Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc
Unique Gravitational-Wave Signals from Negative-Mass Binaries
Oem Trivedi and Abraham Loeb
Negative masses have long been explored, but their observational viability remains unclear. In this work, we develop a unified, observationally testable framework to constrain negative masses using both coupling level and dynamical probes. We establish that while dipole radiation bounds require universality of gravitational charge, the intrinsic dynamics of negative mass binaries generically lead to anomalous behaviors such as anti-chirps, dispersal and runaway motion. These signatures are absent in current gravitational wave observations, providing a robust exclusion channel independent of modified
gravity assumptions.
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Earth and Planetary Astrophysics
Bayesian Doppler Imaging: Simultaneous Inference of Surface Maps and Geometric Parameters
Yamato Ureshino, Hajime Kawahara, Hibiki Yama et al. (+1 more)
We present a fully
Bayesian, pixel-based Doppler imaging framework that enables the simultaneous inference of surface brightness maps and
geometric parameters, including the inclination $i$ and equatorial rotation velocity $v_{\mathrm{rot}}$, from high-resolution spectral time series. We treat the inference as a
Bayesian linear inverse problem conditioned on nonlinear
geometric parameters. The surface map is modeled as a Gaussian Process prior over pixel intensities, introducing a characteristic spatial scale that sets the map resolution. This allows analytical marginalization of the linear coefficients and efficient sampling of the nonlinear parameters with
Hamiltonian Monte Carlo. {Validation with synthetic data demonstrates that our method recovers the longitudes of large-scale surface inhomogeneities and constrains $v_{\mathrm{rot}}$ and $i$ under the adopted model assumptions, while also revealing the limited latitudinal sensitivity intrinsic to Doppler imaging.} We applied this framework to high-resolution VLT/CRIRES observations of the brown
dwarf Luhman 16B. Our analysis reveals a large-scale dark region at mid-latitudes, consistent with previous studies but now with spatially resolved uncertainty estimates. Furthermore, we successfully constrained the
geometric parameters without fixing \(v_{\mathrm{rot}}\sin i\) or $i$ to literature values, deriving an inclination of $i = 61.0_{-12.3}^{+14.3}$ degrees and an equatorial rotation velocity of $v_{\mathrm{rot}} = 31.2_{-3.1}^{+5.3}~\mathrm{km\,s^{-1}}$. These results indicate a radius broadly consistent with evolutionary models and suggest a possible
spin-axis misalignment under the assumption of comparable equatorial rotation velocities for the two components. Our code is publicly available under the MIT license.
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All authors Yamato Ureshino, Hajime Kawahara, Hibiki Yama, Kento Masuda
Astrophysics of Galaxies
Specific Star Formation Rate Enhancement across the Galaxy Merger Sequence: Insights from Citizen Science Classifications
Jacob Lee, Alexandra Le Reste, Claudia Scarlata et al. (+1 more)
We present an analysis of specific
star formation rates (sSFR) across the
galaxy merger sequence using visual classifications from the Zooniverse citizen science project "
Cosmic Disco: Characterizing
Galaxy Collisions". Our sample comprises 4884
galaxy systems pre-selected as merger candidates from SDSS DR17 ($0.01 < z < 0.05$, $M_* > 10^{8.5}M_\odot$) using Zoobot, of which 3690 were classified as mergers spanning pre-interaction through post-coalescence stages by citizen scientist volunteers. We find a weak but statistically significant positive correlation between $\log(\mathrm{sSFR})$ and visual merger stage ($r = 0.161$, $p = 7.23 \times 10^{-23}$), with a best-fit relation $\log\left(sSFR\right)=(0.148\pm0.015)\, S_{\rm Merg}-(1.865\pm0.038)$. The large RMS scatter (0.661 dex) reflects visual merger stages capturing wide merger timescales, and our results corroborate previous findings of increasing SFR enhancement with merger progression. This work shows that citizen science is a viable complement to automated and pair-based approaches to evaluate timescales for
galaxies across the merger sequence.
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All authors Jacob Lee, Alexandra Le Reste, Claudia Scarlata, Kameswara Mantha Bharadwaj
Astrophysics of Galaxies
Unmasking Stellar Feedback-Driven Bubbles: Identification and Properties Analysis
Aaron Angress, Michael M. Foley, Sarah M. R. Jeffreson et al. (+2 more)
The identification and tracking of
stellar feedback-driven
galaxy bubbles is an important topic in
star formation and
galactic structure research. However, current observational analysis of bubbles is limited in scope; information on bubble lifetime is inaccessible. Simulation data thus provides a unique opportunity to glean some of these characteristics at high resolution. We present an investigation into the characteristics and
evolution of hot, ionized bubbles in the interstellar medium of a
dwarf spiral (NGC300-like)
galaxy. We calculate the average radius, lifetime, temperature, density, and spatial distribution of the simulated feedback-driven bubbles using Lagrangian gas parcels, and we examine the relationship between these characteristics and the local
galactic environment. We find exponential distributions of bubble lifetime and size, and we find a positive correlation between bubble lifetime and galactocentric radius. Finally, we predict how the data would appear in H$\alpha$ tracers and compare the simulated values to observations. We find an additional positive correlation between the size of the bubbles and the galactocentric radius using their H$\alpha$ tracers.
