Instrumentation and Methods for Astrophysics
Habitable Worlds Observatory Living Worlds Working Group: Surface Biosignatures on Potentially Habitable Exoplanets
Niki Parenteau, Anna Grace Ulses, Connor Metz et al. (+16 more)
The Habitable Worlds Observatory (HWO) is the first NASA Astrophysics flagship mission with a key science goal of searching for signs of life on rocky habitable
exoplanets beyond our
solar system. The Living Worlds Community Working Group was charged with investigating how HWO could characterize
planets orbiting
stars in the
solar neighborhood, search for signs of life, and interpret potential biosignatures within a false positive and false negative framework. The Surface Biosignatures Task assessed the measurement requirements and instrument needs to detect these biosignatures under an 'Earth through time' scenario. Surface biosignatures are planetary-scale spectral features resulting from absorption and/or scattering of radiation by organisms containing photosynthetic and non-photosynthetic pigments. This secondary class of biosignature can be used to corroborate atmospheric biosignatures by providing multiple lines of evidence to aid in assessing their biogenicity. Furthermore, surface biopigments are the only way to detect more primitive forms of anoxygenic photosynthesis if oxygenic photosynthesis never evolved. Key Findings: To detect biopigments on the surface of
planets under Archean, Proterozoic, and Modern atmospheric compositions (15 percent coverage, 50 percent cloud cover), an SNR of 20-40 would be needed over 500-1100 nm. However, there may be some cases in which lower SNR is required; studies are ongoing. Coronagraph requirements: (1) The detection of surface biosignatures would be greatly enhanced by having as many parallel coronagraph channels as possible across the entire wavelength range with no or minimal gaps between channels. (2)
Retrieval studies revealed that restricted wavelength ranges (e.g., 0.4 - 0.7 microns), such as may be used during initial survey strategies, are not sufficient to deconvolve the biopigment features from the abiotic background.
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All authors Niki Parenteau, Anna Grace Ulses, Connor Metz, Nancy Y. Kiang, Ligia F. Coelho, Edward Schwieterman, Jonathan Grone, Giulia Roccetti, Svetlana Berdyugina, Eleonora Alei, Lucas Patty, Emilie Lafleche, Taro Matsuo, Dawn Cardace, Schuyler Borges, Avi Mandel, Kenneth Gordon, Joshua Krissansen-Totton, Giada Arney
Instrumentation and Methods for Astrophysics
Explainable Galaxy Interaction Prediction with Hybrid Attention Mechanisms
Sathwik Narkedimilli, Satvik Raghav, Om Mishra et al. (+5 more)
Galaxy interaction classification remains challenging due to complex morphological patterns and the limited interpretability of deep learning models. We propose an attentive neural ensemble that combines AG-XCaps, H-SNN, and ResNet-GRU architectures, trained on the
Galaxy Zoo DESI
dataset and enhanced with LIME to enable explainable predictions. The model achieves Precision = 0.95, Recall = 1.00, F1 = 0.97, and Accuracy = 96%, outperforming a Random Forest baseline by significantly reducing false positives (23 vs. 70). This lightweight (0.45 MB) and scalable framework provides an interpretable and efficient solution for large-scale surveys such as Euclid and LSST, advancing data-driven studies of
galaxy evolution.
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All authors Sathwik Narkedimilli, Satvik Raghav, Om Mishra, Mohan Kumar, Aswath Babu H, Tereza Jerabkova, Manish M, Sai Prashanth Mallellu
Astrophysics of Galaxies
Long Term (250 years) Hydrodynamical Simulation of the Supermassive Black Hole Binary OJ287
Ariel Chitan, Sarah C. Gallagher and Shahram Abbassi
With upcoming facilities capable of detecting photometric and gravitational wave signals from supermassive black hole (SMBH) binaries, studying their long-term
accretion-driven variability is timely. OJ287 is a bright, nearby ($z=0.3$), and well-studied candidate for a SMBH binary. As such, it is an excellent case study for how binary dynamics could influence observed active
galactic nucleus (AGN) photometric variability. We present 3D hydrodynamic simulations of OJ287, using the code PHANTOM. We simulate two mass ratios: (i) M$_1$ $=$ 1.835$\times$10$^{10}$ M$_\odot$ with M$_2$ $=$ 1.4$\times$10$^{8}$ M$_\odot$, (ii) M$_1\approx$ M$_2$ ($\sim10^{8}$ M$_\odot$) along and (iii) control of a single SMBH and
accretion disc. We find that the simulation with masses 1.835$\times$10$^{10}$ M$_\odot$ and 1.4$\times$10$^{8}$ M$_\odot$ evolves consistently with the most currently accepted model of OJ287 as a precessing SMBH binary. The secondary's impacts with the disc result in the formation of spiral density waves and a corresponding $\sim$10-20% increases in the mass
accretion rate of the primary SMBH. The impact timings and the mass
accretion rate spikes show quasi-periodic variability as a result of the precession of the secondary's orbit with intervals between impacts ranging from $\sim$ 1 year to $\sim$ 10 years. In the near-equal mass case, the disc of the primary becomes tidally disrupted after $\sim$ 2 years. Consequently, the near-equal mass system with a period of 12 years is not a viable candidate for OJ287. This modeling provides insights into the potential signatures of SMBH binaries by both gravitational wave observatories and the Rubin Legacy Survey of Space and Time.
