Peer Revenue Publish or profit

Papers

Fresh from arXiv, typeset properly. Highlighted words trade on the market.

Physics Astrophysics Astrophysics of Galaxies

astro-ph.GA Watch Astrophysics of Galaxies

Thursday 24 September

Astrophysics of Galaxies · Cross-listed from astro-ph.SR

Metal-Poor Stars as Metal-Rich Impostors via Planet Engulfment

Zongheng Li, Shi Jia, Jie Su et al. (+2 more)

Planet engulfment leads to planetary mass accretion and angular momentum deposition into the stellar envelope. This study uses MESA models to investigate the long-term impact of engulfment on stellar metallicity and rotational velocity, as well as the effect of rotational mixing on metal enrichment. Our models show that engulfment occurring during the late main-sequence (MS) stage yields significantly higher surface enrichment than at the ZAMS. Rotational mixing generally suppresses enrichment; however, metal-poor stars can sustain super-solar abundances for several Gyr, whereas high-metallicity stars remain largely unaffected. Although engulfment causes an instantaneous spin-up, this angular momentum injection is transient, and the star quickly re-converges to its standard rotational evolution. Thus, MS spin-up cannot serve as a long-term observational indicator. Because convective envelope thickness and MS lifetime dictate the magnitude and duration of enrichment, identifying engulfment signatures requires balancing the long-lived but diluted signals in 0.7 M_sun stars against the strong yet short-lived enrichment in 1.2 M_sun stars. Consequently, 1.0 M_sun stars offering both substantial enrichment and a relatively long MS lifetime represent optimal targets for observational searches.
Read the full abstract

All authors Zongheng Li, Shi Jia, Jie Su, Shang-Fei Liu, Jianheng Guo

Astrophysics of Galaxies

Optical spectropolarimetry of extreme H$\alpha$ line profiles in seven active galactic nuclei

J. Biedermann, F. Marin, D. Hutsemékers et al. (+1 more)

Some active galactic nuclei (AGNs) are known to show extremely asymmetric broad Balmer lines, with their main peak redshifted or blueshifted by thousands of km s$^{-1}$, severely challenging our understanding of the standard AGN paradigm. We wanted to explore the causes of such asymmetric features by carrying out a spectropolarimetric study of a sample of bright AGNs with known extreme Balmer line profiles. We present optical spectropolarimetry of seven bright (V $<$ 17.5) Seyfert-1 galaxies obtained with the Very Large Telescope (VLT) FOcal Reducer/low dispersion Spectrograph 2 (FORS2) instrument from March 2012 to January 2013. The main broad Balmer lines (H$\alpha$ and H$\beta$, and H$\gamma$ occasionally) were sampled with a resolving power ranging from 350 to 500. We performed a detailed spectral decomposition of each H$\alpha$ profile to isolate kinematic substructures within the broad line region (BLR) and measured the polarization degree and angle of each component, providing constraints on the inner geometry and scattering properties. The broad H$\alpha$ components exhibit various scattering geometries. Their polarization as a function of full width at half maximum (FWHM) reveals two distinct behaviors, corresponding to either a BLR of roughly constant scale height or a stratified structure with decreasing height at higher velocities. This supports a disk-wind geometry linking equatorial and polar regions.
Read the full abstract

All authors J. Biedermann, F. Marin, D. Hutsemékers, C.M. Gaskell

Astrophysics of Galaxies

Binary-pulsar Timing: A 3D Solar-System Accelerometer and Unknown-Source Probe

Zheng-Long Wang, Zi-Qing Xia, Bo Zhang et al. (+1 more)

The acceleration of the Solar System barycenter (SSB) offers a unique precision probe of the local gravitational environment, enabling searches for otherwise invisible gravitating sources such as Planet Nine and nearby (primordial) black holes. Using the binary-pulsar timing measurements, we develop an analysis framework that combines the line-of-sight differential accelerations of 26 binary pulsars to jointly reconstruct the three-dimensional acceleration of the SSB and place directional upper limits. Across three smooth Galactic-potential baselines, the residual acceleration is consistent with zero. We obtain directional 95% upper limits of $0.198$, $0.262$, and $0.693~\mu\mathrm{as}\,\mathrm{yr}^{-1}$ over 50%, 75%, and all sampled directions, respectively. These limits are tighter by factors of 3.5, 3.6, and 1.6 than a matched Gaia EDR3 benchmark and improve previous pulsar constraints by more than an order of magnitude. We further extend the framework to the full SSB–pulsar two-endpoint response, enabling direct position-dependent mass constraints on unknown gravitational sources. A $10\,M_\odot$ object is excluded within 0.39, 0.34, and 0.21 pc over the same sky fractions. Our unknown-mass limits surpass the tidal-equivalent INPOP19a reference beyond 0.2 pc by about an order of magnitude over most of the sky at 1 pc.
Read the full abstract

All authors Zheng-Long Wang, Zi-Qing Xia, Bo Zhang, Yi-Zhong Fan

Astrophysics of Galaxies

Stellar Collisions from Self-consistent Stellar Dynamics Around Growing Supermassive black Holes

Fupeng Zhang and Pau Amaro Seoane

The centers of galaxies harbor the densest stellar environments, where a massive black hole (MBH) accelerates stars to such high velocities that direct collisions can result in high-energetic phenomena, such as gravitational wave sources, kilonovae, and supernova-like transients. These collisions can reshape the cluster's density profile and release gas that can be subsequently accreted by the MBH. However, the evolving rates of such phenomena from self-consistent dynamics around mass-growing MBHs remain largely unexplored. In this work, we simulate nuclear star clusters (NSCs) across a range of masses and density profiles by employing the GNC Monte Carlo code, that self-consistently models stellar dynamics and the subsequent accretion of released gas. We find that stellar collisions flatten the density cusp in the innermost regions ($r \lesssim 10^{-3}-10^{-2}$ pc) within $\sim 0.1-1$ Gyr. While high initial collision rates in steep cusps quickly decline due to stellar depletion, the interplay between collisions and MBH growth is important only in massive NSCs ($M_\star \sim 10^9 M_\odot$). As MBH grows, increased stellar velocities shift the balance toward destructive collisions of which relative velocities can be $\gtrsim 2500 {\rm \,km\,s^{-1}}$. Consequently, present-day destructive collision rates in massive clusters remain high ($10^{-4}\sim 10^{-3}{\rm yr}^{-1}$), whereas they are smaller in Milky Way-like NSCs or negligible in smaller NSCs. Our results highlight a crucial synergy between stellar dynamics and MBH growth, identifying massive galaxies as prime targets for observing transients from destructive stellar collisions.
Read the full abstract

