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Physics Astrophysics Astrophysics of Galaxies

astro-ph.GA Watch Astrophysics of Galaxies

Tuesday 25 August

Astrophysics of Galaxies

The Mass Dependence of the Fundamental Metallicity Relation in Observations and Simulations

Laura Carnevale, Alex M. Garcia, Paul Torrey et al. (+8 more)

The metal content of galaxies provides direct insight into the underlying physical processes that drive galaxy evolution. An example of this is the three-parameter relationship between stellar mass, gas-phase metallicity, and star formation rate, commonly referred to as the Fundamental Metallicity Relation (FMR). Previous studies have suggested that the FMR is redshift-invariant (at $z \lesssim 4$) and fully accounts for the scatter in the mass-metallicity relation (MZR). In this work, we test this 'fundamental' relation in both cosmological simulations (EAGLE, SIMBA, Illustris, IllustrisTNG) and Sloan Digital Sky Survey (SDSS) observations. We find that the canonical anti-correlation between metallicity and specific star formation rate (sSFR) inverts in massive galaxies ($M_\star \gtrsim 10^{10.5} \mathrm{M}_\odot$) in EAGLE, IllustrisTNG, and SDSS. When including lower star forming galaxies, the positive correlation appears for all four simulations and SDSS. We speculate that this inversion may being driven by strong nuclear outflows (from, e.g., active galactic nuclei or stellar feedback), which quench star formation while simultaneously expelling preferentially enriched gas from the center of the galaxy. We also find that this 'inversion' appears in a number of metallicity diagnostics in observations (though the details depend on diagnostic) and persists out to $z \sim 1$ in the simulations. These results demonstrate that these strong nuclear outflows challenge simple gas regulator-type models and provide a new framework to test models of the baryon cycle in both future simulations and observations.
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All authors Laura Carnevale, Alex M. Garcia, Paul Torrey, Sara L. Ellison, Shweta Jain, Peixin Zhu, Kathryn Grasha, Ryan L. Sanders, Lars Hernquist, Lisa J. Kewley, Jillian M. Scudder

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

Improving the Physical Interpretability of Gaussian Processes in Stellar Activity Modeling: A Study Case on Photometric Variability Among Stellar Clusters

Leslie Moranta, Jonathan Gagné, Jacqueline K. Faherty et al. (+12 more)

Gaussian Processes (GPs) are widely used to model stellar variability in photometric surveys, but a statistically successful fit does not guarantee that the inferred hyperparameters correspond to physically meaningful stellar properties. This is especially important for young, active stars, whose TESS light curves contain evolving spots, harmonics, and non-sinusoidal variability. We use stellar rotation as a case study to examine when the period hyperparameter of a quasi-periodic GP can be interpreted as a physical rotation period. We introduce a regularized GP likelihood that reweights the covariance-complexity term in the marginal likelihood, reducing the tendency of unconstrained models to converge toward preferred but misleading solutions. We test this framework on 539 stars in IC2602, the Tucana-Horologium Association, Pisces-Eridanus, and GroupX, with independently reported and manually vetted rotation periods. This benchmark evaluates GP hyperparameter interpretability and automated period recovery with minimal human intervention. We compare regularized and unregularized models across several regularization strengths, {\lambda}, using literature agreement, sector-level diagnostics, and consistency across TESS sectors. Relative to the standard GP likelihood, regularization improves successful rotation-period recovery by an average of 7%. It also generally reduces the median absolute fractional deviation of periods across sectors, showing that the improvement is not limited to catastrophic failures but also mitigates smaller systematic errors. Regularization is particularly beneficial for non-sinusoidal or evolving modulation, where unconstrained GPs may recover harmonics or spurious timescales. These results show that likelihood regularization and cross-sector consistency are practical diagnostics for assessing when GP-based rotation periods are robust.
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All authors Leslie Moranta, Jonathan Gagné, Jacqueline K. Faherty, Mark Popinchalk, Jason Lee Curtis, Johanna M. Vos, Alexandrine L'Heureux, Andrew Ayala, Eleanor Johnson, Dawn McCullough, Nicole Munoz, Hannah Park, Xue Weng, Livia Poliquin, Ilhem Lazizi

Astrophysics of Galaxies

Spatially resolved molecular gas conditions in the circumnuclear disc of 3C 84

Bin Jia, Tom Oosterloo, Serena Viti et al. (+1 more)

The brightest cluster galaxy NGC 1275, at the centre of the Perseus cluster, hosts the radio-loud AGN 3C 84 and a circumnuclear disc (CND) of cold molecular gas onto which large-scale CO filaments accrete, yet the physical and chemical conditions of the gas in the CND remain poorly constrained. We present a spatially resolved analysis of ALMA CO(2-1), HCN(3-2), and HCO$^+$(3-2) observations at 72 pc. The data are partitioned into beam-sized hexagonal regions and modelled with a Bayesian framework that couples a neural network emulator of time-dependent chemistry (UCLCHEM) with non-LTE radiative transfer (SpectralRadex) to infer the gas density, kinetic temperature, and cosmic ray ionisation rate in each region. All three line ratios peak in the inner disc and decline with radius. The inference shows radial gradients in density ($\log_{10} n({\rm H_2}) \approx 6.3$ to $\sim 5$), kinetic temperature (~200 K to ~160 K), and cosmic ray ionisation rate ($\log_{10}(\zeta/\zeta_0) \approx 4.9$ to $\sim 3$). Despite the powerful radio AGN, the observed HCN(3-2)/HCO$^+$(3-2) ratio remains $\lesssim 1$ across the disc. Our modelling attributes this to optical depth saturation of HCN(3-2) ($\tau \sim 1$-3), which suppresses the intensity ratio even when the HCN abundance exceeds that of HCO$^+$ by a factor of three or more. The HCN/HCO$^+$ intensity ratio therefore cannot be used as an abundance diagnostic without accounting for optical depth, and a low ratio does not necessarily imply weak AGN influence on the chemistry. Azimuthally resolved profiles suggest a localised HCO$^+$/CO enhancement at the western disc boundary, coinciding with the filament-disc accretion interface and consistent with shock processing by velocity shear between the infalling filaments and the rotating disc. These results indicate that the CND is shaped by accretion from its filamentary environment.
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All authors Bin Jia, Tom Oosterloo, Serena Viti, Raffaella Morganti

Astrophysics of Galaxies

Estimator forensics for the wide-binary gravity test: the eccentricity-triple coupling manufactures a pseudo-signal, and a pre-registered protocol for Gaia DR4

