High Energy Astrophysical Phenomena
Time-dependent cosmic-ray escape from wind bubbles: hard spectra formation
Lukas Merten, Sophie Aerdker and Enrico Peretti
Overview: Wind-driven bubbles are dynamic systems that can accelerate
cosmic rays, depending on their physical properties, up to very high energies. We investigate how a time-dependent description of the particle transport may impact the escaping
cosmic-ray flux. Model: The wind bubble system is modeled as spherically symmetric.
Cosmic rays are continuously injected at the position of the termination shock and propagate through advection and
diffusion until the escape at the time-dependent position of the forward shock, which is treated as a free escape boundary. Methods: The one-dimensional spherical time-dependent transport equation is solved by transforming it into the corresponding set of
stochastic differential equations, and integrated with a modified version of the open source
cosmic-ray propagation framework CRPropa. Results: We find that, during the wind driven phase, the downstream escaping spectra from wind bubbles can be harder than $\sim E^{-2}$, the conventional expectation from diffusive shock acceleration. Depending on the
turbulence model the initial energy spectrum can be significantly suppressed at lowest energies, which could be an observable feature to distinguish between different
turbulence realizations. This effect could lead to an efficient confinement of low energy particles, potentially leading to observable implication in terms of multi-messenger radiation and
cosmic-ray accumulated grammage within the bubble.
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Cosmology and Nongalactic Astrophysics
KiDS-Legacy: Joint analysis of second- and third-order cosmic shear
L. Linke, L. Porth, P. Burger et al. (+21 more)
Weak
lensing by large-scale structure is a powerful cosmological probe. While most analyses rely on second-order correlations, these are primarily sensitive to the parameter combination $S_8 = \sigma_8 (\Omega_m/0.3)^{0.5}$, limiting their ability to constrain $\Omega_m$ and other cosmological parameters independently. Higher-order statistics capture non-Gaussian features of the density field and can therefore break parameter degeneracies and extract more cosmological information from weak
lensing surveys. We present a joint analysis of second- and third-order
cosmic shear in the final data release of the Kilo-Degree Survey (KiDS-Legacy). We combine COSEBIs (Complete Orthogonal Sets of E-/B-mode Integrals) at scales between 2' and 300' with third-order aperture mass moments at scales between 4' and 32' to perform a joint analysis of second- and third-order statistics. Compared to previous KiDS analyses, we implement several methodological advances: an intrinsic
alignment model with
redshift and mass dependence, a
baryon correction model validated on multiple hydrodynamical simulations, and corrections for reduced shear and source clustering. Combining COSEBIs with third-order aperture mass statistics in KiDS-Legacy yields $\Omega_m = 0.297^{+0.056}_{-0.040}$ and $S_8 = 0.806^{+0.025}_{-0.023}$, significantly tightening the $\Omega_m$ constraints and more than doubling the figure of merit in the $\Omega_m$–$S_8$ plane compared to the two-point analysis alone. The third-order measurements pass stringent internal consistency tests, are fully compatible with the KiDS-Legacy 2-point constraints, other 2+3-point
lensing results and with Planck CMB measurements within $1\sigma$, providing no evidence for an $S_8$ tension and demonstrating the maturity of 3-point
cosmic shear as a key probe for forthcoming surveys.
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All authors L. Linke, L. Porth, P. Burger, J. Harnois-Déraps, S. Heydenreich, P. Schneider, M. Asgari, M. Bilicki, C. Georgiou, C. Heymans, H. Hildebrandt, H. Hoekstra, P. Jalan, B. Joachimi, S. Joudaki, K. Kuijken, S. Li, L. Moscardini, M. Radovich, R. Reischke, B. Stölzner, A. H. Wright, Z. Yan, Y.-H. Zhang
Solar and Stellar Astrophysics
Three-Phase Evolution of Aspect Ratio in Fast and Slow CMEs from the Sun to 1 AU
Wageesh Mishra, Anjali Agarwal and Nandita Srivastava
Coronal mass ejections (CMEs) undergo significant
geometric evolution as they propagate from the Sun to 1 AU, influencing their radial size, expansion, and space weather impact. We investigate the
evolution of CME aspect ratio and expansion dynamics for four fast and four slow Earth-directed CMEs. Using multipoint coronagraphic observations with the Graduated Cylindrical Shell (GCS) model and corrected in situ measurements of associated
magnetic clouds (MCs) at 1 AU, we track the
evolution of aspect ratio from the low-middle corona to interplanetary space. We find that aspect ratio does not remain constant but exhibits a systematic three-phase
evolution: a rise phase in the low-middle corona ($\lesssim10$-$15\,R_{\odot}$), a saturation phase at intermediate heights, and then a decline phase in the interplanetary space. The ratio of radial expansion speed to leading-edge speed ($V_{\rm exp}/V_{\rm LE}$) decreases substantially from the corona to 1 AU, indicating a reduction in radial expansion efficiency during interplanetary propagation. The consistent
evolution of aspect ratio and $V_{\rm exp}/V_{\rm LE}$ suggests a transition from magnetically dominated expansion in the corona to a regime increasingly controlled by the heliospheric environment. We note that fast CMEs show stronger early expansion and evolve into larger, more radially extended structures, whereas slow CMEs exhibit a more gradual rise and a steeper decline. These results demonstrate that CME geometry evolves significantly during propagation and highlight the need to incorporate aspect ratio
evolution in models to improve predictions of CME size, arrival time, and geoeffectiveness.