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All authors Aaron Angress, Michael M. Foley, Sarah M. R. Jeffreson, Alyssa Goodman, Lars Hernquist
Instrumentation and Methods for Astrophysics
Wideband RFI Monitor Requirements, Design, and Commissioning at DRAO
Nicholas Bruce, Charl Baard, Stephen Harrison et al. (+7 more)
In this paper, we introduce the
radio frequency interference monitor deployed at the Dominion
Radio Astrophysical Observatory. It provides 2 GHz of instantaneous bandwidth, supporting channel bandwidths as fine as ~100 Hz for 1 s integrations, or integration times as low as ~50 ms for the standard 3.33 kHz channel bandwidth. After operating as a prototype instrument for several years, the monitor was commissioned to improve the calibration method, analog section temperature, and gain stability. It now operates both as a transient detector and as a long-term
radio environment characterization tool. We introduce novel applications for the monitor and derive a new method for calculating the effect of gain drift on integrated data.
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All authors Nicholas Bruce, Charl Baard, Stephen Harrison, Mohammad Islam, Abraham J. Otto, Dustin Lagoy, Robert Messing, Benoit Robert, Timothy Robishaw, Peter F. Driessen
Solar and Stellar Astrophysics
Thirty Circumbinary Disk Occultation Systems (KH 15D-like stars) from the OGLE Project
M. A. Urbanowicz, I. Soszyński, P. Pietrukowicz et al. (+14 more)
We present a catalog of 30
stars that are candidates for KH 15D-like binary systems, in which the observed brightness variations are caused by a circumbinary dusty disk that periodically obscures at least one of the
stellar components as it moves along its orbit. Thanks to the regular observations conducted within the Optical Gravitational
Lensing Experiment (OGLE) project, we provide unique light curves in the I and V bands with very long time baselines, in some cases beginning as early as 1997 and extending to the present day. Such long-term monitoring allows us to identify changes in eclipse widths, amplitudes, and light-curve shapes on timescales of many years. We highlight several circumbinary disk occultation (CBO) systems of particular interest and present spectra for three of them.
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All authors M. A. Urbanowicz, I. Soszyński, P. Pietrukowicz, A. Udalski, P. Mróz, M. Wrona, M. Ratajczak, M. K. Szymański, J. Skowron, D. M. Skowron, R. Poleski, S. Kozłowski, P. Iwanek, K. Ulaczyk, K. Rybicki, M. Gromadzki, M. Mróz
Cosmology and Nongalactic Astrophysics
How to augment cosmic shear measurements with radio polarimetry of galaxies?
Liang Dai, Junwu Huang, Weichen Winston Yin et al. (+2 more)
The integral polarization of spiral
galaxies in the
radio band has been proposed as a new tracer of the intrinsic
galaxy shape that augments
lensing shear measurements. We revisit the method of shear estimation in this context. We introduce a new statistical model in which
galaxy shape and polarization are Gaussian random variables with their covariance characterizing the quality of polarization-shape
alignment. Applying the principle of likelihood maximization, we then analytically derive unbiased, minimal-variance
estimators, which allow to simultaneously estimate gravitational shear, intrinsic shape
alignment and line-of-sight polarization rotation, all at once and accurate to first order in these three effects. New to the literature, our
estimators have the merits of being free of biases, robust in situations of few
galaxies or poor polarization-shape
alignment, allowing analytic reconstruction noise covariance, and minimizing uncertainties in power spectrum estimation, thus resolving conceptual issues of the existing estimation methods. This new analytic framework is generally applicable to future research that exploits the polarization-shape
alignment effect of
galaxies.
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All authors Liang Dai, Junwu Huang, Weichen Winston Yin, Rui Zhou, Simone Ferraro
High Energy Astrophysical Phenomena
Discovery of 30 Repeating Fast Radio Burst Sources and Uniform Population Statistics of 80 Repeating Sources from CHIME/FRB
Amanda M. Cook, Kaitlyn Shin, Ziggy Pleunis et al. (+44 more)
We present 30 newly discovered repeating fast
radio burst (FRB) sources from the second catalog of bursts detected by the FRB backend on the Canadian Hydrogen Intensity Mapping Experiment (CHIME/FRB). These repeaters have extragalactic dispersion measures (DMs) spanning $99.4-1446.0\ \text{pc cm}^{-3}$ and burst rates between $10^{-5.7}$ and $10^{-0.5}$ hr$^{-1}$ scaled to a fluence threshold of 5 Jy ms. We report evidence of monotonic, linear DM variations in four repeaters on years-long timescales. The newly discovered sources bring CHIME/FRB's total number of observed repeating FRBs to 80, 79 of which were discovered by CHIME/FRB, between 2018 July 25 and 2023 September 15. In the full CHIME/FRB sample, only 2.4$\pm 0.4\%$ of sources have been observed to repeat, and we do not find evidence for significant
evolution of this value over the duration of the experiment. We find no substantial evidence for bimodal populations of one-off and repeating FRBs in their burst rate distributions; the distribution of upper limits on repeat rates implied from observations of as-yet one-offs is entirely contained within the observed range of repeater burst rates and the distributions do not appear inconsistent. Similarly, using the population analysis framework of C. W. James (2023), we find that our observations of repeating and yet-one-off FRBs are equally well fit assuming a power-law distribution of repeat rates with 50$-$100% of the population repeating.