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Astrophysics of Galaxies
QED V: Variations in metal loading of galactic winds with element nucleosynthetic origin
Aditi Vijayan, Mark R. Krumholz and Benjamin D. Wibking
Type Ia
supernovae, type II
supernovae, and asymptotic
giant branch (AGB)
stars are important sites of
stellar nucleosynthesis, but they differ greatly in their rates, their location within a
galaxy, and the mean thermal energy and abundance distribution of their ejecta. In earlier papers in this series we have shown that a significant fraction of metals newly synthesized by type II
supernovae are promptly lost to
galactic winds – i.e.,
galactic winds are metal loaded. Here we investigate whether the elements returned by type Ia
supernovae and AGB
stars are similarly metal loaded, or whether metal loading varies significantly with nucleosynthetic site. We use a series of high-resolution “tall box” simulations of the interstellar medium with the \quokka~GPU-accelerated code, within which we systematically vary the
galaxy gas surface density,
metallicity, and the scale heights and relative rates of the different nucleosynthetic sources. We show that the metal loadings of
galactic winds differ substantially between metals produced by different sources, with typical variations at the level of $\approx 0.3$ dex, a phenomenon we term differential metal loading. Which set of metals suffers preferential loss from this phenomenon varies depending on the
galactic environment, and is not easily predictable a priori. Our findings call into question the the interpretation of diagnostics of
galaxy formation, for example
star formation timescales and initial mass functions, based on abundance diagnostics, since the abundance variations upon which these techniques rely are often at levels comparable to those we show can be induced by differential metal loading.
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Solar and Stellar Astrophysics · Cross-listed from physics.plasm-ph
Magnetic reconnection as an Adler-Ohmic bifurcation: The topological origin of Bohm resistivity
Magnus F Ivarsen
The physical origin of 'anomalous' resistivity in
magnetic reconnection remains one of the longest-standing problems in space
plasma physics. While the empirical Bohm
diffusion scaling ($\eta \propto T/B$) is widely invoked to explain fast reconnection rates, it lacks a rigorous derivation from first principles. Here, we derive this scaling by modeling the ensemble of electron gyro-axes in a magnetized
plasma as an overdamped spintronic condensate governed by the Landau-Lifshitz-Gilbert equation. We demonstrate that the breakdown of the "frozen-in" condition is rigorously identified as an Adler-Ohmic bifurcation: a topological phase transition where electron gyro-axes lose synchronization with the mean
magnetic field. Unlike
stochastic turbulence models, this framework predicts a coherent, explosive onset of resistivity that naturally saturates at the Bohm limit. We support this thesis with renormalization group theory and a novel analysis of Magnetospheric Multiscale mission data, which reveals an explosive phase space confinement consistent with collective phase slippage rather than chaotic scattering. These results suggest that Bohm resistivity is a universal topological property of magnetized matter at the critical point of reconnection.
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Solar and Stellar Astrophysics
Stellar Rotation in the First Six Million Years: Rotational Velocities and Radii Estimates of T Tauri Stars in IC 5070 and IC 348
Laurin M. Gray, Katherine L. Rhode and Luisa M. Rebull
We have acquired high-resolution optical spectroscopy for a sample of T Tauri
stars (TTSs) in open clusters using Hydra on the WIYN 3.5m
telescope, and present projected rotational velocities (v sin i values) for 54
stars in IC 5070 and 99
stars in IC 348. We combine these with published values for
stellar temperature, luminosity, rotation period, circumstellar disk status, and binarity; we are predominantly interested in how the last two factors may affect the rotation speeds of the
stars. We find evidence to support theories that interaction with circumstellar disks may slow the rotation of TTSs compared to Class III
stars in both clusters. We also identify a higher fraction of slow-rotating Class III
stars in IC 348 compared to other clusters; we suggest that some fraction of these may be
stars that recently lost their disks. We find that a higher fraction of binary
stars are rapid rotators compared to single
stars, though not to a statistically significant degree. We also combine our v sin i measurements with rotation periods to estimate projected
stellar radii, which we compare to predictions from
stellar evolution models using a maximum likelihood method. We continue to show that models with increasing starspot coverage reduce radius inflation and align better with published age estimates than models without starspots.
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High Energy Astrophysical Phenomena
Identification of three new ultraluminous X-ray sources in NGC 4631 and NGC 1097: Evidence for stellar-mass black holes
Sinan Allak, Aysun Akyuz, Yasemin Aladag et al. (+2 more)
Recent observations of
galaxies continue to reveal new ultraluminous X-ray sources (ULXs), increasing their known population and improving the statistics needed to understand their nature. We study the ULX populations of NGC 4631 and NGC 1097 using archival Chandra, XMM-Newton, and Swift/XRT observations to identify new ULXs and investigate their X-ray and optical properties. We analyzed X-ray data spanning 2000-2025. Spectral fitting was performed for sources with sufficient counts using absorbed power-law and diskbb models. Variability analyses, including hardness-intensity diagrams and light curves, were used to assess short- and long-term variability. Optical color-magnitude diagrams and near-infrared (NIR) spectral energy distributions (SEDs) were employed to identify possible donor
stars. In NGC 4631, we identified two new transient ULXs, X-6 and X-7, with X-ray count rates varying by more than an order of magnitude. The LX-T^4 relation from diskbb fits provides strong evidence that NGC 4631 X-6 is powered by a
stellar-mass black hole accreting via a standard disk. The optical sources within the X-ray error circles of X-6 and X-7 are candidate counterparts, suggesting these systems are candidate HMXBs. In NGC 1097, we discovered a new transient ULX, ULX-3, showing X-ray luminosity variations by a factor of about 30 and evidence for spectral state transitions, consistent with either a
stellar-mass black hole or a
neutron star. We identified a unique optical and NIR counterpart. While the optical emission is variable, the NIR emission is stable. The NIR SED is consistent with a blackbody temperature of about 3300 K, compatible with a red supergiant donor with a radius of about 200
solar radii.
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All authors Sinan Allak, Aysun Akyuz, Yasemin Aladag, Lorenzo Ducci, Andrea Santangelo
Astrophysics of Galaxies
Reducing the Dimensions of AGN Lightcurve Manifolds
Shoubaneh Hemmati, Jessica Krick, Daniel Stern et al. (+10 more)
The Active
Galactic Nuclei (AGN) glossary is vast and complex. Depending on selection method, observing wavelength, and brightness, AGNs are assigned distinct labels, yet the relationship between different selection methods and the diversity of time-domain behavior within and across classes remains difficult to characterize in a unified framework. Changing-look AGNs (CLAGNs), which transition between classifications over time, further complicate this picture. In this work, we learn a data-driven, low-dimensional representation of multi-wavelength photometric light curves of AGNs, in which the structure of the projected
manifold correlates with AGN class and independent spectroscopic properties. Using the NASA Fornax Science Platform, we assemble light curves from ZTF, Pan-STARRS,
Gaia, and WISE/NEOWISE for two samples: (1) a heterogeneous set of $\sim$2000 AGNs spanning $z \lesssim 1$, including SDSS
quasars, variability-selected sources, and CLAGNs; and (2) a homogeneous sample of $\sim$65000 narrow-line AGNs at $z \approx 0.1$ with well-characterized optical emission-line measurements. Without using class labels during training, the learned
manifolds organize variability-selected AGNs into coherent regions of the low-dimensional space, distinguish between turn-on and turn-off CLAGNs, and place
tidal disruption events in distinct regions.