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High Energy Astrophysical Phenomena
Stellar mass loading drives dissipation and reacceleration in AGN jets: Explaining VLBI-Gaia offsets and constraining jet power
G. Fichet de Clairfontaine, M. Perucho, J. M. Martí et al. (+1 more)
Recent Very Long Baseline Interferometry (VLBI) and
Gaia astrometry reveal systematic milliarcsecond-scale offsets between the
radio and optical centroids of active
galactic nuclei (AGN). These "
radio-optical offsets" do not alter the standard opacity-driven interpretation of
radio core shifts. Instead, they indicate that the optical emission centroid is frequently displaced downstream of the
radio synchrotron optical depth $\tau = 1$ surface, implying that additional dissipation and particle reacceleration occur beyond the opacity
radio core within relativistic jets. We perform steady-state, axisymmetric relativistic magnetohydrodynamic (RMHD) simulations of AGN jets, including baryonic mass-load from
stellar winds, varying jet kinetic power, and
stellar core radius. Synthetic synchrotron emission maps in
radio and optical bands are generated via a radiative transfer code, and centroid offsets are extracted for comparison with observations. Parsec-scale
radio-optical offsets arise only for jet powers $L_{\rm j} \sim 10^{42.5} - 10^{44}\,\rm{erg}\,\rm{s}^{-1}$. In this regime,
stellar winds trigger jet deceleration at intrinsic distances of a few $10^2-10^3\,\rm{pc}$, shifting the optical centroid downstream and producing offsets of $\sim 0.1 - 4\,\rm{mas}$ (a few tens of parsecs at $z=1$). Offsets depend on
stellar distribution, viewing angle, and optical jet dominance, and vanish outside this power range. We reproduce the observed
redshift evolution of offset incidence, linking it to the
cosmic evolution of thermally pulsing asymptotic
giant branch (TP-AGB) mass loss. Although
stellar mass loading is unlikely to be the sole dissipation mechanism, its unavoidable presence in
galactic nuclei makes it a natural baseline for energy dissipation.
Radio-optical offsets therefore offer a constraint on AGN jet power and jet-host coupling, independent of traditional lobe-based methods.
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All authors G. Fichet de Clairfontaine, M. Perucho, J. M. Martí, Y. Y. Kovalev
Astrophysics of Galaxies
UV-to-optical insights into the BH$^*$ model in little red dots
Rosa M. Mérida, Marcin Sawicki, Chris J. Willott et al. (+2 more)
Little Red Dots (LRDs) are a heterogeneous class of objects, with several proposed scenarios for their physical nature and
evolution. While these theories have been tested on individual LRDs using limited spectral features, a systematic
Bayesian analysis of the LRD population incorporating the different models across a broad wavelength range is still lacking. In this study, we conduct a consistent ultraviolet (UV)-to-optical continuum fitting analysis of 99 LRDs at 2<z<6 using JWST/NIRSpec PRISM spectroscopy. Employing a modified version of Bagpipes-including blackbody (BB) emission affected by Balmer absorption,
stellar and nebular emission attenuated by
dust, and an active
galactic nucleus (AGN) component-we assess the performance of the black hole
star (BH*) model in describing the LRD population. We adopt broad priors and therefore do not impose any specific physical scenario. Our results show that only ~4% of LRDs with statistically robust solutions (81 objects in total) are best-fit by a BH* in the optical and a host
galaxy in the UV. ~9% of LRDs show BB-dominated optical continua but lack a
stellar component or exhibit AGN UV leakage. Most LRDs are dominated by
stellar and/or AGN emission in the optical, with minor BB contribution. When we adopt a prior that disfavors a strong AGN continuum to enforce BH*-like solutions, the percentage of BH* systems increases to ~35%, highlighting the strong degeneracy between a BH* solution and alternative scenarios. Even when BH*-like solutions are enforced, many LRDs still require a
stellar-dominated optical continuum. This could indicate limitations in the BH* model, as further supported by independent evidence, such as the detection of high-ionization emission lines in some LRDs.
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All authors Rosa M. Mérida, Marcin Sawicki, Chris J. Willott, Gaia Gaspar, Kartheik G. Iyer
Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc
A post-selected quantum model of cosmic acceleration
Dimitris Lionas, Charis Anastopoulos and Konstantinos Gourgouliatos
The origin of
cosmic acceleration remains a central problem in cosmology, commonly attributed to a cosmological constant within the $\Lambda$CDM model or to dynamical dark energy. Here, we develop an alternative approach in which acceleration emerges from
quantum post-selection, a standard feature of
quantum theory that is not usually incorporated into cosmological modelling. While
quantum theory admits both pre-selected and post-selected ensembles,
quantum cosmological models are almost exclusively formulated in terms of initial conditions. Building on previous work on post-selected quasiclassical dynamics, we construct a minimal predictive cosmological model in which post-selection and coarse-graining generate effective late-time acceleration without introducing a cosmological constant, dark energy, or modifications of general relativity. The resulting expansion history is highly constrained theoretically and depends on at most two parameters beyond standard Friedmann
evolution. Confrontation with type Ia
supernova and
cosmic chronometer data yields statistically competitive fits while naturally avoiding the coincidence problem. The model also reproduces the standard radiation- and matter-dominated behaviour at early times and predicts a present-day jerk parameter significantly different from the $\Lambda$CDM value. These results suggest that
cosmic acceleration may arise as a macroscopic
quantum cosmological effect rather than from additional cosmological fluids or modified gravitational dynamics.
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Cosmology and Nongalactic Astrophysics
Deep Learning Calibration of the Quasar X-ray/UV Luminosity Relation for Cosmological Applications
Jiaze Gao, Yun Chen, Lixin Xu et al. (+2 more)
Quasars can serve as standard candles through an empirical scaling relation between their ultraviolet (UV) and X-ray luminosities. As high-
redshift probes, it is critical to test whether this relation evolves with
redshift. In this work, we reconstruct the Hubble diagram of the Pantheon+ sample using the deep learning–based LADDER
algorithm and use it as a reference to investigate the
quasar scaling relation. Our results, which are consistent with those from Gaussian process regression and narrow-bin analyses, show that the potentially contaminated sample at $z<0.7$ differs significantly from the $z>0.7$ sample; thus, it should be further screened or excluded when
quasars are used as cosmological probes. We find that the scaling relation exhibits a non-linear
redshift dependence that cannot be accounted for by a simple linear correction, and that this behavior is a feature of the current data sample rather than a consequence of cosmological model misspecification. To use
quasars as standardizable candles, further modeling of the scaling relation and intrinsic dispersion, or more advanced data processing techniques, is required.
