Solar and Stellar Astrophysics
Spectroscopic study of five Mira stars
David Boyd
Mira
stars are popular with amateur astronomers because they are generally bright and their pulsations produce large changes in brightness. This also means they are eminently suitable to study using spectroscopy. We report here on spectroscopic observations of five Mira
stars: RY Cep, SU Cam, T Cep, V667 Cas and OR Cep. We describe the lifecycle of a Mira
star and explain how the carbon-oxygen balance in its atmosphere determines its spectral classification. Atmospheric pulsations in these
stars produce shocks which generate Balmer emission. We present graphically their different spectral behaviours and development of emission lines.
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Astrophysics of Galaxies
Probing Large-scale Structure and the Multi-Phase IGM at the Cosmic Noon – Insights from a Joint Survey with Euclid, CSST, JPCam, and JUST
Jiang-Tao Li, Renato A. Dupke, Yan Gong et al. (+4 more)
We present scientific and technical justifications of a potential coordinated Euclid/CSST/JPCam/JUST survey of the Euclid Deep Field North (EDF-N), aimed at probing the multi-phase circumgalactic and intergalactic medium (CGM/IGM) at the
cosmic noon over ~20 deg$^2$. The survey is structured around three connected goals: (1) improving photometric
redshift (photo-z) accuracy through the combination of broad- and narrow-band photometry, enabling reliable identification of large-scale structures; (2) probing extended CGM emission with dedicated narrow-band imaging; and (3) mapping foreground IGM via absorption-line spectroscopy of background
galaxies. Together, these components establish an integrated observational framework to investigate
galactic ecosystems – linking
galaxies to their circumgalactic and intergalactic environments – at
cosmic noon. We show that the J-PAS-like narrow-band system used in JPCam substantially improves photo-z accuracies from only the Euclid/CSST broad-band data, especially for
star-forming
galaxies at z~1.0-1.4. This enables the identification of
galaxy groups and (proto-)clusters directly from photo-z measurements. Stacked JPCam narrow-band imaging should also detect extended [O II]-emitting CGM
halos. We then construct mock 3D gas distribution model and realistic
galaxy catalog, and further construct mock CSST and JUST background
galaxy spectra adding Lyalpha and Mg II absorptions. The reconstructed 3D H I field from CSST Lyalpha forest reliably recovers large-scale structures; however, our simulations indicate that detecting diffuse IGM Mg II absorption with JUST is infeasible, either through spectral stacking or via the two-point correlation function method. We conclude that constraining the
metallicity of the diffuse IGM will require significantly deeper and higher-resolution spectroscopy expected from future facilities such as the 39 m E-ELT.
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All authors Jiang-Tao Li, Renato A. Dupke, Yan Gong, Zhijie Qu, Weichen Wang, Xiaohu Yang, Xiaodi Yu
Cosmology and Nongalactic Astrophysics
How does a MOND cosmology fare on Gpc scales? - Collisionless $N$-body simulations of $\nu$HDM
Alfie Russell, Indranil Banik, Oscar Cray et al. (+1 more)
We present the largest collisionless $N$-body cosmological simulations in a MOdified Newtonian Dynamics (MOND) cosmology to date. Our 4 simulations cover $\Lambda$CDM as a baseline, a MOND with hot dark matter model known as $\nu$HDM, and 2 unphysical models we call $\Lambda$HDM and $\nu$CDM to test the individual contributions of hot dark matter and MOND
gravity, respectively. $\nu$HDM reproduces the CMB power spectrum whilst also theoretically matching cluster dynamics and preserving MOND predictions for
galactic rotation curves. We test its viability on cosmological scales using simulations with $256^{3}$ particles in a box of size $800/h$ comoving Mpc. We find generically that the MOND models massively overproduce large-scale structures by $z=0$, with a most massive cluster in $\nu$HDM of $\approx 5 \times 10^{17} M_{\odot}/h$ and typical peculiar velocities of several thousand km/s. We also explore a local void solution to the Hubble tension in these models. Analogues to the observed "Local Hole” do form in the MOND models, but values for the deceleration parameter $<-1.5$ in these regions prevent a satisfactory resolution to the Hubble tension. Whilst $\Lambda$CDM significantly underpredicts the observed bulk flow in Cosmicflows-4, the high peculiar velocities that arise in the MOND models create the opposite problem, ruling out $\nu$HDM at $>5\sigma$ confidence. Observations clearly require a much milder enhancement to the rate of structure growth in $\Lambda$CDM than is provided by the $\nu$HDM paradigm. Our results also suggest that replacing cold dark matter with hot dark matter is unlikely to provide a viable cosmological model, regardless of the
gravity law.
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All authors Alfie Russell, Indranil Banik, Oscar Cray, Hongsheng Zhao
Solar and Stellar Astrophysics · Cross-listed from math.NA
Analysis of eigenvalue clustering leads to optimal scaling in numerical radiative transfer
Pietro Benedusi, Simone Riva, Luca Belluzzi et al. (+1 more)
We consider a multidimensional polychromatic radiative transfer (RT) problem, accounting for scattering processes in a general form, i.e. anisotropic (dipole) scattering with partial frequency redistribution. Given a discrete ordinates discretization, we report the corresponding
matrix structures, depending on model and discretization parameters. Despite the possibly dense nature of these
matrices, the use of Krylov methods is effective (especially in the
matrix-free context) and robust. We propose a theoretical analysis, using the spectral tools of the symbol theory, explaining why Krylov convergence is robust w.r.t. all the discretization parameters, even in the unpreconditioned case. In fact, the compactness of the continuous operators used in the modeling leads to zero-clustered dense
matrix sequences plus identity, so that the clustering at the unity of the spectra is deduced. Numerical experiments confirm the theoretical results, which have a direct application, for example, in the simulation of radiative transfer in
stellar atmospheres, a key problem in astrophysical research. In general, we demonstrate that optimal scaling with respect to RT discretization parameters is expected for Krylov solution strategies.