Manifold coordinates correlate with key spectroscopic and host-
galaxy properties, including
stellar mass, [OIII] luminosity, and D$_n$(4000), demonstrating that heterogeneous multi-band variability can be combined in a purely data-driven manner to recover correlations with independent physical diagnostics, without requiring explicit physical modeling. These results show that
manifold learning offers a practical, assumption-light approach for integrating time-domain surveys and prioritizing spectroscopic follow-up.
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All authors Shoubaneh Hemmati, Jessica Krick, Daniel Stern, Vandana Desai, Andreas Faisst, Lucas Martin-Garcia, Varoujan Gorjian, Aryana Haghjoo, Farnik Nikakhtar, Troy Raen, Sogol Sanjaripour, Brigitta M Sipocz, David Shupe
Astrophysics of Galaxies
Investigating quenching in Recently Quenched Elliptical galaxies with HI studies
Deepak K. Deo, Daniel H. McIntosh, Sravani Vaddi et al. (+4 more)
Recently Quenched Elliptical
galaxies (RQEs) represent a critical phase in the transition from
star-forming to quiescent
galaxies. However, the mechanisms driving their quenching remain elusive. We conduct a multi-wavelength analysis of 155 RQEs, along with their precursors (preRQEs) and descendants (postRQEs), focusing on their neutral hydrogen (HI) content and
star formation properties. Contrary to conventional quenching models emphasizing gas depletion, RQEs retain substantial HI reservoirs ($f_{\text{gas}} \geq 17\%$), suggesting that quenching is not primarily driven by gas exhaustion. We identify a critical
halo mass threshold at $\log M_{\text{halo}} = 12.1 M_{\odot}$, delineating different evolutionary pathways for RQEs. This threshold aligns with the transition from cold-mode to hot-mode gas
accretion in theoretical models. RQEs in lower-mass
halos ($\log M_{\text{halo}} < 12.1 M_{\odot}$) likely experience rapid quenching, possibly initiated by major mergers, followed by brief AGN activity and sustained LINER emission. We propose two evolutionary pathways: (a) rapid quenching via major mergers followed by AGN/LINER activity and passive
evolution, and (b) rapid quenching followed by rejuvenation through minor mergers before evolving into more massive, long-term quenched ellipticals. These results challenge the conventional understanding of
galaxy quenching, especially in low-density environments where RQEs typically reside. Our findings suggest that while RQEs may follow a rapid quenching pathway, their
evolution is influenced by interactions between gas
accretion modes, feedback mechanisms, and environmental factors. Future observations with advanced
radio interferometers like SKA will be crucial for elucidating the quenching mechanisms in RQEs and their role in
galaxy evolution.
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All authors Deepak K. Deo, Daniel H. McIntosh, Sravani Vaddi, Kameswara B. Mantha, Ruta Kale, Alfonso G. Franco, Paul Rulis
Earth and Planetary Astrophysics
Democratic heliocentric coordinates underestimate the rate of instabilities in long-term integrations of the Solar System
Hanno Rein, Kavi Dey and Daniel Tamayo
Wisdom-Holman (WH) integrators are
symplectic operator-splitting methods widely used for long-term N-body simulations of planetary systems. Most implementations use either Jacobi coordinates or democratic heliocentric coordinates (DHC) for the
Hamiltonian splitting, resulting in slightly different
algorithms. In this paper we report results from numerical experiments, which show that integrations of the
Solar System using DHC coordinates with typical timesteps of a few days suppress instabilities of the
planet Mercury. We further show that this is due to an eccentricity dependent artificial numerical precession introduced by the DHC splitting. While the DHC splitting converges to the correct results at shorter timesteps of ~0.6 days, we argue that Jacobi coordinates remain reliable to significantly longer timesteps when orbits become moderately eccentric, and are thus a better choice when the innermost
planet can reach high eccentricities.
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Instrumentation and Methods for Astrophysics
The LIRA-Ising Model: Estimating the boundaries of irregularly shaped X-ray sources
Kathryn McKeough, Vinay L. Kashyap, Aneta Siemiginowska et al. (+5 more)
Mapping the boundary of an extended source is a key step in the study of its morphology. The background contamination and statistical fluctuations of typical astronomical images make this a challenging statistical task, particularly for X-ray images with low surface brightness. We develop a three-step
Bayesian procedure to identify the boundaries of irregularly shaped sources. We first apply a
Bayesian multiscale reconstruction
algorithm known as LIRA to obtain posterior pixelwise probability distributions of the source intensity that properly account for known structures, astrophysical background, and the effect of the
telescope point spread function. Next, we adopt an Ising model to group pixels with similar intensities into cohesive regions corresponding to background and source. Finally, the boundary is derived on the basis of the most likely aggregation of pixels into the source region. Because the overall model combines LIRA and the Ising model, we call it LIRA-Ising. We verify the proposed method using a set of simulation studies. We then apply it to the Chandra X-ray Observatory images of two high
redshift quasars, PKS J1421-0643 and 0730+257, to determine the extent and morphology of X-ray jets. Our method shows a uniform X-ray surface brightness of PKS J1421-0643 jet, and identifies knotty structure in the X-ray jet of 0730+257.