Astrophysics of Galaxies

Mass-Dependent Dark Matter Deficit from Inelastic Scattering

Daneng Yang and Yi-Zhong Fan

Recent stellar-kinematic and neutral-hydrogen observations indicate a dark matter deficit within the central tens of kiloparsecs of nearby galaxies that grows systematically with stellar mass relative to hydrodynamical simulations. We show that this mass dependence can arise from exothermic inelastic dark matter with strongly velocity-dependent scattering. Two nearly degenerate dark matter states interact through vector and scalar mediators with opposite-sign contributions and unequal ranges. The resulting coupled-channel dynamics suppresses $s$-wave conversion at low velocity while retaining a $p$-wave enhancement at several hundred $\rm km/s$, where down-scattering injects kinetic energy and lowers central dark matter densities. At dwarf velocities, conversion remains suppressed while elastic scattering can still drive core formation consistent with the observed dwarf-clustering pattern. A late dark-sector phase transition, along with the low-velocity suppression, preserves a large excited-state fraction until halo formation. Using representative halos spanning the four observed stellar-mass bins, we find that the model accounts for the inferred dark matter deficit in all four bins, including its systematic growth with stellar mass, while its impact weakens toward cluster velocities. The growing discrepancy with hydrodynamical simulations may therefore offer a glimpse of previously hidden dark matter microphysics.
Read the full abstract

Astrophysics of Galaxies

High-z galaxies with the JWST and the ELT: Toward Ever-finer Detail

Eros Vanzella

The exploration of the early Universe is being transformed by the James Webb Space Telescope (JWST), which delivers unprecedented angular resolution at infrared wavelengths and opens a unique window redward of the K band (2um). Thanks to NIRCam, NIRISS, NIRSpec, and MIRI instruments, which provide both imaging and spectroscopy with exquisite efficiency, new classes of sources have emerged within the first years of operations. The first half-Gyr of cosmic time is now routinely probed, revealing massive blue/red galaxies and a population of Active Galactic Nuclei (AGN) appearing as "little red dots" together with a rest-frame near-infrared/optical view of sources across the reionization and post-reionization epochs. Angular resolution will remain pivotal in the 2030s - 2040s, when extreme adaptive optics (AO) facilities will be deployed on both (8 - 10)m (e.g., the VLT Multi-Conjugate-Adaptive-Optics (MCAO) - Assisted Visible Imager and Spectrograph, MAVIS) and on extremely large telescopes, like the 39m ELT (e.g., Multi-conjugate adaptive Optics Relay For ELT Observation, MORFEO). Operating at the diffraction limit, these facilities will improve JWST's resolution, with ELT achieving a factor of ~ 6 smaller Point-Spread-Function (PSF). An ELT diffraction-limited PSF (with a Full Width Half Maximum, FWHM ~ 8-12 mas) in the near infrared will resolve spatial scales <100 pc at any redshift (z ~< 18), revealing abundant star-forming clumps with sufficient sensitivity. Leveraging gravitational lensing as a cosmic telescope, even with moderate magnification factors (mu ~ 4-8), diffraction-limited 8m and 39m telescopes will probe physical scales ~< 25 pc, enabling systematic studies of star formation down to star-cluster scale at cosmological distances. Such observations are poised to become routine in the 2030s - 2040s.
Read the full abstract

Astrophysics of Galaxies · Cross-listed from astro-ph.IM

Uber-calibration-based Two-level Radial-velocity Zero-point Correction for APOGEE

Jinming Zhang, Haibo Yuan and Zhijia Tian

APOGEE delivers high-resolution, near-infrared spectroscopy and highly precise radial velocities (RVs), with extensive repeat observations spanning more than a decade. Long-term RV repeatability is nevertheless limited by instrumental zero-point systematics: exposure-to-exposure drift and fiber-dependent offsets that are only partially tracked by lamp-based wavelength calibration, and that can evolve as fibers are serviced or replaced. We infer and remove these zero points directly from the published per-visit RVs using an uber-calibration framework based on shared repeat observations. We solve sequentially for two sets of minimal calibration units: (plate, night) exposure-level offsets and time-dependent (fiber, observing year) offsets. We apply the method independently to APO and LCO DR17 and to APO DR19. After correction, the same-fiber repeatability within two days reaches a limiting precision of ~14 m/s, and the long-baseline single-visit precision improves by a factor of two from 98.2 to 44.7 m/s. We release per-visit, value-added RV catalogs for DR17 (APO+LCO) and DR19 (APO) containing 3,501,727 visits (3,336,141 fully corrected) of 930,519 unique stars, enabling more reliable RV variability, binary, and Galactic-dynamics studies.
Read the full abstract

Astrophysics of Galaxies · Cross-listed from astro-ph.HE

Recurrent double-peaked $\gamma$-ray sub-flares in PKS 1424-418

Na Wang, Tong Liu and Jingran Xu

We report a hint of recurrent double-peaked $\gamma$-ray sub-flares in PKS~1424–418 during two similar major active epochs, MJD 56117–56498 and MJD 59669–59978. The candidate double-peaked sub-flares show a characteristic intra-subflare peak separation of $\sim 11.8$ d and a neighbouring-subflare spacing of $\sim 67$ d. Red-noise Monte Carlo tests indicate that the candidate recurrent double-peaked morphology is not easily reproduced by stochastic variability alone, with false-alarm probabilities of $p_{\rm a}=0.0216$ and $p_{\rm b}=0.0006$ for the two active epochs, respectively. In the simulations of the entire Fermi Large Area Telescope (LAT) light curve, no red-noise realisation reproduces both epoch-like structures. The spectral energy distribution (SED) modelling shows similar radiative properties for the two peaks of one double-peaked candidate, while changes in the Doppler factor appear to play an important role in the flaring activity. Together with the previously reported near-zero lag between the millimetre and $\gamma$-ray emission, these results suggest that the recurrent activity may be associated with the compact mm/sub-mm core region. We discuss a possible structured-jet scenario in which a single disturbance propagates through a chain of quasi-stationary recollimation shocks. In this picture, repeated interactions between the disturbance and the shock structure may qualitatively account for both the double-peaked sub-flare profiles and the observed $\sim 11.8$ d and $\sim 67$ d time-scales. Further active epochs are required to determine whether this similarity represents a recurrent long-term behaviour.
Read the full abstract

Wednesday 23 September

Astrophysics of Galaxies · Cross-listed from astro-ph.HE

Dissecting the variability of Sagittarius A* in the orbiting hotspot framework

Maciek Wielgus and Aristomenis Yfantis

Sagittarius A* (Sgr A*) exhibits intermittent flaring behavior, characterized by strong enhancements in high-energy emission (infrared and X-ray). These events have been interpreted as related to the coherent orbital motion of localized regions of energized plasma - hotspots. While this framework has been quite fruitful in constraining properties of Sgr A*, it is subject to important challenges and limitations. In this brief review we discuss the recent observational and theoretical developments related to this line of research, commenting on the concerns regarding the hotspot model validity and the future perspectives.
Read the full abstract