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All authors Amanda M. Cook, Kaitlyn Shin, Ziggy Pleunis, Maxwell Fine, Naman Jain, Derek Bingham, Alice P. Curtin, Gwendolyn Eadie, B. M. Gaensler, Jason W. T. Hessels, Calvin Leung, Robert Main, Nicole Mulyk, Ayush Pandhi, Paul Scholz, Seth R. Siegel, David C. Stenning, Thomas C. Abbott, Bridget C. Andersen, Mohit Bhardwaj, Alice Cai, Shami Chatterjee, Fengqiu Adam Dong, Emmanuel Fonseca, Danté M. Hewitt, Ronniy C. Joseph, Lordrick Kahinga, Mattias Lazda, Victoria M. Kaspi, Afrokk Khan, Bikash Kharel, Lluis Mas-Ribas, Kiyoshi W. Masui, Kyle McGregor, Daniele Michilli, Ryan Mckinven, Mason Ng, Kenzie Nimmo, Swarali Shivraj Patil, Aaron B. Pearlman, Mawson W. Sammons, Ketan R. Sand, Aylar Sedaei Oghani, Vishwangi Shah, Kendrick Smith, Ingrid Stairs, Tarik J. Zegmott
Astrophysics of Galaxies
The Peculiar Velocity of Messier~87 from Microarcsecond Geodetic VLBI Astrometry
Valeri V. Makarov, Phil Cigan and Kyle Corcoran
Our knowledge of the space velocity of Messier 87, which is the dominant
galaxy in the Virgo cluster, has been limited to the radial velocity component. Using a cadence of precision position measurements with the global geodetic very long baseline interferometry (VLBI) system over 28 years, we determined the proper motion vector of the
radio-emitting core by a robust statistical method involving 1-norm optimization and bootstrapping. The proper motion vector is directed at a position angle $189.2\degr \pm 3.5\degr$ in the equatorial International Celestial Reference Frame, and its magnitude is $10.19$ $\mu$as yr$^{-1}$ with an uncertainty of $0.64$ $\mu$as yr$^{-1}$. The projected velocity of the AGN in the tangential sky plane is ($787\pm50$)~km~s$^{-1}$. The peculiar velocity of Messier 87 with respect to the preferred rest frame of the
cosmic microwave background field is approximately 1037 km s$^{-1}$ (assuming a distance of 16.1 Mpc) with an angle of 65$^\circ$ to the current line of sight, which implies a tangential relative motion of M87 and the
Galaxy. The peculiar velocity of M87 is directionally concordant with the reconstructed and $\Lambda$CDM-simulated motion of the Virgo filament towards the Great Attractor, but the Milky Way moves slower by 470 ~km~s$^{-1}$ in that direction.
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Astrophysics of Galaxies
Identification of Compact Groups of Galaxies in IllustrisTNG300
Seungwu Yoo and Jubee Sohn
We identify compact groups of
galaxies (CGs) in the IllustrisTNG-300 simulation using a Friends-of-Friends (FoF)
algorithm. Our approach is designed to be comparable to systematic CG searches based on spectroscopic surveys, while avoiding the conventional Hickson selection criteria, which can bias samples toward relatively low-density environments. We construct two CG catalogs: one based on a three-dimensional distance linking length of 73 kpc (i.e., $50~h^{-1}$ kpc), and another based on projected and radial linking lengths of 73 kpc and $1000~\rm km~s^{-1}$. We refer to these as the position-position-position (PPP) and position-position-velocity (PPV) CG catalogs, respectively. The PPV catalog provides a direct analog to observed CG samples. At $z = 0$ in TNG300, we identify 383 PPP CGs and 1666 PPV CGs. A large fraction ($\sim 80\%$) of PPV CGs are not physically compact systems but are contaminated by line-of-sight interlopers. We demonstrate that the scaling relation between total group
stellar mass and velocity dispersion is an effective diagnostic for identifying false positives with line-of-sight interlopers. We further examine the large-scale environments of CGs and show that they reside in a wide range of densities, including the central regions of
galaxy clusters. These CG catalogs provide a robust foundation for studying the formation and
evolution of CGs in cosmological simulations.
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Astrophysics of Galaxies
Empirical estimates of how massive galaxies can be in {\Lambda}CDM
Miguel Enríquez-Vargas, Aldo Rodríguez-Puebla, Aditya Manuwal et al. (+3 more)
Using Extreme Value Statistics applied to the observed
galaxy stellar mass and the UV luminosity functions, we empirically estimate masses and luminosities of the most extreme
galaxies in cosmological surveys, including the full sky. We incorporate uncertainties in
stellar mass measurements (Eddington bias) and the scatter in the
stellar-
halo mass relation to derive empirical limits for
galaxies residing in the most massive
halos. The maximum observed $M_\ast$ strongly depends on survey area and
redshift, ranging from $M_\ast \sim 7 \times 10^{12} M_\odot$ for full-sky surveys at $z\sim0$ to $M_\ast \sim 10^{10}M_\odot$ at $z\sim16$. Massive
galaxies, particularly at high
redshift, approach the theoretical maximum baryonic mass available in
halos $M_\ast \sim 0.16 \times M_{\mathrm{vir}}$, consistent with previous claims. Accounting for measurement uncertainties significantly reduces the inferred maximum $M_\ast$ by up to $\sim1$ dex at $z\gtrsim10$, yielding
stellar masses consistent with $M_\ast < 0.16$ at all
redshifts. Assuming a perfect rank-order correspondence between the most massive
halos and
galaxies would guarantee this inequality at all
redshifts. At 2 $\lesssim$ z $\lesssim$ 6, the most massive
galaxies have
stellar masses comparable to the total cold gas reservoir from cold and cooling flows, suggesting near-maximal
star formation efficiencies, SFEs. At higher
redshifts,
halos are predicted to host
galaxies undergoing starburst phases. When accounting for
dust attenuation and adopting empirically inferred SFEs, we find good agreement between the model and the brightest observed UV
galaxies at high
redshifts. At lower
redshifts, however, observed UV
galaxies are too bright. Overall, our results indicate that current observations remain broadly consistent with $\Lambda$CDM once statistical and observational effects are properly accounted for.