Hicham Boufourou

Analyses of Gaia DR3 wide binaries reach opposite verdicts on a claimed low-acceleration anomaly: gamma = Geff/G ~ 1.4 (Chae 2023-2026; Hernandez et al. 2024) versus Newtonian at high significance (Banik et al. 2024; Pittordis et al. 2025), from the same catalogue. We localize the disagreement experimentally. A generative model – Keplerian binaries plus hierarchical triples with photocentre and time-averaging effects – is validated without tuning against Pittordis et al. (2025). Synthetic catalogues of known truth are confronted with three estimator families: a full-median estimator, even with a perfect eccentricity correction, recovers gamma = 1.08-1.13 from purely Newtonian universes containing 20-30% residual triples – half-way to the claimed anomaly – while a tail-truncated estimator and a mixture likelihood recover <= 1.04 and 1.00. An injected MOND-like boost (gamma = 1.4 above 2 kau) is recovered at >= 1.26 by all three: the hypotheses never overlap under robust estimation, so the controversy is decidable. Applying the calibrated estimators to the 81,088-pair Chae (2024) sample we measure gamma = 1.045 [1.025, 1.068] (2-30 kau), and a joint mixture fit gives gamma = 1.05 [1.04, 1.07] with f_trip = 0.15, consistent with the independent 0.17; gamma = 1.4 is rejected at ~16 sigma. We freeze a pre-registered protocol, time-stamped on Zenodo, for Gaia DR4, where sigma_stat(gamma) < 0.005 will make estimator systematics fully dominant.
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Astrophysics of Galaxies · Cross-listed from astro-ph.HE

Probing the Three-Dimensional Structure of a Jet with Faraday Tomography

Sawera Gull, Masaya Kurogi and Keitaro Takahashi

Magnetic fields play a fundamental role in the dynamics and radiation of jets associated with active galactic nuclei (AGNs), where they accelerate and collimate the relativistic plasma and produce the observed synchrotron emission. Faraday tomography is a powerful technique for probing the three-dimensional distribution of magnetic fields and synchrotron-emitting plasma along the line of sight, by reconstructing the Faraday Dispersion Function (FDF) from the observed polarization spectrum. To explore what aspects of AGN-jet structure can be revealed by Faraday tomography, we construct a simple three-dimensional model of an AGN jet that captures its essential features, and compute the resulting FDF for a range of model parameters. The jet is represented as a cylindrical region of uniform thermal-electron density threaded by a coherent helical magnetic field, to which a random turbulent component can optionally be added. The parameters varied include the inclination angle {\theta} between the jet axis and the line of sight, the wavenumber of the helical field, and the amplitude of the random magnetic-field component. By systematically varying these parameters, we examine how the underlying magnetic geometry and turbulence are encoded in the observable Faraday and polarization structures. The main observational signatures identified by our model include top-bottom asymmetry across the jet, curved or double peaked FDF profiles and increasingly fragmented Faraday depth structure along longer lines of sight, providing potential diagnostics of large scale helical magnetic fields and small scale turbulent components. These signatures providing a physical framework for interpreting future polarimetric observations of AGN jets from instruments such as LOFAR, MeerKAT, and the VLA.
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Astrophysics of Galaxies · Cross-listed from astro-ph.CO

Dark-to-black super-accretion as a spin-imprinting mechanism for supermassive Kerr black holes

Saeed Fakhry, Nicolas Sanchis-Gual, Jorge Castelo Mourelle et al. (+2 more)

The existence of supermassive black holes with masses $M\gtrsim10^9\,M_{\odot}$ and large dimensionless spins $\chi\sim0.9-0.99$ at high redshift remains a challenge to our understanding of the early Universe. In this work, we study the adiabatic co-evolution of a Kerr black hole seed surrounded by two ultralight scalar dark matter clouds occupying different bound states, and show that this configuration allows the black hole to grow into the supermassive mass range while imprinting a characteristic final spin. The evolution proceeds through two stages. During the first stage, a spherical cloud described by the $\ell=0$ mode is completely depleted through a runaway dark-to-black accretion mechanism on a timescale of hundreds of millions of years for boson masses $\mu\sim10^{-18}-10^{-17}\,\mathrm{eV}$. Since the accreted material does not carry angular momentum, the black hole spin is universally driven to $\chi\simeq0$, independently of its initial spin. Throughout this stage, the second cloud, described by the $\ell=m=1$ mode, remains in the superradiant regime with negligible evolution. However, once the first stage is completed, this cloud transitions to the accreting regime, rapidly transferring both mass and angular momentum to the black hole. Starting from $\chi\simeq0$, the black hole spin increases until the evolution self-consistently saturates close to the threshold $\chi_{\rm sat}$, defined by the condition $\Omega_H(\chi_{\rm sat})=\mu$, on an e-folding timescale of thousands of years, orders of magnitude shorter than the first stage. This final saturation spin is largely independent of both the initial black hole spin and the mass of the secondary cloud, providing a spin-imprinting mechanism in which the primordial spin is first erased by spherical accretion and then reset to a value determined only by the boson mass and the final black hole mass.
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All authors Saeed Fakhry, Nicolas Sanchis-Gual, Jorge Castelo Mourelle, Darío Núñez, Juan Carlos Degollado

Astrophysics of Galaxies

Interstellar Aromatic Infrared Bands: IR absorption spectroscopy of the lowest triplet state of naphthalene

Priyanka Arvind Paunikar, Hugo Maurer, Lars Reems et al. (+5 more)

The aromatic infrared bands (AIBs), emission features observed ubiquitously across a wide variety of interstellar objects, are commonly attributed to radiative cooling of highly-excited ground-state vibrational levels of polycyclic aromatic hydrocarbons (PAHs) that are populated after UV absorption and internal conversion. However, for neutral PAHs intersystem crossing to the triplet manifold, followed by radiative cooling of vibrational levels within the lowest excited triplet state is expected to be a competing relaxation channel. This state differs in vibrational frequencies, transition moments and internal energy, and therefore gives rise to different emission spectra. Despite their significance, neutral PAHs in their triplet states have remained largely unexplored, primarily because of the lack of direct spectroscopic access. Here, we report the first measurement of the infrared absorption spectrum of the lowest triplet state of naphthalene. The spectrum is markedly different from the vibrational spectrum of the singlet electronic ground state, displaying features that can help identifying PAHs in the triplet states in astronomical spectra. We also show that experimental spectra are closely reproduced by anharmonic frequency calculations. These findings serve as a stepping stone for detecting triplet-state PAHs in the interstellar medium and provide a basis for developing more accurate infrared emission models.
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All authors Priyanka Arvind Paunikar, Hugo Maurer, Lars Reems, Alessandra Candian, Sandra Brunken, Jos Oomens, Piero Ferrari, Wybren Jan Buma

Astrophysics of Galaxies

Synchrotron filaments in radio galaxies: rarity, stability, and environmental influences from LOFAR and ROSAT observations

