear is large, t_mix/t_cool $\leq$ 1, and gas cannot cool below the "cooling bottleneck" at 5000K. Thus, the cloud survival criterion is identical to the well-studied purely atomic case. After entrainment, when shear falls, t_mix/t_cool > 1, and the cloud becomes multi-phase, with comparable molecular and atomic masses. The broad temperature PDF, with abundant gas in the formally unstable 50 K < T < 5000 K range, agrees with previous ISM simulations with driven turbulence and radiative cooling. Our findings have implications for dusty molecular gas in stellar and AGN outflows, cluster filaments, "jellyfish" galaxies and AGB winds. △ Less

Submitted 22 April, 2024; v1 submitted 7 November, 2023; originally announced November 2023.

Comments: 27 pages, 17 figures. Accepted for publication in MNRAS, 22 April 2024

On the Origin of the Variety of Velocity Dispersion Profiles of Galaxies

Authors: San Han, Sukyoung K. Yi, Sree Oh, Mina Pak, Scott M. Croom, Julien Devriendt, Yohan Dubois, Taysun Kimm, Katarina Kraljic, Christophe Pichon, Marta Volonteri

Abstract: Observed and simulated galaxies exhibit a significant variation in their velocity dispersion profiles. We examine the inner and outer slopes of stellar velocity dispersion profiles using integral field spectroscopy data from two surveys, SAMI (for $z < 0.115$) and CALIFA (for $z < 0.03$), comparing them with results from two cosmological hydrodynamic simulations: Horizon-AGN (for $z = 0.017$) and… ▽ More Observed and simulated galaxies exhibit a significant variation in their velocity dispersion profiles. We examine the inner and outer slopes of stellar velocity dispersion profiles using integral field spectroscopy data from two surveys, SAMI (for $z < 0.115$) and CALIFA (for $z < 0.03$), comparing them with results from two cosmological hydrodynamic simulations: Horizon-AGN (for $z = 0.017$) and NewHorizon (for $z\lesssim1$). The simulated galaxies closely reproduce the variety of velocity dispersion slopes and stellar mass dependence of both inner and outer radii ($0.5\,r_{50}$ and $3\,r_{50}$) as observed, where $r_{50}$ stands for half-light radius. The inner slopes are mainly influenced by the relative radial distribution of the young and old stars formed in-situ: a younger center shows a flatter inner profile. The presence of accreted (ex-situ) stars has two effects on the velocity dispersion profiles. First, because they are more dispersed in spatial and velocity distributions compared to in-situ formed stars, it increases the outer slope of the velocity dispersion profile. It also causes the velocity anisotropy to be more radial. More massive galaxies have a higher fraction of stars formed ex-situ and hence show a higher slope in outer velocity dispersion profile and a higher degree of radial anisotropy. The diversity in the outer velocity dispersion profiles reflects the diverse assembly histories among galaxies. △ Less

Submitted 22 November, 2024; v1 submitted 24 October, 2023; originally announced October 2023.

Comments: 22 pages, 16 figures, accepted for publication in ApJ