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All authors Miguel Enríquez-Vargas, Aldo Rodríguez-Puebla, Aditya Manuwal, L. Y. Aaron Yung, Vladimir Avila-Reese, Carlo Cannarozzo
High Energy Astrophysical Phenomena
An Inverse-Compton-Boosted Cool Core Unifies Perseus's Radio and X-ray Halos
Philip F. Hopkins, Emily M. Silich, Jack Sayers et al. (+2 more)
Perseus is the brightest X-ray strong cool-core (SCC) cluster, with a bright central
radio and $\gamma$-ray source plus low-frequency
radio mini and
giant halos. It is the archetype of the cooling flow (CF) problem, with X-rays implying mass cooling rates orders-of-magnitude larger than observed in other channels. Recent work suggested that ancient ($\gtrsim$\,Gyr-old)
cosmic ray (CR)
halos (ACRHs), injected by the central source, would produce thermal-like soft X-ray inverse-Compton (CR-IC) emission 'boosting' the CC and alleviating the CF problem. We examine Perseus and show that a simple model of CRs injected by NGC 1275 (+satellites) simultaneously accounts for the excess CF luminosity and minihalo. The models reproduce Perseus's soft X-ray surface brightness and X-ray inferred density/temperature/pressure/
metallicity/cooling time/mass deposition rates; $\gamma$-ray spectra; extended hard X-rays; and
radio surface brightness and spectral index data, from kpc-Mpc. These also reproduce independent constraints on
magnetic field strengths and mass/potential models. The
evolution of the minihalo spectral index and surface brightness are predicted by an aging population of CRs boosting the apparent SCC luminosity via CR-IC, and match well the observed hard X-ray slopes. The '
giant' low-frequency
halo can be predicted by the sum of ACRHs around satellites distributed throughout the cluster, dominating diffuse synchrotron at $\gtrsim 100\,$kpc. Re-acceleration is neither needed nor important in these models, and implied CR transport speeds are consistent with buoyant advection. Previous claims of upper limits to non-thermal X-rays and CR pressure relied on strong assumptions which are not valid at the CR energies of interest, e.g. a power-law spectrum of CRs. This could resolve many historical puzzles about Perseus, and makes new predictions for future observations.
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All authors Philip F. Hopkins, Emily M. Silich, Jack Sayers, Sam B. Ponnada, Isabel S. Sands
Astrophysics of Galaxies
Satellite Metallicity Enhancement I: Suppressed Star Formation, Stellar Mass Loss, and Enriched Inflow of DESI and EAGLE Galaxies around Massive Clusters
Yuanye Lin, Ying Zu, Jessica Nicole Aguilar et al. (+26 more)
Environmental effects are a primary driver of elevated gas-phase
metallicities in
galaxies around massive clusters, but the underlying physical mechanisms for this satellite
metallicity enhancement (SME) are still unclear. Using the Dark Energy Spectroscopic Instrument (DESI) Data Release 1, we present the first measurement of the average SME as a function of projected cluster-centric distance. The resulting profile reveals three distinct regimes: a steep decline from the cluster center, a plateau near the cluster boundary, and an extended downturn across several cluster radii. Remarkably, the complex shape and amplitude of this observed SME profile are successfully reproduced in the EAGLE cosmological simulation. Drawing insights from EAGLE, we develop a novel satellite chemical
evolution model to decompose the observed SME into physical contributions from suppressed
star formation,
stellar mass loss, and enriched gas inflow. Our analysis shows that continuous
accretion of enriched intracluster medium dominates the SME plateau within the cluster virial radius, while mass loss and quenching jointly drive the rapid
metallicity decline in the cluster core. Our method disentangles the impacts of three environmental processes on
galactic chemical enrichment in the
cosmic web, providing a powerful framework for understanding cluster
galaxy evolution with current and future spectroscopic surveys.
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All authors Yuanye Lin, Ying Zu, Jessica Nicole Aguilar, Steven Ahlen, David Brooks, Todd Claybaugh, Andrei Cuceu, Axel de la Macorra, Andreu Font-Ribera, Jaime E. Forero-Romero, Satya Gontcho A Gontcho, Gaston Gutierrez, Dick Joyce, Martin Landriau, Laurent Le Guillou, Aaron Meisner, Ramon Miquel, John Moustakas, Will J. Percival, Francisco Prada, Ignasi Pérez-Ràfols, Graziano Rossi, Eusebio Sanchez, David Schlegel, Joseph Harry Silber, David Sprayberry, Gregory Tarlé, Benjamin Alan Weaver, Hu Zou
Earth and Planetary Astrophysics
You Shall Not Pass (Without Modeling): High-Resolution Analysis of KMT-2019-BLG-0253 using MORIA
T. Dex Bhadra, Sean K. Terry, David P. Bennett et al. (+6 more)
We present the Microlensing Object high-Resolution Imaging Analysis pipeline, or MORIA. This is an automated procedure to reduce high-resolution HST images of microlensing targets, build empirical point-spread function models from the data, and perform simultaneous multi-
star PSF fitting to blended sources, lenses, and neighbor
stars. We have developed and tested this pipeline using HST observations of the microlensing event KMT-2019-BLG-0253, which shows clear evidence of three highly-blended
stars in HST. Under our assumed source and lens identification, we determine a host mass of $M_{host} = 0.65 \pm 0.04M_{\odot}$. We have reduced the number of possible solutions for this target by a factor of two, with the remaining solution subject to the well known close-wide degeneracy. We determine a
planet mass of $m_{p} = 7.18 \pm 0.40 M_{\oplus}$ (close) or $m_{p} = 9.48 \pm 1.13 M_{\oplus}$ (wide), and distance to the lens system of $D_L= 2.64 \pm 0.22$ kpc. This target lies within the upcoming Roman
Telescope Galactic Bulge Time Domain Survey (GBTDS) field. Future analysis of the Roman data for this event can confirm or reject the initial source and lens identifications presented in this work. Finally, this work demonstrates the importance of using an automated high-resolution imaging tool to inform light curve modeling for microlensing
planets found during the GBTDS.
