Showing 1–50 of 254 results for author: Huang, S

A Tidal Disruption Event from an Intermediate-mass Black Hole Revealed by Comprehensive Multi-wavelength Observations

Authors: Jialai Wang, Mengqiu Huang, Yongquan Xue, Ning Jiang, Shifeng Huang, Yibo Wang, Jiazheng Zhu, Shifu Zhu, Lixin Dai, Chichuan Jin, Bin Luo, Xinwen Shu, Mouyuan Sun, Tinggui Wang, Fan Zou

Abstract: Tidal disruption events (TDEs) occur when a star crosses the tidal radius of a black hole (BH) and is ripped apart, providing a novel and powerful way to probe dormant BHs over a wide mass range. In this study, we present our late-time observations and comprehensive multi-wavelength analyses of an extraordinary TDE at the center of a dwarf galaxy, which exhibited successive flares in the optical,… ▽ More Tidal disruption events (TDEs) occur when a star crosses the tidal radius of a black hole (BH) and is ripped apart, providing a novel and powerful way to probe dormant BHs over a wide mass range. In this study, we present our late-time observations and comprehensive multi-wavelength analyses of an extraordinary TDE at the center of a dwarf galaxy, which exhibited successive flares in the optical, X-ray, and radio bands. Notably, we discovered an unexpected high-state X-ray plateau phase following the peak until the present time. Along with its reported prolonged rise lasting at least 550 days, these unique characteristics are consistent with the scenario of a TDE caused by an intermediate-mass black hole (IMBH) with a mass of approximately $(1-6) \times 10^5$ solar masses. Furthermore, scaling relations derived from the host-galaxy properties indicated a similar BH mass in concert. This discovery highlights the invaluable role of TDEs in the search for elusive IMBHs. △ Less

Submitted 18 December, 2025; originally announced December 2025.

Comments: 35 pages, 10 figures

The Merian Survey: A Statistical Census of Bright Satellites of Milky Way Analogs

Authors: Yue Pan, Shany Danieli, Jenny E. Greene, Jiaxuan Li, Alexie Leauthaud, Erin Kado-Fong, Yifei Luo, Abby Mintz, Alyson Brooks, Song Huang, Annika H. G. Peter, Joy Bhattacharyya, Lee S. Kelvin

Abstract: We present a statistical census of bright, star-forming satellite galaxies around Milky Way (MW) analogs using the first data release of the Merian Survey. Our sample consists of 393 MW analogs with stellar masses $10^{10.5} < M_{\star, \rm host} < 10^{10.9} M_\odot$ at redshifts $0.07 < z < 0.09$, all central galaxies of their own dark matter halos. Using photometric selection -- including magnit… ▽ More We present a statistical census of bright, star-forming satellite galaxies around Milky Way (MW) analogs using the first data release of the Merian Survey. Our sample consists of 393 MW analogs with stellar masses $10^{10.5} < M_{\star, \rm host} < 10^{10.9} M_\odot$ at redshifts $0.07 < z < 0.09$, all central galaxies of their own dark matter halos. Using photometric selection -- including magnitude, color, angular size, photometric redshift, and size-mass cuts -- we identify 793 satellite candidates around these 393 hosts. Our selection leverages two medium-band filters targeting H$α$ and [O \textsc{iii}] emission, enabling a nearly complete sample of star-forming, Magellanic Clouds-like satellites with $M_{\star, \rm sat} \gtrsim 10^{8} M_\odot$. We find that $\sim80\%$ of hosts have 0-3 massive satellites, and $13\pm4\%$ have two satellites (similar to the MW). Satellite abundance correlates with total stellar mass, and we provide significantly improved statistics for the most massive satellites at $\log_{10}[M_{\star, \rm sat}/M_{\odot}] \gtrsim 10$. The completeness-corrected radial distribution is less centrally concentrated than an NFW profile. In contrast, the Milky Way satellites are more centrally concentrated than the 50\% richest Merian systems, but are broadly consistent with the 50\% most centrally concentrated Merian systems. Our results highlight the power of medium-band photometry for satellite identification and provide a key benchmark for studying satellite quenching, environmental effects, and hierarchical galaxy formation. △ Less

Submitted 14 December, 2025; originally announced December 2025.

Comments: 22 pages, 8 figures. Published in ApJ in December, 2025

Measurement of the cosmic ray nickel energy spectrum from 10 GeV/n to 2 TeV/n with the DAMPE

Authors: F. Alemanno, Q. An, P. Azzarello, F. C. T. Barbato, P. Bernardini, X. J. Bi, H. V. Boutin, I. Cagnoli, M. S. Cai, E. Casilli, J. Chang, D. Y. Chen, J. L. Chen, Z. F. Chen, Z. X. Chen, P. Coppin, M. Y. Cui, T. S. Cui, I. De Mitri, F. de Palma, A. Di Giovanni, T. K. Dong, Z. X. Dong, G. Donvito, J. L. Duan , et al. (123 additional authors not shown)

Abstract: Nickel, one of the most stable elements alongside iron, is the most abundant heavy element beyond iron in cosmic rays. With DAMPE's excellent charge resolution and broad energy range, a high-precision energy spectrum provides valuable insights into the acceleration sources of heavy nuclei and their propagation through the interstellar medium. In this analysis, we report the direct measurement of c… ▽ More Nickel, one of the most stable elements alongside iron, is the most abundant heavy element beyond iron in cosmic rays. With DAMPE's excellent charge resolution and broad energy range, a high-precision energy spectrum provides valuable insights into the acceleration sources of heavy nuclei and their propagation through the interstellar medium. In this analysis, we report the direct measurement of cosmic-ray nickel spectrum from 10 GeV/n to 2 TeV/n with nine years of flight data. The nickel spectrum is consistent with a single power law with spectral index -2.60 +/- 0.03 from 40 GeV/n to 1 TeV/n. This work provides an accurate measurement of differential flux of nickel with kinetic energy extending to TeV/n for the first time. △ Less

Submitted 12 December, 2025; originally announced December 2025.

Connection Between Dwarf Galaxies and Globular Clusters: Insights from the Perseus Cluster Using Subaru Imaging and Keck Spectroscopy

Authors: Yimeng Tang, Aaron J. Romanowsky, Song Huang, Nobuhiro Okabe, Jean P. Brodie, Kevin A. Bundy, Maria Luisa Buzzo, Timothy Carleton, Anna Ferré-Mateu, Duncan A. Forbes, Jonah S. Gannon, Steven R. Janssens, Arsen Levitskiy, Alexi M. Musick

Abstract: We present a systematic study of 189 dwarf galaxies and their globular cluster (GC) systems in the Perseus cluster, based on deep Subaru Hyper Suprime-Cam imaging and Keck spectroscopy, supplemented by literature data. This constitutes the largest sample of dwarfs in a single galaxy cluster to date with simultaneous deep imaging, spectroscopic coverage, and GC measurements, while uniquely spanning… ▽ More We present a systematic study of 189 dwarf galaxies and their globular cluster (GC) systems in the Perseus cluster, based on deep Subaru Hyper Suprime-Cam imaging and Keck spectroscopy, supplemented by literature data. This constitutes the largest sample of dwarfs in a single galaxy cluster to date with simultaneous deep imaging, spectroscopic coverage, and GC measurements, while uniquely spanning a broad and continuous range of galaxy properties. We find an anti-correlation between GC specific mass and galaxy stellar mass for dwarfs in Perseus similar to observations in other clusters. At fixed stellar mass, dwarfs with lower surface brightness or larger effective radius tend to be more GC-rich -- suggesting either high GC formation efficiency in an earlier compact-galaxy phase, or less efficient GC disruption. The correlation between GC richness and axis ratio in Perseus is weaker than in other environments. We find some connection between GC richness and infall time, but not with the clear correlations found in Virgo, Coma, and cosmological simulations. More complete observations are needed to test for cluster-to-cluster variations in galaxy and GC evolutionary histories. This work demonstrates the potential of new wide-field imaging and spectroscopy surveys for understanding GCs and dwarf galaxies, and highlights the need for further work in theoretical modeling. △ Less

Submitted 11 December, 2025; originally announced December 2025.

Comments: 22 pages, 13 figures. Resubmitted to ApJ after revision

Long-wavelength UV-LEDs and charge management in the detection of gravitational waves in space

Authors: Yuandong Jia, Yinbowen Zhang, Suwen Wang, Guozhi Chai, Zemin Zhang, Yi Zhang, Hongxin Li, Shuanglin Huang, Hongqing Huo, Zongfeng Li, Yun Kau Lau

Abstract: For the charge management system in gravitational wave detection missions, a continuous discharge strategy is considered by continuously illuminating a test mass (TM) with weak light in such a way to strike a balance between the charging and discharging rates and at the same time avoids the requirement for frequent activation of charge measurements. Built on experiments by one of us based on a sim… ▽ More For the charge management system in gravitational wave detection missions, a continuous discharge strategy is considered by continuously illuminating a test mass (TM) with weak light in such a way to strike a balance between the charging and discharging rates and at the same time avoids the requirement for frequent activation of charge measurements. Built on experiments by one of us based on a simple parallel plate model for inertial sensor, in the present work a more sophisticated inertial sensor model that mimics the surface properties and work function of a cubical TM of an inertial sensor in space (like that of the LISA Pathfinder) is employed to study bipolar charge management system that utilizes UV-LEDs with peak wavelengths of 269 nm, 275 nm, 280 nm, and 295 nm that are longer than the standard 255 nm commonly employed for direct TM illumination. Experimental results indicate that the 275 nm UV-LED achieves optimal performance, maintaining the TM potential closer to zero and at the same time accommodates both rapid discharge and continuous discharge strategies. The present work provides useful input in the future study of system design and optimization for the charge management system. △ Less

Submitted 8 December, 2025; originally announced December 2025.

Machine Learning for Exoplanet Discovery: Validating TESS Candidates and Identifying Planets in the Habitable Zone

Authors: Sarah Huang, Chen Jiang

Abstract: The high-precision photometry from NASA's Kepler and TESS missions has revolutionized exoplanet detection, enabling the discovery of over 5500 confirmed exoplanets via the transit method and around 10000 additional candidates awaiting validation. However, confirming these candidates as true planets demands meticulous vetting and follow-up observations, which hampers the discovery of exoplanets in… ▽ More The high-precision photometry from NASA's Kepler and TESS missions has revolutionized exoplanet detection, enabling the discovery of over 5500 confirmed exoplanets via the transit method and around 10000 additional candidates awaiting validation. However, confirming these candidates as true planets demands meticulous vetting and follow-up observations, which hampers the discovery of exoplanets in large-scale datasets. To address this challenge, we developed a machine learning framework trained on Kepler's catalog of confirmed exoplanets and false positives to accurately identify true planetary candidates. Our model uses transit properties, planetary characteristics, and host stellar parameters as training features. The optimized model achieved 83.9% accuracy in cross-validation. When applied to 3987 TESS candidates with complete observational data, the model identified 1595 new high-confidence planets and correctly recovered 86% (358/418) of all previously confirmed TESS exoplanets in a blinded validation test. Our analysis revealed 100 previously unrecognized multi-planet systems, including five systems--that host habitable-zone exoplanets. Additionally, we identified 15 more planets within the habitable zone of a single system, suggesting strong potential for liquid water stability under conservative planetary albedo assumptions. This work demonstrates that machine learning can accelerate exoplanet validation while maintaining scientific rigor. Our modular design enables direct adaptation to future photometric missions like PLATO or Earth 2.0. △ Less

Submitted 30 November, 2025; originally announced December 2025.

Comments: 37 pages, 12 figures, 9 tables

The Solar Close Observations and Proximity Experiments (SCOPE) mission

Authors: Jun Lin, Jing Feng, Zhenhua Ge, Jiang Tian, Yuhao Chen, Xin Cheng, Hui Tian, Jiansen He, Alexei Pevtsov, Haisheng Ji, Shangbin Yang, Parida Hashim, Bin Zhou, Yiteng Zhang, Shenyi Zhang, Xi Lu, Yuan Yuan, Liu Liu, Haoyu Wang, Hu Jiang, Lei Deng, Xingjian Shi, Lin Ma, Jingxing Wang, Shanjie Huang , et al. (9 additional authors not shown)

Abstract: The Solar Close Observations and Proximity Experiments (SCOPE) mission will send a spacecraft into the solar atmosphere at a low altitude of just 5 R_sun from the solar center. It aims to elucidate the mechanisms behind solar eruptions and coronal heating, and to directly measure the coronal magnetic field. The mission will perform in situ measurements of the current sheet between coronal mass eje… ▽ More The Solar Close Observations and Proximity Experiments (SCOPE) mission will send a spacecraft into the solar atmosphere at a low altitude of just 5 R_sun from the solar center. It aims to elucidate the mechanisms behind solar eruptions and coronal heating, and to directly measure the coronal magnetic field. The mission will perform in situ measurements of the current sheet between coronal mass ejections and their associated solar flares, and energetic particles produced by either reconnection or fast-mode shocks driven by coronal mass ejections. This will help to resolve the nature of reconnections in current sheets, and energetic particle acceleration regions. To investigate coronal heating, the mission will observe nano-flares on scales smaller than 70 km in the solar corona and regions smaller than 40 km in the photosphere, where magnetohydrodynamic waves originate. To study solar wind acceleration mechanisms, the mission will also track the process of ion charge-state freezing in the solar wind. A key achievement will be the observation of the coronal magnetic field at unprecedented proximity to the solar photosphere. The polar regions will also be observed at close range, and the inner edge of the solar system dust disk may be identified for the first time. This work presents the detailed background, science, and mission concept of SCOPE and discusses how we aim to address the questions mentioned above. △ Less

Submitted 27 November, 2025; originally announced November 2025.

