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Physics Astrophysics

astro-ph Watch Astrophysics

Friday 27 March

High Energy Astrophysical Phenomena

Unequal Mass Binary Evolution Driven by High Mach Circumbinary Disks

Madeline Clyburn and Jonathan Zrake

We present a study of the gas-driven orbital evolution of unequal mass black hole binaries with circumbinary gas disks (CBDs), varying Mach number and viscosity (nu). Using two-dimensional grid-based hydrodynamics simulations spanning a thousand binary orbits at fixed separation, we explore low to moderate mass ratios (q = 0.05-1.0) and examine how variations in Mach and q affect the torques and component accretion rates exerted by the CBD and consequently the binary evolution. Equal mass binary systems receive positive torques in low-mach disks but transition to negative torques for Mach >25. As q decreases, the transition moves to higher Mach numbers. For q<0.1, we find no torque sign reversal below Mach~52, except in sufficiently low-viscosity disks. We find that the secondary black hole cannot effectively repel the CBD, it instead accretes most of the inflowing gas from the CBD; these low mass ratio binaries in high viscosity disks therefore tend to outspiral, although inspiral can occur in less viscous environments. We also find that binaries with mass ratios in the range of 0.25 - 0.5 can show preferential accretion favoring the primary when the gas viscosity is low, exemplifying an exception to the established rule of thumb that accretion favors the secondary. We discuss differences between our results and those reported in the literature on the orbital evolution and preferential accretion, and emphasize that our simulations extend into a regime that remains largely unexplored. Overall, our results suggest that intermediate mass ratio inspirals (IMRIs) in CBDs may be less frequent, but this depends sensitively on the interplay between mass ratio, disk temperature, and viscosity.
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High Energy Astrophysical Phenomena

Why Stellar Sequences Turn Over: Fixed Points, Instability, and Equation-of-State Universality

Isaac Legred and Nicolas Yunes

We reformulate the stellar structure equations in the language of dynamical systems and show that the maximum mass of stellar sequences arises from the existence of a fixed point in the relativistic regime. In an appropriate representation of the Tolman-Oppenheimer-Volkoff equations, this fixed point becomes manifest and is directly associated with the turnover of the mass-radius curve. The existence of a fixed point implies an effective reduction in dimensionality near the onset of instability, which provides a simple explanation for several equation-of-state-insensitive relations and predicts new ones. In the weakly relativistic limit, we identify a complementary universal structure shared by stellar sequences at their maximum mass, which we term the "compressible limit," and derive distinct universal relations governing the maximum mass in the Newtonian and post-Newtonian regimes. Combining these theoretical results with current astrophysical constraints, we show that the J0740+6620 pulsar is unlikely to lie near the Tolman-Oppenheimer-Volkoff maximum mass unless the equation of state exhibits a strong first-order phase transition at densities just above its central density.
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High Energy Astrophysical Phenomena

Searching for Binary Black Hole Merger Emission in AGN Disks: Optical and Spectroscopic Follow-up of S240413p

P. Darc, C. R. Bom, A. Santos et al. (+7 more)

The conditions under which binary black hole (BBH) mergers embedded in active galactic nucleus (AGN) disks produce detectable optical counterparts remain poorly constrained observationally. We report multi-epoch optical imaging and spectroscopic follow-up of S240413p, an O4 BBH candidate with 98% classification confidence, obtained with the T80-South telescope through the S-PLUS Transient Extension Program (STEP). Our observations cover the 99% credible region across epochs that span $\sim$300 days post-merger. We prioritize AGN-hosted environments and identify two transient candidates, STEP2024gab/ZTF18acvgziq and STEP2024phe/ZTF19aaflhnr. SOAR/Goodman spectroscopy and archival DESI spectra yield host supermassive black hole masses of $\log M_\mathrm{SMBH}/\mathrm{M}_\odot = 7.15 \pm 0.05$ and $8.02 \pm 0.04$. We compute predicted flare delay distributions for each host using a thermal radiation-driven outflow emission model and the spectroscopically derived host properties. Migration traps produced by thermal torques occur at $R_\text{{BH}}/R_g \approx 10^{4.2}$ and $10^{3.4}$ for the two hosts, with predicted flare delays spanning tens to several hundred days; our late epoch at $\sim$ 300 days coincides with both the peak of these distributions and the migration trap locations, while early epochs overlap only their tails. We find no confirmed counterpart; a seasonal visibility gap leaves open the possibility that a flare occurred undetected, the merger may not have occurred within the AGN disk itself, or any emission may have been obscured by intrinsic AGN variability. These results demonstrate that long-baseline, AGN-prioritized monitoring is a necessary condition for accessing the highest probability region of BBH merger parameter space, and establish the need for physically informed follow-up strategies in the Rubin/LSST era.
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All authors P. Darc, C. R. Bom, A. Santos, S. Panda, J. C. Rodríguez-Ramírez, C. D. Kilpatrick, C. Mendes de Oliveira, A. Kanaan, T. Ribeiro, W. Schoenell

Earth and Planetary Astrophysics

ASTER – Agentic Science Toolkit for Exoplanet Research

Emilie Panek, Alexander Roman, Gaurav Shukla et al. (+3 more)