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All authors Pietro Benedusi, Simone Riva, Luca Belluzzi, Stefano Serra-Capizzano
High Energy Astrophysical Phenomena
Probing Dark Photon Dark Matter with CTAO
Júlia G. Mamprim, Aion Viana and Vitor de Souza
The dark
photon is a hypothetical gauge
boson arising in extensions of the Standard Model, and has emerged as a compelling dark matter candidate. As dark
photon dark matter (DPDM), it can interact with electromagnetic fields via kinetic mixing, and the inelastic scattering process $\gamma A^{\prime} \to e^+ e^-$ becomes kinematically allowed for gamma rays above a characteristic energy threshold. This interaction imprints unique spectral attenuation features at very-high-energies (VHE), offering an observational probe of DPDM models. Using the Cherenkov
Telescope Array Observatory (CTAO) Instrument Response Functions (IRFs), we simulate observations of VHE sources and forecast novel sensitivities to the kinetic mixing parameter for the
photon-dark
photon scattering process. Our study focuses on three key astrophysical targets: the Crab Nebula and the blazars Markarian 421 and Markarian 501. Additionally, we investigate the impact of dark matter spikes around black holes on the upper limits. For the dark matter spike scenario considered in this work, CTAO observations could probe the DPDM parameter space down to a mixing parameter of $\varepsilon \sim 10^{-8}$ for masses around $m_{A^{\prime}} \sim 10^{-1}\,\textrm{eV}$ through high-energy spectral attenuation, at a $95\%$ confidence level.
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Earth and Planetary Astrophysics
Tidal disruptions of rubble piles: The case of Phobos
Harrison Agrusa and Patrick Michel
Many small satellites in the
Solar System have sub-synchronous orbits, meaning their orbits are decaying due to
tidal dissipation. Unless they have substantial material strength, they will eventually tidally disrupt before reaching their
planet's surface. We studied the fate of rubble-pile satellites as they migrate inward, with a particular focus on the case of Phobos. We used a combination of analytic estimates and numerical simulations to determine the failure mode and
tidal disruption distance of a Phobos-like satellite, as a function of its shape and cohesive strength. Both analytically and numerically, we identify a regime for satellites with low cohesive strengths whereby their surface can be tidally stripped without undergoing internal failure. Our numerical simulations demonstrate that Phobos will be destroyed beyond 2 Mars radii if it has a bulk strength similar to those estimated for small bodies recently visited by spacecraft. Based on our results and some additional arguments, we suggest that previous studies on the fate of Phobos have overestimated its strength, and therefore underestimated its
tidal disruption distance. We also speculate that if Phobos undergoes some
tidal stripping, its ultimate fate may be determined by runaway collisional erosion rather than a pure
tidal disruption. However, the ultimate
tidal disruption distance for Phobos will depend on its unknown internal structure and bulk material properties, which will be constrained by JAXA's Martian Moons eXploration (MMX) mission and its IDEFIX rover. These results have implications for theories about the origin and
evolution of the Martian moons and for
tidal disruptions of other small, irregularly shaped satellites.
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Cosmology and Nongalactic Astrophysics
The impact of cosmic filaments on starburst galaxies across cosmic times
Baptiste Jego, Matthieu Béthermin, Katarina Kraljic et al. (+17 more)
Cosmological simulations suggest that various
galaxy properties depend on their location within the
cosmic web. Yet direct observational evidence of the dependence of
star formation activity on distance to filaments remains scarce and is missing at z>1. We investigate how starburst, main-sequence (MS), and quenched
galaxies are distributed with respect to
cosmic web filaments, and how this distribution evolves with
redshift. We first use the SIMBA cosmological simulation to predict the
redshift evolution of the mean distance to the closest filament from z=3 to z=0 for different
galaxy populations after removing
stellar-mass dependencies. We then measure the corresponding signal in the COSMOS field, using COSMOS2020 and COSMOS-Web data, where accurate photometric
redshifts enable reconstruction of the projected
cosmic web from z=2 to z=0.5, and starbursts are identified through far-infrared spectral energy distribution fitting. In agreement with the results from SIMBA, starburst
galaxies are found closer to filaments at z>1 and at larger distances at z<1, MS
galaxies occupy intermediate environments with little
evolution, and quenched
galaxies show progressively shorter distances to filaments toward low
redshift, with a crossing between starburst and MS populations around z~1. In COSMOS-Web, the relative
evolution in the average distance to filaments between starburst and MS
galaxies is detected at a significance level of at least 5{\sigma}. We show that a minimal toy model in which the only environmental ingredient is the sSFR-filament distance modulation measured in simulations is sufficient to reproduce the observed differential
evolution of the average filament distance between starburst and MS
galaxies. These results show that the imprint of large-scale environmental effects on the
star formation activity of
galaxies, predicted by simulations, is detectable from z=2 down to z=0.5.
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All authors Baptiste Jego, Matthieu Béthermin, Katarina Kraljic, Clotilde Laigle, Lingyu Wang, Antonio La Marca, Olivier Ilbert, Hollis B. Akins, Caitlin M. Casey, Gavin Leroy, Ali Hadi, Jeyhan S. Kartaltepe, Anton M. Koekemoer, Henry Joy McCracken, Louise Paquereau, Jason Rhodes, Brant E. Robertson, Marko Shuntov, Greta Toni, Can Xu
Solar and Stellar Astrophysics
A deep HST view of the open cluster NGC2158: binaries, mass functions, and M-dwarf discontinuity
A. V. Marchuk, F. Muratore, A. P. Milone et al. (+13 more)
A significant fraction of
stars in both the
Galactic field and
stellar clusters are members of binary systems. Understanding their properties is therefore essential for a comprehensive view of
stellar structure,
evolution, and cluster dynamics. Despite extensive studies of cluster binaries, key issues remain unresolved, particularly for photometric binaries among low-mass
stars. While the binary fraction in the field strongly depends on
stellar mass, cluster studies have generally suggested an approximately constant fraction over the limited mass ranges explored. In addition, the mass function (MF) of very low-mass
stars is still poorly constrained in clusters older than a few hundred Myr. We use deep Hubble Space
Telescope imaging of the intermediate-age open cluster NGC 2158 to investigate its binary population and derive the luminosity and MFs down to ~0.14
solar masses, enabling the first detailed analysis of binaries in this cluster. We measure a global binary fraction of 38%, consistent with other open clusters, and find a clear mass dependence: it decreases from ~52% at 1.0
solar masses to ~11% at 0.2
solar masses. This trend mirrors that of
Galactic field
stars, suggesting similar binary properties. The MF is characterized by three regimes: high-mass
stars (alpha= -2.49 +- 0.19), low-mass
stars (alpha= -1.11 +- 0.09), and very low-mass
stars (alpha= -0.08 +- 0.07). The slope change near 1.0
solar mass agrees with recent surveys, though we find a deficit below ~0.3
solar masses. We also detect a main-sequence discontinuity around ~0.3
solar masses, possibly linked to the 3He-driven instability predicted by
stellar models and analogous to the Jao Gap seen in nearby field
stars.