Comments: 27 pages, 15 figures

Journal ref: Astronomical Techniques and Instruments, 2(3), 2025

Large gas inflow driven by a matured galactic bar in the early Universe

Authors: Shuo Huang, Ryohei Kawabe, Hideki Umehata, Kotaro Kohno, Yoichi Tamura, Toshiki Saito

Abstract: Bar structures are present in about half of local disk galaxies and play pivotal roles in secular galaxy evolution. Bars impose a non-axisymmetric perturbation to the rotating disk and transport gas inward to feed central starburst and, possibly, the activity of the nuclear supermassive black hole. They are believed to be long-lived structures and are now identified at redshift $z>2$. Yet, little… ▽ More Bar structures are present in about half of local disk galaxies and play pivotal roles in secular galaxy evolution. Bars impose a non-axisymmetric perturbation to the rotating disk and transport gas inward to feed central starburst and, possibly, the activity of the nuclear supermassive black hole. They are believed to be long-lived structures and are now identified at redshift $z>2$. Yet, little is known about the onset and effect of bars in the early cosmic epoch because spectroscopy of distant bars at sufficient resolution is prohibitively expensive. Here, we report a kinematic study of a galactic bar at redshift 2.467, 2.6 billion years after the Big Bang. We observe the carbon monoxide and atomic carbon emission lines of the dusty star-forming galaxy J0107a and find the bar of J0107a has gas distribution and motion in a pattern identical to local bars. At the same time, the bar drives large-scale non-circular motions that dominate over disk rotation, funneling molecular gas into its center at a rate of $\approx600$ solar masses per year. Our results show that bar-driven dynamical processes and secular evolution were already at play 11.1 billion years ago, powering active star formation amid the gas-rich and far-infrared luminous growth phase in a massive disk galaxy. △ Less

Submitted 20 November, 2025; originally announced November 2025.

Comments: Accepted version before copy editing

Journal ref: Nature volume 641, pages 861-865 (2025)

Reaching for the Edge II: Stellar Halos out to Large Radii as a Tracer of Dark Matter Halo Mass

Authors: Katya Leidig, Benedikt Diemer, Song Huang, Shuo Xu, Conghao Zhou, Alexie Leauthaud

Abstract: The diffuse outskirts of brightest cluster galaxies (BCGs) encode valuable information about the assembly history and mass of their host dark matter halos. However, the low surface brightness of these stellar halos has historically made them difficult to observe. Recent deep imaging, particularly with Hyper Suprime-Cam (HSC), has shown that the stellar mass within relatively large projected annuli… ▽ More The diffuse outskirts of brightest cluster galaxies (BCGs) encode valuable information about the assembly history and mass of their host dark matter halos. However, the low surface brightness of these stellar halos has historically made them difficult to observe. Recent deep imaging, particularly with Hyper Suprime-Cam (HSC), has shown that the stellar mass within relatively large projected annuli, such as within $50$ and $100$ kpc, is a promising proxy for halo mass. However, the optimal radial definition of this "outskirt mass" remains uncertain. We construct an HSC-like mock observing pipeline to measure the stellar mass density profiles of BCGs in the IllustrisTNG simulations. Our mock observations closely reproduce HSC profiles across six orders of magnitude in surface density. We then systematically measure stellar masses within different annuli and how tightly they are connected to halo mass. We find that stellar masses measured within simple apertures exhibit considerably more scatter in the stellar mass-halo mass relation than those measured within projected ellipsoidal annuli. We identify an optimal range of definitions, with inner radii between $\sim 70$-$200$ kpc and outer radii between $\sim 125$-$500$ kpc. We also introduce two halo-mass-dependent Sérsic models for the average stellar halo profiles. We present a Sérsic-based fitting function that describes the profiles as a function of the halo mass, $M_{\rm vir}$, with a median error of $54\%$. Adding the central stellar mass of the BCG as a second parameter slightly improves the accuracy to a median error of $39\%$. Together, these results provide fitting functions for BCG stellar halos that can be applied to future wide-field surveys to infer halo masses from deep imaging data. △ Less

Submitted 13 November, 2025; originally announced November 2025.

Comments: 16 pages, 10 figures

A Star's Death by a Thousand Cuts: The Runaway Periodic Eruptions of AT2023uqm

Authors: Yibo Wang, Tingui Wang, Shifeng Huang, Jiazheng Zhu, Ning Jiang, Wenbin Lu, Rongfeng Shen, Shiyan Zhong, Dong Lai, Yi Yang, Xinwen Shu, Tianyu Xia, Di Luo, Jianwei Lyu, Thomas Brink, Alex Filippenko, Weikang Zheng, Minxuan Cai, Zelin Xu, Mingxin Wu, Xiaer Zhang, Weiyu Wu, Lulu Fan, Ji-an Jiang, Xu Kong , et al. (15 additional authors not shown)

Abstract: Stars on bound orbits around a supermassive black hole may undergo repeated partial tidal disruption events (rpTDEs), producing periodic flares. While several candidates have been suggested, definitive confirmation of these events remains elusive. We report the discovery of AT2023uqm, a nuclear transient that has exhibited at least five periodic optical flares, making it only the second confirmed… ▽ More Stars on bound orbits around a supermassive black hole may undergo repeated partial tidal disruption events (rpTDEs), producing periodic flares. While several candidates have been suggested, definitive confirmation of these events remains elusive. We report the discovery of AT2023uqm, a nuclear transient that has exhibited at least five periodic optical flares, making it only the second confirmed case of periodicity after ASASSN-14ko. Uniquely, the flares from AT2023uqm show a nearly exponential increase in energy--a "runaway" phenomenon signaling the star's progressive destruction. This behavior is consistent with rpTDEs of low-mass, main-sequence stars or evolved giant stars. Multiwavelength observations and spectroscopic analysis of the two most recent flares reinforce its interpretation as an rpTDE. Intriguingly, each flare displays a similar double-peaked structure, potentially originating from a double-peaked mass fallback rate or two discrete collisions per orbit. The extreme ratio of peak separation to orbital period draws attention to the possibility of a giant star being disrupted, which could be distinguished from a low-mass main-sequence star by its future mass-loss evolution. Our analysis demonstrates the power of rpTDEs to probe the properties of disrupted stars and the physical processes of tidal disruption, though it is currently limited by our knowledge of these events. AT2023uqm emerges as the most compelling rpTDE thus far, serving as a crucial framework for modeling and understanding these phenomena. △ Less

Submitted 30 October, 2025; v1 submitted 30 October, 2025; originally announced October 2025.

Comments: Submitted. Comments are welcome

Ultraviolet Spectral Evidence for Ansky as a Slowly Evolving Featureless Tidal Disruption Event with Quasiperiodic Eruptions

Authors: Jiazheng Zhu, Ning Jiang, Yibo Wang, Tinggui Wang, Luming Sun, Shiyan Zhong, Yuhan Yao, Ryan Chornock, Lixin Dai, Jianwei Lyu, Xinwen Shu, Christoffer Fremling, Erica Hammerstein, Shifeng Huang, Wenkai Li, Bei You

Abstract: X-ray quasi-periodic eruptions (QPEs) are rare and enigmatic phenomena that increasingly show a connection to tidal disruption events (TDEs). However, the recently discovered QPEs in ZTF19acnskyy ("Ansky") appear to be linked to an active galactic nucleus (AGN) rather than a TDE, as their slow decay and AGN-like variability differ markedly from that of typical TDEs. This finding may imply broader… ▽ More X-ray quasi-periodic eruptions (QPEs) are rare and enigmatic phenomena that increasingly show a connection to tidal disruption events (TDEs). However, the recently discovered QPEs in ZTF19acnskyy ("Ansky") appear to be linked to an active galactic nucleus (AGN) rather than a TDE, as their slow decay and AGN-like variability differ markedly from that of typical TDEs. This finding may imply broader formation channels for QPEs. To further investigate Ansky's nature, we obtained a timely ultraviolet (UV) spectrum, which reveals a featureless, TDE-like spectrum devoid of broad optical or UV emission lines. Additionally, the steep UV continuum, fitted by a power law with an index of -2.6, aligns more closely with TDEs than with AGNs. Compared to other featureless TDEs, Ansky exhibits a significantly lower blackbody luminosity (10^43 erg s^-1) and much longer rise and decay timescales, suggesting a distinct TDE subclass. An offset TDE involving an intermediate-mass black hole is unlikely, given its position consistent with the galactic center with a 3 sigma upper limit of 54 pc. Instead, we propose that Ansky may result from the tidal disruption of a post-main-sequence star by a typical supermassive black hole. Our findings strengthen the growing evidence for TDE-QPE associations, although other formation channels for QPEs remain plausible and await future observational efforts. △ Less

Submitted 25 November, 2025; v1 submitted 25 October, 2025; originally announced October 2025.

Comments: 14 pages, 9 figures, Published in ApJL

Journal ref: ApJL 994 L16 (2025)

Testing the Stellar Feedback-driven Breathing Mode in Low-mass Galaxies with Gas Kinematics

Authors: Yifei Luo, Joseph Wick, Alexie Leauthaud, Andrew Wetzel, Tucker Jones, Erin Kado-Fong, Song Huang, Xinjun Chen, Conghao Zhou, Jiaxuan Li

Abstract: Hydrodynamic simulations have proposed that stellar feedback and bursty star-formation can produce dark matter cores in low-mass galaxies. A key prediction is that feedback-driven gas outflow and inflow cycles can lead to ``breathing modes'' (rapid fluctuations in the global gravitational potential) which drive correlated variations in galaxy size, kinematics, and star-formation rate. In this pape… ▽ More Hydrodynamic simulations have proposed that stellar feedback and bursty star-formation can produce dark matter cores in low-mass galaxies. A key prediction is that feedback-driven gas outflow and inflow cycles can lead to ``breathing modes'' (rapid fluctuations in the global gravitational potential) which drive correlated variations in galaxy size, kinematics, and star-formation rate. In this paper, we test the dynamical effects of feedback-driven breathing modes using a sample of 103 star-forming low-mass galaxies with stellar masses between $7.9<\rm \log M_*/M_\odot<9.6$ and $0.02<z<0.19$. We measure ionized gas velocity dispersions from H$α$ emission lines and compare them to mock observations from the FIRE-2 simulations. We compare gas velocity dispersions ($\rm σ_{gas}$), stellar masses, and specific star-formation rates (sSFR). We find a positive correlation between gas velocity dispersion residuals at fixed stellar masses ($\rm Δσ_{gas}$) and sSFR in both data and simulations. However, the relation is tighter in FIRE-2 compared to the data. FIRE-2 produces more low-sSFR galaxies compared to our observational sample, however, the sSFR distributions agree after limiting both samples to a minimum sSFR. A deeper and more complete photometric sample further indicates that observed low-mass galaxies could span the full range of sSFR predicted in the FIRE-2 simulations. Our results support the existence of short-timescale dynamical effects driven by gas outflow and inflow cycles in low-mass galaxies and motivate additional tests of the breathing mode. △ Less

Submitted 20 October, 2025; originally announced October 2025.

Comments: 23 pages, 12 figures

Mephisto: Self-Improving Large Language Model-Based Agents for Automated Interpretation of Multi-band Galaxy Observations

Authors: Zechang Sun, Yuan-Sen Ting, Yaobo Liang, Nan Duan, Song Huang, Zheng Cai

Abstract: Astronomical research has long relied on human expertise to interpret complex data and formulate scientific hypotheses. In this study, we introduce Mephisto -- a multi-agent collaboration framework powered by large language models (LLMs) that emulates human-like reasoning for analyzing multi-band galaxy observations. Mephisto interfaces with the CIGALE codebase (a library of spectral energy distri… ▽ More Astronomical research has long relied on human expertise to interpret complex data and formulate scientific hypotheses. In this study, we introduce Mephisto -- a multi-agent collaboration framework powered by large language models (LLMs) that emulates human-like reasoning for analyzing multi-band galaxy observations. Mephisto interfaces with the CIGALE codebase (a library of spectral energy distribution, SED, models) to iteratively refine physical models against observational data. It conducts deliberate reasoning via tree search, accumulates knowledge through self-play, and dynamically updates its knowledge base. Validated across diverse galaxy populations -- including the James Webb Space Telescope's recently discovered "Little Red Dot" galaxies -- we show that Mephisto demonstrates proficiency in inferring the physical properties of galaxies from multi-band photometry, positioning it as a promising research copilot for astronomers. Unlike prior black-box machine learning approaches in astronomy, Mephisto offers a transparent, human-aligned reasoning process that integrates seamlessly with existing research practices. This work underscores the possibility of LLM-driven agent-based research for astronomy, establishes a foundation for fully automated, end-to-end artificial intelligence (AI)-powered scientific workflows, and unlocks new avenues for AI-augmented discoveries in astronomy. △ Less

Submitted 9 October, 2025; originally announced October 2025.