The expansion of exoplanet observations has created a need for flexible, accessible, and user-friendly workflows. Transmission spectroscopy has become a key technique for probing atmospheric composition of transiting exoplanets. The analyses of these data require the combination of archival queries, literature search, the use of radiative transfer models, and Bayesian retrieval frameworks, each demanding specialized expertise. Modern large language models enable the coordinated execution of complex, multi-step tasks by AI agents with tool integration, structured prompts, and iterative reasoning. In this study we present ASTER, an Agentic Science Toolkit for Exoplanet Research. ASTER is an orchestration framework that brings LLM capability to the exoplanetary community by enabling LLM-driven interaction with integrated domain-specific tools, workflow planning and management, and support for common data analysis tasks. Currently ASTER incorporates tools for downloading planetary parameters and observational datasets from the NASA Exoplanet Archive, as well as the generation of transit spectra from the TauREx radiative transfer model, and the completion of Bayesian retrieval of planetary parameters with TauREx. Beyond tool integration, the agent assists users by proposing alternative modeling approaches, reporting potential issues and suggesting solutions, and interpretations. We demonstrate ASTER's workflow through a complete case study of WASP-39b, performing multiple retrievals using observational data available on the archive. The agent efficiently transitions between datasets, generates appropriate forward model spectra and performs retrievals. ASTER provides a unified platform for the characterization of exoplanet atmospheres. Ongoing development and community contributions will continue expanding ASTER's capabilities toward broader applications in exoplanet research.
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All authors Emilie Panek, Alexander Roman, Gaurav Shukla, Leonardo Pagliaro, Katia Matcheva, Konstantin Matchev

Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph

Signatures from pion condensation and lepton flavor asymmetries in the cosmological gravitational wave background

Osvaldo Ferreira, Eduardo S. Fraga and Jürgen Schaffner-Bielich

Large lepton flavor asymmetries at the QCD epoch could generate a pion condensation phase in the early Universe. For large enough tau lepton flavor asymmetries, the speed of sound can exceed the conformal value, leaving a distinctive imprint on the low-frequency gravitational wave (GW) spectrum from causal sources. Beyond probing the formation of a pion condensation phase, the detection or non-detection of this signature in future Pulsar Timing Arrays (PTAs) datasets would provide a novel constraint on lepton asymmetries in the early Universe. We determine the corresponding GW spectrum and its tilt, comparing them with the standard case of vanishing lepton asymmetry. Finally, we discuss the implications for the stochastic GW background reported by PTAs, using the NANOGrav 15-year dataset.
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Instrumentation and Methods for Astrophysics

Mitigating Resampling Artifacts for the JWST IFU Spectrometers with Adaptive Trace Modeling

David R. Law and Melanie Clarke

The integral-field unit (IFU) spectrometers on board the James Webb Space Telescope (JWST) undersample the nearly diffraction-limited point spread function provided by the telescope optics. This undersampling produces large oscillating spectral artifacts when the data is resampled into regularly-gridded data cubes, which poses a significant challenge for many scientific analyses. We describe here a generalized technique to use cubic basis spline models to interpolate the observed spectral traces onto a higher-resolution grid prior to data cube rectification, which largely eliminates these artifacts in addition to helping reduce biases in point source spectra from clusters of bad pixels. We demonstrate the utility of this adaptive resampling technique for a variety of JWST NIRSpec and MIRI MRS observations ranging from isolated point sources to embedded AGN, crowded stellar fields with diffuse emission, and protostars with rich molecular bands.
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Astrophysics of Galaxies

Great Balls of Fire: Star Formation in Gas Clouds Accelerated by a Hot Wind

Stephanie Tonnesen, Rory Smith, Bianca Poggianti et al. (+6 more)

Satellite galaxies undergo ram pressure stripping, in which their gas is directly removed by a hydrodynamical interaction with the surrounding host halo gas. In clusters, ram pressure stripped tails of gas have been observed to be multiphase, even forming stars within the stripped material. Some observations find a specific age gradient along the tail, with old stars closer to the galaxy disk, and a “fireball” toy model has been proposed in which a gas cloud being accelerated away from a galaxy continuously forms stars. In this paper, we simulate individual gas clouds (with masses of ~10$^6$ M$_\odot$ and radii of a few-100 pc) interacting with an intracluster medium wind, and include star formation. We find that our accelerating clouds do generally produce a stellar age gradient with younger stars formed farther along the wind direction and with higher velocities. However, our simulations are more physically accurate than an empirical model of monolithic cloud acceleration, leading to strongly nonmonotonic age gradients. First, the evolution of the gas cloud, both from cloud compression and collapse as well as from the shredding of cloud material into downwind filaments, can lead to stars formed simultaneously at a range of heights and velocities. Second, the gravity from the gas and stars of the cloud can lead to velocity evolution of newly-formed stars. We conclude that the most distinct fireball stellar age gradients are formed from star-forming clouds that are rapidly accelerated and shredded by their surroundings.
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All authors Stephanie Tonnesen, Rory Smith, Bianca Poggianti, Benedetta Vulcani, Nina Akerman, Marco Gullieuszik, Eric Giunchi, Antonino Marasco, Alessandro Ignesti

Astrophysics of Galaxies

The Stellar IMF and Dark Matter Halo of ESO0286: Constraints from Strong Lensing and Dynamics

Han Wang, Jens Thomas, Mathias Lipka et al. (+4 more)

The internal mass structure of elliptical galaxies offers critical insights into galaxy formation, yet disentangling stellar mass from dark matter and determining the stellar initial mass function (IMF) remains challenging. We present a detailed analysis of ESO0286-G022 ($z=0.0312$), a rare nearby strong-lens system with a fast-rotating elliptical galaxy, combining high-resolution Hubble Space Telescope (HST) imaging with VLT/MUSE integral-field stellar kinematics. We construct axisymmetric and triaxial Schwarzschild orbit-superposition models to reconstruct its intrinsic shape and mass distribution. Despite being a fast rotator, ESO0286 exhibits clear kinematic signatures of intrinsic triaxiality, characterized by rotation along both the major and minor axes, making it only the second such confirmed case. By incorporating the mass enclosed within the Einstein radius from strong lensing as a complementary constraint, we tightly anchor the total mass at large radii. This significantly reduces the uncertainty on the outer mass profile and orbital structure, demonstrating that only models with strong radial anisotropy beyond the IFU field of view are compatible with the data. In the inner regions, we robustly constrain an upper limit for the stellar mass around $r \sim 0.7$ kpc, ruling out an IMF more bottom-heavy than Kroupa, though a gentle gradient toward a slightly heavier central IMF is permitted. This aligns with recent dynamical studies of local massive early-type galaxies but contrasts with heavier IMFs reported for lenses at $z>0.1$. Our work demonstrates the power of combining lensing and dynamical modeling to resolve the detailed inner structure of massive galaxies.
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All authors Han Wang, Jens Thomas, Mathias Lipka, Sherry H. Suyu, Aymeric Galan, Stefano de Nicola, Tian Li