Astrophysics of Galaxies

Cluster Membership Probabilities: A Review of Methods and Gaia Applications

Tahereh Ramezani, Johana Balciráková, Prapti Mondal et al. (+3 more)

Reliable stellar-cluster membership is essential for deriving cluster ages, distances, reddenings, metallicities, mass functions, dynamical parameters, and Galactic-structure tracers. The Gaia era has produced a proliferation of membership and cluster-detection methods, but the resulting catalogues are not interchangeable. We review the historical development of membership assignment, compare the statistical assumptions of major methods, and explicitly examine the practical consequences of methodological choices on real Gaia data. We consider spatial, proper-motion, maximum-likelihood, photometric, UPMASK, density-based, machine-learning, Bayesian, and bootstrap membership approaches. We add three case studies: a direct comparison of \citet{CantatGaudinAnders2020}, \citet{HuntReffert2023}, and \citet{Perren2023} for common clusters; a Pleiades astrometric comparison; and a critical examination of low-trust candidates in the Unified Cluster Catalogue (UCC), including CWNU, CWWDL, and CKCWDM objects. The literature shows that disagreement is not simply a consequence of Gaia measurement errors. Different definitions of a cluster, different magnitude limits, different treatment of uncertainties, different spatial priors, and different tolerances for extended or low-density populations can lead to substantially different member lists. \citet{Perren2023} reported an average member-list overlap of roughly 75–80% with \citet{CantatGaudinAnders2020} and 70–75% with \citet{HuntReffert2023} at bright magnitudes, with the HUNT23 overlap decreasing to about 35% at $G=20$. The UCC also flags many newly reported candidates as low-trust objects when their member distribution is sparse, their literature support is weak, or they have strong duplicate/non-cluster indicators.
Read the full abstract

All authors Tahereh Ramezani, Johana Balciráková, Prapti Mondal, Katerina Neumannova, Ernst Paunzen, Gabriel Szász

Astrophysics of Galaxies · Cross-listed from astro-ph.SR

Metal-poor Brown Dwarf Kinematics from JWST NIRSpec Spectroscopy

Chih-Chun Hsu, Christopher A. Theissen, Adam J. Burgasser et al. (+14 more)

Galactic archaeology relies on stellar kinematics and chemical abundances to identify various stellar populations and associations. With JWST, Galactic archaeology of ancient metal-poor brown dwarfs is now possible through high-sensitivity, medium-resolution spectroscopy. We present the first metal-poor brown dwarf radial velocity (RV) survey using JWST/NIRSpec G395H spectra ($\lambda/\Delta\lambda \sim$ 3,000) for a sample of 23 LTY dwarfs across a wide range of temperatures and metallicities. We introduce a forward-modeling framework to measure robust RVs for brown dwarfs by focusing on the CO fundamental band at $\sim$4.5 $\mu$m. By comparing to sources with existing high-resolution RV measurements, we demonstrate that G395H RVs can achieve a systematic uncertainty of 5 km s$^{-1}$, sufficient to examine their Galactic space motions. We identify kinematic members of the Milky Way's thin disk, thick disk, and halo populations in this sample. We also confirm WISE J155349.98$+$693355.2 as likely associated with the Gaia-Enceladus merger remnant, and 2MASS J05325346$+$8246465 is likely associated with the Thamnos stream. Our study systematically demonstrates that JWST G395H spectroscopy can provide robust RVs in addition to detailed chemical abundances, necessary for Galactic archaeology studies. Future discoveries and characterization of brown dwarfs associated with Galactic halo substructures and streams will enable a stringent test of stellar/substellar formation and evolutionary models for diverse metallicities.
Read the full abstract

All authors Chih-Chun Hsu, Christopher A. Theissen, Adam J. Burgasser, Adam C. Schneider, Christian Aganze, Aaron M. Meisner, Jonathan Gagné, Nicolas Lodieu, Zenghua Zhang, Genaro Suárez, Eileen C. Gonzales, Jacqueline K. Faherty, Jason J. Wang, Stanimir Metchev, Dan Caselden, Michael C. Cushing, Roman Gerasimov

Astrophysics of Galaxies · Cross-listed from astro-ph.EP

Triggering star formation by free-floating planets

Yu. N. Eroshenko

Recently, a population of free-floating planets has been discovered in the Galaxy. This paper examines the influence of the planets trapped within a protostellar hydrogen clouds on the processes of gravitational instability in the gas. A sufficiently massive planet can become an alternative dynamic center for the contracting cloud. This occurs due to rapid mass growth from accretion onto the planet within the cloud. Owing to residual velocity and density gradients in the cloud, the planet that triggers star formation is likely to end up in a distant orbit around the newborn star. Some second- and subsequent-generation stars in the Galaxy may have formed via this mechanism.
Read the full abstract

Astrophysics of Galaxies

Mapping the Milky Way in Six Dimensions: A contiguous, homogenised, phase-space catalogue of Gaia DR3 tracers up to 250 kpc

Sutirtha Mukherjee, Amogh Srivastav and Subhabrata Majumdar

We present a comprehensive, homogenised catalogue of $32{,}552{,}876$ stellar sources with full 6D phase-space information, spanning Galactocentric distances from the inner galaxy ($\gtrsim 5$\,kpc) to the outer halo ($\sim\!250$\,kpc). By cross-matching Gaia DR3 astrometry with spectrophotometric distances and line-of-sight velocities from 14 surveys (including desi, sdss-boss, apogee, lamost, galah, and ges), we achieve median fractional distance uncertainties of $\approx2.7\%$ for $d_{\rm helio}\le15$\,kpc, and $\approx29\%$ for $15<d_{\rm helio}\le250$\,kpc. The catalogue-wide median fractional radial velocity uncertainty is $\approx8.31\%$. Gaia-anchored zero-point corrections and statistical normalisation suppress both random and systematic errors. Furthermore, we derive spectrophotometric parallaxes from joint photometric and spectroscopic data. Overlapping survey data is aggregated to replace unreliable values and supplement absent velocities, improving completeness and internal consistency. This multi-survey synthesis is externally validated against globular clusters, dwarf galaxies, and stellar streams, yielding precise kinematics. Notably, the sample features $517{,}123$ halo stars extending well beyond the Gaia parallax limit ($\gtrsim\!10$\,kpc). These predominantly faint ($G > 17$) and metal-poor ($[\mathrm{Fe/H}] < -1$) tracers, including RR~Lyrae, blue horizontal-branch, and K~giant stars, constitute the largest well-calibrated sample of outer-halo tracers to date. This unique dataset is ideal for multi-component mass modelling, galactic archaeology, and dark matter searches across the Milky Way.
Read the full abstract