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All authors Kathryn McKeough, Vinay L. Kashyap, Aneta Siemiginowska, David A. Van Dyk, Shihao Yang, Xiao-Li Meng, Brendan Martin, Andreas Zezas
Astrophysics of Galaxies
Evidence of Feedback Effects in Low-luminosity Active Galactic Nuclei Revealed by JWST Spectroscopy
Lulu Zhang, Chris Packham, Erin K. S. Hicks et al. (+17 more)
This letter presents an analysis of the infrared ($\sim 3-28\,\mu m$) spectra extracted from the
nuclear ($r < 150$ pc) regions of four low-luminosity active
galactic nuclei (AGN), observed by JWST NIRSpec/IFU and MIRI/MRS as an extension of the
Galaxy Activity,
Torus, and
Outflow Survey (GATOS). We find that, compared to higher-luminosity AGN, these low-luminosity AGN exhibit distinct properties in their emission of ionized gas, polycyclic aromatic hydrocarbons (PAHs), and molecular hydrogen (H$_2$). Specifically, the low-luminosity AGN exhibit relatively weak high-ionization potential lines (e.g., [Ne V] and [O IV]), and the line ratios suggest that fast radiative shocks (with $v_{\rm s}$ of $\sim \rm 100s\,km\,s^{-1}$) are the primary excitation source of ionized gas therein. Under the low-excitation conditions of their
nuclear regions, these low-luminosity AGN generally exhibit a higher fraction of PAHs with large size ($N_{\rm C} \gtrsim 200$), reflecting the preferential destruction of smaller PAH molecules by AGN feedback. Furthermore, the H$_2$ transitions in these low-luminosity AGN are not fully thermalized, with slow, plausibly jet-driven molecular shocks (with $v_{\rm s} \leq \rm 10\,km\,s^{-1}$) likely being the extra excitation source. Taken together with results from the literature, these findings indicate that feedback operates in both low- and high-luminosity AGN, albeit its impact varies with AGN luminosity. In particular, systematic variations in PAH band ratios are found across AGN, demonstrating the differing influence of feedback in AGN of varying luminosities and highlighting the potential of PAH band ratios as diagnostics for distinguishing kinetic- and radiative-mode AGN feedback.
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All authors Lulu Zhang, Chris Packham, Erin K. S. Hicks, Ric I. Davies, Daniel E. Delaney, Francoise Combes, Miguel Pereira-Santaella, Almudena Alonso-Herrero, Claudio Ricci, Omaira González-Martín, Laura Hermosa Muñoz, Ismael García-Bernete, Cristina Ramos Almeida, Dimitra Rigopoulou, Fergus R. Donnan, Enrica Bellocchi, Nancy A. Levenson, Martin J. Ward, Santiago García-Burillo, Sebastian F. Hoenig
Earth and Planetary Astrophysics
Cosmogenic 10Be as a Tracer for Recent Heliospheric Encounters with Interstellar Cold Clouds
Anna Nica, Merav Opher, Jesse A. Miller et al. (+2 more)
Recent works suggest there are periods when the Sun encountered massive interstellar cold clouds which compressed the heliosphere to within Earth's orbit, exposing Earth to interstellar
galactic cosmic rays and energetic particles of heliospheric origin. We model 10bE production in Earth's atmosphere during possible interstellar cloud encounters and
supernovae. We find that, if the heliosphere is compressed to 0.2 AU (r_TS=0.12 AU), the 10Be production rate is elevated 9x above the background. To be distinguished in marine sediments (iron-manganese crusts) beyond terrestrial variability, this signal must be sustained for >0.01 Myr (>0.5 Myr). A 0.7 AU (r_TS=0.4 AU) compression increases the 10Be production rate 3x above the background, which may be detectable if the event lasts >1 Myr. We find that the 10Be peak observed by Koll et al. (2025) 10 Ma is too prolonged to be produced by a
supernova, but could be attributed to an interstellar cloud crossing.
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All authors Anna Nica, Merav Opher, Jesse A. Miller, Jennifer L. Middleton, Joe Giacalone
Astrophysics of Galaxies
Galaxy interactions in void substructures: Morphology and stellar populations of two triplets from CAVITY
G. M. Azevedo, A. L. Chies-Santos, R. Riffel et al. (+5 more)
Context.
Cosmic voids are underdense regions of the Universe that provide a unique environment to study
galaxy evolution in relative isolation.
Galaxy triplets in voids are rare systems where local interactions may strongly influence
galaxy properties. Aims. We study the
stellar populations, morphologies, mass assembly histories, and dynamical properties of six
galaxies belonging to two void triplets from the Calar Alto Void Integral-field Treasury surveY (CAVITY): CAVITY5273X and VGS31. Methods. We used integral-field unit spectroscopy and performed full spectral fitting with the FADO code, which models
stellar and nebular emission simultaneously. Spatially resolved maps of
stellar age,
metallicity, and
star formation rate were reconstructed using the integrated nested Laplace approximation. Morphological properties were derived using morfometryka, emission-line diagnostics were applied, and mass assembly functions were computed.
Stellar masses and
metallicities were compared to the mass-
metallicity relation for void
galaxies. Results. The two triplets show different evolutionary behaviours. CAVITY52731 is a massive quenched
galaxy hosting an active
galactic nucleus, while its companions and all
galaxies in VGS31 are dominated by young
stellar populations and recent
star formation. Five
galaxies experienced rapid
stellar mass growth in the last 2 Gyr. Disturbed morphologies, including asymmetries and
tidal features, indicate ongoing interactions.
Galaxies in CAVITY5273X follow the expected void mass-
metallicity relation, while VGS31 members show significant deviations. Conclusions. Our results show that local interactions can drive significant
galaxy evolution even in the most underdense
cosmic environments.