Geoffrey Ong'alo, Martin J. Hardcastle, Willice Obonyo et al. (+2 more)

We present a systematic investigation of filamentary synchrotron structures in radio galaxies, using deep 144 MHz observations from the LOFAR Two-Metre Sky Survey (LoTSS) in combination with archival ROSAT X-ray data. These narrow, collimated features, linking radio lobes and often aligned with jet axes, are rare: our visual inspection of 548 cluster-associated sources identified 12 candidates (~2.2%), of which three exhibit clearly resolved filaments suitable for detailed X-ray and synchrotron minimum pressure analysis. Minimum pressures in these filaments are consistently lower than the ambient thermal pressure derived from X-ray measurements. This disparity implies a role for external confinement in filament stability, aligning with theoretical predictions of thermal pressure support and potentially toroidal magnetic field configurations. We discuss filament formation scenarios, including relic AGN outflows, magnetic draping, and plasma instabilities. Our findings highlight the utility of filamentary structures as probes of intracluster magnetic field topology and AGN feedback, and demonstrate the need for high-resolution, multi-frequency studies to constrain their origin and evolution.
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All authors Geoffrey Ong'alo, Martin J. Hardcastle, Willice Obonyo, Marcus Brüggen, Paul Baki

Astrophysics of Galaxies

An HI study of a large sample of ultra-diffuse galaxies

Ruilei Zhou, Ming Zhu, Chuan-Peng Zhang et al. (+5 more)

By cross-matching the SMUDGes catalog with the FASHI and ALFALFA HI surveys, we construct an HI-detected sample of 112 ultra-diffuse galaxies (UDGs) and 48 low-surface-brightness (LSB) galaxies, providing HI-based redshifts for 76 galaxies for the first time. Using DESI DR1 redshifts, we assemble an HI-non-detected sample of 168 galaxies for stacking analysis, with detections in two stellar mass bins below 10^{8.5} M_sun. Combining optical, UV, and HI data, we investigate stellar masses, star formation rates, gas fractions, and kinematics. We present a systematic analysis of the HI mass–optical size relation for UDGs and LSBs, showing both populations follow a mass–optical size scaling similar to normal galaxies, suggesting an average HI surface density, under the assumption that the optical size traces the extent of the HI distribution. Their stellar mass–size relation indicates nearly constant stellar surface densities for galaxies with central surface brightness mu_{0,g}>~24mag arcsec^{-2}, independent of UDG or LSB classification. Many UDGs and LSB galaxies are systematically offset from the baryonic Tully–Fisher relation toward higher baryonic masses at a given velocity, consistent with trends found in UDGs with resolved HI kinematics. Both populations exhibit low star formation efficiencies and long gas depletion times, supporting multiple formation pathways for UDGs.
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All authors Ruilei Zhou, Ming Zhu, Chuan-Peng Zhang, Lin Du, Cheng Cheng, Qi Guo, Tian-Wen Cao, Wenzhe Xi

Astrophysics of Galaxies

SDSS-IV MaNGA: Star Formation Cessation in Low-redshift Galaxies. III. Dependence on Quenching Criteria

Zhuo Cheng, Tao Jing, Cheng Li et al. (+1 more)

This paper is the third in a series of studies investigating star formation cessation in nearby galaxies on kiloparsec scales. Using the final SDSS-IV MaNGA data release, we ask how the inferred importance of global, local, and environmental properties depends on the operational definition of quenched regions. We classify spaxels as star-forming, reliably quenched, or potentially quenched by accounting for measurement uncertainties, and train random forest classifiers with a parameter set chosen for direct comparison with previous work. For reliably quenched regions, the local stellar mass surface density $\Sigma_\ast$ consistently has the highest feature importance, independent of quenching definition. By contrast, the high importance of central velocity dispersion $\sigma_c$, previously interpreted as evidence for galaxy-wide AGN feedback, is recovered mainly when potentially quenched regions are included. The leading parameter also varies with stellar mass: $\Sigma_{\rm 1kpc}$ is most important below $\sim10^{10.2}\,\textrm{M}_{\odot}$, whereas local quantities such as $\Sigma_\ast$ and $\sigma_\ast$ become more prominent at high masses. These results show that quenching criteria and uncertainty treatment can reconcile apparently discrepant feature-importance studies. AGN-related processes may contribute to ambiguous regions, but the reliably quenched population is most tightly linked to high local stellar density.
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All authors Zhuo Cheng, Tao Jing, Cheng Li, Renbin Yan

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

Molecular and Atomic Gas Associated with the Gamma Ray Supernova Remnant RCW 103

H. Inoue, Y. Asano, R. G. Bhuvana et al. (+15 more)

We present a study of the interstellar molecular and atomic gas associated with the gamma-ray supernova remnant (SNR) RCW 103 using the Mopra $^{12}$CO($J$ = 1-0), Atacama Large Millimeter/submillimeter Array $^{13}$CO($J$ = 1-0), and the Australia Telescope Compact Array & Parkes HI data. We find that CO clouds in the velocity range from $-58.7$ to $-43.5$ km s$^{-1}$ show a clear spatial correspondence with the X-ray shell of RCW 103, particularly extending from the northwestern to the southeastern regions. The position-velocity diagram of the CO emission reveals an expanding gas motion with an expansion velocity of $\Delta V \sim$$7.5$ km s$^{-1}$, which may have been produced by shock waves and/or stellar winds from the progenitor system. We estimate the total cosmic-ray proton energy to be $\sim$$3.0^{+1.1}_{-0.6} \times 10^{47}$ erg, adopting a total interstellar proton density of $\sim$$810$ cm$^{-3}$. This value is more than an order of magnitude lower than those inferred for other gamma-ray emitting SNRs of comparable age. Given that a substantial amount of dense gas remains within the interior of RCW 103, where thermal X-ray emission is dominant, our results possibly suggest that a significant fraction of the shock energy may have been converted into thermal energy via gas heating, thereby reducing the efficiency of cosmic-ray acceleration.
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All authors H. Inoue, Y. Asano, R. G. Bhuvana, R. Z. Alsaberi, R. Yamada, K. Tsuge, T. Murase, Y. Fukui, E. M. Reynoso, K. Tachihara, N. Izumi, M. Yamagishi, K. Furuya, N. Harada, K. Tokuda, G. Rowell, M. D. Filipović, H. Sano

Astrophysics of Galaxies

Decoupling candidate dual AGN from chance superpositions in the GOTHIC survey via a deep-learning framework

Bhavesh Mukheja, Snehanshu Saha, Anwesh Bhattacharya et al. (+3 more)