Astrophysics of Galaxies

The quest for high-redshift radio galaxies II. Discovery of the most powerful known radio galaxy at z=4.946

B.Balmaverde, A.Capetti, M.Chiaberge et al. (+3 more)

As part of our quest for high-redshift radio galaxies (HzRGs), we present the results obtained from optical spectroscopy leading to the confirmation of one HzRG candidate selected using the Lyman break technique. The optical emission, associated with the radio source TXS 2354+015, exhibits a prominent drop in the r band, which is characteristic of sources at z~5. The optical spectrum shows a bright asymmetric emission line, with a large equivalent width of ~900 Angstrom. Its identification with the Ly$\alpha$ line is confirmed by the detection of the NV$\lambda$1640, leading to a redshift estimate of z=4.946. Its broadband radio spectrum is well reproduced using a power law with a slope of 0.94. The radio luminosity at the rest frame frequency of 500 MHz is 6.2e29 W/Hz. This result makes this source the most powerful radio galaxy currently known.
Read the full abstract

All authors B.Balmaverde, A.Capetti, M.Chiaberge, F.Massaro, M. Coloma Puga, A. Jimenez-Gallardo

Astrophysics of Galaxies · Cross-listed from astro-ph.HE

Probing the Metallicity Dependence of Fast Radio Burst Progenitors with CHIME/FRB Outrigger Dwarf Host Galaxies

Y. Dong, W. Fong, K. Nimmo et al. (+24 more)

Using the fast radio bursts (FRBs) localized with the CHIME/FRB Outriggers between February and October 2025, we conduct a systematic search for dwarf host galaxies. We identify and characterize eight host galaxies for one repeating and seven apparently non-repeating FRBs, newly classifying five hosts as dwarfs with stellar masses of $\log(M_\ast/M_\odot) \approx 8.1-9.1$. We measure their gas-phase metallicities and, when combined with hosts from the literature, finding that repeating and non-repeating FRBs have statistically distinct metallicity distributions. Non-repeating FRBs inhabit relatively metal-rich environments ($12 + \rm log( O/H) \gtrsim 8.35$) across the full observed mass range, while repeating FRBs have significant preference for dwarf galaxies with $12 + \rm log( O/H) \lesssim 8.35$. Almost all repeaters associated with persistent radio sources (PRSs) are in dwarfs with $12 + \rm log( O/H) \lesssim 8.15$, suggesting a connection between repeaters in metal-poor dwarf environments and PRS formation. We also calculate the host dispersion measure ($\mathrm{DM}_{\rm host}$), Faraday rotation measure ($\mathrm{RM}_{\rm host}$), and scattering timescale ($\tau_{\rm host,1~GHz}$) for 54, 37, and 24 FRBs, respectively, including both our sample and FRBs in the literature. We find no significant ($>3\sigma$) correlation between host metallicity and $\mathrm{DM}_{\rm host}$, $\mathrm{RM}_{\rm host}$, or $\tau_{\rm host,1~GHz}$. The distinct host metallicities of apparently non-repeating and repeating FRBs may reflect metallicity-dependent massive-star evolution, with repeating FRBs and PRSs requiring more extreme magnetar birth spins than the predominantly non-repeating FRB population.
Read the full abstract

All authors Y. Dong, W. Fong, K. Nimmo, N. Loudas, B.C. Andersen, S. Andrew, A. Cai, S. Chatterjee, A.M. Cook, A.P. Curtin, T. Eftekhari, B.M. Gaensler, J. Hessels, V.M. Kaspi, A. Khan, C. Leung, L. Mas-Ribas, K. Masui, A. Moroianu, A.B. Pearlman, J.X. Prochaska, M.W. Sammons, P. Scholz, K. Shin, S. Simha, M. Woodland, Z. Zhuang

Astrophysics of Galaxies · Cross-listed from astro-ph.IM

AstroGenesis: A Domain-Specific Multi-Agent AI for Astrophysical Research

N. Sahakyan, M. Khachatryan, A. Mahabal et al. (+13 more)

Modern astrophysical research requires the integration of rapidly expanding scientific literature, heterogeneous observational data, and increasingly complex physical models. We introduce AstroGenesis (https://astrogenai.com), a domain-specific multi-agent AI framework that integrates literature retrieval, multiwavelength data access and analysis, theoretical modeling, and research ideation within a unified research environment.The current implementation focuses on blazar research, with specialized agents coordinated by a Supervisor Agent and Planner/Replanner architecture. These agents provide capabilities for retrieving and synthesizing literature, accessing and analyzing multiwavelength observations, performing physical modeling, and identifying research directions. A central component is the Theoretical Modeling Agent, which uses pretrained neural-network surrogate models to enable efficient broadband and multimessenger modeling through natural-language interaction. The framework provides natural-language access to science-ready multiwavelength observational data and retrieval-grounded literature through a multi-stage retrieval and ranking pipeline. The literature-retrieval system was evaluated using two benchmarks: a single-paper benchmark, in which each question targets one publication, and a multi-paper benchmark, in which questions may require evidence from several publications. At least one relevant publication was retrieved among the top five results for 76.6% of the single-paper questions and 79.2% of the multi-paper questions. Representative workflows demonstrate how literature, observational data, physical modeling, and hypothesis generation can be combined within traceable analyses. The framework is extensible to additional astrophysical domains, with the goal of streamlining research workflows and enabling efficient, connected, and reproducible scientific investigations.
Read the full abstract

All authors N. Sahakyan, M. Khachatryan, A. Mahabal, D. Pasham, A. Khachatryan, V. Markosyan, N. Unkovskii, V. Vardanyan, D. Bégué, P. Giommi, G. Harutyunyan, D. Israyelyan, A. Tramacere, A. Casotto, Y. Wang, D. Li

Astrophysics of Galaxies

A sub-100 pc view at z~5 of a Multiply-Imaged Massive Quiescent Galaxy

Richard Pan, Danilo Marchesini, Joseph F. V. Allingham et al. (+34 more)