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All authors G. M. Azevedo, A. L. Chies-Santos, R. Riffel, I. Perez, F. Ferrari, R. S. de Souza, M. Argudo-Fernandéz, B. Bidaran
High Energy Astrophysical Phenomena · Cross-listed from gr-qc
General gravitational properties of neutron stars: curvature invariants, binding energy, and trace anomaly
Iván Garibay, Christian Ecker and Luciano Rezzolla
We investigate the behavior of
curvature invariants for a large ensemble of
neutron stars built with equations of state (EOSs) that satisfy constraints from
nuclear theory and perturbative QCD, as well as measurements of
neutron-
star masses, radii, and gravitational waves from binary
neutron-
star mergers. Surprisingly, our analysis reveals that
stars with negative
Ricci scalar $\mathcal{R}$ are rather common and about $\sim 50\%$ of our EOSs produce one or more
stars with
Ricci curvature that is negative somewhere inside the
star. The negative
curvature is found mostly but not exclusively at the highest densities and pressures, and predominantly for stiff EOSs and for the most compact and most massive
stars. Furthermore, we improve the quasi-universal relation between the
stellar gravitational mass $M$ and the baryonic mass $M_\mathrm{b}$, which allows us to express analytically one in terms of the other with a maximum variance of only $\sim 3\%$. Finally, using the relation between the
Ricci scalar and the trace anomaly $\Delta$, we determine the conditions under which $\Delta$ vanishes or becomes negative in
neutron stars.
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Astrophysics of Galaxies
On the Jeans criterion for hydrostatic and infalling gas
Carlo Nipoti
We study the local gravitational instability of non-rotating astrophysical fluids allowing for the presence of an external gravitational potential in addition to the fluid self-
gravity. We present a self-consistent linear-perturbation analysis taking into account pressure and density gradients in the background medium. We explore two different steady-state configurations for the unperturbed gas: hydrostatic
equilibrium and infall into a gravitational potential well. We show that in both cases the instability criterion is the classical Jeans criterion, which, contrary to previous claims, is not modified by the presence of the external gravitational field. While in the case of hydrostatic
equilibrium linear local perturbations are always gravitationally stable, the conditions for gravitational instability can be met in the case of infalling gas, also in the presence of additional non-gravitational forces such as that due to a wind. We conclude that the Jeans criterion can have a role in regulating the formation of clumps and
star clusters in streams or shells of gas infalling into
galactic gravitational potential wells, as well as, on smaller scales, the fragmentation of gas in collapsing molecular clouds.
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High Energy Astrophysical Phenomena
The GRB Intrinsic Duration Distribution: Progenitor Insights Across Cosmic Time
Nicole M. Lloyd-Ronning, Omer Bromberg and Tsvi Piran
We present the distribution of the intrinsic duration of gamma-ray bursts'
prompt emission. This expands upon the analysis of Bromberg et al., 2012 and Bromberg et al. 2013 who showed evidence for collapsar progenitors based on the presence of a plateau in the distribution of $T_{90}$, the duration over which 90 % of the
prompt emission is observed for any given detector. We confirm the presence of this plateau in the distribution of duration corrected for cosmological time dilation (what we call intrinsic duration, $T_{int}$), but shifted to smaller timescales by a factor of $1/(1+z_{\rm av}) \sim 1/3$, where $z_{\rm av}$ is the average GRB
redshift. More significantly, we show this plateau is only present in the sample of GRBs with
redshifts greater than $(1+z) \sim 2$, and does not appear in the duration distribution of lower
redshift GRBs. This result aligns with suggestions that the low
redshift population of GRBs has a significant contribution from non-collapsar progenitors (while the high
redshift sample is dominated by collapsars). We also show the difference in this distribution between spectrally hard and soft GRBs, confirming that a plateau is only present for the soft subset of GRBs. However, when we separate the soft GRBs into low and high
redshift subsets, we find that only the high
redshift soft GRBs show evidence of a plateau, while the low-
redshift soft GRBs do not. This suggests there exists a significant subset of spectrally soft non-collapsar progenitors at low
redshift. Finally, we use the end time of the plateau to constrain the GRB progenitor density profile and radius, and show the maximum size of a collapsar is a few tenths of a
solar radius.
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Solar and Stellar Astrophysics
An eclipsing 8.56 minute orbital period mass-transferring binary
Emma T. Chickles, Joheen Chakraborty, Kevin B. Burdge et al. (+34 more)
We report the discovery of ATLAS J101342.5-451656.8 (hereafter ATLAS J1013-4516), an 8.56 minute orbital period mass transferring AM Canum Venaticorum binary with mean
Gaia magnitude G=19.51. The system was identified via periodic variability in Asteroid Terrestrial-impact Last Alert System light curves of
Gaia white
dwarf candidates. Follow-up spectroscopy with the Large Lenslet Array Magellan Spectrograph reveals a helium dominated
accretion disk, while high speed ULTRACAM photometry shows pronounced primary and secondary eclipses. We construct a decade long orbital timing baseline using ATLAS and
Gaia survey photometry together with high speed observations from ULTRACAM on the NTT and proto Lightspeed on the Magellan Clay
telescope. From this baseline we measure an orbital period derivative Pdot = -1.60 +/- 0.07 x 10^-12 seconds per second. Interpreted in the context of stable mass transfer, the magnitude and sign of Pdot indicate orbital
evolution governed by the interplay between gravitational wave driven angular momentum losses and mass transfer, directly probing the donor
star structural response to mass loss. Assuming angular momentum loss dominated by gravitational radiation, we constrain the component masses and infer the characteristic gravitational wave strain. We predict a four year
Laser Interferometer Space
Antenna signal to noise ratio greater than 10, establishing ATLAS J1013-4516 as a strong prospective space based gravitational wave source that probes long term orbital
evolution in the mass transferring regime.