Dual active galactic nuclei (DAGN) mark a critical phase in the evolution of merging galaxies and the pairing of supermassive black holes, yet they remain difficult to identify in large imaging surveys because of projection effects and limited spatial resolution. Compact foreground stars and unresolved substructure can mimic dual nuclei through chance superposition, complicating automated detection. We revisit the 46,061 galaxies flagged but rejected as DAGN candidates by the GOTHIC pipeline, primarily because the two nuclei fell within the SDSS fibre aperture or exceeded its separation threshold. We train a supervised deep-learning framework based on the YOLOv11 oriented-bounding-box architecture on annotated SDSS imaging to separate genuine dual nuclei from foreground stellar contaminants and other spurious alignments. The final model attains a validation precision of 0.919, recall of 0.905, and $F_1$ of 0.912 for the dual-nuclei class, and yields 29,605 dual-nucleus candidates after removing star-dominated and blended detections. Structured visual inspection indicates that $54.5$–$62\%$ are consistent with genuine dual nuclei, implying $\sim(1.4$–$1.8)\times10^{4}$ plausible systems. Cross-calibrating the YOLO separation against the deterministic GOTHIC centroid measurement and restricting to the compact regime ($d \le 6.87''$) gives a conservative subset of $\sim 13{,}672$ candidates, reaching calibrated separations of $\sim 0.56''$. Spectroscopy of the most compact ($\le 1$~kpc) systems shows they are dominated by passive, absorption-line galaxies with no resolved double-peaked emission, so confirmation requires higher-resolution follow-up. The catalogue is a statistically refined list of candidates, not confirmed DAGN. Nonetheless, deep-learning detection substantially reduces contamination and expands the plausible DAGN census.
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All authors Bhavesh Mukheja, Snehanshu Saha, Anwesh Bhattacharya, Mousumi Das, Françoise Combes, Sudhanshu Barway

Astrophysics of Galaxies

Interplay of Compaction, Quenching, and Black Hole Growth in the Most Massive Galaxies since $z\sim5$: Insights from JWST and Chandra Data

Novan Saputra Haryana, Masayuki Akiyama, Abdurro'uf et al. (+16 more)

The buildup of dense stellar cores is expected to mark an important transition in the star-formation and black-hole growth of massive galaxies. Using spatially resolved spectral energy distribution (SED) fitting of James Webb Space Telescope near-infrared imaging, combined with stacking analysis of Chandra X-ray data, we trace stellar mass buildup and average black hole accretion in the most massive galaxies at $z<5$, selecting 50 most massive galaxies per redshift bin at constant number density of $\sim4.4\times10^{-5}$ cMpc$^{-3}$. To robustly constrain central stellar populations, we separate active galactic nuclei (AGN) components affecting the photometry using multi-band morphological decomposition and SED analysis. We find that the sample selected with constant number density exhibits evolutionary trend of rapid central compaction at $z\sim4$, during which the median central 1 kpc stellar mass increases by $\sim0.60$ dex over $\sim400$ Myr. The majority of X-ray detected AGN ($63\%\pm12\%$) are hosted by galaxies undergoing the compaction, while we find neither individually detected X-ray sources nor a significant stacked X-ray signal at $z>4$, indicating that substantial average black-hole growth emerges primarily during, rather than before, the compaction. Following the compaction, central specific star formation rates (sSFR) decline by $\sim1.24$ dex over $\sim700$ Myr at $z\sim3$ while remaining elevated galaxy-wide, signaling the onset of inside-out quenching. Despite this central suppression, specific black hole accretion rate remains coupled to the total sSFR. Our results suggest that dense-core formation in the most massive galaxies marks the onset of inside-out quenching and a transition toward enhanced black-hole to stellar growth ratio.
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All authors Novan Saputra Haryana, Masayuki Akiyama, Abdurro'uf, Suchetha Cooray, Itsna Khoirul Fitriana, Dian P. Triani, Bovornpratch Vijarnwannaluk, Juan Pablo Alfonzo, Irham Taufik Andika, Muhammad Nur Ihsan Effendi, Ibnu Nurul Huda, Takumi Kakimoto, Anton Timur Jaelani, Ronaldo Laishram, Naoki Matsumoto, Abdurrahman Naufal, Lucky Puspitarini, Ryo Albert Sutanto, Hesti Retno Tri Wulandari

Astrophysics of Galaxies

Comparing the Nebular and Stellar Dust Attenuation Curves in Nearby Star-Forming Galaxies

Jong Chul Lee, Hyunjin Shim, Hyunmi Song et al. (+3 more)

Differences in the spatial distributions of stars and ionized gas relative to dust in galaxies imply that stellar and nebular dust attenuation curves need not be identical. Although stellar attenuation curves have been extensively studied, nebular attenuation curves remain less explored. In this work, we investigate nebular attenuation curves using Balmer line ratios for a sample of 90,958 nearby star-forming galaxies from the Sloan Digital Sky Survey with well-constrained stellar attenuation curves. In the H$\alpha$/H$\beta$ versus H$\alpha$/H$\gamma$ diagram, the nebular attenuation curves are, on average, significantly shallower than typical stellar attenuation curves, which can be qualitatively reproduced by source-dust geometric effects. The nebular attenuation curve slopes show weak positive correlations with the stellar attenuation curve slopes and weak dependences on galaxy properties that broadly follow those of the stellar attenuation curve slopes. These results suggest that nebular attenuation curves are distinct from stellar attenuation curves, while remaining consistent with a connection between them.
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All authors Jong Chul Lee, Hyunjin Shim, Hyunmi Song, Ho Seong Hwang, Woong-Seob Jeong, Jong-Ho Shinn

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

Spatially resolved spectral properties of M87* on event horizon scales

Shan-Shan Zhao, Ru-Sen Lu, Rocco Lico et al. (+2 more)

The supermassive black hole at the center of the nearby radio galaxy M87 (M87*) is a prime target for studying black hole physics. Spatially resolved spectral measurements on event-horizon scales can reveal the origin of the emission and probe the plasma and gravitational environment in the immediate vicinity of the black hole. Here, we present an analysis of spectral properties based on nearly simultaneous high-resolution images at 3.5 mm (86 GHz) and 1.3 mm (230 GHz), obtained in 2018 with the Global Millimeter VLBI Array (GMVA) including ALMA and the Greenland Telescope, and the Event Horizon Telescope (EHT). We obtain the first spatially resolved spectral-index map ($S_\nu \propto \nu^\alpha$) within the compact region ($\leq 100\,\mu$as). We further detect a robust radial gradient with a modest rise in the inner $\lesssim 20~\mu$as (slightly inside the 1.3 mm ring), followed by a systematic decline at larger radii. The spectral index transitions from positive to negative values near $\sim 30~\mu$as, close to the 3.5 mm ring radius, consistent with frequency-dependent synchrotron opacity in the innermost accretion flow. These results provide new observational constraints that can help discriminate between models of the horizon-scale emission and the launching of relativistic jets in M87*.
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All authors Shan-Shan Zhao, Ru-Sen Lu, Rocco Lico, Yuh Tsunetoe, Sijia Peng