High Energy Astrophysical Phenomena · Cross-listed from gr-qc

Dynamical tidal response of neutron stars as a probe of dense-matter properties

Abhishek Hegade K. R., Yumu Yang, Mauricio Hippert et al. (+3 more)

Dynamical tidal deformations play a crucial role in the gravitational waves emitted by binary neutron star systems during their late inspiral. In this work, we systematically explore how relativistic (dynamical and dissipative) tidal deformations depend on the internal structure of a neutron star using two analytic classes of equations of state. The first class is a nucleonic model that is parameterized by nuclear physics observables, such as the symmetry energy coefficients and saturation properties. The second class is a toy model of quark matter, the MIT bag model. To model tidal dissipation, we self-consistently include contributions from weak-interaction-driven bulk-viscous effects while considering both the nucleonic and the quark-matter equations of state. The dissipative tide is sensitive to frequency and temperature, but its magnitude, as predicted by weak-interaction-driven bulk-viscous effects, is too small (within the equation-of-state models studied here) to be detectable by current or future observations. However, we find that the (conservative) dynamical tidal response function depends strongly on the slope of the symmetry energy and on higher-order coefficients of the symmetry energy. This indicates that the (conservative) dynamical tide is sensitive to higher-order coefficients, motivating a dedicated parameter-estimation study to assess how well they can be constrained.
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All authors Abhishek Hegade K. R., Yumu Yang, Mauricio Hippert, Jacquelyn Noronha-Hostler, Jorge Noronha, Nicolás Yunes

High Energy Astrophysical Phenomena

Identifying heating processes in simulations with an entropy-based scheme: A single jet episode in a galaxy cluster

Moun Meenakshi, Rainer Weinberger, Christoph Pfrommer et al. (+1 more)

Understanding heating processes in galaxy clusters is essential for predicting the regulation of radiative cooling and star formation, and for clarifying the mechanisms underlying active galactic nucleus (AGN) feedback in cool-core clusters. We investigate the processes through which AGN jets deposit heat into the intracluster medium (ICM) by tracking passive entropy scalars in magneto-hydrodynamic (MHD) simulations. This enables us to systematically disentangle the contributions from different heating channels. We successfully validate this method with several idealized tests, including turbulent heating, heating by anisotropic Braginskii viscosity, dissipative and adiabatic heating by shocks using in-situ shock-detection methods, and cosmic ray (CR) heating through the excitations and damping of Alfvén waves. Using this methodology, we simulate single-epoch outbursts of high-power jets with varying densities in a cluster environment. Light jets produce wider bubbles, displacing a larger fraction of the gas in the cluster's core, whereas comparatively denser jets propagate more efficiently to larger distances without significantly disturbing the central region. During early evolution, shock heating of the ICM prevails irrespective of jet density. At later times, light jets primarily heat the ICM through turbulently induced heating (which includes dissipation of vortices emerging from a turbulent cascade and mixing gas of different temperatures) and compressible dissipation of sound waves and very weak shocks, while denser jets continue to dissipate most of their energy via shocks. Particularly, turbulently induced heating by solenoidal-shear motions prevails inside the cocoon, whereas shocks and acoustic compressions dominate outside. In light jets, the forward shock weakens rapidly, whereas dense jets can sustain strong bow shocks to large distances.
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All authors Moun Meenakshi, Rainer Weinberger, Christoph Pfrommer, Thomas Berlok

Astrophysics of Galaxies

The ASKAP-FLASH survey: A first look at the multiwavelength properties and redshift distribution of compact radio sources

W. Roster, E. M. Sadler, E. K. Mahony et al. (+15 more)

We present the characterisation, including a photometric redshift (photo-$z$) analysis, of the optical counterparts (CTPs) to over 45 000 bright ($S_{856\rm MHz} \geq$ 30 mJy) compact radio sources, identified across all ASKAP First Large Absorption Survey in HI (FLASH) fields observed up to April 2025. These sources constitute a large, homogeneous population of background continuum sightlines specifically selected to enable statistical studies of cold gas at intermediate redshifts of $0.42 \leq z \leq 1$. As spectroscopic redshift measurements are not available for the majority of these candidate absorbers, we estimate photo-$z$s for the CTPs of all FLASH continuum sources cross-matched to the tenth data release of the DESI Legacy Imaging Surveys (LS10). Using these estimates, we establish the redshift distribution and find that approximately 13% of continuum sources lie at $z<0.42$ (foreground), 35% within the detectability range of FLASH (`in-band'), and 52% at $z>1$ (background). We examine the subset of FLASH continuum sources with CTPs in the eROSITA X-ray survey, providing additional insight into their AGN content, multiwavelength properties, and environments. Finally, we discuss how this information can be used as a statistical prior to aid in distinguishing between associated and intervening HI absorption systems and estimating the total comoving absorption path length of the survey, establishing a framework for incorporating redshift-based priors in future large radio absorption surveys. We release a catalogue of LS10 counterparts to FLASH continuum sources, providing photo-$z$ estimates, associated uncertainties, and measures of redshift degeneracies.
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All authors W. Roster, E. M. Sadler, E. K. Mahony, M. Salvato, H. Yoon, M. Kluge, R. Shirley, E. Kerrison, J. Buchner, Z. Igo, R. Davies, J. R. Allison, S. S. Shabala, V.A. Moss, H. Starck, M. Whiting, K. Nandra, J. Weller

Earth and Planetary Astrophysics

Dust evolution during protoplanetary disk buildup enhances CO ice relative to water