Recent James Webb Space Telescope spectroscopic surveys reveal an abundance of rapidly assembled early galaxies in the first billion years. Cosmological simulations struggle to reproduce this population because models require a rapid, highly efficient conversion of baryons into stars followed by an abrupt cessation of star-formation, known as quenching, in the early Universe. Testing these theoretical models remains difficult because high-redshift field galaxies appear compact and unresolved. This lack of resolution makes it impossible to distinguish compaction-driven quenching from secular evolution. Here we present VENUS-CLJ0152-QG1, a massive post-starburst galaxy at $z=5.18\pm0.15$, with inferred low-levels of star-formation in the last 30 Myr. The foreground cluster CL J0152.7-1357 gravitationally lenses the system into three images with median magnifications of $\mu \sim$ 7, 11, and 0.6. This geometry yields a physical resolution of $\sim 70$ pc, a factor of $\sim 7$ better than the JWST/NIRCam fundamental blurring limit (full-width half-maximum of $\sim$0.48 kpc at $z\sim5$). Our two-dimensional mapping reveals a half-light radius twice as large as expected, a central stellar mass surface density half a dex lower than field analogs, and off-center ionized gas emission. Together, these features show that VENUS-CLJ0152-QG1 abruptly ceased star formation in the absence of a compaction event or an obvious active galactic nucleus. Consequently, this galaxy shows that unresolved observations likely overestimate the global densities of early galaxies, and that theoretical models require alternative pathways to quench massive sources without relying on compaction or unobscured AGN.
Read the full abstract

All authors Richard Pan, Danilo Marchesini, Joseph F. V. Allingham, Seiji Fujimoto, Adi Zitrin, Dan Coe, Vasily Kokorev, Lukas J. Furtak, Jacqueline Antwi-Danso, Yoshihisa Asada, Franz E. Bauer, Maruša Bradač, Larry D. Bradley, Chloe M. Cheng, Pratika Dayal, Andreas L. Faisst, Brenda L. Frye, Norman A. Grogin, Tiger Yu-Yang Hsiao, Gourav Khullar, Anton M. Koekemoer, Conor Larison, Ray A. Lucas, Vladan Markov, Nicholas S. Martis, Minami Nakane, Gaël Noirot, Johan Richard, Massimo Ricotti, Luke Robbins, Fengwu Sun, Francesco Valentino, Eros Vanzella, Chris Willott, Rogier A. Windhorst, Hiroto Yanagisawa, Anita Zanella

Astrophysics of Galaxies · Cross-listed from astro-ph.IM

Differentiable astrophysics at scale: solving and differentiating ODE ensembles on the GPU

A. Spurio Mancini

Astronomers increasingly fit their models with gradient-based methods, such as Hamiltonian Monte Carlo, which need the derivatives of the model with respect to its parameters. In many analyses a prediction requires solving a small system of ordinary differential equations (ODEs) for thousands to millions of parameter sets, and this ensemble of integrations often sets the cost of the analysis. We introduce to the astronomical community GRADSOLVE, a JAX library that moves this computation to graphics processing units (GPUs): it integrates each member of the ensemble in its own GPU thread with its own step size and returns the derivatives with respect to the parameters in the same pass. We measure the speed-up it provides in three examples from different fields of astronomy, stellar orbits in the Galactic potential, the expansion history of a dark-energy cosmology and the spin precession of binary black holes, with every code held to the same accuracy requirement. For a million trajectories GRADSOLVE runs 8.5 to 1500 times faster than the serial CPU code of each example running on all 128 cores of a CPU, and several orders of magnitude faster than on one core. On the same GPU it is also 11 to 15 times faster than DIFFRAX, the state-of-the-art ODE library in JAX, in all three examples. With GRADSOLVE a million such integrations take seconds or less on one GPU, so gradient-based analyses that need ensembles of this size become routine. The code is publicly available at https://github.com/ECLIPSE-AI4Science/gradsolve.
Read the full abstract

Astrophysics of Galaxies · Cross-listed from astro-ph.SR

A Search For Stellar-mass Black Holes Via Astrometric Microlensing II: 2012-2015 Keck Candidates

Mace J. Huston, Jessica R. Lu, Casey Y. Lam et al. (+55 more)

The Milky Way is expected to host $\sim$10$^8$ stellar-mass black holes with an uncertain binary fraction. The only proven method to detect isolated stellar mass black holes is gravitational microlensing. Here we report the results of a microlensing search for black holes with photometry and astrometry. By combining 10 years of seeing-limited photometry from OGLE and MOA with diffraction-limited photometry and astrometry from adaptive optics imagers at the W.~M.~Keck Observatory, we constrain lens masses for OGLE-2012-BLG-0169, OGLE-2014-BLG-0613/MOA-2015-BLG-041, OGLE-2015-BLG-0029/MOA-2015-BLG-170, and OGLE-2015-BLG-0211. Of the four long-duration microlensing events monitored, we ruled out black hole lenses in 3 events, which likely have stellar or white dwarf lenses. OGLE-2015-BLG-0211 remains a black hole candidate with a poorly constrained lens mass with a 1$\sigma$ upper mass limit of 3.2$M_\odot$ and a 3$\sigma$ upper mass limit of 21.6$M_\odot$. This event suffered from poor observing conditions and significant astrometric reference frame uncertainties, but its analysis may benefit from additional astrometric data in the upcoming Gaia Data Release 4. Of the six long-timescale ($t_E>100$ days) microlensing events from this work and previous studies, one black hole has been confirmed with a second not ruled out. We briefly examine Galactic model simulations and find that our result agrees with current expectations. Ultimately, we need a larger sample of isolated black holes to constrain their formation processes. This will be possible in the coming years with Rubin and Roman, as well as improved astrometry from JWST and large, ground-based telescopes equipped with adaptive optics.
Read the full abstract

All authors Mace J. Huston, Jessica R. Lu, Casey Y. Lam, J. Nijaid Arredondo, Natasha S. Abrams, Shep Brooke, Sage H. Remulla, Eran Ofek, Michael S. Medford, Fatima Abdurrahman, Shrihan Agarwal, Edward Broadberry, Matthew Freeman, Matthew W. Hosek Jr., Siyao Jia, Sean K. Terry, The OGLE Collaboration: Andrzej Udalski, Przemek Mroz, Radoslaw Poleski, Jan Skowron, Michal K. Szymanski, Igor Soszynski, Pawel Pietrukowicz, Szymon Kozlowski, Krzysztof Ulaczyk, Krzysztof A. Rybicki, Patryk Iwanek, Marcin Wrona, Mariusz Gromadzki, Mateusz J. Mroz, Michal Malkowski, The MOA Collaboration: Fumio Abe, David P. Bennett, Aparna Bhattacharya, Ian A. Bond, Kotaro Daimon, Ryusei Hamada, Yuki Hirao, Shuma Makida, Stela Ishitani Silva, Shota Miyazaki, Yasushi Muraki, Tutumi Nagai, Kansuke Nunota, Ryo Ogawa, Ryunosuke Oishi, Hideaki Ose, Greg Olmschenk, Clement Ranc, Nicholas J. Rattenbury, Yuki K. Satoh, Takahiro Sumi, Daisuke Suzuki, Takuto Tamaoki, Chihiro Ueda, Paul J. Tristram, Aikaterini Vandorou, Hibiki Yama

Astrophysics of Galaxies

Interstellar extinction of classical Cepheids from neighboring stars I. Methodology and application to 16 Galactic Cepheids