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

Occultation of microlensed images by circum-lens disks: Implications for surveys

Elizabeth Bailey

Microlensing surveys typically apply automated criteria to exclude lightcurves that depart from time-symmetric and achromatic Paczyński curves. In surveys using such automated detection pipelines, occultation of microlensed images by circum-lens material could lead to underdetection or misclassification of ring- or disk-bearing compact object populations. This work characterizes the family of lightcurve morphologies by which uniform thin circum-lens disks of varying size and orientation, and low mass relative to their host lens, can intersect the ray paths produced during microlensing events. These morphology classes are paired with squared residuals relative to an unocculted lightcurve. We find that substantial deviations from an unocculted microlensing curve can occur across a wide range of parameter space. This effect holds relevance for free-floating planets and brown dwarfs where disks or ring systems can be present. Another potential consideration is that disk-shaped accretion flows onto primordial black holes (PBHs) during the cosmic dark ages could have resulted in remnant quiescent disks of baryonic material. Pipelines should be designed to account for disk-bearing lens populations, opening previously underutilized avenues to potentially observe disks and rings in these contexts and ensuring populations are accurately characterized.
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Astrophysics of Galaxies · Cross-listed from astro-ph.HE

Linking high-mass X-ray binaries to binary compact object mergers in Milky Way-like galaxies

Felipe Vivanco Cádiz, M. Celeste Artale, Nicola Masetti et al. (+5 more)

High-mass X-ray binaries (HMXBs) constitute a potential intermediate phase connecting massive stellar binaries to the formation of coalescing binary compact objects (BCOs). Yet, the specific circumstances that allow HMXBs to later develop into merging BCOs are still under debate. In this study, we focus on wind-fed HMXBs and investigate this link by generating synthetic catalogs with the population-synthesis code SEVN and assigning them to a sample of 66 Milky Way-like galaxies. Using stellar particles drawn from the TNG50 cosmological simulation, we assign HMXBs according to particle mass, age, and metallicity, and follow their subsequent evolution to BCOs. In this way, our approach provides a realistic framework for modelling HMXBs in the Milky Way by explicitly accounting for the varied metallicities and spatial distributions of binary systems. Our method recovers the spatial distribution inferred from the observed properties of Galactic HMXBs: their positions follow the spiral arms and agree with the measured radial profile. The age distribution aligns well with observations and shows that BH-HMXBs tend to be younger than NS-HMXBs. We find that the fraction of HMXBs that evolve into merging BCOs within a Hubble time for BH-HMXBs is ~0.2-3.2% (or ~0.3-5.4% when restricting to 10^35 <= L_X <= 10^40 erg s^-1), while for NS-HMXBs is ~3.6-23.4% (or ~3.5-26.0% with the same luminosity cut). We show that common envelope (CE) episodes and natal-kick magnitudes are the primary processes determining the number of merging systems. Successful BCO mergers are typically produced by systems that experienced significant orbital hardening (early CE), whereas stable mass transfer often yields wide, non-merging binaries unless extreme eccentricities are induced by kicks. Metallicity plays a secondary but important role by modulating compact-remnant masses and wind-driven orbital widening.
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All authors Felipe Vivanco Cádiz, M. Celeste Artale, Nicola Masetti, Gaston Escobar, Giuliano Iorio, Ankit Kumar, Boyuan Liu, Michela Mapelli

Monday 24 August

Astrophysics of Galaxies

The Local Origin of a Host Dispersion Measure-Stellar Mass Relation in Fast Radio Bursts

Wasundara Athukoralalage, Liam Connor, Peter K. Blanchard et al. (+1 more)

The origin of fast radio bursts (FRBs) and the relationship to their host galaxy environments remain open questions. Using a sample of 37 FRBs with secure host associations at $z \lesssim 0.25$, and including dwarf, elliptical, and edge-on hosts, we examine the host dispersion measure ($\mathrm{DM_{host}}$) and its dependence on host stellar mass ($M_\star$). We find a statistically significant anti-correlation between the host dispersion measure and host stellar mass (the $\mathrm{DM_{host}}$-$M_\star$ relation; Pearson $r \approx -0.5$, $\log_{10} p \approx -2.8$) that extends across the full range of our sample, $\log_{10}(M_\star/M_\odot) \approx 8$-$11.4$. We find that the rest-frame Faraday rotation measure ($|\mathrm{RM}|_{\mathrm{host}}$) is largest in FRBs that reside in dwarf galaxies, but there is no evidence for a correlation across the full mass range. We show that the $\mathrm{DM_{host}}$-$M_\star$ trend does not arise from the galaxy-averaged interstellar medium (ISM) nor from the circumgalactic medium (CGM). Instead, we argue that the local ($\lesssim 100$ pc) environment is responsible. The spatial statistics of star formation and metallicity-dependent FRB progenitor channels plausibly lead to denser ionized environments in low-mass galaxies and less nearby gas in massive hosts.
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All authors Wasundara Athukoralalage, Liam Connor, Peter K. Blanchard, Edo Berger

Astrophysics of Galaxies

The Evolution of Low-Ionization Electron Densities in Galaxies Across Cosmic Epochs

Mabel G. Stephenson, John Chisholm, Alberto Saldana-Lopez et al. (+12 more)

We investigate the low-ionization electron density in the interstellar medium of galaxies across $0$$<$$z$$<$$8$, derived with the [O II]$\lambda\lambda3727,3730$ and [S II]$\lambda\lambda6718,6733$ doublets, using both deep JWST NIRCam/grism and NIRSpec/MSA spectroscopy. Along with ancillary density samples from the literature at $0$$<$$z$$<$$6$, we assemble three samples containing a total of 703 galaxies spanning $3.7$$<$$z$$<$$7.8$ at $\langle z\rangle\sim5.6$; 691 galaxies in the luminosity-complete NIRCam/grism programs CONGRESS and FRESCO at $\langle z\rangle \sim4.3$ and $\langle z\rangle\sim5.3$, respectively, and 12 galaxies with high-resolution NIRSpec/MSA spectra from the GO 1871 and GLASS programs. We find median electron densities of $n_{\rm{e}}$[S II]$=$$463^{+281}_{-203}~{\rm{cm}}^{-3}$ for CONGRESS, $n_{\rm{e}}$[S II]$=$$301^{+388}_{-206}~{\rm{cm}}^{-3}$ for FRESCO, and $n_{\rm{e}}$[O II]$=$$202^{+145}_{-102}~{\rm{cm}}^{-3}$ for the NIRSpec/MSA sample. The median low-ionization $n_{\rm{e}}$ increases from $z= 0$ to $z=4$, in agreement with previous studies and those using JWST observations. However, beyond $z\sim4$ median $n_{\rm{e}}$ begins to deviate from a monotonically increasing evolution with $z$. We find a positive, but shallow, correlation between O$_{32}$ (a proxy for the ionization parameter) and $n_{\rm{e}}$, while also confirming a positive correlation between O$_{32}$ and $z$. We suggest that these trends are possibly due to an evolving ISM gas density and ionization structure, and propose a toy model where the gas clumping evolves with $z$ to explain the observed density and ionization variations.
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All authors Mabel G. Stephenson, John Chisholm, Alberto Saldana-Lopez, Jorryt Matthee, Alaina Henry, Rohan P. Naidu, Sophia R. Flury, Taylor A. Hutchison, Steven L. Finkelstein, Natalia G. Guseva, Yuri I. Izotov, Rui Marques-Chaves, Pascal A. Oesch, Naveen A. Reddy, Daniel Schaerer