Joanna Drazkowska

Water ice is expected to be the dominant volatile component of bodies formed in the outer Solar System. However, recent observations of comets and trans-Neptunian objects suggest that the relative abundances of ices can vary substantially, with some bodies exhibiting unusually high CO/H$_2$O ratios. We study the prospects of producing CO-rich pebbles and planetesimals. We use a one-dimensional protoplanetary disk model with dust evolution including coagulation, fragmentation, and radial drift, water and CO ice and vapors evolution, and planetesimal formation via the streaming instability. We compare models with and without the disk formation stage. CO-rich pebbles can be formed at the CO snow line due to the cold finger effect, regardless of whether the disk buildup is included. Models including disk buildup show stronger CO enhancement relative to water in the outer disk. However, CO-rich planetesimals do not form in the smooth disk models. The formation of CO-rich planetesimals likely requires mechanisms that preserve the CO-enriched ice reservoir, such as pressure traps or gas removal processes. Models concerning the chemical evolution of protoplanetary disks and its impact on the atmospheric C/O ratio of forming planets should consider the disk buildup stage.
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Astrophysics of Galaxies

An unexplored enrichment stochasticity and its implications for stellar abundance patterns

Anmol Aggarwal and Ralph Schoenrich

Extremely low metallicity stars are intensely studied as they take observations the closest to the very first generations of stars in the universe. Widely assumed to be enriched by just one dying massive star, some of these very metal poor stars have abnormal chemical abundance ratios and have been taken to reflect a rare hypernova (with high explosion energy $\gtrsim \ 10^{52}$ erg.). Here we remodel the enrichment of three such stars and show that their abundances are better explained by enrichment from a normal (less energetic) supernova accounting for inhomogeneous distribution of the ejecta. This work establishes the importance of the inhomogeneity of supernovae, serves as a template for a required reassessment of all metal-poor/peculiar stars, and raises the need to quantify this inhomogeneity both in theory and in observations.
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Astrophysics of Galaxies

A cosmological framework for stellar collisions at high redshift in proto-globular clusters, nuclear star clusters, and Little Red Dots

Claire E. Williams, Smadar Naoz, Sanaea C. Rose et al. (+8 more)

Observations and cosmological simulations indicate that the early Universe hosted numerous compact, high-density stellar systems, where close encounters and physical collisions between stars were likely common. We develop a bottom-up framework for stellar dynamics in such environments, spanning systems with and without intermediate- and supermassive black holes, and covering regimes where stellar collisions may or may not dominate the evolution. This radially-resolved analytic model connects dense star clusters in their cosmological context to observable outcomes mediated by stellar collisions. Initial conditions and environmental properties are drawn from high-resolution cosmological simulations, enabling exploration across a broad region of parameter space. The analytic predictions are validated against Monte Carlo simulations, demonstrating good agreement across key regimes. We find that stellar collisions are ubiquitous in many high-redshift environments, with runaway sequences naturally leading to the formation of very massive stars at early times. Finally, we show that high rates of destructive collisions can rapidly build up extremely dense gaseous environments around massive black holes, potentially providing an analogue to the observed population of Little Red Dots.
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All authors Claire E. Williams, Smadar Naoz, Sanaea C. Rose, Blakesley Burkhart, Naoki Yoshida, Avi Chen, Kyle Kremer, William Lake, Federico Marinacci, Shyam H. Menon, Mark Vogelsberger

High Energy Astrophysical Phenomena

ASAS-SN Rates IV: Constraints on the Kilonova Rate

Dhvanil D. Desai, Benjamin J. Shappee, Christopher S. Kochanek et al. (+10 more)

Kilonovae (KNe) are the electromagnetic signatures of neutron star mergers and are likely the dominant site of cosmic $r$-process nucleosynthesis. However, their intrinsic rate remains poorly constrained due to a paucity of confirmed events. We use the All-Sky Automated Survey for Supernovae (ASAS-SN) to place limits on the rate of bright, nearby KNe over an 11-year baseline ranging from 2014 to 2024. To evaluate the survey's completeness for KNe, we employ an injection-recovery simulation using a shock-cooling cocoon model calibrated to the early blue emission of the only well-sampled KN, SSS17a (AT 2017gfo). Finding no KNe within the survey, we calculate a $2\sigma$ ($\sim95\%$) upper limit on the local volumetric KN rate of $R_{\mathrm{KN}} < 4400\,\mathrm{yr}^{-1}\,\mathrm{Gpc}^{-3}$. Despite ASAS-SN's shallower limiting magnitude compared to other time-domain searches, its continuous, high-cadence, all-sky monitoring yields a constraint that is competitive with the strongest results from electromagnetic surveys but remains a factor of 18 higher than the LIGO-Virgo-KAGRA GWTC-4 estimate of the binary neutron star merger rate.
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All authors Dhvanil D. Desai, Benjamin J. Shappee, Christopher S. Kochanek, Krzysztof Z. Stanek, Katie Auchettl, John F. Beacom, Jeff Cooke, Subo Dong, Willem B. Hoogendam, Jose L. Prieto, Todd A. Thompson, Michael A. Tucker, Natasha Van Bemmel

Astrophysics of Galaxies

The velocity dispersion function of red galaxies in four Hubble Frontier Fields galaxy clusters