Comments: 17 pages main text + 13 pages appendix. A conference abstract is available at arXiv:2409.14807. Submitted to AAS journal. Comments and feedback are welcome!

Investigation of hadronic cross sections of cosmic ray carbon and oxygen on BGO from 200 GeV to 10 TeV energy at the DAMPE experiment

Authors: F. Alemanno, Q. An, P. Azzarello, F. C. T. Barbato, P. Bernardini, X. J. Bi, H. Boutin, I. Cagnoli, M. S. Cai, E. Casilli, E. Catanzani, J. Chang, D. Y. Chen, J. L. Chen, Z. F. Chen, Z. X. Chen, P. Coppin, M. Y. Cui, T. S. Cui, Y. X. Cui, I. De Mitri, F. de Palma, A. Di Giovanni, T. K. Dong, Z. X. Dong , et al. (122 additional authors not shown)

Abstract: The Dark Matter Particle Explorer (DAMPE) has made significant progress in measuring the fluxes of cosmic rays. These new measurements are pivotal in advancing our understanding of the origins and propagation mechanisms of cosmic rays. The bismuth germanium oxide (BGO) calorimeter plays a crucial role in these measurements, particularly in the precise determination of cosmic ray fluxes. However, f… ▽ More The Dark Matter Particle Explorer (DAMPE) has made significant progress in measuring the fluxes of cosmic rays. These new measurements are pivotal in advancing our understanding of the origins and propagation mechanisms of cosmic rays. The bismuth germanium oxide (BGO) calorimeter plays a crucial role in these measurements, particularly in the precise determination of cosmic ray fluxes. However, for a calorimetric experiment like DAMPE, uncertainties in hadronic models persist as a major barrier in achieving more accurate measurements of fluxes of cosmic ray nuclei. This study centers on the measurement of the inelastic hadronic cross sections of carbon and oxygen nuclei interacting with BGO crystals target over an extensive energy range, spanning from 200 GeV to 10 TeV. For carbon nuclei interacting with the BGO target, the measurements of the cross sections have achieved a total relative uncertainty of less than 10% below 8 TeV for carbon, and below 3 TeV for oxygen. For oxygen nuclei, the same level of precision was attained below 3 TeV. Additionally, we compare the experimental results with Geant4 and FLUKA simulations to validate the accuracy and consistency of these simulation tools. Through comprehensive analysis of the inelastic hadronic interaction cross sections, this research provides validation for the hadronic interaction models used in DAMPE's cosmic-ray flux measurements. △ Less

Submitted 21 September, 2025; originally announced September 2025.

Probing the meV QCD Axion with the $\texttt{SQWARE}$ Quantum Semiconductor Haloscope

Authors: Jaanita Mehrani, Tao Xu, Andrey Baydin, Michael J. Manfra, Henry O. Everitt, Andrew J. Long, Kuver Sinha, Junichiro Kono, Shengxi Huang

Abstract: We propose the Semiconductor-Quantum-Well Axion Radiometer Experiment ($\texttt{SQWARE}$) -- a new experimental platform for direct detection of axion dark matter in the meV mass range -- based on resonantly enhanced axion-photon conversion through the inverse Primakoff effect in engineered quantum semiconductor heterostructures. The core of the radiometer is a GaAs/AlGaAs multiple quantum well st… ▽ More We propose the Semiconductor-Quantum-Well Axion Radiometer Experiment ($\texttt{SQWARE}$) -- a new experimental platform for direct detection of axion dark matter in the meV mass range -- based on resonantly enhanced axion-photon conversion through the inverse Primakoff effect in engineered quantum semiconductor heterostructures. The core of the radiometer is a GaAs/AlGaAs multiple quantum well structure forming a magnetoplasmonic cavity, containing an ultrahigh-mobility two-dimensional electron gas, which realizes a tunable epsilon-near-zero resonance in the terahertz frequency range. By controlling the orientation of the cavity within a strong external magnetic field, both the resonance frequency and the axion-induced current are optimized $\textit{in situ}$, enabling efficient scanning across a broad mass range without complex mechanical adjustment. The axion-induced electromagnetic signal radiatively emitted from the magnetoplasmonic cavity is detected by a state-of-the-art photodetector. We present the theoretical basis for resonant enhancement, detail the experimental design and benchmarks through extensive simulations, and project the sensitivity of $\texttt{SQWARE}$ for several realistic configurations. Our results demonstrate that $\texttt{SQWARE}$ can probe the well-motivated quantum chromodynamics axion parameter space and close a critical gap in direct searches at meV masses. △ Less

Submitted 17 September, 2025; originally announced September 2025.

Comments: 5+19 pages, 3+15 figures

Improving cosmological reach of a gravitational wave observatory using Deep Loop Shaping

Authors: Jonas Buchli, Brendan Tracey, Tomislav Andric, Christopher Wipf, Yu Him Justin Chiu, Matthias Lochbrunner, Craig Donner, Rana X. Adhikari, Jan Harms, Iain Barr, Roland Hafner, Andrea Huber, Abbas Abdolmaleki, Charlie Beattie, Joseph Betzwieser, Serkan Cabi, Jonas Degrave, Yuzhu Dong, Leslie Fritz, Anchal Gupta, Oliver Groth, Sandy Huang, Tamara Norman, Hannah Openshaw, Jameson Rollins , et al. (6 additional authors not shown)

Abstract: Improved low-frequency sensitivity of gravitational wave observatories would unlock study of intermediate-mass black hole mergers, binary black hole eccentricity, and provide early warnings for multi-messenger observations of binary neutron star mergers. Today's mirror stabilization control injects harmful noise, constituting a major obstacle to sensitivity improvements. We eliminated this noise t… ▽ More Improved low-frequency sensitivity of gravitational wave observatories would unlock study of intermediate-mass black hole mergers, binary black hole eccentricity, and provide early warnings for multi-messenger observations of binary neutron star mergers. Today's mirror stabilization control injects harmful noise, constituting a major obstacle to sensitivity improvements. We eliminated this noise through Deep Loop Shaping, a reinforcement learning method using frequency domain rewards. We proved our methodology on the LIGO Livingston Observatory (LLO). Our controller reduced control noise in the 10--30Hz band by over 30x, and up to 100x in sub-bands surpassing the design goal motivated by the quantum limit. These results highlight the potential of Deep Loop Shaping to improve current and future GW observatories, and more broadly instrumentation and control systems. △ Less

Submitted 11 October, 2025; v1 submitted 17 September, 2025; originally announced September 2025.

Comments: Re-added a reference that was dropped by mistake in the published paper. Fixed date of experiment in text

Journal ref: Science 389, 6764 (2025) 1012-1015

Unveiling Stellar Feedback and Cloud Structure in the $ρ$ Ophiuchi A Region with ALMA and JWST: Discovery of Substellar Cores, C$^{18}$O Striations, and Protostellar Outflows

Authors: Fumitaka Nakamura, Ryohei Kawabe, Shuo Huang, Kazuya Saigo, Naomi Hirano, Shigehisa Takakuwa, Takeshi Kamazaki, Motohide Tamura, James Di Francesco, Rachel Friesen, Kazunari Iwasaki, Chihomi Hara

Abstract: In clustered star-forming regions, stellar feedback-such as HII regions/photon-dominated regions (PDRs), and protostellar jets/outflows-shapes cloud structures and influences star formation. Using high-resolution ALMA millimeter and JWST infrared data, we analyze the cloud structure and the impact of stellar feedback in the nearest dense cluster-forming region Oph A. All 6 known Class 0/I and 2 of… ▽ More In clustered star-forming regions, stellar feedback-such as HII regions/photon-dominated regions (PDRs), and protostellar jets/outflows-shapes cloud structures and influences star formation. Using high-resolution ALMA millimeter and JWST infrared data, we analyze the cloud structure and the impact of stellar feedback in the nearest dense cluster-forming region Oph A. All 6 known Class 0/I and 2 of 6 Flat Spectrum/Class II objects are detected in the 1.3 mm dust continuum. Additionally, we newly detected 7 substellar cores, three of which show compact near-infrared emission, suggesting they are young substellar objects. The remaining cores, with masses of 0.01 Msun and high densities, are likely gravitationally bound. They appear connected by faint CO finger-like structures extending from the triple Class 0 system VLA1623-2417 Aa+Ab+B, suggesting they may have been ejected from the close binary VLA1623 Aa+Ab. 12CO and near-infrared data reveal multiple protostellar outflows. From the comparison, we identified several new outflows/jets, and shocked structures associated to the GSS30 large bipolar bubble. Strong 12CO emission traces the eastern edge of the Oph A ridge, forming part of the expanding HII/PDR bubble driven by the nearby Herbig Be star S1. The northern ridge appears blown out, with warm gas flowing toward GSS 30, injecting additional turbulent momentum. Several C18O striations in the S1 bubble align with magnetic fields, and position-velocity diagrams show wave-like patterns, possibly reflecting magnetohydrodynamic waves. Stellar feedback significantly influences Oph A's cloud structure. △ Less

Submitted 1 September, 2025; originally announced September 2025.

Comments: ApJ in press, 24 pages, 10 figures

Primordial planet spin driven by boundary layer effects in a decretion disc

Authors: Rebecca G. Martin, Stephen H. Lubow, David Vallet, Madeline Overton, Stephen Lepp, Zhaohuan Zhu, Shunquan Huang

Abstract: Accretion of material from a protoplanetary disc on to a forming giant planet can spin the planet up to close to its breakup rate, $Ω_{\rm b}=(G M_{\rm p}/R_{\rm p}^3)$, where $M_{\rm p}$ is the mass and $R_{\rm p}$ is the radius of the planet. After the protoplanetary disc dissipates, the rapidly rotating planet may eject a decretion (outflowing) disc in a similar way to a Be star. Boundary layer… ▽ More Accretion of material from a protoplanetary disc on to a forming giant planet can spin the planet up to close to its breakup rate, $Ω_{\rm b}=(G M_{\rm p}/R_{\rm p}^3)$, where $M_{\rm p}$ is the mass and $R_{\rm p}$ is the radius of the planet. After the protoplanetary disc dissipates, the rapidly rotating planet may eject a decretion (outflowing) disc in a similar way to a Be star. Boundary layer effects in a hydrodynamic disc allow for decretion disc formation at spin rates below the breakup spin rate of the planet. The decretion disc exerts a torque on the planet that slows its spin to an equilibrium value that is sensitive to the planet temperature. By considering steady state circumplanetary decretion disc solutions, we show that the equilibrium spin rate for planets is around $0.4\,Ω_{\rm b}$ for $H/R=0.2$ and around $0.2\,Ω_{\rm b}$ for $H/R=0.3$, where $H$ is the disc scale height at radius $R$. These values are in line with the spins of the giant planets in the solar system and observed exoplanet spins. △ Less

Submitted 12 August, 2025; originally announced August 2025.

Comments: Accepted for publication in MNRAS

A MaNGA about the Legacy I: Connecting the Assembly of Stellar Halo with the Average Star Formation History in Low-Redshift Massive Galaxies

Authors: Xiao-Ya Zhang, Song Huang, Meng Gu

Abstract: We investigate the connection between stellar mass distribution, assembly history, and star formation timescales in low-redshift massive early-type galaxies (ETGs) by combining deep LegacySurvey imaging with MaNGA's spatially resolved spectroscopy. Focusing on stellar population properties, especially the [Mg/Fe] abundance ratio, we analyze stacked spectra using both absorption line indices and fu… ▽ More We investigate the connection between stellar mass distribution, assembly history, and star formation timescales in low-redshift massive early-type galaxies (ETGs) by combining deep LegacySurvey imaging with MaNGA's spatially resolved spectroscopy. Focusing on stellar population properties, especially the [Mg/Fe] abundance ratio, we analyze stacked spectra using both absorption line indices and full-spectrum fitting. We find that, among massive ETGs with identical average stellar mass distributions beyond 5 kpc, those with higher central velocity dispersion ($σ_{cen}$) are older and more $α$-enhanced, suggesting a connection between the in-situ star formation in the past and the central gravitational potential today for massive ETGs with a similar stellar accretion history. Conversely, at fixed $σ_{cen}$ and total stellar mass, galaxies with more extended stellar halos show lower [Fe/H], higher [Mg/Fe], and older ages, indicating an intriguing link between early starburst and quenching and later ex-situ assembly. These results demonstrate that the evolution of massive galaxies cannot be fully described by simple scaling relations alone, as the interplay between in-situ star formation and ex-situ accretion leaves distinct imprints in both their inner and outer stellar populations. Our findings highlight the importance of extending stellar population studies to large radii and underscore the scientific potential of next-generation IFU surveys and deep, high-resolution spectroscopy for probing the galaxy-halo connection. △ Less

Submitted 30 July, 2025; originally announced July 2025.