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All authors A. V. Marchuk, F. Muratore, A. P. Milone, M. V. Legnardi, F. D'Antona, G. Cordoni, A. Mastrobuono-Battisti, E. Bortolan, F. Dell'Agli, E. Dondoglio, E. P. Lagioia, A. F. Marino, M. Tailo, C. Ventura, P. Ventura, T. Ziliotto
Astrophysics of Galaxies
The Dawes Review 14: A Decade of Ultra-Diffuse Galaxies
Jonah S. Gannon, Anna Ferré-Mateu and Duncan A. Forbes
It has been 10 years since the initial discovery of Ultra-Diffuse
Galaxies (UDGs) in the Coma cluster and the revelation that large, low surface brightness
galaxies may constitute a greater fraction of
galaxies than first thought. This left an open question: Are UDGs something special, or just an extension of the previously known
dwarf galaxy population? Seeking to answer this question, in the decade following, dedicated simulations have studied and proposed a myriad of formation pathways to create UDGs. Observations have then pushed the limits of world-class observatories to perform detailed studies of these
galaxies in large numbers across the full range of environments in the local Universe. These observations stress test simulations and challenge previous
galaxy formation wisdom, with UDGs posing many open puzzles beyond just their unknown formation mechanism. To provide a few pertinent examples: there is observational evidence that not all UDGs follow the standard
stellar mass –
halo mass relationship; there is evidence for UDGs with extraordinarily high levels of alpha enhancement; and there is evidence that some UDGs are much more globular cluster rich than other
dwarfs of similar
stellar mass. In this Dawes review, we undertake the task of summarising the decade of science since the discovery of UDGs. We focus on the quiescent population of UDGs and review their general properties, their proposed formation scenarios, their internal properties and their globular cluster systems. We also provide a brief
conjecture on some future directions for the next decade of UDG research.
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High Energy Astrophysical Phenomena · Cross-listed from gr-qc
Analytic force-free jet from disk-fed rotating black holes
Luis Villarin and Ian Vega
We present a new analytic model of a force-free electromagnetic jet launched from a disk-fed rotating black hole. The jet solution is force-free to first order in the black hole
spin and is obtained through a systematic construction based on previously developed analytical methods. The black hole jet modeled here exhibits an asymptotically
parabolic structure and is parametrized by the location of the current concentration and sign reversal on the thin magnetized disk in the equatorial plane. We find that the jet properties show negligible dependence on the disk parameter, suggesting a possible universality of slowly rotating black hole jets with respect to disk structure. Our jet model reproduces the key features expected from the Blandford-Znajek mechanism.
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Cosmology and Nongalactic Astrophysics
Impact and interplay of $\Lambda$CDM analysis choices for LSST cosmic shear
N. C. Robertson, C. Heymans, J. Zuntz et al. (+9 more)
We forecast cosmological parameter constraints for a
cosmic shear analysis of the Rubin Observatory Legacy Survey of Space and Time (LSST), defining an analysis framework that can accurately recover the $\Lambda$CDM model in the presence of astrophysical and data-related systematics. When accounting for our present uncertainty on the suppression of the non-linear matter power spectrum through
baryon feedback, we find that the error on the composite parameter $S_8=\sigma_8\sqrt{\Omega_{\rm m}/0.3}$ almost doubles compared to an LSST analysis which neglects this astrophysical phenomenon. After the first year of observations, LSST will extend beyond the magnitude limit of existing representative spectroscopic calibration samples, requiring photometric
redshifts to be calibrated using an alternative strategy. Adopting literature measurements of the reduced
redshift calibration precision found from
galaxy cross-correlation techniques, combined with current levels of
baryon feedback uncertainty, we forecast final year LSST
cosmic shear constraints that barely improve upon the first year analysis. This forecast therefore serves as encouragement to the community to develop methodology and observations to constrain models of
baryon feedback and enhance photometric
redshift calibration at depths where spectroscopy is unrepresentative. With tight priors on both these systematic terms, we forecast that LSST
cosmic shear can deliver constraints on $S_8$ that are more than five times as constraining as existing
cosmic shear surveys.
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All authors N. C. Robertson, C. Heymans, J. Zuntz, P. Burger, C. D. Leonard, I. G. McCarthy, J. G. Paine, J. Salcido, N. Šarčević, M. Schaller, J. Schaye, M. P. van Daalen
Solar and Stellar Astrophysics
The accretion discs in WZ Sge-type stars in deep quiescence. How do they outburst?
Vitaly Neustroev, Paula Kvist, Miikka Siitonen et al. (+1 more)
WZ Sge-type
stars are an extreme subclass of
dwarf novae characterised by very rare, large-amplitude superoutbursts. Within the disc instability model (DIM), such events are explained as being triggered by enhanced mass transfer from the donor
star. We present an analysis of observations of a sample of WZ Sge-type systems in deep quiescence to assess the consistency of DIM predictions with their observed properties. We find that
accretion discs in quiescent WZ Sge-type systems have very low mass-
accretion rates of a few $\times$$10^{-13}$ M$_\odot$ yr$^{-1}$. The discs are entirely optically thin, and their physical conditions – such as surface density and effective temperature – remain well below the DIM thresholds required to trigger an outburst. Observationally, no increase in disc brightness is detected prior to the superoutburst, indicating the absence of a transition to an optically thick state, in contrast to DIM predictions of a gradual disc thickening preceding the instability. We therefore find no observational evidence that superoutbursts in WZ Sge-type systems are triggered by enhanced mass transfer from the donor. Furthermore, the inferred mass-transfer rates in these objects ($\dot{M}_{\rm tr}$~5$\times$$10^{-12}$ M$_\odot$ yr$^{-1}$) are at least an order of magnitude lower than commonly assumed. We argue that the widely adopted value of $\dot{M}_{\rm tr}$ for the prototype object WZ Sge is likely overestimated. Finally, we show that in quiescence the
accretion disc radius in all systems is close to the
tidal truncation radius and exceeds the 3:1 resonance radius, confirming earlier results and calling into question the standard interpretation of superhump formation.