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

An analysis of the Herbig star population and their protoplanetary disks within 1 kpc

L. M. Stapper, M. Vioque, A. J. Winter et al. (+6 more)

Herbig stars are intermediate mass pre-main sequence stars of 1.5 to $\sim15$~M$_\odot$ and are in between low and high-mass star formation. This work provides a catalog of all 243 known bona-fide Herbig stars with clear infrared excess and in many cases accretion signatures within 1~kpc. It contains archival, recalibrated, and newly derived stellar parameters, accretion rate properties, and disk dust mass measurements. We derive the latter by using newly obtained millimeter photometry and literature values. We find that 50% of Herbig dust disks are more massive than 10~M$_\oplus$, while this is only true for 20% and 5% of the T~Tauri disks in Lupus and Upper~Scorpius respectively. Furthermore, the Herbig disk dust mass distribution is bimodal, it consists of a high and low disk mass population with a mean dust mass of 21~M$_\oplus$ and 0.45~M$_\oplus$ respectively. We find that the catalog is near complete for within 300~pc, however, this decreases to 24% out to 1~kpc. We observe a flat relation for Herbig disks due to objects with short disk lifetimes, caused by a combination of low disk masses and high accretion rates. Furthermore, we find the peak of the occurrence rate of massive (>10~M$_\oplus$) disks to occur at $\sim$1-2~M$_\odot$ stars, coinciding with the peak in occurrence rate of giant exoplanets. The small number of Herbig stars with low accretion rates ($<10^{-8}$~M$_\odot$~yr$^{-1}$) or low disk dust masses ($\lesssim1$~M$_\oplus$), combined with the lack of an age dependence in the disk dust mass distribution, suggests that the observed Herbig star population represents the surviving disk-hosting phase in the optically visible late stages of intermediate-mass star formation. We argue that this is either due to the formation of deep dust traps in these disks or replenishment by late-infall, or a combination of the two.
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All authors L. M. Stapper, M. Vioque, A. J. Winter, D. J. Wilner, J. P. Williams, M. Benisty, A. S. Booth, S. L. Grant, M. R. Hogerheijde

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

The Highly Unusual Behavior and Chemical Composition of Interstellar Comet 2I/Borisov

Allison N. Bair, David G. Schleicher, Theodore Kareta et al. (+2 more)

We report on imaging, spectroscopy, and narrowband photometry of interstellar comet 2I/Borisov obtained at Lowell Observatory from 2019 September 13 to December 16. We measured chemical composition on four nights before perihelion, from October 4 to November 25 (2.466 to 2.028 au), with CN detections on all nights. Our measurements from October 27 represent the earliest reported detections of C$_2$ and C$_3$, where C$_2$-to-CN and C$_3$-to-CN log production rate ratios were $-$0.7 and $-$1.3, respectively. Both ratios increased by nearly 4$\times$ to $-$0.3 and $-$0.9 by November 25, an extremely large increase with heliocentric distance that is unprecedented in the Lowell Observatory comet database. We additionally observed OH and NH on November 25, with a derived H$_2$O production rate of 4.5$\times $10$^{26}$ mol s$^{-1}$ and very high log production rate ratios for CN-to-OH ($-$2.0) and NH-to-OH ($-$1.7). Monitoring from broadband $R$ images from September 13 to December 16 suggests dust ($A(0^{\circ})f\rho$) production peaked around October 19, 50 days before its December 8 perihelion passage. Narrowband images from October 4 and 27 reveal a nearly symmetric CN distribution in Borisov's coma, suggesting activity over its entire sunward hemisphere and possibly its entire nucleus. Our results, combined with those from others, reveal a chemical composition and behavior with heliocentric distance unlike any other comet we have observed.
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All authors Allison N. Bair, David G. Schleicher, Theodore Kareta, Matthew M. Knight, Michael S.P. Kelley

Astrophysics of Galaxies

Cool CGM MgII Absorption Across the Star-Forming, Green Valley, and Quiescent Transition

Simon Xinlin Wu, Rongmon Bordoloi, Robert A. Simcoe et al. (+4 more)

We investigate the distribution and kinematics of cool circumgalactic medium (CGM) gas across the star-forming to quiescent transition using MgII absorption for 716 galaxies spanning $0.07<z<2.7$ (169 new and 547 archival galaxies). To compare galaxies uniformly across 10 billion years of cosmic time, we introduce a star-formation offset metric ($\sigma_{\mathrm{SFO}}$), which measures a galaxy's deviation from the star-forming main sequence of its epoch. A key advantage of $\sigma_{\mathrm{SFO}}$ is its ability to identify transitional green valley galaxies as a distinct population across redshift, which would otherwise be obscured by binary star-forming-passive classifications. We fit a virial-radius-normalized radial profile and find that the MgII absorption strength declines with increasing projected distance from the host galaxy. The scatter around this mean profile correlates strongly with star-formation activity: radial profile residuals correlate positively with $\log sSFR$ and $\sigma_{\mathrm{SFO}}$, with star-forming galaxies showing excess absorption above the profile, green-valley galaxies showing intermediate residuals, and quiescent galaxies falling preferentially below it. The MgII covering fraction in the inner CGM ($R/R_{200} < 0.25$) follows the same sequence, declining monotonically from star-forming through green-valley to quiescent systems. MgII absorption kinematics are consistent with a predominantly bound cool CGM. Star-forming galaxies further exhibit a bimodal azimuthal dependence, with MgII absorption enhanced along both the polar and disk directions, consistent with bipolar outflows and co-planar accretion. Together, these results indicate that the cool CGM tracks the quenching of star-formation in galaxies, with $\sigma_{\mathrm{SFO}}$ revealing a gradual decline in cool gas across the green valley rather than an abrupt star-forming-to-passive transition.
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All authors Simon Xinlin Wu, Rongmon Bordoloi, Robert A. Simcoe, Andrew J. Fox, Jessica K. Werk, Jason Tumlinson, J. Xavier Prochaska