Wilma Kiviaho, Pierre Kervella, Mika Juvela et al. (+21 more)

Galactic Cepheid variable stars are fundamental calibrators of the cosmic distance scale through their Period-Luminosity (PL) relation. The high-precision parallaxes expected from Gaia Data Release 4 (DR4) will enable a calibration of the Milky Way PL relation with unprecedented precision. This will place stringent requirements on interstellar extinction corrections, which remain a dominant source of uncertainty. We strive to derive highly accurate extinction values for Galactic Cepheids. We present an innovative methodology relying on the analysis of neighboring field stars and apply it to a pilot sample of 16 Cepheids. We identify physically near field stars using Gaia DR3 astrometry. For these stars, we determine atmospheric parameters from medium- to high-resolution VLT/FLAMES spectroscopy. Fixing these parameters, we derive individual extinctions by fitting spectral energy distributions constructed from Gaia XP spectra and infrared photometry. We then reconstruct the three-dimensional distribution of extinction and interpolate extinction to the Cepheid position. We report extinction Av, total-to-selective extinction ratio Rv, and color excess E(B-V) for all 16 Cepheids. Our method achieves a mean precision of approximately 5%, improving upon typical literature values, with no significant systematic offset detected. We demonstrate that using field stars bypasses uncertainties associated with Cepheid variability and can provide robust extinction estimates for Galactic Cepheids.
Read the full abstract

All authors Wilma Kiviaho, Pierre Kervella, Mika Juvela, Alexandre Gallenne, Nicolas Nardetto, Carine Babusiaux, Rosine Lallement, Vincent Hocdé, Garance Bras, Nancy Remage Evans, Antoine Mérand, Grzegorz Pietrzyński, Gergely Hajdu, Henryka Netzel, Ricardo Salinas, Bogumił Pilecki, Cezary Gałan, Frédéric Arenou, Manon Bailleul, Katia Sivkova, Daniela González, Louise Breuval, Rajeev Singh Rathour, Brankica Apostolova

Astrophysics of Galaxies · Cross-listed from astro-ph.CO

The Lumina Project: Morphology of Ionized Bubbles and Neutral Islands

Meredith Neyer, Aaron Smith, Ali Sadain et al. (+10 more)

The Epoch of Reionization is characterized by the nucleation, expansion, and percolation of ionized bubbles in the intergalactic medium. Interpreting emerging multi-wavelength observations from facilities such as JWST and next-generation 21 cm interferometers requires a detailed theoretical understanding of the 3D morphology of these HII regions and of the residual neutral structures that survive near the end of reionization. We analyze the geometry and physical properties of ionized bubbles and late-time neutral islands in the large-volume 500 Mpc$^3$ radiation-hydrodynamics simulation Lumina. We identify discrete structures with a 3D watershed method and measure their volumes, shape tensors, and internal gas properties. The volume-weighted bubble size distributions evolve substantially across the EoR: characteristic radii shift from Reff~1 cMpc at z>10 to Reff>100 cMpc by z< 6, while watershed-derived sizes exceed line-of-sight mean-free-path measurements by roughly a factor of 3 at intermediate redshifts. The bulk bubble population is predominantly prolate through most of the EoR. By z~6, however, the volume-weighted distribution of the triaxiality parameter T, which distinguishes flattened from elongated structures, becomes bimodal in the fiducial segmentation, with a sharp oblate peak near T~0.25 associated with a small number of very large bubbles during late percolation. The properties of bubble interiors are consistent with inside-out reionization, with median gas overdensities within bubbles decreasing from $\delta$~1 at z=15 toward the cosmic mean by z=6. Beyond a minimum near the resolution scale, the median internal UV radiation energy density increases with bubble size. The residual neutral islands at z< 6 peak in volume-weighted size near Reff~10 cMpc and remain predominantly prolate, consistent with anisotropic residual neutral structure near the end of reionization.
Read the full abstract

All authors Meredith Neyer, Aaron Smith, Ali Sadain, Oliver Zier, Mark Vogelsberger, Teodora-Elena Bulichi, Xuejian Shen, Sonja M. Koehler, Volker Springel, Rahul Kannan, Rongrong Liu, Lars Hernquist, Changhyun Cho

Astrophysics of Galaxies

Investigating the ionization mechanisms powering the extreme emission lines in metal-poor galaxies

C. Daoutis, V. Lebouteiller, D. Schaerer et al. (+11 more)

Extreme emission metal-poor galaxies (EEMPGs) are excellent local laboratories for understanding the extreme physical conditions and ionizing radiation fields in the early Universe. However, the exact source of high-ionization emission lines in them, whether from intermediate-mass black holes (IMBHs), ultra-luminous X-ray sources (ULXs), or radiative shocks, remains debated. We characterize the fundamental properties and ionizing radiation field on metal-poor EEMPGs, aiming to identify the dominant sources of the highly ionizing photons that drive these lines. We selected a sample of 11 EEMPGs, among the most metal-poor galaxies with JWST/MIRI observations known so far (12+log(O/H) < 8.0, or Z/Z$_\odot$ < 20%). Using optical and IR diagnostic diagrams for ions of both high and low ionization potential, we constrain the ionization source dominating their spectral features. We detect high-ionization lines, notably He II$\lambda$4686 in all galaxies and [Ne V] 14.3 $\mu$m in 42% of a broader sample of local EEMPGs. The multi-wavelength diagnostic diagrams reveal that our EEMPGs are located in areas that normally are occupied by active galactic nuclei (AGNs) or between the star-formation and AGN sequences. Evaluating the energetics required to produce these lines, we find that radiative shocks and ULXs are not sufficient. Instead, our analysis suggests that a combination of sources with star-formation and a small contribution from an IMBH provide enough high-energy photon budget to explain the emission lines of ions with high-ionization potentials (> 54 eV). Our EEMPG sample, covering various properties, is ideal for studying the first galaxies. Their flux ratios of low- and high-ionization lines suggest stellar radiation as the likely ionization source, with a small contribution from an IMBH (4-8%). Pure shocks fail to explain the observed emission line ratios and ionizing photon budget.
Read the full abstract

All authors C. Daoutis, V. Lebouteiller, D. Schaerer, I. Morel, O. Bait, S. Satyapal, S. Doan, B. Trahin, A. Gurpide, Y. Izotov, N. Guseva, L. Ramambason, A. Verhamme, SpeXion Team

Astrophysics of Galaxies · Cross-listed from astro-ph.CO

JWST evidence for a sharp "Cosmic Daybreak" at z = 15

Jiashuo Zhang, Tom Broadhurst, Tzihong Chiueh et al. (+9 more)