Comments: 27 pages, 16 figures

Insights from the "Red devil" AT 2022fpx: A Dust-reddened Family of Tidal Disruption Events Excluded by Their Apparent Red Color?

Authors: Zheyu Lin, Ning Jiang, Yibo Wang, Xu Kong, Shifeng Huang, Zesen Lin, Chen Qin, Tianyu Xia

Abstract: We report unnoticed but intriguing features in the peculiar nuclear transient AT 2022fpx, and investigate its type. These features include the constantly red optical color of $g-r>0$, a stable soft X-ray flare ($kT\sim100$ eV) in the past $\sim$550 days, a prominent mid-infrared echo peaked at $\sim$$10^{43.3}$ erg s$^{-1}$ and the confirmation of a weak active galactic nucleus by weak flares in p… ▽ More We report unnoticed but intriguing features in the peculiar nuclear transient AT 2022fpx, and investigate its type. These features include the constantly red optical color of $g-r>0$, a stable soft X-ray flare ($kT\sim100$ eV) in the past $\sim$550 days, a prominent mid-infrared echo peaked at $\sim$$10^{43.3}$ erg s$^{-1}$ and the confirmation of a weak active galactic nucleus by weak flares in pre-event Wide-field Infrared Survey Explorer mid-infrared light curves with no contemporary optical, radio or X-ray counterparts. The combination of the optical red color and possible origin of a tidal disruption event (TDE) of AT 2022fpx is particularly attractive, as it challenges the most widely accepted and adopted "blue color" criterion for optical TDE selection. Although we still cannot confirm whether the red color is intrinsic, we do find that the "blue color" criterion can filter out normal TDEs whose optical-UV spectral energy distributions (SEDs) are either severely contaminated by prominent emission lines (especially H$α$) or heavily dust-reddened. Hence, its potential selection effect may have been imprinted on the whole optical TDE family. Blackbody fitting on the optical (rest-frame $\sim$$4000-7000$ Å) and optical-UV ($\sim$$2000-7000$ Å) SEDs of four TDEs with high-cadence UV observations shows that $T_\mathrm{bb}$ rise by $\sim$40$-$110 \% when the UV bands are included. The power-law models ($f_λ\proptoλ^{-α}$ with $α=2-3$) can fit the rest-frame $\sim$$2000-7000$ ÅSEDs more consistently, indicating that SEDs should peak at shorter wavelengths, but not simple blackbodies. Hence, the estimated released energy for the optical-UV bright but X-ray faint TDEs based on blackbody SED fitting should be significantly lower than the intrinsic energy. △ Less

Submitted 5 September, 2025; v1 submitted 7 July, 2025; originally announced July 2025.

Comments: 22 pages, 10 figures, 3 tables, accepted by ApJ

Journal ref: ApJ 990 22 (2025)

Can AI Dream of Unseen Galaxies? Conditional Diffusion Model for Galaxy Morphology Augmentation

Authors: Chenrui Ma, Zechang Sun, Tao Jing, Zheng Cai, Yuan-Sen Ting, Song Huang, Mingyu Li

Abstract: Observational astronomy relies on visual feature identification to detect critical astrophysical phenomena. While machine learning (ML) increasingly automates this process, models often struggle with generalization in large-scale surveys due to the limited representativeness of labeled datasets -- whether from simulations or human annotation -- a challenge pronounced for rare yet scientifically va… ▽ More Observational astronomy relies on visual feature identification to detect critical astrophysical phenomena. While machine learning (ML) increasingly automates this process, models often struggle with generalization in large-scale surveys due to the limited representativeness of labeled datasets -- whether from simulations or human annotation -- a challenge pronounced for rare yet scientifically valuable objects. To address this, we propose a conditional diffusion model to synthesize realistic galaxy images for augmenting ML training data. Leveraging the Galaxy Zoo 2 dataset which contains visual feature -- galaxy image pairs from volunteer annotation, we demonstrate that our model generates diverse, high-fidelity galaxy images closely adhere to the specified morphological feature conditions. Moreover, this model enables generative extrapolation to project well-annotated data into unseen domains and advancing rare object detection. Integrating synthesized images into ML pipelines improves performance in standard morphology classification, boosting completeness and purity by up to 30\% across key metrics. For rare object detection, using early-type galaxies with prominent dust lane features ( $\sim$0.1\% in GZ2 dataset) as a test case, our approach doubled the number of detected instances from 352 to 872, compared to previous studies based on visual inspection. This study highlights the power of generative models to bridge gaps between scarce labeled data and the vast, uncharted parameter space of observational astronomy and sheds insight for future astrophysical foundation model developments. Our project homepage is available at https://galaxysd-webpage.streamlit.app/. △ Less

Submitted 19 June, 2025; originally announced June 2025.

Comments: We have submitted to AAS journals. See another independent work for further reference -- Category-based Galaxy Image Generation via Diffusion Models (Fan, Tang et al.). Comments are welcome

Unveiling the Cosmic Dance of Repeated Nuclear Transient ASASSN-14ko: Insights from Multiwavelength Observations

Authors: Shifeng Huang, Tinggui Wang, Ning Jiang, Rong-Feng Shen, Zhaohao Chen, Yuanming Wang, Jiazheng Zhu, Yibo Wang, Yunguo Jiang, Xinwen Shu, Hucheng Ding, Xiongjun Fang, Yifan Wang, Jie Lin, Jingran Xu, Xu Chen, Zheyu Lin, Zhengfeng Sheng

Abstract: ASASSN-14ko is a periodically repeating nuclear transient. We conducted high-cadence, multiwavelength observations of this source, revealing several recurrent early bumps and rebrightenings in its UV/optical light curves. The energy released during these bumps and rebrightenings shows a diminishing trend in recent UV/optical outbursts, which we monitored through multiwavelength observations. These… ▽ More ASASSN-14ko is a periodically repeating nuclear transient. We conducted high-cadence, multiwavelength observations of this source, revealing several recurrent early bumps and rebrightenings in its UV/optical light curves. The energy released during these bumps and rebrightenings shows a diminishing trend in recent UV/optical outbursts, which we monitored through multiwavelength observations. These features can be ascribed to the interaction between stream debris and the expanded disk in the repeated partial tidal disruption event. The X-ray light curve exhibits an inverse pattern compared to the UV/optical bands, displaying sporadic outbursts. Furthermore, our observations demonstrate that the blackbody temperature and radius in each outburst increase with the UV/optical luminosity, and such evolution resembles that observed in X-ray quasiperiodic eruptions, whereas distinguishing it from typical tidal disruption events. △ Less

Submitted 17 June, 2025; originally announced June 2025.

Comments: Accepted for publication in ApJ, 16 pages, 10 figures

A Resonant Beginning for the Solar System Terrestrial Planets

Authors: Shuo Huang, Chris Ormel, Simon Portegies Zwart, Eiichiro Kokubo, Tian Yi

Abstract: In the past two decades, transit surveys have revealed a class of planets with thick atmospheres -- sub-Neptunes -- that must have completed their accretion in protoplanet disks. When planets form in the gaseous disk, the gravitational interaction with the disk gas drives their migration and results in the trapping of neighboring planets in mean motion resonances, though these resonances can later… ▽ More In the past two decades, transit surveys have revealed a class of planets with thick atmospheres -- sub-Neptunes -- that must have completed their accretion in protoplanet disks. When planets form in the gaseous disk, the gravitational interaction with the disk gas drives their migration and results in the trapping of neighboring planets in mean motion resonances, though these resonances can later be broken when the damping effects of disk gas or planetesimals wane. It is widely accepted that the outer Solar System gas giant planets originally formed in a resonant chain, which was later disrupted by dynamical instabilities. Here, we explore whether the early formation of the terrestrial planets in a resonance chain (including Theia) can evolve to the present configuration. Using N-body simulations, we demonstrate that the giant planet instability would also have destabilized the terrestrial resonance chain, triggering moon-forming giant impacts in 20--50\% of our simulated systems, dependent on the initial resonance architecture. After the instability, the eccentricity and inclination of the simulated planets match their present-day values. Under the proposed scenario, the current period ratio of 3.05 between Mars and Venus -- devoid of any special significance in traditional late formation models -- naturally arises as a relic of the former resonance chain. △ Less

Submitted 7 June, 2025; v1 submitted 4 June, 2025; originally announced June 2025.

Comments: Main text: 9 pages, 5 figures. Appendix: 6 pages, 6 figures. Accepted for publication in ApJ

Stability of a cluster-disrupted mean-motion resonance (chain) in HR 8799 and PDS 70

Authors: Brent Maas, Shuo Huang, Simon Portegies Zwart

Abstract: HR~8799 is a planetary system with four planets potentially in a mean-motion resonance chain. It is unclear from the observations if they are in mean-motion resonance. Similarly, PDS~70 has two observed planets also potentially in mean-motion resonance. We simulate HR~8799 and PDS~70 under external perturbations to study their responds if in resonance or mean-motion resonance. We integrate the equ… ▽ More HR~8799 is a planetary system with four planets potentially in a mean-motion resonance chain. It is unclear from the observations if they are in mean-motion resonance. Similarly, PDS~70 has two observed planets also potentially in mean-motion resonance. We simulate HR~8799 and PDS~70 under external perturbations to study their responds if in resonance or mean-motion resonance. We integrate the equations of motion for HR~8799 and PDS~70 starting with either in resonance or in mean-motion resonance and study their in isolation and in a star cluster. In the star cluster, we take the effects of passing stars into account. The dynamics of the star cluster is resolved using the Lonely Planets module in AMUSE. HR~8799 and PDS~70 in mean-motion resonance are stable, whereas in non-resonance they dissolve in $0.303\pm0.042$Myr and $1.26\pm0.25$Myr, respectively. In a cluster, the non-resonant HR~8799 is slightly more stable than in isolation, but still dissolves in $0.300\pm0.043$Myr, whereas the resonant planetary system remains stable for at least $0.71$Myr. In contrast, a non-resonant PDS~70 system is approximately equally stable in a cluster compared to isolation, and dissolves in $1.03\pm0.20$Myr, whereas the resonant PDS~70 system remains stable for at least $0.83$Myr. Considering the more stable solutions of mean-motion resonance for HR~8799, we argue that the planetary system was born in mean-motion resonance and that the mean-motion resonance was preserved. If HR~8799 was not born in resonance, the probability that it survived until the present day is negligible. Similarly, we argue that PDS~70 was probably born in mean-motion resonance and that its state was preserved. We also find that it is almost possible for planetary systems with a broken mean-motion resonance chain to survive longer in a perturbing cluster environment compared to isolation. △ Less

Submitted 2 June, 2025; originally announced June 2025.

Comments: accepted for publication in A&A

Journal ref: A&A 700, A108 (2025)

Mapping the Star Formation and HI Gas Properties of Galaxies Along Large-scale Structures Around the Virgo Cluster

Authors: Hyein Yoon, O. Ivy Wong, Aeree Chung, Shan Huang

Abstract: We investigate the star formation and neutral atomic hydrogen (HI) gas properties of galaxies along three large-scale filaments and two galaxy groups in the wide field around the Virgo cluster. Our goal is to understand how galaxies are processed in low-density environments before falling into high-density regions. Combining the spatial distribution of galaxies with multiwavelength colors such as… ▽ More We investigate the star formation and neutral atomic hydrogen (HI) gas properties of galaxies along three large-scale filaments and two galaxy groups in the wide field around the Virgo cluster. Our goal is to understand how galaxies are processed in low-density environments before falling into high-density regions. Combining the spatial distribution of galaxies with multiwavelength colors such as W3-W1, NUV-r, and g-r, we find a predominance of blue galaxies across the structures, indicating normal-to-enhanced star formation, similar to that of isolated galaxies. However, one filament and one group show a significant number of red galaxies (32% and 20%, respectively), suggesting that star formation has been suppressed in low-density environments before reaching high-density regions. Intriguingly, these red galaxies span a wide range of stellar masses, and the presence of red dwarfs support that not only mass but also environment plays an important role in the quenching of star formation in cluster outskirts. One particular filament, potentially connected to Virgo, already has a group of red populations outside Virgo's R_200, making these galaxies good candidates for being "preprocessed" before entering the Virgo cluster. In addition, several galaxies in the filaments and groups possess relatively low HI gas contents, similar to cluster galaxies. However, the overall fraction of HI-deficient galaxies is not as significantly high as the fraction of red galaxies in these structures. This suggests that HI gas properties are less influenced by the environment than star formation properties in low-density regions, possibly due to gas replenishment through accretion. △ Less

Submitted 26 May, 2025; originally announced May 2025.