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All authors Jiaze Gao, Yun Chen, Lixin Xu, Jianping Hu, Xiaoyue Cao
Cosmology and Nongalactic Astrophysics
Towards Practical Field-Level Inference for Weak Lensing
Yuuki Omori, Justine Zeghal, Chihway Chang et al. (+2 more)
Nonlinear structure growth generates higher-order correlations and morphological features in the
cosmic density field that cannot be fully characterized by two-point statistics. Upcoming surveys will measure these features with greater precision, making it essential to develop methods capable of extracting as much cosmological information as possible from them. Field-level inference (FLI) is one such approach, in which cosmological parameters are constrained by comparing observed maps to forward-modeled maps, either directly or through learned summaries that retain map-level information. In this work, we compare FLI with power-spectrum-based inference using the same forward-modeling pipeline for generating weak
lensing maps, with the goal of quantifying the gain from map-level analysis relative to two-point statistics. We perform this comparison with both implicit and explicit inference methods, using 8-million-parameter forward models based on Lagrangian perturbation theory and particle-mesh (PM) N-body
evolution. The two FLI approaches yield closely consistent posteriors; this agreement, together with coverage tests confirming the calibration of the implicit analyses, gives us confidence in the recovered field-level constraints. Relative to the power-spectrum-based analyses, these results show significant gains in cosmological information, especially when small scales are included in the PM-based forward model. We then discuss the remaining challenges that must be addressed before PM-based explicit FLI can be applied to observational
datasets.
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All authors Yuuki Omori, Justine Zeghal, Chihway Chang, François Lanusse, Laurence Perreault-Levasseur
Astrophysics of Galaxies
Investigating the young stellar populations and hierarchies in nearby galaxies with the UVIT. II. Presenting the properties of ~25,000 UV-detected star-forming clumps
Gairola Shashank, Smitha Subramanian, Chayan Mondal et al. (+2 more)
Studying young
stellar populations within
galaxies can help refine our understanding of recent
star formation in
galaxies and their
evolution. With this motivation, we present a catalog of ~25,000 recently formed (within 400 Myr)
star-forming clumps (SFCs) in 17 morphologically diverse nearby
galaxies, including 8 massive, classic spirals, 6 intermediate-mass, flocculent spirals, and 3
dwarf irregulars. We used far- and near-UV observations from the UltraViolet Imaging
Telescope (UVIT), whose ~1.5" angular resolution and 28' field-of-view allow us to probe SFCs at a mean physical scale of ~54 parsec, within the full extent of our
galaxies. We adopted a homogeneous SFC detection criterion, corrected for spatially varying
dust attenuation (using 6" resolution A_V maps, made by combining FUV with archival infrared observations), and estimated the SFC ages by comparing the observed UV color-magnitude diagrams with Starburst99 simple
stellar population models. Using our SFC catalog, we studied the age demographic of the recently formed
stellar populations across different
galaxy morphologies and observed age trends consistent with several well-known phenomena, such as the inside-out formation of disc
galaxies, local gravitational instabilities leading to flocculent spiral arms, and the
stochastic nature of
star formation in
dwarf galaxies. Leveraging full
galaxy coverage and FUV data, our catalog complements existing optically-identified
star cluster catalogs in the literature towards improving our understanding of
star formation across a wide range of
galaxy morphologies, masses, and environments. We make the SFC catalog and A_V maps of our 17
galaxies publicly available with this paper.
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All authors Gairola Shashank, Smitha Subramanian, Chayan Mondal, Shyam H. Menon, Annapurni Subramaniam
Astrophysics of Galaxies
Spatially Resolved Nebular-Stellar Reddening with JWST/NIRISS
Peter J. Watson, Benedetta Vulcani, Tommaso Treu et al. (+7 more)
An accurate determination of the
dust attenuation within
galaxies is essential to derive key physical properties such as the
star formation rate (SFR). We present an analysis using the JWST/NIRISS data from the GLASS-JWST ERS programme to investigate and characterise the
stellar and nebular reddening of
galaxies at $1.0<z<2.4$, down to the sub-kpc scale. We use a multiregion fitting method to extract high-quality H$\alpha$ and H$\beta$ emission line maps for 99 individual
galaxies across a
stellar mass range $7.0<\log_{10}(M_*/\mathrm{M}_{\odot})<10.5$. We find no evidence for ratios of the Balmer decrement (H$\alpha$/H$\beta$) below the intrinsic limit for Case B recombination, beyond the expected variation from observational uncertainties. We reproduce the local correlation between the Balmer decrement and total
stellar mass, and find no measurable difference when splitting the sample by
redshift, with negligible attenuation below $\log_{10}(M_*/\mathrm{M}_{\odot})\lesssim8.5$. Similarly, the best-fit relation between the nebular and continuum reddening follows the same relation as in local starburst
galaxies, $E(B-V)_{\mathrm{SED}} = (0.46\pm0.02)E(B-V)_{\mathrm{neb}}$, together indicating no significant
evolution in the
dust geometry within
galaxies out to $z\lesssim2.4$. We derive best-fit linear relations between the differential nebular-
stellar reddening and the SED-derived
star formation rate (SFR) and
stellar mass, finding statistically significant relations for both quantities. We use our spatially-resolved measurements to derive an empirical calibration between the resolved differential reddening, and the SFR surface density. These will enable crucial
dust attenuation corrections for spatially-resolved science at higher
redshifts where the Balmer lines are inaccessible, such as with future Roman grism observations.
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All authors Peter J. Watson, Benedetta Vulcani, Tommaso Treu, Ayan Acharyya, Marc Rafelski, Anahita Alavi, Matthew Hayes, Keunho Kim, Faezeh Manesh, Claudia Scarlata
Instrumentation and Methods for Astrophysics
Barycentric Corrections for HST/STIS Data
Joshua D. Lothringer, Joleen K. Carlberg and Sean Lockwood
We describe $\texttt{stistools.barycentric_correction}$, a new Python utility for calculating barycentric timing corrections for HST/STIS observations. This tool replaces the deprecated $\texttt{stsdas.hst_calib.stis.odelaytime}$ IRAF function that was previously used for HST barycentric corrections. Our new utility uses $\texttt{astropy}$ for conversion between time formats and standards and introduces a new way to calculate HST's position through JPL Horizons, replacing the need to download separate HST orbital ephemeris files. Here, we describe the methods used in the new utility, the tests that were carried out to verify its accuracy, and explain some of the complexities involved in determining light travel times to accuracies down to a millisecond for HST. We also summarize the current understanding of the absolute accuracy of STIS time stamps.