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All authors Vitaly Neustroev, Paula Kvist, Miikka Siitonen, Veera Vuolteenaho
Instrumentation and Methods for Astrophysics
pythonradex: a fast Python re-implementation of RADEX with extended functionality
Gianni Cataldi
A common task in astronomical research is to estimate the physical parameters (temperature, mass, density etc.) of a gas by using observed line emission. This often requires a calculation of how the radiation propagates via emission and absorption (so-called radiative transfer). In
radio and infrared astronomy, the Fortran code RADEX (van der Tak et al., 2007) is a popular tool to solve the non-LTE radiative transfer of a uniform medium in a simplified geometry. I present pythonradex, a Python re-implementation of RADEX. Written in Python, it provides an easy and intuitive user interface, improved performance as well as additional functionality not included in RADEX, such as continuum effects and overlapping lines. In addition, pythonradex provides a self-consistent computation of the total flux for all geometries, including spherical geometries.
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Astrophysics of Galaxies
The supersonic nature of jellyfish galaxies
Alessandro Ignesti, Francesca Loi, Antonino Marasco et al. (+20 more)
All gas-rich
galaxies in cluster environments are expected to experience ram-pressure stripping from the intra-cluster medium. However, only a fraction of these develop ongoing
star-formation in their stripped tail, becoming the so-called “jellyfish”
galaxies. In this work we provide observational evidence that
magnetic fields can signal differences in the extraplanar
star formation and explore what are the physical conditions that lead to the formation of a jellyfish
galaxy. We first focus on JO147, a jellyfish
galaxy that features weak
star formation activity in its tail. Using MeerKAT
radio continuum observations, we discover polarized emission only in a small fraction of its tail, with an average fraction of $~10\%$, and a low Mach number $\mathcal{M}=1.3-1.6$, which suggests a possible association between
magnetic field draping, shock-compression of the gas, and extraplanar
star formation activity. Then, we test this scenario in a sample of 17 jellyfish
galaxies from the GASP project. We combine dynamical models for their orbits within the host clusters with realistic cluster temperature profiles to infer their Mach number, and we find a positive correlation between it and the
star formation activity in their tail. We conclude that supersonic motion is a necessary condition for triggering
star formation in the stripped tails of jellyfish
galaxies. Our findings provide empirical evidence that the critical factor preventing the stripped gas evaporation is the shock compression induced by the supersonic motion through the cluster. This process likely enhances the
magnetic field surrounding the
galaxy and the properties of the stripped material.
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All authors Alessandro Ignesti, Francesca Loi, Antonino Marasco, Benedetta Vulcani, Bianca M. Poggianti, Christoph Pfrommer, Marco Gullieuszik, Alessia Moretti, Paolo Serra, Stephanie Tonnesen, Rory Smith, Cecilia Bacchini, Marc A. W. Verheijen, Myriam Gitti, Anna Wolter, Koshy George, Yara Jaffe, Rosita Paladino, Giorgia Peluso, Mario Radovich, Augusto E. Lassen, Neven Tomicic, Peter Kamphuis
High Energy Astrophysical Phenomena
Classical, large scale 3D MHD simulations of interacting pulsar wind nebulae
D. M.-A. Meyer and D. F. Torres
Magnetized rotating
neutron stars, or
pulsars, are a possible end product of massive
star evolution. Their relativistic wind successively interacts with the
supernova ejecta of their defunct progenitor, then with the circumstellar medium of the progenitor, and eventually with the interstellar medium. If a massive
star is static with respect to its ambient medium, then its resulting circumstellar medium is elongated along the direction of the local
magnetic field, and its
supernova remnant transiently appears as a rectangle. The
pulsar wind nebula forming in it is, in its turn, elongated, as long as the
pulsar axis of rotation matches the direction of the local magnetization. In this work, we explore how the angle between the direction of the local
magnetic field of the interstellar medium and the
pulsar axis of rotation influences the shaping of its
pulsar wind nebula with 3D MHD simulations are carried out with the PLUTO. We use those models to perform radiative transfer calculations to derive non-thermal
radio emission maps of the
pulsar wind nebulae. When the polar elongation of the
pulsar develop, they bend in opposite directions under the effects of the cavity carved by the
stellar wind and already filled by
supernova ejecta. This induces a complex distribution of magnetized
supernova ejecta and
pulsar wind, resulting in various observable structures, appearing as rectangles, circles, or irregular oblong shapes, in the
radio waveband. The angle between the direction of the
pulsar rotation axis and that of the local ambient magnetization is a governing parameter for the shaping and non-thermal
radio properties of the
pulsar wind nebulae of static massive
stars; however, the mixing of material, once the
pulsar wind nebula is old (50 to 80 kyr), is not strongly affected by that factor.
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Astrophysics of Galaxies
CALIMA: On-the-fly dust and PAH evolution for radiation-hydrodynamics galaxy formation simulations
Francisco Rodríguez Montero, Yohan Dubois, Harley Katz et al. (+2 more)
Dust grains and polycyclic aromatic hydrocarbons (PAHs) actively contribute to the thermodynamics, chemistry, and radiative state of the interstellar medium (ISM), yet most ISM models and
galaxy simulations either exclude them altogether or adopt simplified treatments. We present CALIMA, a new module for
dust and PAH formation and
evolution in radiation-hydrodynamics simulations for RAMSES, designed to self-consistently couple
dust physics to radiative transfer and non-
equilibrium thermochemistry in a multiphase ISM. The model employs a two-size, two-composition
dust framework with log-normal grain populations, explicitly evolving
stellar dust injection,
turbulence-informed gas-phase
accretion, shattering, coagulation, thermal and non-thermal sputtering, and shock destruction, while PAHs are separate components with their own
evolution. The evolving
dust populations and radiation field determine local, wavelength-dependent opacities, photoelectric heating efficiencies, grain-assisted recombination,
dust-gas collisional heating/cooling, and H$_2$ formation on both grains and PAHs. Updated treatments of thermal sputtering and collisional cooling that include finite grain sizes and modern ion-solid physics reduce sputtering rates at high temperatures and extend the regime where
dust significantly cools hot gas. One-zone ISM tests show that
dust and PAH
evolution modifies classical thermal phase diagrams and C-bearing chemistry, while isolated disc
galaxy simulations reveal environment-dependent variations in
dust-to-metal ratio, small-to-large grain ratio, PAH fraction, and interstellar radiation field intensity that drive non-trivial structure in infrared emission, UV transparency, and H$_2$ formation. CALIMA provides a physically motivated framework to interpret
dust- and PAH-based observables and to assess
dust-mediated feedback in
galaxy formation across
cosmic time.