Comments: 24 pages, 14 figures, 4 tables, accepted for publication in ApJ

Zangetsu: A Candidate of Isolated, Quiescent, and Backsplash Ultra-Diffuse Galaxy in the COSMOS Field

Authors: Leyao Wei, Song Huang, Jiaxuan Li, Zechang Sun, Mingyu Li, Jiaxin Tang

Abstract: Deep imaging surveys have changed our view of the low surface brightness (LSB) Universe. The "renaissance" of the low surface brightness dwarf galaxy population, as the prime example of such recent development, continues to challenge our understanding of galaxy formation. Here, We report the serendipitous discovery of Zangetsu, an isolated, quiescent, and distorted ultra-diffuse galaxy (UDG) candi… ▽ More Deep imaging surveys have changed our view of the low surface brightness (LSB) Universe. The "renaissance" of the low surface brightness dwarf galaxy population, as the prime example of such recent development, continues to challenge our understanding of galaxy formation. Here, We report the serendipitous discovery of Zangetsu, an isolated, quiescent, and distorted ultra-diffuse galaxy (UDG) candidate in the COSMOS field, using images from the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP). Zangetsu exhibits an extremely low central surface brightness ($\mathrm{μ_{0,g}}=26.60\pm0.01$ mag arcsec$^{-2}$), a very shallow inner surface brightness profile ($\mathrm{n}_{\rm Sersic}=0.40\pm0.01$), and a large angular size ($\mathrm{R_e}\approx 10.44$ arcsec). Surprisingly, Zangetsu also has a quiescent stellar population ($\mathrm{g-i}=0.96$), an unusually elongated shape ($\mathrm{b/a}\sim 0.25$), and mild morphological asymmetry, making it a rare case among known UDGs. Surface brightness fluctuation analysis of HSC and Hubble Space Telescope (HST) images only provides a distance lower limit of $D>25.4$ Mpc (thus $\mathrm{R_e}>1.38$ kpc). However, Zangetsu remains an extreme outlier in the luminosity-size relation of known LSB galaxies, suggesting that it could be an exceptionally large and/or diffuse system. Classic internal or external UDG formation mechanisms alone struggle to explain such a system. A backsplash origin may account for its isolation and quiescent nature. This finding also raises the possibility that current works may overlook similarly extreme, elongated systems that could further our understanding of the LSB Universe. △ Less

Submitted 21 May, 2025; v1 submitted 20 May, 2025; originally announced May 2025.

Comments: 25 pages, 11 figures

Oort Cloud Ecology. III. The Sun left the parent star cluster shortly after the giant planets formed

Authors: Simon Portegies Zwart, Shuo Huang

Abstract: The Sun was born in a clustered environment with 10,000 other stars. Being an isolated star today, the Sun must have left the nest. We do not directly know when that happened, how violent the ejection was, or how far the Solar siblings have drifted apart. The mass of the fragile outer Opic-Oort cloud, (between $r_{\rm inner} \sim 30,000$\,au and $200\,000$au from the Sun) and the orbital distribut… ▽ More The Sun was born in a clustered environment with 10,000 other stars. Being an isolated star today, the Sun must have left the nest. We do not directly know when that happened, how violent the ejection was, or how far the Solar siblings have drifted apart. The mass of the fragile outer Opic-Oort cloud, (between $r_{\rm inner} \sim 30,000$\,au and $200\,000$au from the Sun) and the orbital distribution of planetesimals in the inner Hills-Oort cloud (between $\sim 1000$\,au and $\sim 30\,000$ au) are sensitive to the dynamical processes involving the Sun in the parent cluster. We aim at understanding the extend to which observing the Oort cloud constrains the Sun's birth environment. This is achieved by a combination of theoretical arguments and N-body simulations. We show that the current mass of the Opic-Oort cloud (between 0.2 and $2.0$ Earth masses) is best explained if the Sun left the nest within $\sim 20$\,Myr after the giant planets formed and migrated. As a consequence, the possible dynamical encounter with another star carving the Kuiper belt, the Sun's abduction of Sedna, and other perturbations induced by nearby stars then must have happened shortly after the giant planets in the Solar system formed, but before the Sun left the parent cluster. Signatures of the time spend in the parent cluster must still be visible in the outer parts of the Solar system today. The strongest constraints will be the discovery of a population of relatively low-eccentricity ($e < 0.9$) inner Oort-cloud (but $500 < a < 10^4$\,au) objects. △ Less

Submitted 19 May, 2025; originally announced May 2025.

Comments: Accepted for publication in A&A

Journal ref: A&A 698, L27 (2025)

Measurement of separate electron and positron spectra from 10 GeV to 20GeV with the geomagnetic field on DAMPE

Authors: DAMPE Collaboration, F. Alemanno, Q. An, P. Azzarello, F. C. T. Barbato, P. Bernardini, X. J. Bi, H. Boutin, I. Cagnoli, M. S. Cai, E. Casilli, E. Catanzani, J. Chang, D. Y. Chen, J. L. Chen, Z. F. Chen, Z. X. Chen, P. Coppin, M. Y. Cui, T. S. Cui, Y. X. Cui, I. DeMitri, F. dePalma, A. DiGiovanni, T. K. Dong , et al. (127 additional authors not shown)

Abstract: The cosmic-ray (CR) electrons and positrons in space are of great significance for studying the origin and propagation of cosmic-rays. The satellite-borne experiment DArk Matter Particle Explorer (DAMPE) has been used to measure the separate electron and positron spectra, as well as the positron fraction. In this work, the Earth's magnetic field is used to distinguish CR electrons and positrons, a… ▽ More The cosmic-ray (CR) electrons and positrons in space are of great significance for studying the origin and propagation of cosmic-rays. The satellite-borne experiment DArk Matter Particle Explorer (DAMPE) has been used to measure the separate electron and positron spectra, as well as the positron fraction. In this work, the Earth's magnetic field is used to distinguish CR electrons and positrons, as the DAMPE detector does not carry an onboard magnet. The energy range for the measurements is from 10 to 20 GeV, being currently limited at high energy by the zenith pointing orientation of DAMPE. The results are consistent with previous measurements based on the magnetic spectrometer by AMS-02 and PAMELA, while the results of Fermi-LAT seem then to be systematically shifted to larger values. △ Less

Submitted 21 August, 2025; v1 submitted 9 May, 2025; originally announced May 2025.

Comments: Accepted for publication in Chinese Physics C

Excitation of post-AGB Star Binary Eccentricity by Massive Polar-Aligned Circumbinary Disks

Authors: Shunquan Huang, Rebecca G. Martin, Stephen H. Lubow

Abstract: Many post-AGB star binaries are observed to have relatively high orbital eccentricities (up to 0.6). Recently, AC Her was observed to have a polar-aligned circumbinary disk. We perform hydrodynamic simulations to explore the impact of a polar-aligned disk on the eccentricity of a binary. For a binary system with central masses of 0.73 M_sun and 1.4 M_sun, we find that a disk with a total mass of 0… ▽ More Many post-AGB star binaries are observed to have relatively high orbital eccentricities (up to 0.6). Recently, AC Her was observed to have a polar-aligned circumbinary disk. We perform hydrodynamic simulations to explore the impact of a polar-aligned disk on the eccentricity of a binary. For a binary system with central masses of 0.73 M_sun and 1.4 M_sun, we find that a disk with a total mass of 0.1 M_sun can enhance the binary eccentricity from 0.2 to 0.7 within 5000 years, or from 0.01 to 0.65 within 15000 years. Even if the disk mass is as low as 0.01 M_sun, the binary eccentricity grows within our simulation time while the system remains stable. These eccentricity variations are associated with the variations of the inclination between the disk and the binary orbit due to von Zeipel-Kozai-Lidov oscillations. The oscillations eventually damp and leave the binary eccentricity at a high value. The numerical results are in good agreement with analytical estimates. In addition, we examine the AC-Her system and find that the disk mass should be on the order of 10^(-3)M_sun for the disk to remain polar. △ Less

Submitted 23 April, 2025; originally announced April 2025.

Comments: Accepted for publication in The Astrophysical Journal. 11 pages, 11 figures

Oxyster: A Circumgalactic Low-ionization Oxygen Nebula next to a Starburst Galaxy at $z\sim1$

Authors: Pengjun Lu, Mingyu Li, Dalya Baron, Minghao Yue, Song Huang, Zheng Cai

Abstract: Extended emission line nebulae around galaxies or active galactic nuclei (AGNs) provide a unique window to investigate the galactic ecosystem through the circumgalactic medium (CGM). Using Subaru Hyper-Suprime Cam narrow-band imaging and spectroscopic follow-up, we serendipitously discover "Oxyster" - a large ionized nebula next to an interacting starburst galaxy at $z=0.924$. The nebula is traced… ▽ More Extended emission line nebulae around galaxies or active galactic nuclei (AGNs) provide a unique window to investigate the galactic ecosystem through the circumgalactic medium (CGM). Using Subaru Hyper-Suprime Cam narrow-band imaging and spectroscopic follow-up, we serendipitously discover "Oxyster" - a large ionized nebula next to an interacting starburst galaxy at $z=0.924$. The nebula is traced by extended [OII]3726,3729 ($\sim 30$ kpc) and [OIII]5007 ($\sim 20$ kpc) emission lines. On the nebula luminosity-size plane, Oxyster surpasses the extended narrow-line regions around low-$z$ AGNs, resembling a higher-$z$ analog of "Hanny's Voorwerp". However, its uniformly low [OIII]/[OII] ratio (O32) sets it apart from typical AGN light echoes. For the host galaxy, HST and JWST images reveal a disturbed red disk galaxy with a single blue spiral "arm". Spectral energy distribution (SED) fitting suggests the $2-6\times 10^{10} ~\rm M_{\odot}$ host galaxy sits above the star-forming main sequence with an ongoing starburst, especially in the "arm", and have $<5\%$ luminosity contribution from AGN, consistent with X-ray non-detection and radio continuum. Standard photoionization and shock models struggle to explain simultaneously Oxyster's emission line luminosities, low O32 ratio, and the non-detection of H$β$ line. A plausible explanation could involve the combination of a recent ($<10^8$ yrs) starburst and a low-luminosity AGN ($L_{\rm{bol}} \sim 1\times10^{42}$ erg/s). While Oxyster's nature awaits future investigation, its discovery highlights the potential of ground-based narrow-band imaging to uncover extended emission line nebulae around non-AGN systems, opening new avenues for studying the CGM of normal galaxies in the early Universe. △ Less

Submitted 3 November, 2025; v1 submitted 15 April, 2025; originally announced April 2025.

Comments: 20 pages, 9 figures, 4 tables, published at ApJ

Journal ref: ApJ 990 168 (2025)

ADF22+: a declining faint end in the far-infrared luminosity function in the SSA22 protocluster at z=3.09

Authors: Shuo Huang, Hideki Umehata, Ian Smail, Kouichiro Nakanishi, Bunyo Hatsukade, Mariko Kubo, Yoichi Tamura, Tomoki Saito, Soh Ikarashi

Abstract: Protoclusters represent the densest regions of cosmic large-scale structure in the early universe and are the environment where present-day massive elliptical galaxies are assembled. Millimeter continuum emission offers a powerful probe of obscured star formation at high redshifts across various environments. In this paper, we present a deep ALMA 1.17 mm mosaic of the central 8 arcmin$^2$ (… ▽ More Protoclusters represent the densest regions of cosmic large-scale structure in the early universe and are the environment where present-day massive elliptical galaxies are assembled. Millimeter continuum emission offers a powerful probe of obscured star formation at high redshifts across various environments. In this paper, we present a deep ALMA 1.17 mm mosaic of the central 8 arcmin$^2$ ($\approx30$ comoving Mpc$^{2}$) region in the SSA22 protocluster at $z=3.09$ to study the faint dusty star-forming galaxy (DSFG) population. The continuum map achieves an RMS noise level of $\approx25$ $μ$Jy beam$^{-1}$ at $\approx1\arcsec$ spatial resolution, $\approx2\times$ the depth of previous observation of this field. We detected 53 sources with a signal-to-noise ratio above 4.2, doubling the number of detections. Utilizing optical to mid-infrared ancillary data, we search for spectroscopic redshift and identify 18 of 53 as cluster members. For sources with more than two photometric data points in the near-infrared, stellar mass ($M_\star$) and star formation rate (SFR) from spectral energy distribution fitting are presented. The 1.17 mm number count shows $>2\times$ excess at flux density $\gtrsim1$ mJy but are consistent with blank field in fainter flux bins. The monochromatic far-infrared luminosity function of the SSA22 protocluster core region suggests a lack of faint DSFGs. All SSA22 protocluster member galaxies detected at 1.17 mm have SFR within the $M_\star$-SFR relation of general star-forming galaxies. Our results suggest that an early overdense environment like SSA22 protocluster predominantly enhances the formation of massive early-type galaxies in present-day galaxy clusters, but that the star formation in individual member galaxies is likely driven by gas supply along the cosmic web and occurs in a secular way. △ Less

Submitted 24 June, 2025; v1 submitted 30 March, 2025; originally announced March 2025.