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Solar and Stellar Astrophysics
Shaping the horizontal branch: The role of envelope mass in the evolution of stripped core-helium-burning stars
Eduardo Arancibia-Rojas, Mónica Zorotovic, Maja Vučković et al. (+2 more)
The location of a
star along the horizontal branch (HB) during core-helium burning is primarily determined by the amount of mass lost by its progenitor. We investigate the formation and properties of stripped core-helium-burning
stars, focusing on how the residual hydrogen-envelope mass ($M_{\mathrm{env}}$) and the timing of envelope removal shape their properties. We used the MESA
stellar evolution code to model
stars that lose their hydrogen envelopes on the first
giant branch. We explored two limiting cases for the timing of stripping, corresponding to the minimum and maximum core masses for helium ignition, for progenitors with initial masses below $\sim$6 $M_{\odot}$ at two
metallicities ($Z=0.02$ and $Z=0.004$), while systematically varying $M_{\mathrm{env}}$. As expected, the effective temperature along the HB decreases as $M_{\mathrm{env}}$ increases. We determined the maximum $M_{\mathrm{env}}$ required to avoid subsequent
evolution through the thermally pulsing asymptotic
giant branch, which ranges from $\sim0.05$ $M_{\odot}$, for low-mass progenitors to $\sim0.30$ $M_{\odot}$ for intermediate-mass progenitors. In low-mass progenitors, early envelope removal triggers a late hot flash, naturally explaining the hottest blue hook
stars. In intermediate-mass systems, partial envelope stripping can produce extended pre-HB configurations consistent with puffed-up stripped
stars observed in binaries with Be companions. Our post-stripping evolutionary tracks are publicly available for use in binary
evolution and population synthesis studies.
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All authors Eduardo Arancibia-Rojas, Mónica Zorotovic, Maja Vučković, Alexey Bobrick, Alex Durán-Reyes
High Energy Astrophysical Phenomena
Evidence for additional structure in the effective spin distribution hints at multiple formation pathways in GWTC-5.0
Sofia Alvarez-Lopez, Jack Heinzel and Salvatore Vitale
The distribution of the effective inspiral
spin ($\chi_\mathrm{eff}$) of the binary black holes detected by LIGO-Virgo-KAGRA can shed light on their formation pathways. We analyze the GWTC-5.0
dataset with two models-one flexible, one fully parametric-that jointly describe $\chi_\mathrm{eff}$ and primary mass. We clarify that the previously-reported skewness in the $\chi_\mathrm{eff}$ distribution is better understood as additional structure beyond a non-skewed Gaussian bulk centered at small $\chi_\mathrm{eff}$. This additional structure extends to larger $|\chi_\mathrm{eff}|$, a result previously reported using GWTC-4.0 data. We measure the asymmetry of the distribution of $\chi_\mathrm{eff}$ outside the Gaussian bulk from the data. With both the parametric and the flexible analyses, we find suggestive evidence for a mass-dependent excess of positive $\chi_\mathrm{eff}$ over negative ones outside the Gaussian bulk. We find only a mild statistical preference for a negative $\chi_\mathrm{eff}$ component outside the Gaussian bulk. This preference is highest at $m_1 \in [47,65]\,M_\odot$, with $13\text{:}1$ odds. Excluding the event GW191109, whose data have known data-quality issues, reduces these odds to $5\text{:}1$. If $\chi_\mathrm{eff}$ outside the Gaussian bulk are produced by hierarchical mergers-as has been suggested-then a fraction of those mergers may be produced in environments that can generate a surplus of binaries with positive $\chi_\mathrm{eff}$, such as the disks of active
galactic nuclei.
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Cosmology and Nongalactic Astrophysics
A Stochastic Framework for the Spherical Jeans Equation Motivated by Scalar-Tensor Gravity
Velasquez-toribio and A. M
We develop a
stochastic framework for the stationary spherical Jeans equation, motivated by the field-dependent nature of the gravitational coupling in scalar–tensor theories. We model unresolved spatial fluctuations of the scalar sector as an effective
stochastic contribution to the gravitational coupling, $\Geff(r,\omega)=\Gbar(r)+\Gamma_G(r)\xi(r,\omega)$. This approach induces a linear Itô
stochastic differential equation for the radial velocity dispersion $y(r)=\sigma_r^2(r)$, defining a nonautonomous radial random flow rather than a time-
evolution problem. We derive the associated Fokker–Planck equation and obtain integral expressions for the mean, variance, and covariance of the radial velocity dispersion. Because the noise is additive, the deterministic Jeans solution is recovered as the mean profile, while the
stochastic sector produces a probability band around it. We specialize the construction to Navarro–Frenk–White, Hernquist, and Einasto
halo models and propagate the radial covariance to the projected line-of-sight velocity dispersion. This provides a semi-analytical framework for assessing how effective gravitational fluctuations can affect
halo kinematic observables in the stationary Jeans regime.