G. Granata, L. Tortorelli, C. Grillo et al. (+6 more)

We present a detailed study of the stellar kinematic properties of red member galaxies in the cores of four strong lensing galaxy clusters at intermediate redshifts included in the the Hubble Frontier Fields programme: Abell 2744 ($z=0.307$), Abell S1063 ($z=0.346$), MACS J0416.1$-$2403 ($z=0.397$), and MACS J1149.6$+$2223 ($z=0.542$). We focussed on a sample of 723 red cluster members in the four clusters and we measured their structural parameters using MORPHOFIT for all Hubble Frontier Fields bands. Taking advantage of deep (3.1 h to 17 h of exposure) integral-field spectroscopy from MUSE on the Very Large Telescope, we tested a pipeline based on the public spectral fitting code pPXF to systematically measure the line-of-sight stellar velocity dispersion $\sigma$ of cluster members with a spectral $S/N\geq 10$, with a statistical uncertainty consistently below 5%. The resulting catalogue contains 213 measured $\sigma$ values across the four clusters. We calibrated the Fundamental Plane relation in the rest-frame $r$ band for the early-type cluster members, selected from their colour and morphology; we found compatible parameters both across the clusters, and noting hints of zero-point evolution with redshift. Finally, we used the calibrated Fundamental Plane relations to assign a velocity dispersion value to all 723 red cluster members and studied the velocity dispersion function for each cluster, down to $\log \sigma \, \mathrm{[km \, s^{-1}] = 1.5}$. A Schechter function fit of the velocity functions suggests compatible parameters: a positive $\alpha$ slope with values in the range $0.55-1.60$, and $\log\sigma^*\, [\mathrm{km\,s^{-1}}]$ between $2.18$ and $2.47$. Unlike previous works, we extended the systematic study of the central velocity dispersion of cluster galaxies to lower-$\sigma$ regimes.
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All authors G. Granata, L. Tortorelli, C. Grillo, P. Rosati, M. D'Addona, A. Mercurio, G. Angora, P. Bergamini, G. B. Caminha

Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph

Global Structure, Non-Invertible PQ Symmetry, and the DFSZ Domain Wall Problem

Gongjun Choi, Sungwoo Hong and Seth Koren

In recent years it has become increasingly clear that the previously overlooked “global structure” of symmetry groups can encode significant theoretical structure and, more importantly, have substantial phenomenological implications. With this in mind we re-examine the DFSZ axion, which suffers from a domain wall problem due to the Standard Model generation structure. We show that global structure $(G_{\text{EW}} \times U(1)_{\text{PQ}})/\mathbb{Z}_2$ acting between the Peccei-Quinn symmetry and the electroweak gauge group plays a crucial role in determining the precise nature of the domain wall problem, which has important implications in both cubic and quartic DFSZ. We then demonstrate that the stability of the domain walls is enforced by a non-invertible chiral symmetry in quark flavor $Z'$ models which have additional global structure $(SU(3)_C \times G_F)/\mathbb{Z}_3$ acting between the color and the gauged quark flavor groups. The strategy of Non-invertible Naturalness then leads us to UV theories that resolve the domain wall problem through small-instanton-induced breaking of non-invertible symmetries. Finally, we sketch potential gravitational wave signatures arising from the annihilation of axion domain walls. Our work illustrates the importance of considerations of global structure in realistic models of particle physics.
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Cosmology and Nongalactic Astrophysics

Precision Constraints on New Dark Energy Parametrization from DESI BAO DR2

D. Revanth Kumar and Santosh Kumar Yadav

In this article, we investigate a new parametrization of the dark energy equation of state (EoS) with a single parameter for a barotropic fluid that deviates from the standard $\Lambda$CDM cosmology. We derive observational constraints on the model parameters using recent datasets including Observational Hubble Data (OHD), Pantheon+SH0ES (PPS), and Dark Energy Spectroscopic Instrument Baryon Acoustic Oscillations Data Release 2 (DESI BAO DR2). We constrain the best fit value of the parameter as, $\alpha =0.239 \pm 0.07$ at 68% CL from joint analysis, which is non-null and suggests deviations from the cosmological constant. The model accommodates varying values of Hubble constant from different datasets and joint analysis yields $H_0 = 68.40 \pm 0.23$ $\mathrm{Km\,s^ {-1} Mpc^{-1}}$ at 68% CL. We examine the physical behavior of the model by analyzing the deceleration parameter, the age of the universe, and the Om(z) diagnose. The deceleration parameter confirms a smooth transition from the past deceleration phase to the present cosmic acceleration as well as and also a second future transition back to deceleration, when PPS data is employed.
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Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc

High Sensitivity Methodologies to Detect Radio Band Gravitational Waves

Wei Hong, Peng He, Tong-Jie Zhang et al. (+2 more)

Gravitational waves (GWs) can resonate with magnetic fields through the Gertsenshtein-Zeldovich effect, producing electromagnetic signals at the same frequency. In pulsar magnetospheres, this conversion may yield a faint radio-band signal that could be detected. In this work, we focus on two specific pulsars, PSR J1856-3754 and PSR J0720-3125, and use numerical simulations to evaluate how well the FAST and SKA2-MID telescopes could detect such signals. We consider transient events, including primordial-black-hole-like mergers, as well as stochastic backgrounds, including primordial GWs. To improve detection sensitivity, we propose four observational methods to lower the detectable energy-density limit of very high-frequency (VHF) GWs; the "Multiple Pulsars with Multiple Telescopes" (MPMT) method performs best because it allows cross-validation and rejection of false candidates. Under the assumption of nearly 6000 hours of observation at 3 GHz and a $5\sigma$ detection threshold, the minimum detectable characteristic strain is projected to be $h_c \approx 10^{-23}$ for transient events and $h_c \approx 10^{-33}$ for stochastic backgrounds. Under optimistic assumptions on integration time and conversion efficiency, these projections suggest that radio-band searches may approach the sensitivity needed to begin testing representative VHF GW scenarios. More broadly, this conversion in pulsar magnetospheres could be relevant to the origin of some repeating fast radio bursts in the our galaxy.
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All authors Wei Hong, Peng He, Tong-Jie Zhang, Shi-Yu Li, Pei Wang

High Energy Astrophysical Phenomena

Gaia Sees Blazars Move: Locating Optical Flares Using Astrometry

Alexander Plavin

When blazars flare, their optical position moves. We show this by combining Gaia DR3 proper motions with epoch photometry for blazars with strong optical jet emission. In 60 of 74 sources with significant proper motion, rising flux drives the centroid upstream while fading flux drives it downstream - a near-universal pattern captured by a simple two-component model of constant extended emission and a flaring region. Using this connection, we geometrically localize the optical flares to within <1 mas of the VLBI position - a few parsecs at typical blazar distances - placing them in the innermost jet or accretion disk. This purely geometric method requires no multi-wavelength correlations or model-dependent assumptions, and provides an independent spatial anchor for localizing higher-energy flares. Per-epoch astrometry from Gaia DR4 is set to tighten our constraints even further.
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Instrumentation and Methods for Astrophysics · Cross-listed from cs.LG