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All authors Emma T. Chickles, Joheen Chakraborty, Kevin B. Burdge, Vik S. Dhillon, Paul Draghis, Kareem El-Badry, Matthew J. Green, Aaron Householder, Sarah Hughes, Christopher Layden, Stuart P. Littlefair, James Munday, Ingrid Pelisoli, Maya S. Redden, John Tonry, Jan van Roestel, F. Elio Angile, Alex J. Brown, Noel Castro Segura, Jack Dinsmore, Martin Dyer, Gabor Furesz, Michelle Gabutti, James Garbutt, Juliana García-Mejía, Daniel Jarvis, Mark R. Kennedy, Paul Kerry, James McCormac, Geoffrey Mo, Dave Osip, Steven Parsons, Eleanor Pike, Jack Piotrowski, Roger W. Romani, David Sahman, Rob Simcoe
Cosmology and Nongalactic Astrophysics
Sahyadri: A simulation suite for the cosmology dependence of the Cosmic Web
Saee Dhawalikar, Shadab Alam, Aseem Paranjape et al. (+1 more)
We present Sahyadri, a suite of cosmological $N$-body simulations designed to enable precision studies of the low-
redshift Universe with next-generation spectroscopic surveys. Sahyadri includes systematic variations of four cosmological parameters around Planck 2018 constraints, with seed-matched initial conditions enabling cosmological parameter derivatives. It is planned to ultimately extend to six parameters. Each simulation evolves $2048^3$ particles in a periodic box of side length $200$ $h^{-1}$ Mpc, yielding a particle mass of $m_{\rm{p}} = 8.1 \times 10^{7}\,h^{-1}\,M_{\odot}$ in the fiducial Planck 2018 cosmology. This resolution enables robust identification of dark matter
halos down to $M_{\rm min} = 3.2 \times 10^{9}$ $h^{-1}$ $M_\odot$, which represents a factor of $\sim$25 improvement over the AbacusSummit suite, and is over two orders of magnitude better than the Quijote and Aemulus suites. We estimate that approximately 40% of DESI BGS
galaxies at
redshift $z < 0.15$ - roughly 1.6 million objects - reside in
halos accessible to Sahyadri but beyond the reach of existing parameter-varying simulation suites. We demonstrate Sahyadri's capabilities through measurements of the matter power spectrum,
halo mass function and power spectrum, and beyond 2-point statistics such as the Voronoi volume function and $k^{\rm th}$ nearest neighbour statistics, showing excellent agreement with theoretical predictions and significant sensitivity to $\Omega_{\rm m}$ variations. We implement a custom compression scheme reducing storage requirements by a factor of $\sim$3 while maintaining sub-percent clustering accuracy. Key data products are publicly available.
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All authors Saee Dhawalikar, Shadab Alam, Aseem Paranjape, Arka Banerjee
Solar and Stellar Astrophysics
A persistent bow shock in a diskless magnetised accreting white dwarf
Krystian Ilkiewicz, Simone Scaringi, Domitilla de Martino et al. (+9 more)
Stellar bow shocks are formed when an
outflow interacts with the interstellar medium. In white
dwarfs accreting from a binary companion,
outflows are associated with either strong winds from the donor
star, the
accretion disk, or a thermonuclear runaway explosion on the white
dwarf surface. To date, only six accreting white
dwarfs are known to harbour disk-wind driven bow shocks that are not associated to thermonuclear explosions. Here, we report the discovery of a bow shock associated with a high-proper-motion disk-less accreting white
dwarf, 1RXS J052832.5+283824. We show that the white
dwarf has a strong
magnetic field in the range B~42-45 MG, making RXJ0528+2838 the a bonafide known polar-type cataclysmic variable harbouring a bow shock. The resolved bow shock is shown to be inconsistent with a past thermonuclear explosion, or being inflated by a donor wind, ruling out all accepted scenarios for inflating a bow shock around this system. Modelling of the energetics reveals that the observed bow shock requires a persistent power source with a luminosity significantly exceeding the system
accretion energy output. This implies the presence of a powerful, previously unrecognized energy loss mechanism - potentially tied to
magnetic activity - that may operate over sufficiently long timescales to influence the course of binary
evolution.
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All authors Krystian Ilkiewicz, Simone Scaringi, Domitilla de Martino, Christian Knigge, Sara E. Motta, Nanda Rea, David Buckley, Noel Castro Segura, Paul J. Groot, Anna F. McLeod, Luke T. Parker, Martina Veresvarska
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Charting the Flavour Structure of Dark Matter
Simone Biondini, Admir Greljo, Xavier Ponce Díaz et al. (+1 more)
What flavour structure of $t$-channel thermal dark matter remains compatible with current flavour physics and direct detection bounds? We broadly chart the space of hypotheses using the framework of flavour
symmetries and their breaking patterns. We then focus on scenarios in which the fermionic dark matter and its scalar mediator are flavour singlets, falling into the class of rank-1 flavour violation. For two representative
benchmarks, quarkphilic ($q_L$) and leptophilic ($e_R$), we perform a comprehensive phenomenological analysis, fitting the relic abundance and examining the interplay among flavour observables, direct detection, and
collider searches. Our results quantify the allowed deviations from flavour-symmetric limits and assess the discovery prospects in future flavour and direct detection experiments.
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All authors Simone Biondini, Admir Greljo, Xavier Ponce Díaz, Alessandro Valenti
High Energy Astrophysical Phenomena
Dense gas linked to star-forming regions photoionised by embedded gamma-ray bursts
Aishwarya Linesh Thakur, Luigi Piro, Alfredo Luminari et al. (+4 more)
The 1-100 pc region
embedding long-duration gamma-ray bursts (lGRBs) has been hitherto unexplored, as extremely high ionisation by the GRB prevents application of optical absorption spectroscopy on such distances. We show that the GRB ionising flux imprints a unique time- and spatially-dependent ionisation structure on the gas, that can be probed by X-ray absorption. Application of this model to a selected sample of 7 bright GRB X-ray afterglow spectra observed by XMM-Newton EPIC-pn enables an independent, quantitative estimation of the density (log(n) $\sim$ 2-4) and distances (5-100 pc) of the ionized absorber directly from the GRB X-ray spectrum, thereby allowing us to locate the absorbing medium of this representative sample of long GRBs in the region of the density-size diagram populated by
star-forming regions versus other gravitationally bound objects in the Universe. Our results provide one of the most direct links between lGRBs and
star formation and open the potential of high-resolution X-ray spectroscopy as a powerful probe of
star-forming regions that embed GRBs up to the highest
redshifts.