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All authors Francisco Rodríguez Montero, Yohan Dubois, Harley Katz, Adrianne Slyz, Julien Devriendt
Cosmology and Nongalactic Astrophysics
Linear Perturbations and Multi-Probe Diagnostics in Dark-Sector Selective $f(R,T_{\chi})$ Gravity
L. Yildiz, D. Kayki and E. Gudekli
We develop a dark-sector selective trace-coupled extension of
gravity in which the matter–
curvature coupling depends exclusively on the trace of the dark-matter energy–momentum tensor, $T_{\chi}$, defined from a canonical dark-matter field $\chi$. This construction provides a microphysically specified trace sector, removes the usual matter-Lagrangian ambiguity of $f(R,T)$-type models, and preserves minimal coupling of visible matter by design. We derive the full field equations, the exact dark-sector exchange structure, and the linear scalar-perturbation system in gauge-ready form. In the sub-horizon regime, we derive effective modified-
gravity functions governing structure growth and light deflection, and show that the model generically produces correlated, scale- and time-dependent departures from General Relativity in growth and
lensing observables. Building on this structure, we formulate a perturbation-focused multi-probe framework based on
redshift-space distortions, weak
lensing, and CMB
lensing, explicitly targeting degeneracy breaking beyond background-expansion tests. The analysis establishes the action-level and perturbation-level foundations of the model and provides a conservative, reproducible framework for translated linear-regime constraints within a dark-sector selective modified-
gravity setting.
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Astrophysics of Galaxies
Formation timescales for stellar bars in diverse galactic discs
Matthew Frosst, Danail Obreschkow and Aaron Ludlow
We study the formation of
stellar bars using 145 simulations of disc
galaxies embedded in live and static dark matter
haloes. We use the exponential bar growth timescale, $\tau_{\rm bar}$, to quantify how disc structure and kinematics regulate the onset and rate of secular bar formation. We extend previous work to thicker and more turbulent discs, motivated by those observed at high
redshift ($z>1$). By revisiting several commonly used disc stability criteria - the Efstathiou-Lake-Negroponte parameter ($\epsilon_{\rm ELN}$), the Ostriker-Peebles ratio ($t_{\rm OP}$), and the disc
stellar mass fraction within 2.2 disc scale radii ($f_{\rm disc}$) - we find that $\tau_{\rm bar}$, when expressed in terms of the disc's orbital period, follows a tight power law with each criteria. In Milky Way-like discs embedded in live
haloes, bars form within a Hubble time if $f_{\rm disc} \geq 0.18$, $t_{\rm OP} \geq 0.27$, and $\epsilon_{\rm ELN} \leq 1.44$. We show discs with higher velocity dispersion experience delayed bar growth and introduce an empirical relation that correctly describes the bar formation timescales of all our live
halo models. Bars in static
haloes grow at roughly half the rate of those in live
haloes and require substantially greater disc instability to do so.
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Astrophysics of Galaxies
A Robust Analysis of QU-fitting Behavior for 800-1088 MHz and 1296-1440 MHz
Lindsey Oberhelman, Cameron L. Van Eck, N. M. McClure-Griffiths et al. (+9 more)
QU-fitting is a powerful tool for interpreting spectro-polarimetric
radio continuum observations by linking them to physical models, enabling estimates of the
magnetic fields in, for example, the Milky Way,
galaxy clusters, and
radio jets. We present a comprehensive investigation into the effectiveness and limitations of QU-fitting within the ASKAP POSSUM survey frequency ranges (800-1088 MHz and 1296-1440 MHz) with projections to other spectro-polarimetric
radio observations. We simulate different physical polarization sources: Faraday simple, Burn slab, internal
turbulence, external
turbulence, and two-component models in the POSSUM frequencies, and assess their observational degeneracies and fit accuracies. Our results highlight the model-dependent nature of reliable fitting and identify specific regions of parameter space where model selection, and therefore characterization of the physical medium, becomes ambiguous. For QU-fitting we find the Bayes factor, computed using the marginal likelihood, outperforms more traditionally used goodness-of-fit metrics such as
Bayesian Information Criterion (BIC), Akaike Information Criterion (AIC), and chi-squared for model selection. We provide empirical relationships to delineate the boundaries where model distinguishability is impossible. Finally, we evaluate how accurately QU-fitting recovers model parameters and their associated uncertainties, thereby assessing its ability to correctly characterize the Faraday-rotating medium in both point and extended sources in Faraday depth space.
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All authors Lindsey Oberhelman, Cameron L. Van Eck, N. M. McClure-Griffiths, Yik Ki Ma, Alec J. M. Thomson, Jason M. Price, Shinsuke Ideguchi, Craig S. Anderson, Marijke Haverkorn, Denis Leahy, Takuya Akahori, Jennifer West
Cosmology and Nongalactic Astrophysics
A sound horizon independent measurement of $H_0$ from BOSS, DESI and DES Y3
Zhiyu Lu, Théo Simon, Vivian Poulin et al. (+1 more)
We present a sound horizon independent measurement of the Hubble parameter using a multiprobe large-scale structure analysis. Removing the dependency on the sound horizon with a rescaling procedure at the matter power spectrum level, we analyse the BOSS full-shape power spectrum and bispectrum (for the first time) using the effective field theory of large-scale structure up to one loop. We combine this analysis with the auto- and cross-angular power spectra from the DESI Legacy Imaging Survey DR9, the $3 \times 2$pt analysis from DES Y3, and the CMB gravitational
lensing power spectrum from Planck PR3. Our baseline analysis, that does not rely on
supernovae data, yields $h = 0.702^{+0.022}_{-0.024}$, $\Omega_m = 0.310 \pm 0.013$, and $\sigma_8 = 0.799 \pm 0.020$, corresponding to $3-4 \%$ precision measurements. When adding
supernovae data from Pantheon+, we obtain a $2.6 \%$ measurement of $h$, with $h = 0.686 \pm 0.018$. We further note that our EFTBOSS analysis indicates a slight deviation of the BAO scale parameter (at $1.8 \sigma$) from its $\Lambda$CDM value, caused by the small scales of the bispectrum. We finally use the sound horizon-free EFTBOSS analysis as a diagnosis for the presence of new physics, finding that our results are consistent with the recent hints of evolving dark energy.