Comments: Accepted for publication in A&A

Journal ref: A&A 699, A324 (2025)

Optical Monitoring and Long-term Optical Spectral Variability of BL Lacertae Object S5 0716+714

Authors: Huai-Zhen Li, Di-Fu Guo, Long-Hua Qin, Fen Liu, Hong-Tao Liu, Ting-Feng Yi, Quan-Gui Gao, Shi-Feng Huang, Xing Gao, Xu Chen

Abstract: We present photometric observations of the BL Lacertae object S5 0716+714 with a temporal resolution of 120 s in the Sloan i' and r' bands. These observations were conducted using the Comet Search Program telescope at Xingming Observatory from 2018 December 22 to 2020 February 15, and more than 5600 effective images were obtained on each filter across 79 nights. Additionally, we compiled long-term… ▽ More We present photometric observations of the BL Lacertae object S5 0716+714 with a temporal resolution of 120 s in the Sloan i' and r' bands. These observations were conducted using the Comet Search Program telescope at Xingming Observatory from 2018 December 22 to 2020 February 15, and more than 5600 effective images were obtained on each filter across 79 nights. Additionally, we compiled long-term variability data spanning 34 yr in the optical UBVRI bands. Using the power-enhanced F-test and nested ANOVA test, we found intraday variability (IDV) on 31 nights and possible IDV on 20 nights in the i' band. Similarly, IDV was detected on 35 nights in the r' band, while possible IDV was observed on 22 nights. The minimum variability timescale is 7.33 minutes, and the estimated black hole masses are (0.68- 5.12)*10^8 Msun. The spectral variability and long-term optical light curves reveal a bluer-when-brighter trend on intraday timescales. The long-term optical flux density and spectral index exhibit periodic variability with a timescale of about 1038 days. An anticorrelation between optical flux and spectral index was observed, with a time delay of -140 days. Variability across different optical bands exhibited a strong correlation, with no discernible time lag. From the IDV, spectral variability, correlation, and time delays between different bands, we conclude that these radiation characteristics may result from the shock-in-jet model scenario. △ Less

Submitted 14 March, 2025; originally announced March 2025.

Comments: 30 pages, 14 figures

Journal ref: The Astrophysical Journal Supplement Series,2025

Fundamental Physics and Cosmology with TianQin

Authors: Jun Luo, Haipeng An, Ligong Bian, Rong-Gen Cai, Zhoujian Cao, Wenbiao Han, Jianhua He, Martin A. Hendry, Bin Hu, Yi-Ming Hu, Fa Peng Huang, Shun-Jia Huang, Sang Pyo Kim, En-Kun Li, Yu-Xiao Liu, Vadim Milyukov, Shi Pi, Konstantin Postnov, Misao Sasaki, Cheng-Gang Shao, Lijing Shao, Changfu Shi, Shuo Sun, Anzhong Wang, Pan-Pan Wang , et al. (10 additional authors not shown)

Abstract: The exploration of the surrounding world and the universe is an important theme in the legacy of humankind. The detection of gravitational waves is adding a new dimension to this grand effort. What are the fundamental physical laws governing the dynamics of the universe? What is the fundamental composition of the universe? How has the universe evolved in the past and how will it evolve in the futu… ▽ More The exploration of the surrounding world and the universe is an important theme in the legacy of humankind. The detection of gravitational waves is adding a new dimension to this grand effort. What are the fundamental physical laws governing the dynamics of the universe? What is the fundamental composition of the universe? How has the universe evolved in the past and how will it evolve in the future? These are the basic questions that press for answers. The space-based gravitational wave detector TianQin will tune in to gravitational waves in the millihertz frequency range ($10^{-4} \sim 1$ Hz, to be specific), opening a new gravitational wave spectrum window to explore many of the previously hidden sectors of the universe. TianQin will discover many astrophysical systems, populating the universe at different redshifts: some will be of new types that have never been detected before, some will have very high signal-to-noise ratios, and some will have very high parameter estimation precision. The plethora of information collected will bring us to new fronts on which to search for the breaking points of general relativity, the possible violation of established physical laws, the signature of possible new gravitational physics and new fundamental fields, and to improve our knowledge on the expansion history of the universe. In this white paper, we highlight the advances that TianQin can bring to fundamental physics and cosmology. △ Less

Submitted 27 February, 2025; originally announced February 2025.

Comments: 113 pages

Relationship between 2D and 3D Galaxy Stellar Mass and Correlations with Halo Mass

Authors: Conghao Zhou, Alexie Leauthaud, Shuo Xu, Benedikt Diemer, Song Huang, Katya Leidig, Tesla Jeltema, Marco Gatti, Yifei Luo, Carlo Cannarozzo, Sven Heydenreich

Abstract: Recent studies suggest that the stars in the outer regions of massive galaxies trace halo mass better than the inner regions and that an annular stellar mass provides a low scatter method of selecting galaxy clusters. However, we can only observe galaxies as projected two-dimensional objects on the sky. In this paper, we use a sample of simulated galaxies to study how well galaxy stellar mass prof… ▽ More Recent studies suggest that the stars in the outer regions of massive galaxies trace halo mass better than the inner regions and that an annular stellar mass provides a low scatter method of selecting galaxy clusters. However, we can only observe galaxies as projected two-dimensional objects on the sky. In this paper, we use a sample of simulated galaxies to study how well galaxy stellar mass profiles in three dimensions correlate with halo mass, and what effects arise when observationally projecting stellar profiles into two dimensions. We compare 2D and 3D outer stellar mass selections and find that they have similar performance as halo mass proxies and that, surprisingly, a 2D selection sometimes has marginally better performance. We also investigate whether the weak lensing profiles around galaxies selected by 2D outer stellar mass suffer from projection effects. We find that the lensing profiles of samples selected by 2D and 3D definitions are nearly identical, suggesting that the 2D selection does not create a bias. These findings underscore the promise of using outer stellar mass as a tool for identifying galaxy clusters. △ Less

Submitted 7 February, 2025; originally announced February 2025.

Comments: 31 pages 11 figures. To be submitted to JCAP

The Dynamical History of the Kepler-221 Planet System

Authors: Tian Yi, Chris W. Ormel, Shuo Huang, Antoine C. Petit

Abstract: Kepler-221 is a G-type star hosting four planets. In this system, planets b, c, and e are in (or near) a 6:3:1 three-body resonance even though the planets' period ratios show significant departures from exact two-body commensurability. Importantly, the intermediate planet d is not part of the resonance chain. To reach this resonance configuration, we propose a scenario in which there were origina… ▽ More Kepler-221 is a G-type star hosting four planets. In this system, planets b, c, and e are in (or near) a 6:3:1 three-body resonance even though the planets' period ratios show significant departures from exact two-body commensurability. Importantly, the intermediate planet d is not part of the resonance chain. To reach this resonance configuration, we propose a scenario in which there were originally five planets in the system in a chain of first-order resonances. After disk dispersal, the resonance chain became unstable and two planets quickly merged to become the current planet d. In addition, the b/c/e three-body resonance was re-established. We run N-body simulations using REBOUND to investigate the parameter space under which this scenario can operate. We find that our envisioned scenario is possible when certain conditions are met. First, the reformation of the three-body resonance after planet merging requires convergent migration between planets b and c. Second, as has previously pointed out, an efficient damping mechanism must operate to power the expansion of the b/c/e system. We find that planet d plays a crucial role during the orbital expansion phase due to destabilizing encounters of a three-body resonance between c, d, and e. A successful orbital expansion phase puts constraints on the planet properties in the Kepler-221 system including the planet mass ratios and the tidal quality factors for the planets. Our model can also be applied to other planet systems in resonance, such as Kepler-402 and K2-138. △ Less

Submitted 27 February, 2025; v1 submitted 3 February, 2025; originally announced February 2025.

Comments: Accepted for publication in A&A. 21 pages, 14 figures, 6 tables

Journal ref: A&A 695, A191 (2025)

Observation of a spectral hardening in cosmic ray boron spectrum with the DAMPE space mission

Authors: DAMPE Collaboration, F. Alemanno, C. Altomare, Q. An, P. Azzarello, F. C. T. Barbato, P. Bernardini, X. J. Bi, H. Boutin, I. Cagnoli, M. S. Cai, E. Casilli, E. Catanzani, J. Chang, D. Y. Chen, J. L. Chen, Z. F. Chen, Z. X. Chen, P. Coppin, M. Y. Cui, T. S. Cui, Y. X. Cui, I. De Mitri, F. de Palma, A. Di Giovanni , et al. (121 additional authors not shown)

Abstract: Secondary cosmic ray fluxes are important probes of the propagation and interaction of high-energy particles in the Galaxy. Recent measurements of primary and secondary cosmic ray nuclei have revealed unexpected spectral features that demand a deeper understanding. In this work we report the direct measurement of the cosmic ray boron spectrum from 10 GeV/n to 8 TeV/n with eight years of data colle… ▽ More Secondary cosmic ray fluxes are important probes of the propagation and interaction of high-energy particles in the Galaxy. Recent measurements of primary and secondary cosmic ray nuclei have revealed unexpected spectral features that demand a deeper understanding. In this work we report the direct measurement of the cosmic ray boron spectrum from 10 GeV/n to 8 TeV/n with eight years of data collected by the Dark Matter Particle Explorer (DAMPE) mission. The measured spectrum shows an evident hardening at $182\pm24$ GeV/n with a spectral power index of $γ_1 = 3.02 \pm 0.01$ before the break and an index change of $Δγ= 0.31 \pm 0.05$ after the break. A simple power law model is disfavored at a confidence level of 8$σ$. Compared with the hardenings measured in the DAMPE proton and helium spectra, the secondary boron spectrum hardens roughly twice as much as these primaries, which is consistent with a propagation related mechanism to interpret the spectral hardenings of cosmic rays observed at hundreds of GeV/n. △ Less

Submitted 18 December, 2024; v1 submitted 16 December, 2024; originally announced December 2024.

Comments: 10 pages, 10 figures, submitted to PRL

The Outskirt Stellar Mass of Low-Redshift Massive Galaxies is an Excellent Halo Mass Proxy in Illustris/IllustrisTNG Simulations

Authors: Shuo Xu, Song Huang, Alexie Leauthaud, Benedikt Diemer, Katya Leidig, Carlo Cannarozzo, Conghao Zhou

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

Submitted 15 September, 2025; v1 submitted 4 December, 2024; originally announced December 2024.

Comments: 21 pages, 8 figures, accepted for publication in ApJ

HiFAST: An HI Data Calibration and Imaging Pipeline for FAST III. Standing Wave Removal

Authors: Chen Xu, Jie Wang, Yingjie Jing, Fujia Li, Hengqian Gan, Ziming Liu, Tiantian Liang, Qingze Chen, Zerui Liu, Zhipeng Hou, Hao Hu, Huijie Hu, Shijie Huang, Peng Jiang, Chuan-Peng Zhang, Yan Zhu

Abstract: The standing waves existed in radio telescope data are primarily due to reflections among the instruments, which significantly impact the spectrum quality of the Five-hundred-meter Aperture Spherical radio Telescope (FAST). Eliminating these standing waves for FAST is challenging given the constant changes in their phases and amplitudes. Over a ten-second period, the phases shift by 18$^{\circ}$ w… ▽ More The standing waves existed in radio telescope data are primarily due to reflections among the instruments, which significantly impact the spectrum quality of the Five-hundred-meter Aperture Spherical radio Telescope (FAST). Eliminating these standing waves for FAST is challenging given the constant changes in their phases and amplitudes. Over a ten-second period, the phases shift by 18$^{\circ}$ while the amplitudes fluctuate by 6 mK. Thus, we developed the fast Fourier transform (FFT) filter method to eliminate these standing waves for every individual spectrum. The FFT filter can decrease the root mean square (RMS) from 3.2 to 1.15 times the theoretical estimate. Compared to other methods such as sine fitting and running median, the FFT filter achieves a median RMS of approximately 1.2 times the theoretical expectation and the smallest scatter at 12%. Additionally, the FFT filter method avoids the flux loss issue encountered with some other methods. The FFT is also efficient in detecting harmonic radio frequency interference (RFI). In the FAST data, we identified three distinct types of harmonic RFI, each with amplitudes exceeding 100 mK and intrinsic frequency periods of 8.1, 0.5, and 0.37 MHz, respectively. The FFT filter, proven as the most effective method, is integrated into the HI data calibration and imaging pipeline for FAST (HiFAST, https://hifast.readthedocs.io). △ Less

Submitted 19 November, 2024; originally announced November 2024.