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Astrophysics of Galaxies
Quenching of Star Formation in Massive Galaxies
Katherine E. Whitaker and Rachel Bezanson
The shutdown of
star formation - quenching - marks a pivotal transition in the lives of massive
galaxies, which dominate the present-day
stellar mass density. This review synthesizes our current understanding of the mechanisms that trigger and maintain quiescence. We discuss the nuances of how quiescent systems are identified across
cosmic time and summarize the evolving physical properties of the growing massive population, including their
stellar populations, chemical enrichment histories, and gas and
dust reservoirs, highlighting several key results: (1) Quiescent
galaxies can be identified with empirical color selections, but evolving specific
star formation rate thresholds offer a more robust physical distinction from
star-forming systems. (2) The earliest massive quiescent
stellar populations show rapid formation histories and high
metallicities, with enhanced $\alpha$-elemental abundances often distinct from local analogs. (3) Nascent studies of gas and
dust in quiescent
galaxies reveal diverse multiphase reservoirs and
outflows, pointing to fast ejective and slow regulatory modes of
galaxy quenching. (4) In situ processes establish
galaxy central density, while assembly continues via (minor) mergers post-quenching, reshaping all massive
galaxies and disrupting rotation in most cases. We distill observations into two broad modes by which massive
galaxies form and quench: one involves a rapid, early shutdown driven by supermassive black hole
outflows on short timescales; the other proceeds gradually through gas exhaustion, virial heating, or preventative feedback, each leaving distinct observational signatures. Together, these pathways offer a testable framework for modeling the formation and
evolution of massive
galaxies, which will be informed by future studies of their
stars, gas,
dust, and dynamics.
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Solar and Stellar Astrophysics
Near-core magnetic field strengths inferred from gravity modes in intermediate-mass stars
Oliver Durfeldt-Pedros, Victoria Antoci, Daniel Lecoanet et al. (+2 more)
In this work, we derive upper limits for the strength of the near-core
magnetic field in intermediate-mass
stars, since high-order g-modes can be fully suppressed by a critical
magnetic field. Both poloidal and toroidal components of the
magnetic field are included. We examine how the upper limits on
magnetic field strengths are affected by the degree and azimuthal order of the oscillations, as well as the
magnetic field configuration. We consider two gamma-Doradus
stars hosting high-order g-modes and an evolved delta-Scuti
star with mixed modes, all with prior mode identification from observations. We determine the best structural model from their
stellar parameters through grid-based modeling with MESA. Frequencies for the best models are extracted using GYRE and matched to the observed modes. The critical
magnetic fields for all calculated frequencies in our models are obtained from the Dedalus code, from which we can infer an upper limit on the near-core field strength. We find an upper limit on the near-core radial field strength of Br ~ 130 kG and Br ~ 13 kG, assuming a dipole field configuration, for the two gamma-Doradus
stars KIC 3127996 and KIC 5876187, respectively. For 44 Tau, analysis of mixed modes yields a field strength of Br ~ 1771 kG. Different
magnetic field configurations and mode degrees lead to different estimates. The results for the radial component of the
magnetic field in the main sequence gamma-Doradus
stars are consistent with estimates of
magnetic field strengths in red
giant stars that assume an internal field generated by a core dynamo, although the stronger of the two inferred
magnetic fields may require some enhancement by a fossil field. The toroidal component does not affect g-modes significantly and is required to be more than 200 times stronger than the radial component to suppress g-modes. (abridged for arXiv)
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All authors Oliver Durfeldt-Pedros, Victoria Antoci, Daniel Lecoanet, Zhao Guo, Jonathan Labadie-Bartz
Cosmology and Nongalactic Astrophysics
A Unified Halo Mass Function Across Dark Matter Models from High-Resolution Multi-Scale Simulations
Andrew J. Benson, Ethan O. Nadler, Xiaolong Du et al. (+1 more)
We measure the dark matter
halo mass function, with backsplash
halos removed, from a wide range of cosmological-box and zoom-in simulations. These include the MultiDark Planck boxes, along with a suite of zoom-in simulations of Group, Milky Way, and LMC-mass
halos. The Milky Way simulations include both CDM and non-CDM initial conditions. Using these measurements, we calibrate the parameters of flexible fitting functions for the
halo mass function and the window function, along with parameterized models for various systematics, including finite box size effects,
halo isolation criteria,
halo detection efficiency, and contamination by artificial
halos (objects forming from particle noise in the initial conditions). We show that this model shows remarkable consistency with N-body simulations over a broad range of
redshifts, and ten orders of magnitude in
halo mass ($10^6\mathrm{M}_\odot$ to $10^{16}\mathrm{M}_\odot$). Our model typically maintains a high precision of 12% and captures complex behaviors, including small-scale cut-offs, oscillations, and enhancements. In specific mass intervals for certain power spectra, we see larger deviations of 40-50%. Furthermore, when integrated with a simple model for environmental dependence, this fitting function provides a robust description of how environmental density influences the
halo mass function. This precision model captures a wide variety of dark matter paradigms (including thermal relics,
axions, and models with dark-sector interactions), is accurate for
halo masses down to $10^7\mathrm{M}_\odot$, and is a critical ingredient for model-independent dark-matter inference from forthcoming data.
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All authors Andrew J. Benson, Ethan O. Nadler, Xiaolong Du, Vera Gluscevic
Earth and Planetary Astrophysics
Atmospheric Dynamics of Asymmetrically Magnetized Hot Jupiter
Miaoyin Tang and Cong Yu
We investigate the influence of asymmetric
magnetic fields on the atmospheric circulation of hot Jupiters based on a Shallow-Water Magnetohydrodynamic (SWMHD) model. The Shallow-Water Hydrodynamic (SWHD) models predict eastward equatorial jets and hotspot offsets, while some observations have revealed westward hotspots, suggesting that
magnetic fields may play an important role. We incorporate asymmetric
magnetic fields between hemispheres, and analyze their effects through linear perturbation analysis and numerical calculations. Our results indicate that strong
magnetic fields play a dominant role in momentum transport. Asymmetric
magnetic field configurations lead to hemispheric temperature contrasts, with the dayside temperature maxima in the hemisphere of stronger
magnetic field located closer to the equator. With the
magnetic field fixed in one hemisphere, the equatorial hotspots shift westward then eastward as the other hemisphere's field strengthens, exhibiting a pronounced westward offset only at moderate field strengths and weak hemispheric asymmetry. These findings highlight the significance of
magnetic field geometry in explaining observed atmospheric dynamics and hotspot variability in hot Jupiters.