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

Signatures of Compact Object Mergers Inside Stars in AGN Disks

Matteo Cantiello, Alexander J. Dittmann, Saavik Ford et al. (+4 more)

Disks of gas accreting onto supermassive black holes, powering active galactic nuclei (AGN), can capture stars from nuclear star clusters or form stars in situ via gravitational instability. The dense, hot disk environment can drive rapid accretion onto embedded stars, dramatically altering their evolution. Models predict that, for sufficiently rapid accretion, fresh gas replenishes hydrogen in stellar cores as quickly as it is burned, and the stars reach a quasi-steady state. Here we study encounters of such massive, long-lived (”immortal”) stars with compact objects in AGN disks. We estimate the encounter rate and the timescale for a single compact remnant to spiral into an AGN star; depending on how strongly feedback regulates the ensuing accretion, the star is either consumed in a collapsar-like, engine-driven transient or converted into a long-lived, quasi-star-like object hosting a central black hole. We then study the merger of a binary black hole (BBH) inside the AGN star, and show that gas drag hardens the binary to merger far faster than gravitational-wave emission alone. The resulting merger is a loud LIGO-Virgo-KAGRA (LVK) source, but the characteristic imprint of the dense environment -a strong suppression and dephasing of the inspiral relative to vacuum- falls in the deci-Hz band rather than the milli-Hz LISA band, and is best resolved by next-generation detectors such as DECIGO. We estimate that this channel could contribute a BBH merger rate of up to $\sim8\,{\rm Gpc^{-3}\,yr^{-1}}$ in favorable scenarios, and discuss the model uncertainties and directions for future work.
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All authors Matteo Cantiello, Alexander J. Dittmann, Saavik Ford, Barry McKernan, Carlos Palenzuela, Rosalba Perna, Taeho Ryu

Astrophysics of Galaxies

A simulation-based quality-control framework for the broad-line region radius-luminosity relation

Juri Wladimir Seib, Francisco Pozo Nuñez and Sarah Elena Ivana Bosman

The broad-line region (BLR) radius-luminosity (R-L) relation underpins single-epoch black hole mass estimates in active galactic nuclei (AGN). The published H\beta sample is heterogeneous in observational quality, and it remains unclear how much of its scatter is intrinsic rather than caused by systematics in lag recovery. We quantify the contribution of unreliable lag recovery to the observed scatter of the H\beta R-L relation and provide tools for quality control. We compile a publicly available database of reverberation mapping measurements for ~1200 AGN from 32 campaigns spanning more than three decades, including lags, luminosities, line widths, black hole masses, and observational metadata. We develop a simulation-based consistency framework in which damped random walk light curves are sampled according to each campaign's baseline, cadence, and signal-to-noise ratio, and lags are recovered with the interpolated cross-correlation function (ICCF). Comparing expected, reported, and simulation-retrieved lags defines a four-tier flagging scheme. We refit the R-L relation with UltraNest for progressively cleaner samples and construct consensus samples across three reference slopes to reduce model dependence. Of 248 H\beta sources, ~40% show discrepancies between reported and simulation-retrieved lags, while ~5% show direct inconsistencies between expected and retrieved lags. Excluding flagged sources and correcting for model bias reduces the inferred intrinsic scatter from \sigma = 0.26^{+0.02}_{-0.01} dex to 0.11\pm0.01 dex, with a corrected slope of \alpha = 0.48\pm0.02. Our results indicate that a substantial fraction of the observed H\beta R-L scatter arises from observational limitations and lag-recovery biases rather than intrinsic AGN diversity. The database, simulation code, and RM-Scout campaign-planning tool are publicly available.
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Astrophysics of Galaxies

Spin inference with the Black Hole Explorer. I. Fisher information matrix forecast

Joseph R. Farah, Daniel C. M. Palumbo, Michael D. Johnson et al. (+1 more)

General relativity predicts the presence of a thin, bright ring of light superimposed on the image of a black hole (the “photon ring”), whose geometry is sensitive to the spin of the black hole. Detecting this photon ring in observations of nuclear supermassive black holes would yield insight into gravity in the strong-field regime as well as their growth histories. The Black Hole Explorer (BHEX) is a mission being developed to detect the photon ring for the first time, raising the question of how precisely we can constrain spin from its observations. We use the method of Fisher information matrices (FIMs) along with a simple dual-cone semi-analytic emission model to forecast BHEX spin posterior widths for the primary science targets (M87* and Sgr~A*) in a variety of configurations. We find that BHEX can constrain the dimensionless spin of its targets to a precision of $\sigma_{a_*} \ll 0.1$ after 30 orbits, even in the presence of significant systematic errors. We validate our results via numerical checks for stability and robustness, as well as synthetic data cross-validation to assess handling of covariances and prior information in the FIM against a full posterior exploration.
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All authors Joseph R. Farah, Daniel C. M. Palumbo, Michael D. Johnson, Dominic O. Chang

Astrophysics of Galaxies

More Numerous and Bluer: Companions of the Brightest Little Red Dots Differ from Control Galaxies at $>3\sigma$, Hinting at Synchronized Black Hole Seed Formation

Fabio Pacucci and C. Megan Urry

The Little Red Dots (LRDs) are compact, red sources at $4 \lesssim z \lesssim 9$, likely powered by accreting massive black holes. Multiple studies have detected blue companions in their vicinity: we compare $253$ LRDs, uniformly selected across several JWST deep fields, against $>7000$ matched controls in the same mosaics. We find that $27.7\%$ of the brightest LRD quartile (in F444W) hosts a blue ($\beta<-1$) companion at $0.5-2$ kpc, versus $11.6\%$ of redshift-matched controls: a $\times 2.39$ excess, significant at $3.3\sigma$. Against controls additionally matched in brightness and compactness, the excess ratio is similar ($\times 2.17$), although constrained only at $1.4\sigma$ by the small size of that control pool. This phenomenon is limited to the brightest LRDs, as the full LRD sample pairs at a rate indistinguishable from controls. Moreover, the excess is confined to the close-pair window ($< 2$ kpc), outside which LRD environments are ordinary. Their companions are overwhelmingly ($92\%$) blue and significantly bluer than those of controls ($\beta\approx-2.32$ versus $-1.92$), rejecting a common parent distribution at $3.4\sigma$. The signal is thus directional in brightness, separation, and companion color, as expected for synchronized-pair seed formation. Therefore, we conclude that the association between the brightest LRDs and their close blue companions is physical, i.e., the two phenomena are causally connected: either one drives the other, or both emerge from the same synchronized formation event. A natural explanation is that the radiation from these young, star-forming neighbors enabled the direct collapse of the massive black holes powering the LRDs themselves.
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Astrophysics of Galaxies