Comments: 16 pages, 12 figures; accepted by RAA

MUltiplexed Survey Telescope: Perspectives for Large-Scale Structure Cosmology in the Era of Stage-V Spectroscopic Survey

Authors: Cheng Zhao, Song Huang, Mengfan He, Paulo Montero-Camacho, Yu Liu, Pablo Renard, Yunyi Tang, Aurelien Verdier, Wenshuo Xu, Xiaorui Yang, Jiaxi Yu, Yao Zhang, Siyi Zhao, Xingchen Zhou, Shengyu He, Jean-Paul Kneib, Jiayi Li, Zhuoyang Li, Wen-Ting Wang, Zhong-Zhi Xianyu, Yidian Zhang, Rafaela Gsponer, Xiao-Dong Li, Antoine Rocher, Siwei Zou , et al. (19 additional authors not shown)

Abstract: The MUltiplexed Survey Telescope (MUST) is a 6.5-meter telescope under development. Dedicated to highly-multiplexed, wide-field spectroscopic surveys, MUST observes over 20,000 targets simultaneously using 6.2-mm pitch positioning robots within a ~5 deg$^2$ field of view. MUST aims to conduct the first Stage-V spectroscopic survey in the 2030s, mapping the 3D Universe with over 100 million galaxie… ▽ More The MUltiplexed Survey Telescope (MUST) is a 6.5-meter telescope under development. Dedicated to highly-multiplexed, wide-field spectroscopic surveys, MUST observes over 20,000 targets simultaneously using 6.2-mm pitch positioning robots within a ~5 deg$^2$ field of view. MUST aims to conduct the first Stage-V spectroscopic survey in the 2030s, mapping the 3D Universe with over 100 million galaxies and quasars, spanning from the nearby Universe to a redshift of z ~ 5.5, corresponding to approximately 1 billion years after the Big Bang. To cover this extensive redshift range, we present an initial conceptual target selection algorithm for different types of galaxies, ranging from local bright galaxies and luminous red galaxies to emission-line galaxies, and high-redshift (2 < z < 5.5) Lyman-break galaxies. Using Fisher forecasts, we demonstrate that MUST can address fundamental questions in cosmology, including the nature of dark energy, tests of gravity theories, and investigations into primordial physics. This is the first paper in the series of science white papers for MUST, with subsequent developments focusing on additional scientific cases such as galaxy and quasar evolution, Milky Way physics, and dynamic phenomena in the time-domain Universe. △ Less

Submitted 5 June, 2025; v1 submitted 12 November, 2024; originally announced November 2024.

Comments: Submitted to SCPMA

ADF22-WEB: A giant barred spiral starburst galaxy in the z = 3.1 SSA22 protocluster core

Authors: H. Umehata, C. C. Steidel, I. Smail, A. M. Swinbank, E. B. Monson, D. Rosario, B. D. Lehmer, K. Nakanishi, M. Kubo, D. Iono, D. M. Alexander, K. Kohno, Y. Tamura, R. J. Ivison, T. Saito, I. Mitsuhashi, S. Huang, Y. Matsuda

Abstract: In the present-day universe, the most massive galaxies are ellipticals located in the cores of galaxy clusters, harboring the heaviest super-massive black holes (SMBHs). However the mechanisms that drive the early growth phase and subsequent transformation of these morphology and kinematics of galaxies remain elusive. Here we report (sub)kiloparsec scale observations of stars, gas, and dust in ADF… ▽ More In the present-day universe, the most massive galaxies are ellipticals located in the cores of galaxy clusters, harboring the heaviest super-massive black holes (SMBHs). However the mechanisms that drive the early growth phase and subsequent transformation of these morphology and kinematics of galaxies remain elusive. Here we report (sub)kiloparsec scale observations of stars, gas, and dust in ADF22.A1, a bright dusty starburst galaxy at z=3.1, hosting a heavily obscured active galactic nucleus and residing in a proto-cluster core. ADF22.A1 is a giant spiral galaxy with the kinematics of a rotating disk with rotation velocity Vrot=530+/-10km/s and diameter larger than 30 kpc. The high specific stellar angular momentum of this system, j*=3400+/-600 kpc km/s, requires a mechanism to effectively spin-up ADF22.A1, indicating the importance of accretion from the cosmic web to supply both gas and angular momentum to galaxies in their early gas-rich starburst phase. In its inner region, gas flows along dust lanes in a bar connected with the bright dusty core and the estimated mass ratio of a bulge to SMBH matches the local relation, suggesting that bars are a key mechanism to shape the early co-evolution of these components. Comparison with cosmological simulations shows that ADF22.A1 will likely evolve into a massive elliptical at the present day, experiencing a significant reduction in angular momentum associated with subsequent galaxy mergers. △ Less

Submitted 6 February, 2025; v1 submitted 29 October, 2024; originally announced October 2024.

Comments: 14 pages, 12 figures. accepted for publication in PASJ

Improving Galaxy Cluster Selection with the Outskirt Stellar Mass of Galaxies

Authors: Matthew Kwiecien, Tesla Jeltema, Alexie Leauthaud, Song Huang, Eli Rykoff, Sven Heydenreich, Johannes Lange, Spencer Everett, Conghao Zhou, Paige Kelly, Yuanyuan Zhang, Tae-Hyeon Shin, Jesse Golden-Marx, J. L. Marshall, M. Aguena, S. S. Allam, S. Bocquet, D. Brooks, A. Carnero Rosell, J. Carretero, L. N. da Costa, M. E. S. Pereira, T. M. Davis, J. De Vicente, P. Doel , et al. (31 additional authors not shown)

Abstract: The number density and redshift evolution of optically selected galaxy clusters offer an independent measurement of the amplitude of matter fluctuations, $S_8$. However, recent results have shown that clusters chosen by the redMaPPer algorithm show richness-dependent biases that affect the weak lensing signals and number densities of clusters, increasing uncertainty in the cluster mass calibration… ▽ More The number density and redshift evolution of optically selected galaxy clusters offer an independent measurement of the amplitude of matter fluctuations, $S_8$. However, recent results have shown that clusters chosen by the redMaPPer algorithm show richness-dependent biases that affect the weak lensing signals and number densities of clusters, increasing uncertainty in the cluster mass calibration and reducing their constraining power. In this work, we evaluate an alternative cluster proxy, outskirt stellar mass, $M_{\textrm{out}}$, defined as the total stellar mass within a $[50,100]$ kpc envelope centered on a massive galaxy. This proxy exhibits scatter comparable to redMaPPer richness, $λ$, but is less likely to be subject to projection effects. We compare the Dark Energy Survey Year 3 redMaPPer cluster catalog with a $M_{\textrm{out}}$ selected cluster sample from the Hyper-Suprime Camera survey. We use weak lensing measurements to quantify and compare the scatter of $M_{\textrm{out}}$ and $λ$ with halo mass. Our results show $M_{\textrm{out}}$ has a scatter consistent with $λ$, with a similar halo mass dependence, and that both proxies contain unique information about the underlying halo mass. We find $λ$-selected samples introduce features into the measured $ΔΣ$ signal that are not well fit by a log-normal scatter only model, absent in $M_{\textrm{out}}$ selected samples. Our findings suggest that $M_{\textrm{out}}$ offers an alternative for cluster selection with more easily calibrated selection biases, at least at the generally lower richnesses probed here. Combining both proxies may yield a mass proxy with a lower scatter and more tractable selection biases, enabling the use of lower mass clusters in cosmology. Finally, we find the scatter and slope in the $λ-M_{\textrm{out}}$ scaling relation to be $0.49 \pm 0.02$ and $0.38 \pm 0.09$. △ Less

Submitted 24 May, 2025; v1 submitted 26 October, 2024; originally announced October 2024.

Comments: 22 pages, 8 figures, 4 tables, accepted for publication in Phys. Rev. D. on 22 May, 2025

Report number: FERMILAB-PUB-24-0765-PPD

On the origin of transition disk cavities: Pebble-accreting protoplanets vs Super-Jupiters

Authors: Shuo Huang, Nienke van der Marel, Simon Portegies Zwart

Abstract: Protoplanetary disks surrounding young stars are the birth places of planets. Among them, transition disks with inner dust cavities of tens of au are sometimes suggested to host massive companions. Yet, such companions are often not detected. Some transition disks exhibit a large amount of gas inside the dust cavity and relatively high stellar accretion rates, which contradicts typical models of g… ▽ More Protoplanetary disks surrounding young stars are the birth places of planets. Among them, transition disks with inner dust cavities of tens of au are sometimes suggested to host massive companions. Yet, such companions are often not detected. Some transition disks exhibit a large amount of gas inside the dust cavity and relatively high stellar accretion rates, which contradicts typical models of gas-giant-hosting systems. Therefore, we investigate whether a sequence of low-mass planets can produce cavities in the dust disk. We evolve the disks with low-mass accreting embryos in combination with 1D dust transport and 3D pebble accretion, to investigate the reduction of the pebble flux at the embryos' orbits. We vary the planet and disk properties. We find that multiple pebble-accreting planets can efficiently decrease the dust surface density, resulting in dust cavities consistent with transition disks. The number of low-mass planets necessary to sweep up all pebbles decreases with decreasing turbulent strength and is preferred when the dust Stokes number is $10^{-2}-10^{-4}$. Compared to dust rings caused by pressure bumps, those by efficient pebble accretion exhibit more extended outer edges. We also highlight the observational reflections: the transition disks with rings featuring extended outer edges tend to have a large gas content in the dust cavities and rather high stellar accretion rates. We propose that planet-hosting transition disks consist of two groups. In Group A disks, planets have evolved into gas giants, opening deep gaps in the gas disk. Pebbles concentrate in pressure maxima, forming dust rings. In Group B, multiple Neptunes (unable to open deep gas gaps) accrete incoming pebbles, causing the appearance of inner dust cavities. The morphological discrepancy of these rings may aid in distinguishing between the two groups using high-resolution ALMA observations. △ Less

Submitted 3 October, 2024; originally announced October 2024.

Comments: 12 pages, 9 figures. Accepted for publication in A&A

Journal ref: A&A 691, A155 (2024)

A Nonparametric Morphological Analysis of H$α$ Emission in Bright Dwarfs Using the Merian Survey

Authors: Abby Mintz, Jenny E. Greene, Erin Kado-Fong, Shany Danieli, Jiaxuan Li, Yifei Luo, Alexie Leauthaud, Vivienne Baldassare, Song Huang, Annika H. G. Peter, Joy Bhattacharyya, Mingyu Li, Yue Pan

Abstract: Using medium-band imaging from the newly released Merian Survey, we conduct a nonparametric morphological analysis of H$α$ emission maps and stellar continua for a sample of galaxies with $8\lesssim\log (M_\star/M_\odot) < 10.3$ at $0.064<z<0.1$. We present a novel method for estimating the stellar continuum emission through the Merian Survey's N708 medium-band filter, which we use to measure H… ▽ More Using medium-band imaging from the newly released Merian Survey, we conduct a nonparametric morphological analysis of H$α$ emission maps and stellar continua for a sample of galaxies with $8\lesssim\log (M_\star/M_\odot) < 10.3$ at $0.064<z<0.1$. We present a novel method for estimating the stellar continuum emission through the Merian Survey's N708 medium-band filter, which we use to measure H$α$ emission and produce H$α$ maps for our sample of galaxies with seven-band Merian photometry and available spectroscopy. We measure nonparametric morphological statistics for the H$α$ and stellar continuum images, explore how the morphology of the H$α$ differs from the continuum, and investigate how the parameters evolve with the galaxies' physical properties. In agreement with previous results for more massive galaxies, we find that the asymmetry of the stellar continuum increases with specific star formation rate (SSFR) and we extend the trend to lower masses, also showing that it holds for the asymmetry of the H$α$ emission. We find that the lowest-mass galaxies with the highest SSFR have H$α$ emission that is consistently heterogeneous and compact, while the less active galaxies in this mass range have H$α$ emission that appears diffuse. At higher masses, our data do not span a sufficient range in SSFR to evaluate whether similar trends apply. We conclude that high SSFRs in low-mass galaxies likely result from dynamical instabilities that compress a galaxy's molecular gas to a dense region near the center. △ Less

Submitted 2 October, 2024; originally announced October 2024.