Automatic Laplace Collapsed Sampling: Scalable Marginalisation of Latent Parameters via Automatic Differentiation

Toby Lovick, David Yallup and Will Handley

We present Automatic Laplace Collapsed Sampling (ALCS), a general framework for marginalising latent parameters in Bayesian models using automatic differentiation, which we combine with nested sampling to explore the hyperparameter space in a robust and efficient manner. At each nested sampling likelihood evaluation, ALCS collapses the high-dimensional latent variables $z$ to a scalar contribution via maximum a posteriori (MAP) optimisation and a Laplace approximation, both computed using autodiff. This reduces the effective dimension from $d_\theta + d_z$ to just $d_\theta$, making Bayesian evidence computation tractable for high-dimensional settings without hand-derived gradients or Hessians, and with minimal model-specific engineering. The MAP optimisation and Hessian evaluation are parallelised across live points on GPU-hardware, making the method practical at scale. We also show that automatic differentiation enables local approximations beyond Laplace to parametric families such as the Student-$t$, which improves evidence estimates for heavy-tailed latents. We validate ALCS on a suite of benchmarks spanning hierarchical, time-series, and discrete-likelihood models and establish where the Gaussian approximation holds. This enables a post-hoc ESS diagnostic that localises failures across hyperparameter space without expensive joint sampling.
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High Energy Astrophysical Phenomena

Recoil geometry determines electromagnetic counterparts from supermassive black hole merger remnants

Yoonsoo Kim, Elias R. Most and Hai-Yang Wang

Merging binary black holes embedded in gaseous environments, such as supermassive black hole binaries following gas-rich galaxy mergers, are promising sources of multi-messenger transients in the upcoming age of space-based gravitational wave detections. In case a gravitational radiation recoil is imparted to the merger remnant, subsequent interactions between the recoiled black hole and its circumbinary disk may lead to unique post-merger electromagnetic counterparts. We present the first general relativistic magnetohydrodynamic simulations of a recoiling black hole interacting with a magnetically arrested circumbinary disk the evolution of which has been consistently tracked through the inspiral phase. We show that the post-merger accretion dynamics, depending on the recoil geometry, exhibits qualitatively disparate jet and disk behavior. For recoils perpendicular to the disk, the inner disk remains gravitationally bound and sustains relativistic jets, while in-plane recoils lead to copious shock heating and potential jet quenching for black holes directly colliding with the disk. Oblique recoils, on the other hand, produce intermittent outbursts from jet-disk interactions owing to the tilt introduced in the accretion disk. Multi-wavelength monitoring of these electromagnetic counterparts, in conjunction with the coincident gravitational wave detection, will be able to aid in characterizing the physical conditions of the merger environment.
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Cosmology and Nongalactic Astrophysics

Universality of Halo Shape and its Morphological Evolution across Cosmic Time

Ayan Nanda, Nishikanta Khandai, J. S. Bagla et al. (+1 more)

We investigate the evolution of dark matter halo shapes in cosmological N-body simulations both in scale free Einstein-De Sitter (EdS) and $\Lambda$CDM cosmologies. We compute the axis ratios ($q=b/a,s=c/a$) of well resolved central halos using the shape tensor. These halos are identified using two different halo finding algorithms, SUBFIND and ROCKSTAR. We find that at fixed mass, halos become more spherical with decreasing redshift. The distribution $P(q,s)$ along with their median values ($q$ and $s$) shows self-similar behaviour as a function of mass scaled by the non-linear mass, $(M/M_{nl})$ across power-law spectral indices for scale free EdS models. However the median $q$ and $s$ show a tighter self-similar evolution as a function of peak height $\nu=\delta_c/\sigma(M,z)$. We find that the median $q(\nu)$ and $s(\nu)$ are consistent with an evolution along a universal curve described by $y=\alpha-\delta \tanh \left[ \omega \left(\log_{10}(\nu) - \mu\right)\right]$ across the spectral indices ranging from $n=-1.0$ to $n=-2.2$. Our results hold for both SUBFIND and ROCKSTAR, although there are some differences between them. The universality of the evolution of median $q(\nu)$ and $s(\nu)$ also holds for the $\Lambda$CDM runs, although with a different behaviour at small $\nu$ compared to the scale free models. The width of the distributions of $P(q)$ and $P(s)$ in both, scale-free and $\Lambda$CDM, classes of simulations can be reduced further by classifying halos as oblate, triaxial and prolate, each of which also follows a universal behaviour. Although oblate halos are relatively rare at all redshifts, their fraction increases over time at the expense of the other two populations.
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All authors Ayan Nanda, Nishikanta Khandai, J. S. Bagla, Swati Gavas

Instrumentation and Methods for Astrophysics · Cross-listed from physics.ins-det

On the Codesign of Scientific Experiments and Industrial Systems

Tommaso Dorigo, Pietro Vischia, Shahzaib Abbas et al. (+84 more)