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All authors Zhiyu Lu, Théo Simon, Vivian Poulin, Yifu Cai
Solar and Stellar Astrophysics
Sub-second cadence structure of optical flares on AD Leo
B. Schmercz, B. Seli, K. Vida et al. (+4 more)
Stellar flares are sudden brightenings caused by
magnetic reconnection and are frequently observed on late-type
stars. High-cadence photometry of
flares provides valuable insights into the mechanisms of these events, yet such observations remain scarce. We seek to explore the sub-second fine structure of
stellar flares and assess the information content in high-speed photometry. New 0.3 s-cadence photometry from a six-year-long observing campaign of the active M-
dwarf AD Leo is presented. We use time–frequency analysis to detect quasi-periodic pulsations in the decay phase of
flares. We explore statistical measures of time series complexity of the detected
flares to quantify the information gain achievable with high-cadence photometry. We detect 42
flares in 211 hours of observations. The
flare frequency distribution is consistent with the previous literature. We find no quasi-periodic pulsations with periods below a few seconds, and identify two candidate signals with periods around 1 and 3 min. Using different measures of complexity on the binned
flare light curves we confirm the advantages of high observing cadence. However, we also find a plateau up to a binning of ~4–5 s for a few complex
flares, suggesting that an exposure time of a few seconds is usually enough to retain most of the information carried by a single-filter observation. New photometric observations of AD Leo revealed sub-structures of
flare light curves on the timescale of a few seconds, but we found no features on timescales below that.
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All authors B. Schmercz, B. Seli, K. Vida, L. Kriskovics, A. Görgei, K. Oláh, Zs. Regály
Solar and Stellar Astrophysics
Is Mira B a low mass white dwarf?
R. K. Zamanov, V. Irincheva, B. Spassov et al. (+8 more)
We report photometric observations in Johnson B and V bands of the short term variability (flickering) of Mira (omicron Ceti). The observations were performed during 7 nights in the period August - October 2025, in the course of the last minimum of the Mira pulsations. The observed peak-to-peak amplitude of the flickering is 0.11-0.28 mag in B band. For the flickering source we find luminosity in the range 0.10-0.46 L_sun. Using the amplitude-flux relation, we estimate an average luminosity of the
accretion disc L_d = 0.91 +/- 0.28 L_sun. Assuming that the white
dwarf accretes material through Wind Roche Lobe Overflow (WRLOF), we find that Mira B is a low mass white
dwarf with M_wd = 0.24 +/- 0.04 M_sun accreting at a rate 6.8x10^{-9} M_sun/yr. This value of the mass is in the range of the extremely low mass white
dwarfs. The data are available on Zenodo: zenodo.org/records/18756532
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All authors R. K. Zamanov, V. Irincheva, B. Spassov, A. Kurtenkov, D. Marchev, M. Minev, M. F. Bode, L. Dankova, B. Borisov, M. Dechev, G. Yordanova
Solar and Stellar Astrophysics
Retarded Stellar Dynamo in Tidally Deformed M Dwarfs
Song Wang, Wenbo Li, Henggeng Han et al. (+3 more)
Current studies of
stellar dynamos primarily focus on spherical
stars, leaving their behavior in distorted
stars largely unexplored. We utilize
stars of varying distortions to examine the relation between
stellar cycle periods ($P_{\rm cyc}$) and rotational periods ($P_{\rm rot}$), which are closely linked to dynamo processes. By analyzing a sample of tidally distorted M
dwarfs in cataclysmic variables, we identify an anti-correlation between $P_{\rm cyc}$ and $P_{\rm rot}$, in contrast to the lack of such a relation in single M
dwarfs. This means that
stars with greater deformation have longer cycle periods, suggesting variations in dynamo behavior under non-spherical geometries. Our numerical simulations further reveal that, the thermal convection weakens in highly distorted
stars, and subsequently, the differential rotation is also reduced. These effects may lengthen the conversion timescale between poloidal and toroidal
magnetic fields, potentially explaining the newly discovered $P_{\rm cyc}$-$P_{\rm rot}$ relation in cataclysmic variables.
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All authors Song Wang, Wenbo Li, Henggeng Han, Dali Kong, Jifeng Liu, Xinlin Zhao
Astrophysics of Galaxies
AVID: A Near-Major Post-Merger of Late-Type Dwarfs beneath a Regularly Rotating HI Disk (VCC 693)
Fujia Li, Hong-Xin Zhang, Elias Brinks et al. (+23 more)
On the periphery of
galaxy clusters, moderately high
galaxy densities and velocity dispersions favour interactions and mergers that influence
galaxy evolution prior to cluster infall. Observational studies of this phase in
dwarfs remain rare. We present a high-resolution study of the merger remnant VCC 693 in the outskirts of Virgo cluster, using observations from the Atomic gas in Virgo Interacting
Dwarf galaxies (AVID) project. We explore the origin of VCC 693 and the consequences of the merger on its
star formation and structure through a joint analysis of VLA and FAST HI emission line observations, together with complementary optical imaging and spectroscopy. We employ hydrodynamical simulations to help interpret the observations. Our analysis favours a near-major merger between two
dwarfs with a
stellar mass ratio of 3:1-4:1, with one likely gas-poor progenitor (i.e., a damp merger). The optical appearance of VCC 693 is dominated by complex
tidal structures throughout the system, whereas the HI gas has settled to a regular rotating disk. Compared with similar-mass
dwarfs, the central
star formation and gas-phase
metallicity are moderately enhanced. The global
star formation rate, HI gas content, and HI-to-optical size ratio of VCC 693 are broadly consistent with those of typical
dwarfs of similar mass, albeit somewhat lower. Decomposition of the HI rotation curve into baryonic and dark matter indicates a high
halo concentration, suggesting post-merger relaxation into a more centrally peaked configuration. Together with two recent studies of AVID post-merger systems, these results support the view that even major
dwarf mergers can produce remnants with overall
stellar structures indistinguishable from ordinary
dwarfs, and that the environmental effects in cluster outskirts can promote damp or mixed mergers, constituting an integral part of
galactic pre-processing.