Comments: 33 pages, 15 figures, 2 tables. Accepted to ApJ

Merian: A Wide-Field Imaging Survey of Dwarf Galaxies at z~0.06-0.10

Authors: Shany Danieli, Erin Kado-Fong, Song Huang, Yifei Luo, Ting S Li, Lee S Kelvin, Alexie Leauthaud, Jenny E. Greene, Abby Mintz, Xiaojing Lin, Jiaxuan Li, Vivienne Baldassare, Arka Banerjee, Joy Bhattacharyya, Diana Blanco, Alyson Brooks, Zheng Cai, Xinjun Chen, Akaxia Cruz, Robel Geda, Runquan Guan, Sean Johnson, Arun Kannawadi, Stacy Y. Kim, Mingyu Li , et al. (10 additional authors not shown)

Abstract: We present the Merian Survey, an optical imaging survey optimized for studying the physical properties of bright star-forming dwarf galaxies. Merian is carried out with two medium-band filters ($N708$ and $N540$, centered at $708$ and $540$ nm), custom-built for the Dark Energy Camera (DECam) on the Blanco telescope. Merian covers $\sim 750\,\mathrm{deg}^2$ of equatorial fields, overlapping with t… ▽ More We present the Merian Survey, an optical imaging survey optimized for studying the physical properties of bright star-forming dwarf galaxies. Merian is carried out with two medium-band filters ($N708$ and $N540$, centered at $708$ and $540$ nm), custom-built for the Dark Energy Camera (DECam) on the Blanco telescope. Merian covers $\sim 750\,\mathrm{deg}^2$ of equatorial fields, overlapping with the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP) wide, deep, and ultra-deep fields. When combined with the HSC-SSP imaging data ($grizy$), the new Merian DECam medium-band imaging allows for photometric redshift measurements via the detection of H$\rmα$ and [OIII] line emission flux excess in the $N708$ and $N540$ filters, respectively, at $0.06<z<0.10$. We present an overview of the survey design, observations taken to date, data reduction using the LSST Science Pipelines, including aperture-matched photometry for accurate galaxy colors, and a description of the data included in the first data release (DR1). The key science goals of Merian include: probing the dark matter halos of dwarf galaxies out to their virial radii using high signal-to-noise weak lensing profile measurements, decoupling the effects of baryonic processes from dark matter, and understanding the role of black holes in dwarf galaxy evolution. This rich dataset will also offer unique opportunities for studying extremely metal-poor galaxies via their strong [OIII] emission and H$\rmα$ lines, as well as [OIII] emitters at $z\sim 0.4$, and Ly$\rmα$ emitters at $z\sim 3.3$ and $z\sim 4.8$. Merian showcases the power of utilizing narrow and medium-band filters alongside broad-band filters for sky imaging, demonstrating their synergistic capacity to unveil astrophysical insights across diverse astrophysical phenomena. △ Less

Submitted 8 October, 2024; v1 submitted 2 October, 2024; originally announced October 2024.

Comments: 24 pages, 13 figures, 2 tables. Submitted to ApJ

Gravitational Wave Astronomy With TianQin

Authors: En-Kun Li, Shuai Liu, Alejandro Torres-Orjuela, Xian Chen, Kohei Inayoshi, Long Wang, Yi-Ming Hu, Pau Amaro-Seoane, Abbas Askar, Cosimo Bambi, Pedro R. Capelo, Hong-Yu Chen, Alvin J. K. Chua, Enrique Condés-Breña, Lixin Dai, Debtroy Das, Andrea Derdzinski, Hui-Min Fan, Michiko Fujii, Jie Gao, Mudit Garg, Hongwei Ge, Mirek Giersz, Shun-Jia Huang, Arkadiusz Hypki , et al. (28 additional authors not shown)

Abstract: The opening of the gravitational wave window has significantly enhanced our capacity to explore the universe's most extreme and dynamic sector. In the mHz frequency range, a diverse range of compact objects, from the most massive black holes at the farthest reaches of the Universe to the lightest white dwarfs in our cosmic backyard, generate a complex and dynamic symphony of gravitational wave sig… ▽ More The opening of the gravitational wave window has significantly enhanced our capacity to explore the universe's most extreme and dynamic sector. In the mHz frequency range, a diverse range of compact objects, from the most massive black holes at the farthest reaches of the Universe to the lightest white dwarfs in our cosmic backyard, generate a complex and dynamic symphony of gravitational wave signals. Once recorded by gravitational wave detectors, these unique fingerprints have the potential to decipher the birth and growth of cosmic structures over a wide range of scales, from stellar binaries and stellar clusters to galaxies and large-scale structures. The TianQin space-borne gravitational wave mission is scheduled for launch in the 2030s, with an operational lifespan of five years. It will facilitate pivotal insights into the history of our universe. This document presents a concise overview of the detectable sources of TianQin, outlining their characteristics, the challenges they present, and the expected impact of the TianQin observatory on our understanding of them. △ Less

Submitted 2 December, 2024; v1 submitted 29 September, 2024; originally announced September 2024.

Comments: TianQin Gravitational Wave Whitepaper, 72 pages, 30 figures

Interpreting Multi-band Galaxy Observations with Large Language Model-Based Agents

Authors: Zechang Sun, Yuan-Sen Ting, Yaobo Liang, Nan Duan, Song Huang, Zheng Cai

Abstract: Astronomical research traditionally relies on extensive domain knowledge to interpret observations and narrow down hypotheses. We demonstrate that this process can be emulated using large language model-based agents to accelerate research workflows. We propose mephisto, a multi-agent collaboration framework that mimics human reasoning to interpret multi-band galaxy observations. mephisto interacts… ▽ More Astronomical research traditionally relies on extensive domain knowledge to interpret observations and narrow down hypotheses. We demonstrate that this process can be emulated using large language model-based agents to accelerate research workflows. We propose mephisto, a multi-agent collaboration framework that mimics human reasoning to interpret multi-band galaxy observations. mephisto interacts with the CIGALE codebase, which includes spectral energy distribution (SED) models to explain observations. In this open-world setting, mephisto learns from its self-play experience, performs tree search, and accumulates knowledge in a dynamically updated base. As a proof of concept, we apply mephisto to the latest data from the James Webb Space Telescope. mephisto attains near-human proficiency in reasoning about galaxies' physical scenarios, even when dealing with a recently discovered population of "Little Red Dot" galaxies. This represents the first demonstration of agentic research in astronomy, advancing towards end-to-end research via LLM agents and potentially expediting astronomical discoveries. △ Less

Submitted 4 August, 2025; v1 submitted 23 September, 2024; originally announced September 2024.

Comments: Accepted at the NIPS ML4PS Workshop 2024. The journal version is in preparation. Code and data will be fully made public following the journal publication. We welcome any comments and feedback

Boundary Layers of Circumplanetary Disks around Spinning Planets II. Global Modes with Azimuthal Magnetic Fields

Authors: Zhihao Fu, Shunquan Huang, Cong Yu

Abstract: The accretion of material from disks onto weakly magnetized objects invariably involves its traversal through a material surface, known as the boundary layer (BL). Our prior studies have revealed two distinct global wave modes for circumplanetary disks (CPDs) with BLs exhibit opposite behaviors in spin modulation.We perform a detailed analysis about the effect of magnetic fields on these global mo… ▽ More The accretion of material from disks onto weakly magnetized objects invariably involves its traversal through a material surface, known as the boundary layer (BL). Our prior studies have revealed two distinct global wave modes for circumplanetary disks (CPDs) with BLs exhibit opposite behaviors in spin modulation.We perform a detailed analysis about the effect of magnetic fields on these global modes, highlighting how magnetic resonances and turning points could complicate the wave dynamics. The angular momentum flux becomes positive near the BL with increasing magnetic field strength. We also examine the perturbation profile to demonstrate the amplification of magnetic fields within the BL. The dependence of growth rates on the magnetic field strength, and the spin rate are systematically investigated. We find that stronger magnetic fields tend to result in lower terminal spin rates. We stress the potential possibility for the formation of angular momentum belts and pressure bumps. The implication for the spin evolution and quasi-period oscillations observed in compact objects are also briefly discussed. Our calculations advance the understanding of magnetohydrodynamical (MHD) accretion processes and lays a foundation for observational studies and numerical simulations. △ Less

Submitted 29 August, 2024; originally announced August 2024.

Comments: 20 pages, 13 figures, accepted for publication in the Astrophysical Journal (APJ)

The effects of the carbon-to-oxygen ratio on the condensate compositions around Solar-like stars

Authors: Cody J. Shakespeare, Min Li, Shichun Huang, Zhaohuan Zhu, Jason H. Steffen

Abstract: The initial stellar carbon-to-oxygen (C/O) ratio can have a large impact on the resulting condensed species present in the protoplanetary disk and, hence, the composition of the bodies and planets that form. The observed C/O ratios of stars can vary from 0.1-2. We use a sequential dust condensation model to examine the impact of the C/O ratio on the composition of solids around a Solar-like star.… ▽ More The initial stellar carbon-to-oxygen (C/O) ratio can have a large impact on the resulting condensed species present in the protoplanetary disk and, hence, the composition of the bodies and planets that form. The observed C/O ratios of stars can vary from 0.1-2. We use a sequential dust condensation model to examine the impact of the C/O ratio on the composition of solids around a Solar-like star. We utilize this model in a focused examination of the impact of varying the initial stellar C/O ratio to isolate the effects of the C/O ratio in the context of Solar-like stars. We describe three different system types in our findings. The Solar system falls into the silicate-dominant, low C/O ratio systems which end at a stellar C/O ratio somewhere between 0.52 and 0.6. At C/O ratios between about 0.6 and 0.9, we have intermediate systems. Intermediate systems show a decrease in silicates while carbides begin to become significant. Carbide-dominant systems begin around a C/O ratio of 0.9. Carbide-dominant systems exhibit high carbide surface densities at inner radii with comparable levels of carbides and silicates at outer radii. Our models show that changes between C/O=0.8 and C/O=1 are more significant than previous studies, that carbon can exceed 80% of the condensed mass, and that carbon condensation can be significant at radii up to 6 AU. △ Less

Submitted 14 August, 2024; originally announced August 2024.

Comments: Submitted

Generalized flow-composed symplectic methods for post-Newtonian Hamiltonian systems

Authors: Shixiang Huang, Kaiming Zeng, Xinghua Niu, Lijie Mei

Abstract: Due to the nonseparability of the post-Newtonian (PN) Hamiltonian systems of compact objects, the symplectic methods that admit the linear error growth and the near preservation of first integrals are always implicit as explicit symplectic methods have not been currently found for general nonseparable Hamiltonian systems. Since the PN Hamiltonian has a particular formulation that includes a domina… ▽ More Due to the nonseparability of the post-Newtonian (PN) Hamiltonian systems of compact objects, the symplectic methods that admit the linear error growth and the near preservation of first integrals are always implicit as explicit symplectic methods have not been currently found for general nonseparable Hamiltonian systems. Since the PN Hamiltonian has a particular formulation that includes a dominant Newtonian part and a perturbation PN part, we present the generalized flow-composed Runge--Kutta (GFCRK) method with a free parameter $λ$ to PN Hamiltonian systems. It is shown that the GFCRK method is symplectic once the underlying RK method is symplectic, and it is symmetric once the underlying RK method is symmetric under the setting $λ=1/2$. Numerical experiments with the 2PN Hamiltonian of spinning compact binaries demonstrate the higher accuracy and efficiency of the symplectic GFCRK method than the underlying symplectic RK method in the case of weak PN effect. Meanwhile, the numerical results also support higher efficiency of the symplectic GFCRK method than the semi-explicit mixed symplectic method of the same order. △ Less

Submitted 29 September, 2024; v1 submitted 12 August, 2024; originally announced August 2024.

On the suppression of giant planet formation around low-mass stars in clustered environments

Authors: Shuo Huang, Simon Portegies Zwart, Maite J. C. Wilhelm

Abstract: Context: Current exoplanet formation studies tend to overlook the birth environment of stars in clustered environments. The effect of this environment on the planet-formation process, however, is important, especially in the earliest stage. Aims: We investigate the differences in planet populations forming in star-cluster environments through pebble accretion and compare these results with the pla… ▽ More Context: Current exoplanet formation studies tend to overlook the birth environment of stars in clustered environments. The effect of this environment on the planet-formation process, however, is important, especially in the earliest stage. Aims: We investigate the differences in planet populations forming in star-cluster environments through pebble accretion and compare these results with the planet formation around isolated stars. We try to provide potential signatures on the young planetary systems to guide future observation. Methods: We design and present a new planet population synthesis code for clustered environments. The planet formation model is based on pebble accretion and includes migration in the circumstellar disk. The disk's gas and dust are evolved in 1D simulations considering the effects of photo-evaporation of the nearby stars. Results: Planetary systems in a clustered environment are different than those born in isolation; the environmental effects are important for a wide range of observable parameters and the eventual architecture of the planetary systems. Planetary systems born in a clustered environment lack cold Jupiters compared to isolated planetary systems. This effect is more pronounced for low-mass stars ($\lesssim$0.2 $M_\odot$). On the other hand, planetary systems born in clusters show an excess of cold Neptune around these low-mass stars. Conclusions: In future observations, finding an excess of cold Neptunes and a lack of cold Jupiters could be used to constrain the birth environments of these planetary systems. Exploring the dependence of cold Jupiter's intrinsic occurrence rate on stellar mass provides insights into the birth environment of their proto-embryos. △ Less

Submitted 2 August, 2024; v1 submitted 26 July, 2024; originally announced July 2024.

Comments: 13 pages 10 figures. Accepted for publication in A&A

Journal ref: A&A 689, A338 (2024)