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All authors T. Dex Bhadra, Sean K. Terry, David P. Bennett, Aparna Bhattacharya, Ian A. Bond, Jon Hulberg, Stela Ishitani Silva, Przemek Mróz, Aikaterini Vandorou
High Energy Astrophysical Phenomena · Cross-listed from hep-ph
Revisiting predictions for cosmic-ray antinucleon fluxes from Galactic Dark Matter
Lorenzo Stefanuto, Mattia Di Mauro, Fiorenza Donato et al. (+3 more)
The data on
cosmic antiprotons have reached an outstanding precision on energies spanning from GeV to hundreds of TeV, thanks to the space-based AMS-02 experiment. The balloon-borne GAPS experiment, which just completed its first Antarctic flight, will address antiproton and antideuteron fluxes well below GeV energies. Antinuclei in
cosmic rays, as well as being produced by spallation reactions between
cosmic-ray
nuclei and the atoms of the interstellar medium, may hide contributions from exotic sources, such as particle dark matter annihilation in the
Galaxy. In this paper, we present predictions for
cosmic antiproton, antideuteron and antihelium fluxes both from secondary and dark matter origin. We use state-of-the-art production spectra,
nuclear coalescence for antinuclei, and
Galactic propagation models to derive upper limits on the dark matter annihilation cross-section from AMS-02 antiproton data in different propagation scenarios (BIG and QUAINT). We quantify the impact of future GAPS data, showing that its sensitivity to sub-GV antiprotons could improve the $\langle\sigma v\rangle$ constraints by up to an order of magnitude for light DM ($m_{\chi} \lesssim 50$ GeV). For heavier antinuclei, the detection perspective with existing and upcoming experiments are derived for those scenarios consistent with AMS-02 antiproton flux. The detectability of such signals strongly depends on the experiment, the propagation model, and the hadronization tuning. Our analysis underscores the complementarity of antinuclei channels for indirect DM searches and the critical role of low-energy windows in constraining light DM candidates.
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All authors Lorenzo Stefanuto, Mattia Di Mauro, Fiorenza Donato, Nicolao Fornengo, Jordan Koechler, David Maurin
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Primordial Black Hole Hotspots Beyond Flat Spacetime
Doojin Kim, TaeHun Kim, Jong-Chul Park et al. (+1 more)
Light
primordial black holes heat the surrounding
plasma via Hawking radiation, forming localized hotspots whose temperature may far exceed that of the cosmological background. Previous studies of hotspot formation and cooling have treated the subsequent energy transport in flat spacetime, thereby neglecting the expansion of the Universe. We formulate the
diffusion equation governing the hotspot
evolution, in an expanding universe, and clarify the regime in which the formalism is valid. We find that hotspot formation is robust against cosmological expansion. We show that the critical distance scale, where Hubble expansion overtakes
diffusion, coincides with the decoupling radius introduced in earlier work, and the temperature profile $T\propto r^{-7/11}$ essentially remains unchanged. However, the cooling stage is substantially modified. We find that the plateau temperature of a cooling hotspot initially undergoes a rapid drop and then follows $T_{\rm plt} \propto t^{-11/15}$, steeper than the flat-spacetime scaling $t^{-7/15}$. This scaling cannot be obtained by simply redshifting the flat-spacetime solution, because expansion also suppresses diffusive transport. As a consequence, all hotspots disappear within a finite time, as opposed to the flat-spacetime prediction of everlasting hotspots in part of the parameter space.
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All authors Doojin Kim, TaeHun Kim, Jong-Chul Park, Jong-Hyun Yoon
Cosmology and Nongalactic Astrophysics
CMB Limits on the Absorption of Light Vector and Axial-Vector Dark Matter
Gabriele Montefalcone, Nicola Bellomo and Kimberly K. Boddy
Leptophilic sub-MeV
spin-1 dark matter (DM) can be converted into a
photon via inelastic scattering with a free electron or absorption by a neutral hydrogen atom in the
primordial plasma. We study for the first time the impact of the energy injection resulting from such processes on
cosmic microwave background (CMB) anisotropies. We obtain upper limits on the vector and axial-vector DM-electron couplings using Planck 2018 temperature, polarization, and
lensing data for DM masses between 100 eV and 100 keV. We find that, due to the suppression of the hydrogen atomic form factor at high energies, inelastic scattering provides the dominant constraint for DM masses above the keV scale. At lower masses, hydrogen ionization through DM absorption is the leading channel, driven by the higher efficiency of post-recombination energy injection in modifying the free-electron fraction. Although the bounds we derive are considerably weaker than existing laboratory and astrophysical limits, they provide a robust and independent cosmological probe of leptophilic DM interactions.