The optimization of large experiments in fundamental science, such as detectors for subnuclear physics at particle colliders, shares with the optimization of complex systems for industrial or societal applications the common issue of addressing the inter-relation between parameters describing the hardware used in data production and parameters used to analyse those data. While in many cases this coupling can be ignored – when the problem can be successfully factored into simpler sub-tasks and the latter addressed serially – there are situations in which that approach fails to converge to the absolute maximum of expected performance, as it results in a mis-alignment of the optimized hardware and software solutions. In this work we consider a few use cases of interest in fundamental science collected primarily from particle physics and related areas, and a pot-pourri of industrial and societal applications where the matter is similarly of relevance. We discuss the emergence of strong hardware-software coupling in some of those systems, as well as co-design procedures that may be deployed to identify the global maximum of their relevant utility functions. We observe how numerous opportunities exist to advance methods and tools for hardware-software co-design optimization, bridging fundamental science and industry through application- and challenge-driven projects, and shaping the future of scientific experiments and industrial systems.
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All authors Tommaso Dorigo, Pietro Vischia, Shahzaib Abbas, Tosin Adewumi, Lama Alkhaled, Lorenzo Arsini, Muhammad Awais, Maxim Borisyak, András Bóta, Florian Bury, Sascha Caron, James Carzon, Long Chen, Prakash C. Chhipa, Paul Christakopoulos, Jacopo De Piccoli, Andrea De Vita, Zlatan Dimitrov, Michele Doro, Luigi Favaro, Francesco Ferranti, Santiago Folgueras, Rihab Gargouri, Nicolas R. Gauger, Andrea Giammanco, Christian Glaser, Tobias Golling, João A. Gonçalves, Hui Han, Hamza Hanif, Lukas Heinrich, Yan Chai Hum, Florent Imbert, Andreas Ipp, Michael Kagan, Noor Kainat Syeda, Rukshak Kapoor, Aparup Khatua, Eduard J. Kerkhoven, Jan Kieseler, Tobias Kortus, Ashish Kumar Singh, Marius S. Köppel, Daniel Lanchares, Ann Lee, Pelayo Leguina, Christos Leonidopoulos, Giuseppe Levi, Boying Li, Chang Liu, Marcus Liwicki, Karl Lowenmark, Enrico Lupi, Carlo Mancini-Terracciano, Dominik Maršík, Leonidas Matsakas, Hamam Mokayed, Federico Nardi, Amirhossein Nayebiastaneh, Xuan T. Nguyen, Aitor Orio, Jingjing Pan, Jigar Patel, Carmelo Pellegrino, María Pereira Martínez, Karolos Potamianos, Shah Rukh Qasim, Martin Ravn, Luis Recabarren Vergara, Humberto Reyes-González, Hipolito A. Riveros Guevara, Ippocratis D. Saltas, Rajkumar Saini, Fredrik Sandin, Alexander Schilling, Kylian Schmidt, Nicola Serra, Saqib Shahzad, Foteini Simistira Liwicki, Giles C. Strong, Kristian Tchiorniy, Mia Tosi, Andrey Ustyuzhanin, Xabier Cid Vidal, Kinga A. Wozniak, Mengqing Wu, Zahraa Zaher

Astrophysics of Galaxies

The influence of the Cosmic Web on the properties of dwarf galaxies in the Fornax-Eridanus Supercluster

X. Xu, P. Ravichandran, R. F. Peletier et al. (+4 more)

We analyze a sample of low surface brightness dwarf galaxies (mu_e,g > 24.2 mag arcsec^-2), detected using interpretable machine learning tools from the DES survey. We use the Tanoglidis et al. (2021) sample, identified with machine learning, supplemented by Thuruthipilly et al. (2024). We focus on the Fornax-Eridanus Supercluster, where our group determined its 3D filamentary spine using massive galaxies. We study the effect of the large-scale environment on dwarfs in the Fornax-Eridanus Complex. To do this, we compare the properties of dwarfs in clusters, groups, and the field, and examine how these properties vary with distance to the spine of the Fornax Wall. We check if dwarfs trace the Fornax Wall spine, defined by massive galaxies. We identify Fornax Wall members from our photometric dwarf catalog, dividing them into i) within one virial radius of a galaxy group or cluster and ii) outside this radius (field galaxies). We assume dwarfs near the Fornax Wall are at the same distance as the massive galaxies. We then study their distribution within the complex. We probe the morphology-density relation and examine galaxy properties versus distance from the Fornax Wall spine. Red dwarfs are mostly in or near groups close to the Fornax Wall, dominating the population, while blue dwarfs dominate the field. Larger-sized red dwarfs tend to reside in group environments, with significantly larger effective radii than those in the field. Red dwarfs are more concentrated towards the Fornax Wall than blue dwarfs. This suggests that the group environment plays a significant role in the evolution of dwarfs. Mass density distribution in field and group/cluster is similar, indicating the group/cluster population could be an aged version of the field. The group/cluster objects with excess sizes must have been made through interactions in the groups/clusters.
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All authors X. Xu, P. Ravichandran, R. F. Peletier, Junais, M. A. Raj, P. Awad, R. Smith

Solar and Stellar Astrophysics

Competition between gravity waves excited by convection and tides in stars that host a companion

M. Esseldeurs, J. Ahuir, L. Amard et al. (+2 more)

Asteroseismology has become a powerful tool in stellar astrophysics, offering unprecedented insights into the internal structures and dynamics of stars. It enables precise characterization of stellar interiors across a wide range of stellar masses and of evolutionary phases, from the main sequence to the white dwarf phase. At the same time, the number of detected close stellar and planetary companions throughout the entire stellar evolutionary phases has increased significantly, prompting key questions about the interplay between stellar evolution and binarity. We investigate the competition between gravity waves (IGW) excited by internal convection and those excited by tides in stars that host a companion. By modelling the energy and angular momentum luminosities transported by IGWs stochastically excited by convection and by tides, we seek to quantify their relative contributions and identify the key parameters that govern their efficiency. We compute the energy and angular momentum luminosities transported by both types of waves for a range of stellar masses and evolutionary stages, with a particular focus on understanding how the presence of a companion influences the angular momentum transport of the radiative layers of the host star. The competition between the two excitation mechanisms is sensitive to the mass and orbital properties of the companion, as well as the internal structure of the host star. We find that for a Jupiter-mass companion, the stochastic excitation dominates over tidal excitation during all evolutionary phases. Only for close-in stellar companions around late-type stars does the tidal excitation become more efficient. The presence of a companion is unlikely to significantly alter the internal angular momentum transport in the radiative layers of the host star, simplifying the modelling of IGW-driven angular momentum transport in stars that host a companion.
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All authors M. Esseldeurs, J. Ahuir, L. Amard, S. Mathis, L. Decin