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All authors Fujia Li, Hong-Xin Zhang, Elias Brinks, Se-Heon Oh, Rory Smith, Zesen Lin, Weibin Sun, Yu-Zhu Sun, Tie Li, Minsu Kim, Jaebeom Kim, Lijun Chen, Lanyue Zhang, Patrick Côté, Alessandro Boselli, Pierre-Alain Duc, Laura Ferrarese, Matteo Fossati, Stephen Gwyn, Xu Kong, Sanjaya Paudel, Eric W. Peng, Thomas H. Puzia, Rubén Sánchez-Janssen, Matthew Taylor, Yinghe Zhao
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-th
On the Kalb-Ramond field with non-minimal coupling to gravity
Anamaria Hell and Ippei Obata
We consider a massive Kalb-Ramond field with a general non-minimal coupling to
gravity. We first study the theory in flat space-time, taking into account the non-linearities. We show that the coupling with the
Ricci scalar gives rise to the strong coupling of the two transverse pseudo-vector degrees of freedom, which are absent in the massless theory. We then show that if the theory is instead coupled to the
Ricci tensor or the Riemann tensor, the two tensor modes become strongly coupled in addition to the transverse pseudo-vector modes. We then extend our analysis to homogeneous and isotropic space-time, with vanishing background value of the Kalb-Ramond field. We show that in this case, the couplings with the
Ricci and Riemann tensor give rise to the runaway instability. Finally, we discuss the inclusion of the disformal coupling as a possible resolution to this unnatural behavior.
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High Energy Astrophysical Phenomena
Spectral and photometric variability of SS 433 observed with XRISM and simultaneous optical and near-infrared telescopes
Yusuke Sakai, Shinya Yamada, Yuta Okada et al. (+36 more)
We present results from coordinated multiwavelength observations of the SS 433, obtained with XRISM, optical
telescopes, and near-infrared camera during 2024 April and 2025 March. The XRISM exposures amounted to ~200 ks in 2024 and ~100 ks in 2025. With XRISM/Resolve's high spectral resolution and large effective area, we clearly resolved numerous emission lines even in short time segments, achieving improved accuracy in Doppler-shift measurements relative to earlier observations. The simultaneously obtained X-ray and optical Doppler shifts suggest a possible tendency for the optical emission to lag slightly behind the X-rays. In the Resolve data, the Doppler shifts of the two jet components exhibited apparent asymmetries, with jet speeds fluctuating around ~0.26$\pm$0.01$c$ in 2024 and ~0.30$\pm$0.01$c$ in 2025. The velocity variations indicated modulations on a timescale of ~6.3 d, with a phase offset of about -90$^{\circ}$ relative to the nutation cycle. The observed line widths and flux of the approaching and receding jets appear consistent with the expected geometrical effects, indicating systematically larger line widths in the inner regions of the jets, as proposed by Shidatsu et al. (2025). Optical light curves show
flares of ~400 s in 2024 and ~1600 s in 2025, with amplitudes up to ~15% during out-of-eclipse intervals, while the XRISM/Xtend light curves show no significant variability within the overlapping intervals and given the statistical uncertainties. Near-infrared photometry in 2024, obtained during an out-of-eclipse interval at a different epoch from the optical observations, showed no
flare-like variability, and the X-ray band also remained constant within uncertainties. These coordinated observations provide a foundation for future XRISM studies aimed at probing the dynamical properties of the relativistic jets in SS 433.
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All authors Yusuke Sakai, Shinya Yamada, Yuta Okada, Toshihiro Takagi, Tomoya Usuki, Megumi Shidatsu, Shogo B Kobayashi, Robert Petre, Yoshihiro Ueda, Hideki Uchiyama, Miho Tan, Taro Kotani, Taichi Igarashi, Mami Machida, Haruka Sakemi, Nobuyuki Kawai, Daiki Miura, Hiroya Yamaguchi, Kanta Fujiwara, Daichi Hiramatsu, Keisuke Isogai, Chulsoo Kang, Mariko Kimura, Katsuhiro L Murata, Takahiro Nagayama, Taichi Nakamoto, Kosuke Namekata, Yuki Niida, Yuu Niino, Masafumi Niwano, Kyuseok Oh, Shigeyuki Sako, Mahito Sasada, Hiromasa Suzuki, Kenta Taguchi, Ichiro Takahashi, Miyu Uenishi, Yoichi Yatsu, Marina Yoshimoto
High Energy Astrophysical Phenomena
$r$-mode stabilization in rotating hyperon-rich neutron stars and its implications for GW190814
Athira S and Monika Sinha
The GW190814 event, involving a black hole of mass $22.2$–$24.3 M_{\odot}$ and a compact object of mass $2.50$–$2.67 M_{\odot}$, challenges our understanding of the mass gap between the heaviest
neutron stars and the lightest black holes. If the secondary is a
neutron star exceeding $2.5 M_{\odot}$, hyperons are likely to appear in its core, softening the equation of state. Rapid rotation can offset some of this softening, enabling higher maximum masses, but it may simultaneously excite the Chandrasekhar–Friedman–Schutz $r$-mode instability. Bulk viscosity arising from nonleptonic weak interactions in hyperonic matter provides an efficient damping mechanism that can stabilize such configurations. In this work, we investigate the combined effects of rotation, thermal
evolution, and hyperon-induced bulk viscosity on the stability of massive
neutron stars. We demonstrate a direct connection between the suppression of $r$-mode instabilities and the long-term dynamical stability of hyperon-rich
stars, offering a plausible interpretation of the GW190814 secondary as a rapidly rotating, hyperon-rich
neutron star rather than a low-mass black hole. Our unified framework extends beyond previous studies restricted to static equations of state or extreme viscous damping assumptions, providing new insights into the stability of massive, exotic
neutron star configurations.