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High Energy Astrophysical Phenomena
Magnetar field dynamics driven by chiral anomalies without magnetic helicity
Clara Dehman
The
chiral magnetic effect (CME), arising from the
chiral anomaly and enabling a mutual conversion between
magnetic topology and fermionic chirality, is a key mechanism in magnetar field
evolution. Previous work by Dehman & Pons (2025) demonstrated that the CME can efficiently generate dipolar fields $\left(B_{\rm dip} \gtrsim 10^{14}\,\mathrm{G}\right)$, consistent with magnetar timing measurements, provided that the initial
magnetic field carries net helicity. However, whether
neutron stars are born with
magnetic helicity remains uncertain. In this work, we investigate the CME across a range of initial helicity configurations, including non-helical initial conditions. We find that the CME efficiently generates magnetar-strength dipoles on timescales of decades, independently of the initial helicity content. The
chiral instability is driven by localized helical structures that induce a residual
chiral asymmetry and is primarily governed by the maximum
chiral chemical potential, requiring $\mu_5^{\rm max} \gtrsim \mathrm{few}\times10^{-11}\,\mathrm{MeV}$ for onset in the magnetar regime. Our results further show that these dipoles may either remain stable and subsequently evolve through standard Ohmic decay, or become unstable if they acquire sufficient helicity, in which case they decay through the
chiral anomaly, transferring energy to less helical modes. This outcome depends sensitively on the initial helicity distribution. These findings extend the applicability of the CME to more realistic
magnetic-field configurations and underscore the importance of the helicity distribution at birth, a quantity that remains poorly constrained in newborn
neutron stars, yet is crucial for determining their
magnetic evolution and the emergence of magnetars.
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Solar and Stellar Astrophysics
Period spacings and global seismic parameters for K2 red giants using deep learning
Nipun Ghanghas, Siddharth Dhanpal, Shravan Hanasoge et al. (+2 more)
Gravity-mode period spacings (DPi_1) of red
giants probe the
stellar core directly, constraining its structure, mass and evolutionary state. Their measurement requires resolving narrow, densely spaced mixed modes and has so far relied on the four-year baseline of Kepler. Recovering DPi_1 from the much shorter (~80-day) baselines typical of K2 remains largely unexplored at the ensemble scale. We develop an automated machine-learning technique to measure global asteroseismic parameters and
gravity-mode period spacings for red
giants from single-campaign K2 photometry. Two deep residual neural networks take the full-resolution power spectrum of an ~80-day light curve as input, without background fitting or mode identification, and return a probability distribution for each parameter, yielding a point estimate and asymmetric uncertainties. They are trained on ~8 million synthetic spectra and evaluated on held-out synthetics, on Kepler data degraded to K2-like resolution, and on K2 observations. On Kepler data at K2-like resolution, numax and Dnu are recovered for 96% and 91% of
stars with robust dispersions of 3.6% and 1.2%; DPi_1 for 22%, with a dispersion of 0.9%. Applied to 18,704 K2 red
giants, the inferred numax and Dnu agree with catalogue values to 5.8% and 1.9%, the additional scatter arising from known K2 artefacts. Among the 2,059 young red
giants we obtain DPi_1 for 232
stars with a median fractional uncertainty of 1.3%, following the same Dnu-DPi_1 sequence as the Kepler sample although the training set carries no imprint of that relation. We show that numax, Dnu and - for a subset of young red
giants - DPi_1 can be recovered from a single ~80-day K2 campaign within an automated, probabilistic machine-learning framework. This approach can also be extended to short-baseline samples from TESS and, in future, Roman and PLATO.
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All authors Nipun Ghanghas, Siddharth Dhanpal, Shravan Hanasoge, Praneeth Netrapalli, Karthikeyan Shanmugam
High Energy Astrophysical Phenomena · Cross-listed from hep-ph
Producing the GeV Galactic Center Excess via Cosmic Ray-Dark Matter Scattering
Bhaskar Dutta, Debopam Goswami, Jason Kumar et al. (+2 more)
In this work, we propose a novel mechanism for generating gamma rays from the
Galactic Center via scattering of
cosmic-ray
protons off dark matter in the Milky Way
halo, in contrast to conventional explanations based on dark matter annihilation. We present two examples of this framework that produce an observable
photon signal. In the inelastic dark matter model,
cosmic rays up-scatter a lighter dark matter particle, with the subsequent decay of the heavier particle yielding two
photons. In the elastic dark matter model, an energetic
photon is directly produced in the final state of a 2-to-3 scattering process. We show that, for a range of viable model parameters, this framework provides a fit to the observed
Galactic Center gamma-ray excess spectrum comparable to those obtained from dark matter annihilation and millisecond
pulsar models. Our results open a new avenue for interpreting gamma-ray observations of the
Galactic Center.
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All authors Bhaskar Dutta, Debopam Goswami, Jason Kumar, Mudit Rai, Deepak Sathyan
Astrophysics of Galaxies
The Spitzer Spectroscopic Data Fusion – Merged Spectroscopic Redshift Catalogs in Spitzer Fields
Mattia Vaccari
I present the Spitzer Spectroscopic Data Fusion, a collection of merged spectroscopic
redshift catalogs covering fourteen of the most widely studied extragalactic survey fields. Building on the Spitzer Data Fusion multi-wavelength photometric database, the collection merges several publicly available spectroscopic
redshift catalogs within each field using a 1 arcsec matching radius, delivers a single best
redshift per source together with provenance and overlap flags, and is available on Zenodo at https://zenodo.org/doi/10.5281/zenodo.6368347 The
dataset is regularly updated as new spectroscopic surveys are published. It is intended as a community calibration resource for photometric
redshift training, SED fitting, and multi-wavelength cross-identification studies.