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Earth and Planetary Astrophysics
Reinterpreting the JWST Observations of 55 Cancri e with a Non-Grey General Circulation Model
Ruizhi Zhan and Daniel D.B. Koll
Recent observations of 55 Cancri e suggest an atmosphere rich in CO or CO$_2$ (Hu et al. 2024); other observations indicate the
planet's eclipse depth is highly variable (e.g. Patel et al. 2024). So far, these observations have only been interpreted using 1D models without self-consistent heat redistribution, as the
planet's extreme temperatures make it inaccessible to most 3D models. Here we perform cloud-free GCM simulations of 55 Cancri e using custom correlated-$k$ coefficients developed from the ExoMol database. Our best-fit simulations match the JWST spectra from Hu et al. (2024) well, favoring an atmosphere that is both thick ($\ge$ 10 bar) and CO$_2$-rich ($>1\%$ CO$_2$ volume mixing ratio), while ruling out thin ($<$ 10 bar) and pure-CO/CO$_2$-poor atmosphere, which were previously proposed based on 1D models (Hu et al. 2024; Zilinskas et al. 2025). We also find large-scale atmospheric dynamics, i.e. weather, is insufficient to explain the observed variability. A thick, CO$_2$-rich atmosphere implies that 55 Cancri e likely formed with significantly more volatiles than Earth and Venus. In addition, a thick atmosphere makes it unlikely that the
planet's variability is caused by transient outgassing (Heng 2023), favoring other variability mechanisms (e.g. clouds). Our work provides model constraints for upcoming JWST observations of 55 Cancri e, and highlights the importance of interpreting thermal emission observations with self-consistent 3D models.
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High Energy Astrophysical Phenomena
SN 1006: A Cosmic Laboratory for Investigating Shock Acceleration Physics
Emma McGinness, Rebecca Diesing, Damiano Caprioli et al. (+1 more)
SN 1006 is a historical Type Ia
supernova remnant that exhibits non-thermal emission ranging from
radio to multi-TeV $\gamma$-rays. Most of this emission (particularly X-rays and $\gamma$-rays) is concentrated in polar caps aligned with the ambient
magnetic field, which makes it an ideal laboratory for studying
cosmic ray (CR) acceleration at different shock obliquities and the hadronic/leptonic nature of the $\gamma$-ray emission. We model SN 1006's morphology, multi-wavelength spectrum, and radial profile using a self-consistent multi-zone kinetic model of particle acceleration that accounts for: CR-driven shock modification,
magnetic field amplification, drift in
magnetic fluctuations, and temporal dynamics including adiabatic and synchrotron losses. Our model can reproduce both the observed spectral and spatial properties, with the exception of the
radio profile that we argue requires 3D hydrodynamic effects to replicate. We find that quasi-parallel regions (where the shock normal aligns with the ambient
magnetic field) exhibit very prominent CR acceleration ($\sim$20% efficiency), while quasi-perpendicular regions exhibit efficiencies below 1%, consistent with the results of kinetic simulations. We also find that electrons are responsible for the majority of the $\gamma$-ray emission from SN 1006 (i.e., it is a leptonic source), with the exception of the northwest region due to an encounter with a dense cloud.
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All authors Emma McGinness, Rebecca Diesing, Damiano Caprioli, Fabio Acero
High Energy Astrophysical Phenomena
Broadened Lensing Rings of Compact Boson Stars: Enhanced Imprint of Accretion Flow in Images and Visibilities
Xiangyu Wang, Xinyu Wang, Minyong Guo et al. (+1 more)
In this work, we systematically study the gravitational
lensing properties and observational signatures of compact
boson stars. Unlike black holes, the
photon effective potential of a compact
boson star develops a nearly flat region, whose width increases with the compactness of the
star. This flat structure significantly broadens the range of impact parameters that can produce large-angle deflections, leading to noticeably wider
lensing rings of all orders.
Photons constituting these rings traverse more complex paths, rendering the resulting images more sensitive to the spatial distribution of the
accretion flow. Ray tracing results show that, compared to black hole models, the image
topology and visibility amplitudes of compact
boson stars exhibit a stronger dependence on the
accretion flow structure. These results highlight qualitative differences in the observational properties of compact
boson stars and black holes.
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All authors Xiangyu Wang, Xinyu Wang, Minyong Guo, Hai-Qing Zhang
Astrophysics of Galaxies
X-ray luminosity function of Compton-thick AGN in the early Universe (z > 3). Robustness and biases of the CTK population
Angel Ruiz, Ektoras Pouliasis and Ioannis Georgantopoulos
The population of Compton-thick (CTK) AGN represents a critical yet elusive phase in the growth of supermassive black holes. Constraining their abundance and
evolution at high z is essential for understanding both SMBH growth and the origin of the
cosmic X-ray background. We investigate the X-ray luminosity function (XLF) of CTK AGN at z > 3 using one of the largest available samples of X-ray-selected AGN at high z, containing 811 sources from XMM-Newton XXL-N and Chandra CCLS and CDF-S/N surveys. We first selected a subsample of ten high-probability CTK candidates, identified through x-ray spectral fitting. Their multiwavelength properties are examined through SED modelling to assess the robustness of their CTK classification. For most sources, the inferred X-ray luminosities appear overestimated when compared with their IR luminosities. After updating the NH posteriors with IR-informed priors, only three sources remain consistent with the CTK regime. To compute the XLF for the entire CTK AGN population, we used 24 microns photometry to estimate IR luminosities and update the X-ray posteriors for all the remaining sources. Incorporating IR priors systematically reduces the inferred CTK number densities, yielding a more conservative and physically consistent estimate of the XLF. We find that CTK AGN constitute 17 per cent of the total AGN population at 3 < z < 6, consistent with results at lower z. Our analysis reveals no statistically significant
evolution in the CTK fraction up to z about 6, suggesting that the most heavily obscured
accretion phase remains a persistent component of black hole growth throughout
cosmic history. While the overall obscured AGN fraction (NH > 1e23 cm-2) increases toward higher
redshifts, the stable CTK fraction supports the interpretation that, at these epochs, the interstellar medium in typical host
galaxies cannot produce CTK levels of obscuration.