The descendants of $z \gtrsim 10$ JWST galaxies in the COLIBRE simulations

Xu Zhao, Carlos S. Frenk, Andrew Pontzen et al. (+9 more)

Recent observations with JWST have revealed a population of UV-bright galaxies at $z\gtrsim 10$. This discovery naturally raises the question: what do such early galaxies evolve into by the present day? In this work, we address this descendant question using the new-generation COLIBRE cosmological hydrodynamical simulations to trace bright galaxies selected at $z=10$ and follow their descendants to the present day. Most of the high-redshift galaxies do not survive as distinct, self-bound objects to $z=0$; instead, the majority are incorporated into more massive systems through merging or disruption. The surviving descendants span a broad range of present-day stellar masses, although they are most commonly intermediate- to high-mass, $M_\star\sim10^{10}$–$10^{11} M_\odot$. They typically reside in galaxy groups and clusters, with host halo masses, $M_{200c}\sim10^{13}$–$10^{14} M_\odot$. The large scatter in descendant stellar mass shows that present-day outcomes retain only a weak memory of the stellar mass of the high-redshift progenitor. We show that the evolution of descendant host halo masses is consistent with the forward conditional distribution predicted by extended Press–Schechter (EPS) theory, both in the median growth and in the large scatter in descendant mass. In particular, EPS confirms that massive present-day galaxies typically do not originate from the most massive objects at high redshift. A galaxy observed at $z\gtrsim10$ therefore cannot be interpreted as the direct progenitor of a single class of $z=0$ galaxies.
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All authors Xu Zhao, Carlos S. Frenk, Andrew Pontzen, Kyle A. Oman, Evgenii Chaikin, Isabel Santos-Santos, Shengdong Lu, Joop Schaye, Alejandro Benítez-Llambay, Filip Huško, Alexander J. Richings, Matthieu Schaller

Astrophysics of Galaxies

The ALMA EGO-10 Survey of Massive Protoclusters: Correlation of 1.3 mm Continuum Source Clustering with Evolutionary State

Michael C. Logue, Claudia J. Cyganowski, Crystal L. Brogan et al. (+4 more)

Massive stars characteristically form in clustered environments. Characterising young massive 'protoclusters' is therefore crucial to constraining the mechanism(s) of massive star formation, and of the assembly of stellar clusters. We present 1.3 mm continuum results from the ALMA EGO-10 imaging survey, targeting ten Spitzer GLIMPSE Extended Green Objects (EGOs) - massive protostars with active outflows traced by extended 4.5 $\mu$m emission. Our sensitive 1'.6$\times$1'.6 mosaics reveal rich protoclusters associated with all targets. With a mean spatial resolution 2200$\times$1600 AU, we identify 570 cores - between 13 and 135 per field. We quantify protocluster structure with the $Q$-parameter, finding structural diversity with 0.5 $\lesssim Q \lesssim$ 0.9. The sample is notable for the wealth of complementary high-resolution multiwavelength data available. Correlating our cores with these observations, we find only 2%, 5% and 4% of cores host 6.7 GHz CH$_3$OH masers, 22 GHz H$_2$O masers and cm-$\lambda$ continuum sources, respectively. The massive protostars traced by 6.7 GHz masers typically reside near protocluster centres (median offset 0.045 pc), and all at $d<$ 3 kpc are found in clustered locales, with $>$10 cores within 10,000 AU. Using VLA cm-$\lambda$ continuum observations, we construct a new evolutionary indicator: the ratio of protocluster cm-$\lambda$ continuum luminosity to the mass of the associated ATLASGAL clump ($L_\text{cm}/M_\text{AGAL}$). This ratio correlates positively with $Q$, with the correlation driven primarily by the cm-$\lambda$ continuum emission from MYSOs. This suggests dynamic protocluster structure, evolving from subclustered to centrally condensed, consistent with the global collapse in hierarchical, clump-fed models of massive star formation.
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All authors Michael C. Logue, Claudia J. Cyganowski, Crystal L. Brogan, Todd R. Hunter, Alessio Traficante, Allison P. M. Towner, Stella S. R. Offner

Astrophysics of Galaxies

The Road to Normalcy: Environment-Driven Evolutionary Pathways for Primordial Black Holes

Saiyang Zhang, Junehyoung Jeon, Boyuan Liu et al. (+2 more)

We investigate how cosmological environment regulates the evolution of primordial black hole (PBH) seeds in the early universe using a suite of hydrodynamical simulations. Unlike traditional seeding channels, PBHs provide early BH seeds without the need of special conditions for gas collapse/fragmentation that favor overdense regions, thus covering diverse large-scale environments. We find that PBHs follow distinct evolutionary pathways depending on the gas supply and halo assembly history. In underdense regions, limited inflow suppresses both accretion and star formation, producing faint, metal-poor systems, while in overdense environments, sustained gas inflow drives rapid BH growth and the formation of compact, centrally concentrated stellar components. These differences lead to large variations in BH-to-stellar mass ratio, metallicity, and morphology, collectively bracketing a range of possible evolutionary pathways for PBH-seeded systems. We show that compact, BH-dominated sources resembling recently observed Little Red Dots naturally arise as one phase within these evolutionary pathways before evolving into more extended galaxy–AGN systems. Our results suggest that both the initial seed properties and cosmological environment jointly shape early BH–galaxy co-evolution, while subsequent environmental regulation can erase the memory of the initial seeding channel.
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All authors Saiyang Zhang, Junehyoung Jeon, Boyuan Liu, Volker Bromm, Priyamvada Natarajan

Astrophysics of Galaxies

Fragmentation and tidal locking in young quadruple systems

Xunchuan Liu

Young quadruple systems provide a particularly simple setting in which the connection between successive levels of fragmentation can be studied. Motivated by the recurring symmetric configurations observed in a small number of young systems, we propose a theoretical framework in which such configurations arise naturally during rapid collapse. Rotational fragmentation followed by secondary fragmentation can produce two comparable-mass components of a wide pair, each of which further fragments into an unequal-mass close pair. The combination of tidal forces and accretion-driven shear can then establish a preferred phase relation, with the lower-mass component located on the inner, preceding side of the higher-mass component in each close pair. During subsequent capture, this phase relation can shift, placing the lower-mass component on the inner, trailing side. Asymmetric partitioning of a coherent, rapidly accreting flow can also tilt the spin axes of the fragments, providing a possible origin for spin misalignments without requiring an initially incoherent large-scale flow. The proposed mechanism therefore provides a possible physical origin for the characteristic phase relations in young quadruple configurations and for stochastic spin orientations within star clusters.
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