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Astrophysics of Galaxies
Space as a spectroscopic laboratory: High-resolution spectroscopy of the [$^{13}$C II] hyperfine structure with SOFIA/upGREAT
S. Kabanovic, V. Ossenkopf-Okada, S. Schlemmer et al. (+13 more)
The [$^{12}$C II] emission at 158 $\mu$m is a key cooling line of the interstellar medium and traces gas kinematics in spectrally resolved observations. Its spectral profile is often modified by optical depth effects. The intrinsic line shape can be reconstructed by comparison with emission from the less abundant $^{13}$C isotope. Due to the additional
neutron spin, [$^{13}$C II] emission splits into three hyperfine structure (hfs) transitions. Laboratory measurements have provided the centroid frequency and the strongest component ($F=2-1$); the two weaker components ($F=1-0$ and $F=1-1$) have been inferred only from
quantum-mechanical calculations. The
magnetic-dipole hfs constants, from which the transition frequencies follow, have not been measured experimentally. The high spectral resolution of observations with the upgraded German Receiver for Astronomy at Terahertz Frequencies (upGREAT) on board SOFIA enabled simultaneous detection of all three hfs transitions. From these astronomical data we determine, for the first time, the
magnetic-dipole hfs constants $A_{1/2}^{\rm hf} = 810.71(11)$ MHz and $A_{3/2}^{\rm hf} = 162.18(5)$ MHz of the [$^{13}$C II] $2s^2\,2p\,{}^2P^\circ$ ground term. Combined with the laboratory centroid frequency, this yields the rest frequencies of all three hfs lines. Using [$^{12}$C II] as a reference, we also improve the precision of the [$^{13}$C II] centroid frequency. This work shows that spectrally resolved astronomical observations can constrain fundamental atomic properties, with hfs precision rivaling laboratory measurements. The approach extends to other atomic and molecular transitions where laboratory data are difficult to obtain.
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All authors S. Kabanovic, V. Ossenkopf-Okada, S. Schlemmer, J. Stutzki, N. Schneider, U. U. Graf, O. Asvany, D. A. Riechers, C. Guevara, R. Higgins, R. Simon, Y. Okada, M. Mertens, L. Schneider, R. Güsten, A. G. G. M. Tielens
Astrophysics of Galaxies
Testing the BH* model: A UV-to-optical spectral fitting of The Cliff
Rosa M. Mérida, Marcin Sawicki, Gaia Gaspar et al. (+2 more)
In the BH* framework, the V-shaped SED of LRDs is produced by an accreting BH embedded in a dense neutral-gas envelope with a near-unity covering factor. This envelope reprocesses the radiation and emits as a ~5,000 K blackbody, producing the optical continuum. Meanwhile, the UV is powered by a low-mass,
dust-free, metal-poor host. The BH* model is promising but has yet to undergo detailed testing; conducting a self-consistent UV-to-optical spectral-fitting analysis of LRDs would provide a robust assessment of the model. In this work, we tested the BH* scenario by fitting the full JWST/NIRSpec PRISM spectrum of The Cliff ($z_{spec}=3.55$), an LRD that played a pivotal role in the development of this model. A Bagpipes fit that allows
stellar, nebular, AGN, and blackbody components naturally yields a BH*-like solution for The Cliff, even with broad priors. Our method allows us to characterize its host despite it remaining unresolved in JWST imaging. From the continuum, we infer the host to be low-mass (log $M_\star/M_\odot$~7.7),
star-forming, metal-poor, and affected by non-negligible
dust attenuation ($A_V$~0.5 mag) acting on both
stellar and nebular components. Higher $M_\star$ (up to log $M_\star/M_\odot$~8.1) and attenuations (up to $A_V$~1 mag) are obtained depending on the assumed
dust law. Modest AGN UV leakage is consistently allowed-and sometimes preferred-by the code but remains weak and not robustly constrained, with both AGN+host and host-dominated UV scenarios yielding statistically equivalent fits. The SFH of the host is relatively smooth, with the
galaxy already assembling log $M_\star/M_\odot$~7 about 200 Myr before $z=3.55$. The BH-to-$M_\star$ ratio consistently exceeds the values expected from BH-host scaling relations, especially at recent times. This tension may indicate either inaccurate estimates of the BH properties or non-coeval BH-host
evolution in this LRD.