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All authors Aishwarya Linesh Thakur, Luigi Piro, Alfredo Luminari, Fabrizio Nicastro, Sandra Savaglio, Yair Krongold, Bruce Gendre
High Energy Astrophysical Phenomena
Relativistic jets from millisecond proto-magnetars
Dhruv K. Desai, Luciano Combi, Daniel M. Siegel et al. (+1 more)
Rapidly rotating, strongly magnetized
neutron stars (“millisecond proto-magnetars”) formed in
stellar core-collapse,
neutron star mergers, and white
dwarf accretion-induced collapse have long been proposed as central engines of gamma-ray bursts (GRB) and accompanying
supernovae/kilonovae. However, during the first few seconds after birth,
neutrino heating drives
baryon-rich winds from the
neutron star surface, potentially limiting the magnetization and achievable Lorentz factors of the
outflow and casting doubt on whether proto-magnetars can launch ultra-relativistic jets at early times, as needed to power short-duration GRB. We present 3D general-relativistic magnetohydrodynamic simulations of
neutrino-heated proto-magnetar winds that incorporate M0
neutrino transport. While the global wind properties broadly agree with previous analytic estimates calibrated to one-dimensional models, our simulations reveal essential multidimensional effects. For rapidly rotating models with
spin periods P = 1 ms, centrifugal forces strongly enhance mass loss near the rotational equator, producing a dense, sub-relativistic
outflow ( ~0.1c). This equatorial wind naturally confines and collimates less
baryon-loaded
outflows emerging from higher latitudes, leading to the formation of a structured bipolar jet with a peak magnetization up to ~ 30-100 along the pole, sufficient to reach bulk Lorentz factors ~ 100 on larger scales. The resulting angular stratification of the
outflow energy into ultra-relativistic polar and sub-relativistic equatorial components is broadly consistent with the observed partition between beaming-corrected GRB energies and
supernova/kilonova ejecta. Our results demonstrate that millisecond proto-magnetars can launch relativistic jets within seconds of formation and highlight their potential role in powering the diverse electromagnetic counterparts of compact-object explosions.
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All authors Dhruv K. Desai, Luciano Combi, Daniel M. Siegel, Brian D. Metzger
Astrophysics of Galaxies
FROST-CLUSTERS – III. Metallicity-dependent intermediate mass black hole formation by runaway collisions in dense star clusters
Antti Rantala, Thorsten Naab, Natalia Lahén et al. (+4 more)
We explore the formation of intermediate mass black holes (IMBHs), potential seeds for supermassive black holes (SMBHs), via runaway
stellar collisions for a wide range of
star cluster (surface) densities ($4\times10^3 M_\odot$ pc$^{-2} \lesssim \Sigma_\mathrm{h} \lesssim 4\times10^6 M_\odot$ pc$^{-2}$) and
metallicities $(0.01 Z_\odot \lesssim Z \lesssim 1.0 Z_\odot)$. Our sample of isolated (>1400) and hierarchical (30) simulations of young, massive
star clusters with up to $N=1.8\times10^6$
stars includes collisional
stellar dynamics,
stellar evolution, and post-Newtonian equations of motion for black holes using the BIFROST code. High
stellar wind rates suppress IMBH formation at high
metallicities ($Z\gtrsim0.2 Z_\odot$) and low collision rates prevent their formation at low densities ($\Sigma_\mathrm{h}\lesssim 3\times10^4 M_\odot$ pc$^{-2}$). The assumptions about
stellar wind loss rates strongly affect the maximum final IMBH masses ($M_\bullet\sim 6000 M_\odot$ vs. $25000 M_\odot$). The total
stellar mass loss from collisions and collisionally boosted winds before $t=3$ Myr can together reach up to $5$–$10\%$ of the final cluster mass. We present fitting formulae for IMBH masses as a function of host
star cluster $\Sigma_\mathrm{h}$ and $Z$ which can be used to seed SMBHs in high resolution cosmological hydrodynamical simulations and in semi-analytic models for
galaxy formation. Our results favour IMBH formation in dense low
metallicity environments similar to $z\sim10$ James Webb Space
Telescope (JWST) proto globular clusters. IMBH formation is suppressed in the high
metallicity and low density conditions of the local Universe.
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All authors Antti Rantala, Thorsten Naab, Natalia Lahén, Klaus Reuter, Markus Rampp, Martyna Chruślińska, Bastián Reinoso
Astrophysics of Galaxies
MUSEQuBES: Investigating the Physical and Chemical Properties of Circumgalactic Gas Around Ly$\alpha$ Emitters at $z \approx 3.3$
Eshita Banerjee, Sowgat Muzahid, Joop Schaye et al. (+2 more)
We present a detailed study of the physical properties of absorbers associated with $z\approx3.3$ \lya\ emitters (LAEs) from the MUSEQuBES survey. Using \HI\ and ionic column densities derived from Voigt profile fitting, we determine the density and
metallicity of 75 absorbers associated with 59 LAEs through a custom-built
Bayesian framework. The overall sample shows a median density $\log\,(n_{\rm H}/{\rm cm^{-3}})=-2.7\pm0.7$ and
metallicity \met$=-1.6^{+1.2}_{-0.9}$ with $\approx15\%$ ($\approx 40\%$ including upper limits) of systems showing
metallicities consistent with the IGM at these
redshifts (\met$\lesssim -2.8$). Intriguingly, absorbers with $\log\, N(\rm HI)/{\rm cm^{-2}} \gtrsim 16.5$, corresponding to an overdensity of $\sim 100$ at $z=3$, exhibit a bimodal
metallicity distribution with peaks at \met$=-3.8\pm 0.2$ and $-1.8\pm 0.6$. The latter are observed at large impact parameters ($\gtrsim150$~pkpc) and often exhibit low-ionization species (e.g., \SiII, \AlII). We interpret the former as pristine inflowing gas from the
cosmic web, while the latter likely traces metal-enriched CGM associated with
outflows from faint
galaxies not detected in Ly$\alpha$ emission. We find no significant correlations between absorber
metallicity or density and host
galaxy properties, including
redshift, impact parameter, SFR, Ly$\alpha$ luminosity, or environment. Absorbers separated by $\lesssim500$~\kms\ show $\sim$1~dex
metallicity and $\sim$0.5~dex density variations, indicating physical and chemical inhomogeneity of the medium around these LAEs.