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High Energy Astrophysical Phenomena
AT2024lhc and AT2024kmq in the landscape of featureless tidal disruption events
Yuhan Yao, Ryan Chornock, Andrew Mummery et al. (+39 more)
We study AT2024kmq and AT2024lhc, two
tidal disruption events (TDEs) with blue featureless spectra associated with high-mass black holes ($M_{\rm BH}\sim 10^8\,M_\odot$). Both events show optical precursors consistent with shock dissipation from stream self-intersection. Their X-ray emission is luminous ($L_{\rm X}\sim 10^{44}\,{\rm erg\,s^{-1}}$), highly variable (with minimum observed variability timescales of 1.3\,hr and 4.8\,hr for factor of $\sim3$ flux changes), long-lasting ($>1\,\rm yr$), emerging no later than the optical peak, and well characterized by power-laws with $1.7<\Gamma<3$ (where $f_\nu \propto \nu^{1-\Gamma}$). The X-ray properties and
radio non-detections support a compact corona ($\lesssim 10 r_{\rm g}$) producing Comptonized X-ray emission. Using all published featureless TDEs, we find statistically significant bimodality in the distribution of their peak UV/optical blackbody luminosities and radii. We assemble a comparison TDE sample with early-time X-ray observations with eROSITA, in which we find different $M_{\rm BH}$ distributions in TDEs with different X-ray spectral
evolution properties: low-mass black holes ($M_{\rm BH} \sim 10^6 M_\odot$) remain soft ($\Gamma>4$) within $t\lesssim 2$\,yr, intermediate masses ($\sim 10^7 M_\odot$) transition from soft to hard at $\sim$1 yr, while high masses ($\sim 10^8 M_\odot$) are hard ($1.5<\Gamma\lesssim 3$) from the outset. We interpret this result as evidence that the soft-to-hard state transition in TDEs occurs at the critical threshold of $\dot{M}_{\rm acc} \sim 0.03 \dot M_{\rm Edd}$ (similar to X-ray binaries), using the fact that the transition timescale predicted by simple disk theory scales with black hole mass as $t_{\rm tr}\propto M_{\rm BH}^{-3/4}$.
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All authors Yuhan Yao, Ryan Chornock, Andrew Mummery, Raffaella Margutti, Marat Gilfanov, Muryel Guolo, Eric R. Coughlin, Wenbin Lu, Joheen Chakraborty, Dheeraj R. Pasham, Kate D. Alexander, Olivia Aspegren, Charlotte R. Angus, Xinze Guo, Xander J. Hall, Erica Hammerstein, K.-Ryan Hinds, Anna Y. Q. Ho, Xiaoshan Huang, Elias Kammoun, Natalie LeBaron, Matteo Lucchini, Zoë McGrath, Matt Nicholl, Daniel A. Perley, R. Michael Rich, Genevieve Schroeder, Xinyue Sheng, Jesper Sollerman, Jean Somalwar, Jacob R. Wise, Michael W. Coughlin, Andrew Drake, Matthew J. Graham, George Helou, Joahan C. Jaimes, Mansi M. Kasliwal, Ashish A. Mahabal, Pavel Medvedev, Josiah Purdum, Ben Rusholme, Rashid Sunyaev
High Energy Astrophysical Phenomena · Cross-listed from gr-qc
Direction-of-arrival estimation of a gravitational wave by correlations between quadrupole moments of pulsar timing data
Taichi Ueyama, Hodaka Tamura and Hideki Asada
Can we estimate the direction of arrival (DOA) of a gravitational wave (GW) signal from
pulsar timing array observations? The present paper addresses the inverse problem, for which we consider quadrupole moments of
pulsar timing data due to GWs from a dominant isolated source such as a binary of supermassive black holes over an isotropic
stochastic background. Correlations between the quadrupole moments are discussed as a possible alternative to the matched filtering technique, where the correlations between
pulsar pairs over the full sky are taken into account. The correlations turn out to be in the form of a three-dimensional traceless
matrix with rank 3 that can be closely related with a projection tensor for the GW. Thereby, we demonstrate that the rank-3
matrix allows to estimate the DOA of the GW without assuming a template bank nor a priori Gaussian noise. A mean over the celestial sphere is adopted instead of the
pulsar averaging. A weighted average is used for a non-uniform distribution of
pulsars on the sky, for which the Voronoi tessellation is employed to numerically calculate an area-weighted mean. In expectation of the forthcoming Square Kilometre Array, DOA estimation errors are also examined.
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Earth and Planetary Astrophysics
HATPI Pre-Perihelion Time-series Photometry of the Interstellar Comet 3I/ATLAS
Joel D. Hartman, Gáspár Á. Bakos, Andrés Jordán et al. (+10 more)
HATPI is a recently commissioned time-domain facility at Las Campanas Observatory, Chile, that uses 64 wide-angle, 9.6 cm diameter lenses and back-illuminated CCDs, yielding a mosaic field-of-view of 7,100 square arcdegrees, observing the night sky at a cadence of 45 s and a spatial scale of 19.7 arcsec pixel$^{-1}$. In this paper, we present moving object time-series photometry with this facility, focusing on the interstellar comet 3I/ATLAS. 3I/ATLAS was first robustly recovered by HATPI on the night of 2025 July 2 (one night after its discovery) at a
Gaia $G$-band magnitude of $G = 17.796 \pm 0.082$ mag ($\pm 0.030$ mag systematic uncertainty). The comet then increased in brightness to $G = 14.071 \pm 0.073$ mag $\pm 0.030$ mag by 2025 Sep 13, after which it became unobservable by HATPI as it approached perihelion. Before 3I/ATLAS achieved a brightness of $G = 16.396 \pm 0.029$ mag $\pm 0.030$ mag on 2025 Aug 6, it could be detected when stacking all HATPI observations from a single night, while after this date it is sufficiently bright to detect in individual 45 s exposures. We do not detect evidence for significant short-time-scale variations in the brightness of 3I/ATLAS after Aug 6. Compared to other light curves in the literature, the HATPI photometry exhibits a somewhat steeper rise in brightness with decreasing heliocentric distance, $r_{H}$. The HATPI magnitudes are well-fit as a power law function of $r_{H}$, with an exponential index of $n = 5.167 \pm 0.095$, over the range $2.14$ AU $ < r_{H} < 4.44$ AU, compared to $n = 3.94 \pm 0.10$ when fitting together with other literature observations. We find that the phase function is constrained to $\beta = 0.0552 \pm 0.0032$ mag deg$^{-1}$.
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All authors Joel D. Hartman, Gáspár Á. Bakos, Andrés Jordán, Sarah Thiele, Zoltán Csubry, Geert Jan Talens, Attila Bódi, Sándor Pigai, István Domsa, Anthony Keyes, Vincent Suc, Adriana Gaitan, Antoine Thibault