Astrophysics of Galaxies

New star clusters discovered towards the Galactic anticentre direction using Gaia DR3 data

F. A. Ferreira, M. S. Angelo, J. F. C. Santos Jr. et al. (+2 more)

We report the discovery of 31 new open clusters (OCs) identified in Gaia~DR3 data through a systematic search over 220 adjacent $1^\circ\times1^\circ$ fields towards the Galactic anticentre, in the direction of the Perseus arm gap. Eight of them display low-density structures, possibly indicating open cluster remnants properties. The objects were identified and characterized through a combined analysis of photometric, kinematic, and spatial distributions, a methodology successfully applied in our previous works. Their structural properties, mean proper motions, ages, distances and reddening were derived and their centres cross-matched with the available catalogues. The clusters are low-concentrated systems and are mostly located within $3<d<5$ kpc, exhibiting reddening up to $E(B-V)\approx1.5$, and ages from $\sim$20 Myr to 1 Gyr. The new OCs represent a significant increase in the anticentre cluster census: $31\%$ for $3<d<4$ kpc and $12\%$ for $d>4$ kpc. They do not belong to the Perseus arm, but may be associated with the Outer Norma arm. The Gulf of Camelopardalis region appears as an interruption in the Perseus arm, possibly reflecting low star-formation activity, dust obscuration, or that the Milky Way is a flocculent, rather than a grand-design spiral galaxy.
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All authors F. A. Ferreira, M. S. Angelo, J. F. C. Santos Jr., W. J. B. Corradi, F. F. S. Maia

Cosmology and Nongalactic Astrophysics

Towards the Reconstruction of a Unified Dark Matter Halo: a Phenomenological Approach

Claudia Caputo, Daniele Bertacca, Alberto Bassi et al. (+1 more)

We investigate static, spherically symmetric halo configurations within Unified Dark Matter (UDM) scalar-field models, developing a systematic mapping between standard cold dark matter (CDM) density profiles and their UDM counterparts. Exploiting the equivalence-class structure of UDM models, we show that, in principle, different Lagrangian realisations can share the same weak-field rotation curve while exhibiting distinct field properties. We reconstruct the effective energy density, radial and tangential pressures from a phenomenological circular velocity profile, ensuring the absence of ghosts and instabilities and the preservation of the Null Energy Condition (NEC). Applying our procedure to several commonly used CDM halo profiles – including Persic, Salucci & Stel, NFW, and Burkert models – we demonstrate that their phenomenological success can be retained within a relativistic UDM framework, reproducing the observed flatness of rotation curves without introducing separate dark matter and dark energy components.
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All authors Claudia Caputo, Daniele Bertacca, Alberto Bassi, Sabino Matarrese

Cosmology and Nongalactic Astrophysics

Exploring the interplay of late-time dynamical dark energy and new physics before recombination

Alex González-Fuentes and Adrià Gómez-Valent

Cosmological models exhibiting crossing of the phantom divide improve the fit to current data, suggesting late-time dark energy (DE) dynamics at $\sim3\sigma$ CL. However, they favor low values of $H_0$, in tension with SH0ES. This may point to the presence of new physics prior to the decoupling era. In this work, we reconstruct the background DE functions using the Weighted Function Regression (WFR) method, introducing three main improvements compared to our previous JCAP 12 (2025) 049. First, we adopt the Frequentist-Bayesian approach for the weights. Second, we combine CMB and BAO with the DES-Dovekie SNIa sample and compare our findings with those derived from Pantheon+, still assuming standard recombination. Third, we study in a model-independent manner the viability of early-time “solutions” to the Hubble tension and how they affect the evidence for dynamical DE at late times, under the influence of the SH0ES and the more conservative CCHP calibration of the cosmic ladders, separately. We find that, if the physics prior to decoupling is unmodified, the probability of phantom crossing is $\sim 96.7\text{--}98.5\%$, with $\Lambda$CDM excluded at $\sim 2.5\sigma$ and $\sim 3\sigma$ CL. New physics before recombination can alleviate the Hubble tension, but requires extremely large values of the reduced matter density parameter when the SH0ES calibration is employed, in strong tension with those inferred from full CMB analyses. This raises serious concerns about the actual viability of these models to explain the SH0ES measurement. We find that phantom crossing, while not excluded, is no longer required, with only a very mild preference for quintessence. Nevertheless, given the aforesaid tension in $\omega_m$, it would be rash to draw firm conclusions about how the dynamical DE signal is affected in these scenarios. [abridged]
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Solar and Stellar Astrophysics · Cross-listed from physics.flu-dyn

Helicity subgrid-scale models and their numerical validation

Nobumitsu Yokoi, Pablo D. Mininni, Annick Pouquet et al. (+2 more)

Large-eddy simulations (LES) with an appropriate subgrid-scale (SGS) model provide a powerful tool for investigating real-world turbulence. The Smagorinsky model, one of the simplest and most used SGS models, often shows an over-dissipative behavior even when using dynamic procedures to adjust the model coefficient. By incorporating the structural or geometrical information of turbulence provided by helicity (velocity-vorticity correlations), the helicity SGS model is expected to alleviate these issues in the standard Smagorinsky framework, in which only information of turbulence intensity is considered through the turbulent energy. The validity of helicity SGS models is investigated here with the aid of direct numerical simulations (DNSs). Using configurations with and without net rotation, and with large-scale helicity gradients sustained by a mechanical forcing, we show that to better model SGS turbulence, SGS helicity effects should be incorporated into the model together with the Smagorinsky-like eddy viscosity.
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All authors Nobumitsu Yokoi, Pablo D. Mininni, Annick Pouquet, Duane Rosenberg, Raffaele Marino