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All authors Rosa M. Mérida, Marcin Sawicki, Gaia Gaspar, Chris J. Willott, Kartheik G. Iyer
Astrophysics of Galaxies
A Changing-Look Seyfert Discovered by eROSITA Reveals a Two-Component Broad-Line Region
Alex Markowitz, Mirko Krumpe, David Homan et al. (+12 more)
Extreme sudden changes in the flow of accreting gas onto SMBHs manifest themselves via large-amplitude continuum variability and changes to broad Balmer emission profiles, driving changing-look AGN. X-ray flux monitoring with SRG/eROSITA revealed that in the Seyfert AGN HE 1237-2252 the soft X-ray flux dipped abruptly, by a factor of 17 within 18 months. We initiated a follow-up campaign that caught the luminosity recovery after the dip, and enabled us to study how the various
accretion components responded during this flux recovery. Our campaign included multiband photometry, X-ray spectroscopy, and optical spectroscopy. We tracked as the
accretion rate relative to Eddington increased by a factor of 7 in 3 years. Based on broad Hbeta variability, HE 1237-2252 was subtype 1.0-1.2 in 2002, transitioned to subtype 1.8 by the time of the luminosity dip, and then transitioned back to subtype 1.0 within 3 months as luminosity recovered. Both transitions saw broad Hbeta integrated line flux change by factors of 4-6. The broad Balmer profile is decomposed into a broad Gaussian consistent with virialized gas at 27+/-3 lt-dy, plus a double-peaked profile, consistent with a diskline structure at more than roughly 5 lt-dy. The diskline component's relative contribution to the total profile increases as continuum flux rises. The lack of obscuration in the X-ray spectra, as well as the IR continuum dip, point to an intrinsic pause in the
accretion rate as opposed to variable line-of-sight obscuration. Candidates for the underlying mechanisms include propagating cold and warm fronts in the
accretion disk. The increased prominence of the diskline BLR component's emission could be due to
evolution in the physical extent of the X-ray corona, and in the fraction of >13.6 eV
photons intercepted by the diskline, as the
accretion rate increases.
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All authors Alex Markowitz, Mirko Krumpe, David Homan, Bożena Czerny, Mariusz Gromazdki, Hartmut Winkler, Joern Wilms, Steven Hämmerich, Georg Lamer, Tathagata Saha, David A.H. Buckley, Malte Schramm, Daniel E. Reichart, Mara Salvato, Pietro Baldini
Instrumentation and Methods for Astrophysics
Systematic Comparison between Constrained Transport and Mixed Divergence Cleaning Methods for Astrophysical Magnetohydrodynamic Simulations
Kengo Tomida, Kenji Eric Sadanari, Shinsuke Takasao et al. (+1 more)
Magnetohydrodynamic (MHD) simulations are indispensable research infrastructure in astrophysics today. In order to satisfy the solenoidal constraint of the MHD equations on discretized grids, modern simulation codes often employ either constrained transport (CT) with a staggered grid or divergence cleaning using an additional variable. We compare CT and Dedner's mixed divergence cleaning schemes systematically, and find that the divergence cleaning scheme can produce substantial artifacts in certain situations. Through numerical experiments including both idealized tests and practical applications, we show that the original implementation of Dedner's scheme becomes inaccurate when
magnetic fields are strongly localized or when the timestep suddenly changes. We find that some previous results, such as the extremely rapid growth of
magnetic fields during
star formation in the early Universe, may be affected by the spurious behavior of the divergence cleaning scheme. We propose a few modifications to improve the robustness of the divergence cleaning method. Nevertheless, we find that the CT scheme is more accurate and reliable in many situations.
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All authors Kengo Tomida, Kenji Eric Sadanari, Shinsuke Takasao, Kazunari Iwasaki
Astrophysics of Galaxies
Constraining the Galactic bar using the M92 stellar stream
Amanda Byström, Sergey E. Koposov, Ting. S. Li et al. (+42 more)
Stellar streams are excellent probes of the gravitational potential in which they evolve. In the Milky Way (MW), globular cluster (GC) streams are routinely used to infer properties about time-dependent perturbations of the underlying potential. This implies that streams with Galactocentric radii small enough to be perturbed by the MW bar should offer constraints on it, such as its pattern speed, which currently has a wide range of values reported in the literature and is important when studying
stellar kinematics. The GC M92 has a small pericentre and should be affected by the bar. It has a diffuse
stellar stream, but confirming stream members has previously been hindered by a lack of spectroscopic data. In this paper, we use Dark Energy Spectroscopic Instrument (DESI) observations together with photometric and astrometric data to obtain spectroscopic members of the M92 stream for the first time. We identify a clear spatial distribution and gradients in distance
moduli, proper motions, and radial velocities that confirm the stream's existence. We compare the observed stream to mock streams generated in different barred potentials and estimate the MW bar's pattern speed $\Omega = 29.1^{+0.7}_{-0.4}$ km s$^{-1}$ kpc$^{-1}$ and $\dot \Omega = 0.7^{+3.5}_{-2.3}$ km s$^{-1}$ kpc$^{-1}$ Gyr$^{-1}$. This is the first time a
stellar stream is used to probabilistically infer these bar properties, and it opens up an exciting realm of inner
Galactic potential characterisation using
stellar streams.
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All authors Amanda Byström, Sergey E. Koposov, Ting. S. Li, Constance M. Rockosi, Arjun Dey, Guillaume F. Thomas, Raymond G. Carlberg, Oleg Y. Gnedin, Namitha Kizhuprakkat, Mika Lambert, Nasser Mohammed, Gustavo E. Medina, Joan Najita, Alexander H. Riley, Nathan R. Sandford, Leandro Beraldo e Silva, Jessica N. Aguilar, Steven Ahlen, Davide Bianchi, David Brooks, Todd Claybaugh, Andrew P. Cooper, Andrei Cuceu, Axel de la Macorra, Peter Doel, Jaime E. Forero-Romero, Satya Gontcho A Gontcho, Gaston Gutierrez, Richard Joyce, Stephanie Juneau, Anthony Kremin, Martin Landriau, Laurent Le Guillou, Aaron Meisner, Ramon Miquel, Will J. Percival, Francisco Prada, Ignasi Pérez-Ràfols, Graziano Rossi, Eusebio Sanchez, David Schlegel, Joseph H. Silber, Gregory Tarlé, Benjamin A. Weaver, Hu Zou