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High Energy Astrophysical Phenomena
Marek Nikołajuk, Tomasz Karpiuk and Mirosław Brewczyk
Our study focuses on the strong
tidal disruption of a cold helium white
dwarf passing a black hole. We model the white
dwarf as a Bose-
Fermi droplet and use
quantum hydrodynamic equations to simulate the binary system's
evolution. As the white
dwarf passes through periastron, it loses a significant amount of mass. This mass falls onto the black hole and forms an
accretion disc. Quantized
vortices appear in the
accretion disc, manifesting as strong electromagnetic radiation signals that exhibit characteristic flickering patterns changing on a timescale of a few seconds. Meanwhile, the white
dwarf moves away from the black hole. As the white
dwarf moves through space,
vortices run along its surface. This elongates its geometry, causing it to rotate and emit gravitational waves.
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Solar and Stellar Astrophysics
Oscillations of red giant stars with magnetic damping in the core. II. Mixed mode visibilities on the red-giant branch
Jonas Müller and Saskia Hekker
Mode visibilities can be estimated from observed power spectra or from theory by making assumptions about the damping processes occurring in the
star. However, a quantitative comparison between the two approaches was so far not feasible due to observational biases. The biases arise from the fact that in observations, the power spectrum is divided into frequency segments in which modes of a certain spherical degree are expected to dominate. In this work, we used synthetic power spectra to calculate the visibility as it has been done in observations and compare it with published observed visibilities to quantify the influence of the biases. We find that, taking the biases into account, the observed spatial response of the dipole modes is 1.47, which is closer to the theoretical value than previous estimates. In particular, we predict that the normalized dipole mode visibility of late red-
giant branch (RGB)
stars might be overestimated by up to 20% in published observations. For
stars with depressed dipole modes, we find that the normalized dipole mode visibilities estimated in observational studies might be overestimated by 20% throughout their entire
evolution on the RGB. The quadrupole mode visibility, on the other hand, appears to be largely unaffected by the biases, expect on the late RGB. In addition, we investigated the
evolution of the visibility and detectability of the mixed mode signature while testing different prescriptions for the energy loss caused by a strong internal
magnetic field in the
stellar core. We argue that taking into account the inner turning point of the g-mode cavity could allow a portion of the mode energy to be preserved when interacting with a strong
magnetic field. We further show that such partial dissipation allows the mixed mode signature to be both present or absent in the observable power spectra, which is consistent with observations.
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Earth and Planetary Astrophysics
The 35-Myr old infant planet TOI-837 b has a mildly misaligned orbit
G. Mantovan, L. Malavolta, F. Marzari et al. (+6 more)
The measurement of the
spin-orbit obliquity, that is, the angle between the orbital axis of a
planet and the
stellar spin axis, provides crucial insights into how
planets form and migrate. Observations of young transiting
planets, which have not yet experienced significant
tidal alterations, offer a unique opportunity to study their original obliquity configuration. We observed the warm Saturn-sized TOI-837 b (member of the 35 Myr old open cluster IC 2602) in-transit using ESPRESSO at VLT, collecting high-precision radial velocities to measure the Rossiter-McLaughlin effect. We found a sky-projected obliquity of $\lambda = 341.1^{+2.3}_{-2.5}$ deg. Using our knowledge of the
stellar rotation period ($3.00 \pm 0.02$ d), we estimated a true obliquity of $\psi = 25.9^{+7.5}_{-6.3}$ deg, which indicates prograde motion and suggests a mildly misaligned orbit. This places TOI-837 b as the first
planet younger than 100 Myr with accessible $\psi$ incompatible with an aligned orbit. Together with the
primordial circular orbit of TOI-837 b and the presence of a bound
stellar companion, this mild misalignment favours the possibility of a
primordial obliquity excitation (secular torque on the protoplanetary disc) followed by disc-driven migration, rather than high-eccentricity migration after formation.
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All authors G. Mantovan, L. Malavolta, F. Marzari, A. F. Lanza, F. Borsa, D. Nardiello, S. Benatti, M. Damasso, S. Desidera
Instrumentation and Methods for Astrophysics
Calibration of an Analog-to-Digital Conversion Nonlinearity in JWST/NIRISS
Shashank Dholakia, Shishir Dholakia, Benjamin J. S. Pope et al. (+4 more)
We quantify an unusual flux-dependent systematic which is periodic in raw counts in flight data from the James Webb Space
Telescope's Near Infrared Imager and Slitless Spectrograph (JWST/NIRISS), used extensively for
exoplanet imaging and spectroscopy. Originally discovered in the aperture masking interferometry (AMI) mode, it also manifests in the Single Object Slitless Spectroscopy (SOSS) mode with the same dominant period of 1024 in raw analog-to-digital units (ADU). The likely cause of the signal is an analog-to-digital converter (ADC) integral nonlinearity (INL) in which case it will apply to all observations taken with the NIRISS instrument. Fortunately, it is straightforward to correct the data in postprocessing. The periodic INL is shown to be flux-dependent, increasing in amplitude with higher pixel counts on the detector. We derive a model of this periodic INL by fitting a combination of a
polynomial and sinusoid multiplied with the residuals of ramp fits to the uncalibrated data and find an amplitude of 125ppm, up to a 2.5-count shift for a pixel with 20,000ADU. We apply this model to correct the well-studied NIRISS SOSS Program ERS1366
dataset of WASP-39b and reduce the data into a transmission spectrum. We find that our corrected transmission spectrum removes the INL systematic from the uncorrected spectrum at the 30ppm level across both orders, and also corrects a 55ppm offset between Order 1 and Order 2. We recommend a larger scale data-driven calibration of the periodic INL and the adoption of the outcome into NIRISS data pipelines.