Luminous young galaxies have been uncovered with relative ease by JWST, extending to z=14.5, so it is puzzling that deeper spectroscopy of fainter candidates now finds only interlopers. This redshift `ìmpasse" is underscored by the measured stellar ages of these high-z galaxies, which we show converge to zero by z=15, with a marked absence of earlier star-formation. Taken literally, such a late transition from the Dark Ages to luminous galaxies is unlike the gradual Cosmic Dawn of standard LCDM, but does confirm a key prediction of Wave Dark Matter, $\psi$DM, as a Bose-Einstein condensate. The de Broglie wave pressure resists gravity until a substantial Jeans mass of $4\times 10^9M_\odot$ is overcome at z$=$15, corresponding to a light boson $m_\psi=2.2_{-0.3}^{+0.4} \times 10^{-22}$eV, and similar to independent estimates from lensing anomalies and dwarf galaxies. Furthermore, the substantial luminosities of the highest redshift galaxies appear to converge to the initial Jeans scale of $\psi$DM, whereas LCDM predictions extend to lower luminosities and larger ages than observed. These contrasting predictions can be definitively tested as JWST observations accumulate, with diametric implications for Dark Matter as heavy particles beyond the Standard Model or ultra-light bosons motivated by the String Axiverse.
Read the full abstract

All authors Jiashuo Zhang, Tom Broadhurst, Tzihong Chiueh, Hsi-Yu Schive, Keiichi Umetsu, Jose M. Diego, Paloma Morilla, Alvaro Pozo, Chian-Chou Chen, Jeremy Lim, Pablo G. Perez-Gonzalez, Rogier Windhorst

Astrophysics of Galaxies

Detection of metal absorption lines in quasar spectra: a neural network approach using U-Net

Elena Sofia Mangola, Francesco Pistis, Michele Fumagalli et al. (+7 more)

Current and future large spectroscopic surveys are significantly enhancing the volume and resolution of quasar spectra that are observed, which requires the creation of efficient and precise automated techniques to detect absorption features. This study focuses on the detection of metal absorption features using a novel U-Net model on WEAVE-like mock spectra in the quasar rest-frame wavelength interval $1230\,\mathring{\mathrm{A}} \leq \lambda_{\rm RF} \leq 3095\,\mathring{\mathrm{A}}$. We test the network performance for absorption detection both on ideal data and after simulating the continuum fitting step as applied on real data. The performance of these architectures is evaluated by the completeness, purity, and F1 score reached in bins of signal-to-noise ($\mathrm{S}/ \mathrm{N}_\mathrm{line} $) for the absorption lines and with the absolute fractional flux error for the continuum. The ability to recover the correct line centers is also studied. The U-Net reaches scores of $\approx 90\%$ for all metrics (completeness, purity, and F1 score) at $\mathrm{S}/ \mathrm{N}_\mathrm{line} \approx 4$. All false positive detections with $\mathrm{S}/ \mathrm{N}_\mathrm{line} \geq 5$ fall in the tails of the broad Ly$\alpha$ absorbers distribution of damped Ly$\alpha$ systems. The combination of continuum fitting and line detections has negligible effects on the detection performance at $\mathrm{S}/ \mathrm{N}_\mathrm{line} \geq 4$. Our proposed U-Net architecture offers a competitive tool for the analysis of absorption lines in current and upcoming large spectroscopic surveys and is well-suited to the identification of any absorption line feature.
Read the full abstract

All authors Elena Sofia Mangola, Francesco Pistis, Michele Fumagalli, Matteo Fossati, Ting-Yun Cheng, Ryan J. Cooke, Rajeshwari Dutta, Ignasi Pérez-Ràfols, Matthew Pieri, Emanuel Gafton

Astrophysics of Galaxies

The Neutral Hydrogen Gas Content of Star-forming and Quiescent S0 Galaxies

D. A. A. Lee, Karen L. Masters, David V. Stark et al. (+1 more)

Lenticular (or S0) galaxies that remain actively star-forming (SFS0s) are a unique transition population among galaxies. We investigated the HI (21cm) neutral hydrogen content of a sample of lenticular galaxies identified from within the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey and which have been classified as star-forming or quiescent (qS0s). We compared these populations to each other and to a sample of star-forming spiral galaxies in MaNGA. We found that the HI Mass fraction and HI Deficiency of the SFS0s were intermediate between the quiescent S0s and the star-forming spirals, but most similar to the spirals. The HI depletion times of the quiescent S0's is very much longer than that of the SFS0 and spirals, which have roughly similar times. We also compared the molecular gas fractions of the three groups which shows that the lowest fraction of the three populations, followed by the star-forming S0s and then the star-forming spirals. A comparison of total baryonic mass comparisons indicates that the star-forming S0s have significantly lower masses than the qS0s in the sample. This suggests that the star-forming S0s must form from lower-mass progenitors (unobserved by MaNGA) which either accrete external gas, or loose spiral arms. The more massive quiescent S0s are a completely separate population, most likely to be formed either from fading star-forming spirals or from medium- to high-mass spirals undergoing mergers. The SFS0s in this sample cannot form from the quiescent S0s in this sample that receive in-falling gas, nor can they fade to create these qS0s.
Read the full abstract

All authors D. A. A. Lee, Karen L. Masters, David V. Stark, Z. Z. Abidin

Astrophysics of Galaxies · Cross-listed from astro-ph.HE

Multi-Band Optical Variability Characteristics of the $\gamma$-ray emitting blazar 1ES 0647+250 during its 2020 flare

K.Subbu Ulaganatha Pandian, C. S. Stalin, S. Muneer et al. (+4 more)

We present a multi-band optical variability study of the $\gamma$-ray emitting high-synchrotron-peaked blazar 1ES~0647+250 during its enhanced optical activity in 2020. The analysis utilizes 107 epochs of high-precision $B$, $V$, and $R$-band photometry obtained with the 75 cm telescope at the Vainu Bappu Observatory, combined with high-cadence $z_g$ and $z_r$ survey data from the Zwicky Transient Facility. The combined light curves reveal coherent variability across all optical filters, with the source reaching a peak $R$-band magnitude of 15.74 mag. We calculated the variability amplitude, finding the highest intrinsic variability in the B- band. Spectral analysis using color–magnitude diagrams reveals a statistically significant “Bluer-When-Brighter” trend, supported by a Pearson correlation coefficient of $r = 0.68$ ($p < 0.001$) for the (V$-$R) index. Furthermore, the discrete correlation function analysis indicates a near-zero time lag between the $V$ and $R$ bands, suggesting simultaneous emission within the observational cadence. The observed spectral hardening is consistent with synchrotron-dominated optical emission, likely associated with enhanced particle acceleration within the jet during the active phase of 1ES~0647+250.
Read the full abstract