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All authors Eshita Banerjee, Sowgat Muzahid, Joop Schaye, Sean D. Johnson, Sebastiano Cantalupo
Instrumentation and Methods for Astrophysics
Quantifying Symmetry: Transformation Information for Planetary Nebulae and Supernova Remnants
Dmitry Shishkin and Amir Michaelis
We present a quantitative
symmetry-identification pipeline for astrophysical images based on Transformation Information (TI), an information measure of self-similarity under
geometric transformations. TI is expressed as a Kullback-Leibler (cross-
entropy) divergence between an image and its rotated or reflected counterpart on the overlapping domain. By scanning rotation angles and reflection axes, we obtain TI curves whose local minima identify
symmetry operations. We validate the method on a wind-rose pattern and then apply it to planetary nebulae, where the recovered axes trace bipolar and multipolar lobes consistent with morphology-based classifications. Applying TI to
supernova remnants yields estimate axes associated with protrusions, rims, and substructure. To emphasize global morphology, we introduce a thresholded two-level variant that compares binary silhouettes and can reveal outline-driven
symmetries. Finally, we quantify
symmetry using a minima prominence-to-width score and show that this compact descriptor separates Type Ia and core-collapse remnants into distinct populations for an X-ray sample. TI provides a non-parametric, reproducible framework for
symmetry identification, classification and population studies.
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Astrophysics of Galaxies
Relatively Fast and Reasonably Furious: Evidence for Increased Burstiness in Smaller Halos at Cosmic Dawn
Julian B. Muñoz, John Chisholm, Guochao Sun et al. (+7 more)
We introduce an effective framework to model
star-formation burstiness and use it to jointly fit
galaxy UV luminosity functions (UVLFs), clustering, and H$\alpha$/UV ratios, providing the first robust empirical evidence that early
galaxies hosted in lower-mass
halos are burstier. Using $z\sim 4-6$ observations, we find that
galaxies show approximately $0.6$ dex of SFR variability if hosted in
halos of $M_h = 10^{11}\, M_\odot$ (typical of $M_{\rm UV}\approx -19$
galaxies at $z = 6$). This translates into a scatter of $\sigma_{M_{\rm UV}}\approx 0.75$ mag in the UVLF, in line with past findings. Strikingly, we find that burstiness grows for
galaxies hosted in smaller
halos, reaching $\gtrsim 1$ dex for $M_h \leq 10^{9}\, M_\odot$ (corresponding to $\sigma_{M_{\rm UV}} \approx 1.5$ mag for faint $M_{\rm UV} \gtrsim -15$
galaxies). Extrapolating to higher
redshifts, when small
halos were more prevalent, the inferred mass-dependent burstiness can reproduce observed UVLFs up to $z\sim 17$ within 1$\sigma$, potentially alleviating the tension between pre- and post-JWST
galaxy-formation models. Current observations allow us to constrain the main burst timescale to approximately $20$ Myr, consistent with expectations from
supernova feedback, and suggest broad distributions of ionizing efficiencies at fixed $M_{\rm UV}$. Our results demonstrate that mass-dependent burstiness, as predicted by hydrodynamical simulations, is critical for understanding the mass assembly of early
galaxies.
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All authors Julian B. Muñoz, John Chisholm, Guochao Sun, Jenna Samuel, Jordan Mirocha, Emily Bregou, Alessandra Venditti, Mahdi Qezlou, Charlotte Simmonds, Ryan Endsley
Cosmology and Nongalactic Astrophysics
New Cold Dark Matter Crisis Revealed by Multiscale Cluster Lensing
Priyamvada Natarajan, Barry T. Chiang and Isaque Dutra
The properties of substructure in
galaxy clusters, exquisitely probed by gravitational
lensing, offer a stringent test of dark matter (DM) models. Combining strong- and weak-
lensing data for massive clusters, we map their total mass – dominated by DM – over the dynamic range needed to confront small-scale predictions for collisionless cold DM (CDM). Using state-of-the-art lens models, we extract four key subhalo properties: the mass function, projected radial distribution, internal density profile, and
tidal truncation radius. We find that the subhalo mass functions and truncation radii are consistent with CDM expectations. In contrast, the inner density profiles and radial distributions of subhalos are strongly discrepant with CDM. The incidence of
galaxy-
galaxy strong
lensing from subhalo cores exceeds CDM predictions by nearly an order of magnitude, requiring inner density slopes as steep as $\gamma \gtrsim 2.5$ within $r \lesssim 0.01R_{200}$ consistent with core-collapsed self-interacting DM (SIDM), while the same subhalos behave as collisionless in their outskirts. Additionally, the observed radial distribution of subhalos hosting bright cluster member
galaxies, explicitly modeled in the lens reconstructions, remains incompatible with CDM. Taken together, these small-scale stress tests reveal an intriguing paradox and challenge the DM microphysics of purely collisionless CDM, motivating hybrid scenarios – such as a dual-component model with both CDM and SIDM or entirely new classes of DM theories.
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High Energy Astrophysical Phenomena · Cross-listed from gr-qc
Signatures of a subpopulation of hierarchical mergers in the GWTC-4 gravitational-wave dataset
Cailin Plunkett, Thomas Callister, Michael Zevin et al. (+1 more)
Repeated black-hole mergers in dense
stellar clusters are a plausible mechanism to populate the predicted gap in black hole masses due to the pair-instability
supernova process. These hierarchical mergers carry distinct
spin characteristics relative to first-generation black holes. We introduce an astrophysically motivated model in the joint space of effective inspiral and precessing
spins, which captures the dominant
spin dynamics expected for hierarchical mergers. We find decisive evidence for a transition at $m_1 = 46.2_{-7.2}^{+12.6} M_\odot$, above which the population is nearly entirely hierarchical, a location consistent with the anticipated onset of the pair-instability gap. We also infer a global peak in the hierarchical merger rate at $m_1 = 15.7_{-1.1}^{+3.2} M_\odot$. The existence of low- and high-mass subpopulations of higher-generation black holes suggests the contribution of both near-
solar-
metallicity and metal-poor
star clusters to the hierarchical merger population. Our results reinforce the growing evidence for detailed, mass-dependent substructure in the
spin distribution of the binary black hole population.
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All authors Cailin Plunkett, Thomas Callister, Michael Zevin, Salvatore Vitale