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All authors Shashank Dholakia, Shishir Dholakia, Benjamin J. S. Pope, Louis Desdoigts, Shrishmoy Ray, Peter G. Tuthill, Anand Sivaramakrishnan
Earth and Planetary Astrophysics
$^{13}$CO and potential variability in $\beta$ Pictoris b with GRAVITY+
Antonia von Stauffenberg, Jonas Sauter, Paul Mollière et al. (+18 more)
The $^{12}$CO/$^{13}$CO ratio was introduced as an indicator for where in the disk a
planet has formed. Previously a lower value compared to the host
star's was suggested to show that a
planet accreted CO ice beyond the disk's CO ice line. In this letter we aim to determine the $^{12}$CO/$^{13}$CO value of the directly imaged
planet $\beta$ Pictoris b, and whether we can link it to its formation. Its apparent brightness results in an exceptional S/N of up to ~60 per wavelength point. We present the first science observations with the upgraded
GRAVITY+ instrument at a spectral resolution of R ~ 4000, which we analyse with petitRADTRANS. Our
retrievals robustly indicate the presence of $^{13}$CO with a $^{12}$CO/$^{13}$CO ratio of 91$^{+24}_{-17}$, consistent with both a
solar to ISM-like value. Our $^{12}$CO/$^{13}$CO value corroborates recent interpretations that $^{13}$CO may be a less useful tracer of formation location in the disk than previously thought; nonetheless, we discuss theories with which this value is consistent. As our observations span ~7 hours, this enabled us to search for atmospheric variability in $\beta$ Pictoris b; we report a tentative constraint on the variability amplitude of about 1.4$^{+0.6}_{-0.7}$%.
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All authors Antonia von Stauffenberg, Jonas Sauter, Paul Mollière, Matthieu Ravet, David Trevascus, Wolfgang Brandner, Anthony Berdeu, Mickaël Bonnefoy, Guillaume Bourdarot, Jean-Baptiste Le Bouquin, Gaël Chauvin, Frank Eisenhauer, Mathis Houllé, Laura Kreidberg, Elisabeth Matthews, Florentin Millour, Jules Scigliuto, Jason Wang, Jerry W. Xuan, Yapeng Zhang, the GRAVITY+ Collaboration
High Energy Astrophysical Phenomena
Emergent gravity from Michel flow with position dependent adiabatic index
Apashanka Das, Souvik Ghose and Tapas K. Das
Spherically symmetric, general relativistic Bondi
accretion is known as the Michel flow. The stationary integral transonic solutions for the Michel flow has been constructed for multi-component
accretion described by an equation of state where the adiabatic index varies with the radial distance along which the streamlines are studied, and the corresponding phase portrait spanned by such radial distance and the flow Mach number has been obtained. Borrowing the techniques used in the dynamical systems theory, the nature of the transonic points of the aforementioned flow has been classified. The steady state flow has been perturbed to study the stability of the stationary solutions, and it has been found that such flows are stable under the (linear) radial perturbation. As a consequence of the stability analysis, the corresponding acoustic space time embedded within the accreting matter has been obtained, and the horizon of the metric of such sonic space time has been identified by constructing the causal structure with the help of the Carter-Penrose diagrams. In this way, the accreting black hole systems in the general relativistic set up has been investigated from various different perspectives - from its astrophysical aspects, from the dynamical systems point of view, as well as within the realm of the classical analogue
gravity phenomena.
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High Energy Astrophysical Phenomena
Identifiability of $g$ mode Resonances in Eccentric Binary Neutron Stars with Multidetector Observations
Mengfei Sun, Jie Wu, Qianning Hu et al. (+6 more)
$g$ mode resonances in eccentric binary
neutron star systems are potential probes of internal stratification, superfluidity, composition gradients, and the equation of state. Although such weak dynamical
tidal signatures are unlikely to be resolved with current detector sensitivities, third generation observations may make them accessible, in which case identifying the weak resonant phase shift would provide information beyond the bulk adiabatic
tidal deformability. We build a four class
dataset in an eccentric harmonic framework, containing point particle, adiabatic tide, resonant $g$ mode, and pure noise samples, and use Einstein
Telescope (ET) and
Cosmic Explorer (CE) detector data to test whether this weak resonant phase signature can be identified from noisy time domain strain. The ET, CE, and ET+CE deep learning models reach accuracies of $0.655$, $0.815$, and $0.897$, respectively. On the same simulated samples, the matched filtering method reaches lower accuracies of $0.514$, $0.677$, and $0.689$. This result arises from the fact that the resonant correction manifests as a weak phase morphology difference superimposed on the adiabatic
tidal background, whereas matched filtering is sensitive only to the overall similarity. Hence, in the presence of weak phase differences, the neural classifier employed in deep learning is better able to learn these local phase and morphology features from the complete time domain strain segment. The results indicate that joint third generation observations improve the identifiability of weak internal mode phase information.
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All authors Mengfei Sun, Jie Wu, Qianning Hu, Jin Li, Nan Yang, Xianghe Ma, Borui Wang, Minghui Zhang, Yuanhong Zhong
High Energy Astrophysical Phenomena
Detection of a parsec-scale, compact, and fading ejecta from an accreting massive black hole
Chao Li, Ning Chang, Jun Yang et al. (+2 more)
Dwarf galaxies, characterized by their low luminosities and masses, are excellent candidates for searches for intermediate-mass black holes (IMBHs), particularly when they show strong
accretion and ejection activity. The
dwarf galaxy SDSS J101747.09+393207.7 has recently been found to display a very high X-ray luminosity and an X-shaped optical structure, possibly caused by a
dwarf–
dwarf merger. To explore its potential IMBH ejection activity, we performed very long baseline interferometry (VLBI) observations at 4.9 GHz. In this work, we present the detection of a milliarcsecond-scale, compact, sub-microjansky
radio component near the optical centroid. According to some existing
radio sky survey data, the
radio component was not detected until 2015; it displayed an optically thin steep
radio spectrum and declining flux densities across 0.8–5 GHz from 2019 to 2025. Therefore, we identify it as a short-lived and rarely seen ejecta that was produced by unstable
accretion onto a massive black hole and likely faded away in a few decades. These results indicate that short-lived, episodic jet activity from accreting IMBHs in
dwarf galaxies might exist.
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All authors Chao Li, Ning Chang, Jun Yang, Lang Cui, Luis C. Ho