All authors K.Subbu Ulaganatha Pandian, C. S. Stalin, S. Muneer, S. Umayal, Aditi Agarwal, Amit Kumar Mandal, B. Natarajan

Astrophysics of Galaxies · Cross-listed from astro-ph.HE

On the rates of binary star collisions around hypermassive black holes

Megha Sharma, Alexander Heger, Evgeni Grishin et al. (+1 more)

Observations of the Milky Way show that galaxies have binary stars in their centres. Using Monte Carlo simulations, we model the population statistics of encounters of such binaries with galactic central black holes (BHs) of mass 10^5-10^{10} Msun (hypermassive BHs >= 10^8 Msun HMBHs). Whereas main-sequence single stars cannot undergo tidal disruption events around HMBHs, stellar collisions of main-sequence binary stars may produce observable transients. We use the post-Newtonian Einstein-Infeld-Hoffmann (EIH) equations as implemented in the three-body code Multistar. We simulate 100,000 models each for six BH masses and 10 different binary parameter distributions. We find that stellar collisions occur in all models, with collision fractions ranging from ~7% for circular, equal-mass binaries to ~0.2% for the observationally motivated Moe2017 binary distribution. Most collisions occur for prograde, tight binaries at low impact parameters beta = r_t/r_p, where the tidal force of the BH drives up the binary eccentricity during pericentre passage. Collision velocities are close to the binary escape velocity for lower-mass BHs (<= 10^8 Msun), but span a wider range for higher-mass BHs, implying an increasing fraction of stellar mergers. Using empirical loss-cone rates and the local BH mass function, we estimate detectable LSST collision rates of ~8,600 and ~3,000 events per year for our Kroupa mass function, Opik's law, inclined orbit model and our MS17 model, respectively, around 10^6 Msun BHs; ~330 and ~150 events per year around 10^8 Msun BHs; and ~3.5 and ~2.8 events per year around 10^9 Msun BHs. These results suggest that binary stellar collisions around HMBHs represent a potentially observable population of nuclear transients that may contribute to the growing sample of ambiguous nuclear transients detected by wide-field optical surveys.
Read the full abstract

All authors Megha Sharma, Alexander Heger, Evgeni Grishin, Daniel J. Price

Astrophysics of Galaxies

Ubiquitous nuclear disks and bars embedded in massive galaxies in the cosmic morning

Jianyuan Luo, Fangzhou Jiang, Jinning Liang et al. (+8 more)

The morphology of the central regions of high-redshift galaxies remains relatively unexplored, while recent case studies suggest that giant disks can emerge without first developing a prominent central spheroid. Here, we investigate the inner structures of a mass-complete sample of 45 massive galaxies at $z=3$ in the TNG50 simulation. Through double-Sérsic profile decomposition, isodensity ellipse fitting, intrinsic three-dimensional shape measurements, and stellar kinematics, we find that these central structures are ubiquitously flattened and rotation-supported with low Sérsic indices ($n \lesssim 1$). This indicates that the central regions are predominantly nuclear disks and bars rather than bulges. Tracking their evolution, we show that these nuclear disks and bars emerge during gas-rich compaction and do not transform into spheroidal and dispersion-dominated systems until $z \lesssim 1$, before which extended stellar disks have already developed. Our results suggest that massive disks can assemble around rotation-supported centers and bulge-deficient massive galaxies may be a common outcome of galaxy evolution.
Read the full abstract

All authors Jianyuan Luo, Fangzhou Jiang, Jinning Liang, Boris S. Kalita, Pinsong Zhao, Jinyi Shangguan, Bingcheng Jin, Zeyu Gao, Weichen Wang, Luis C. Ho, Yingjie Peng

Astrophysics of Galaxies

Distance Estimation using Globular Clusters and Ultra-Compact Dwarfs

Bas van Heumen, Jonah S. Gannon, Duncan A. Forbes et al. (+2 more)

The tight scaling relation between absolute magnitude and internal velocity dispersion ($\sigma$) for globular clusters (GCs), referred to as the GC velocity dispersion (GCVD) relation, has shown great potential as a distance estimator. However, at the high-luminosity end of the GC luminosity function, GCs mix with ultra-compact dwarfs (UCDs). As GCs appear to smoothly transition into UCDs with dynamical mass, we investigate the possibility of a unified distance estimation relation applicable to both GCs and UCDs. To this end, we exploit the transition between scaling relations with dynamical mass, using the Milky Way and M31 GCs alongside literature UCDs. Additionally, we look at the influence of UCDs, and of GC size, on GCVD-derived distances. Using the GCVD for UCDs gives a systematic distance underestimation of $\sim$33 per cent, but a cut to select UCDs with GC-like sizes can eliminate this bias. The minor systematics on GC size produce systematic offsets smaller than the uncertainty of the GCVD. Using the bilinear relation formed by the GCs and UCDs in the absolute magnitude - log dynamical mass plane for distance estimation yields per-object distance uncertainties of $\sim$30-35 per cent (0.12-0.16 dex). We find that the GC - UCD division occurs at $M_V \simeq -10.8$ mag and $M_{dyn} \simeq 3.1\times10^6$ $M_{\odot}$, consistent with previous findings. Applied to the dwarf galaxy NGC1052-DF2, whose distance is strongly debated, the relation returns 19.1 $\pm$ 4.3 Mpc, consistent with literature values.
Read the full abstract

All authors Bas van Heumen, Jonah S. Gannon, Duncan A. Forbes, Jean P. Brodie, Aaron J. Romanowsky

Astrophysics of Galaxies · Cross-listed from gr-qc

Quasinormal-mode redshifts of black holes in galactic halos with radial pressures

Che-Yu Chen, Hassan Hassanabadi and Soroush Zare

We investigate the black-hole quasinormal mode redshifts induced by a galactic dark-matter halo with nonvanishing radial pressure. The halo is described by an anisotropic fluid with a generalized density profile and a constant radial equation-of-state parameter $w$. We construct the corresponding static, spherically symmetric spacetime and study the resulting corrections to the unstable light ring and quasinormal-mode spectrum. For dilute halos and $w\neq -1$, the light-ring angular frequency and Lyapunov exponent acquire the same leading-order gravitational redshift, implying a universal shift of the real and imaginary parts of the quasinormal frequencies. The magnitude of this effect depends on both the halo structure and the radial pressure. This universal redshift relation holds not only in the case of $w=0$ that has been discovered in the literature but also in a much wider scenario, supporting its importance in black hole spectroscopy. On the other hand, the case $w=-1$ is qualitatively different: the factor that corresponds to the leading common redshift vanishes, the corrections are further suppressed by the hierarchy between the black-hole and halo scales, and the universal relation is broken, with the dominant contribution controlled by the inner halo profile. Our numerical computations of scalar-field quasinormal mode spectra confirm the analytic eikonal results.
Read the full abstract