Earth and Planetary Astrophysics
Climates of temperate rocky planets with He-dominated atmospheres
Viviane Kuss, Robin Wordsworth, Collin Cherubim et al. (+1 more)
We present radiative-convective modeling of rocky
exoplanets with $He$-dominated atmospheres and low envelope mass fractions. Helium has a steeper adiabatic temperature profile than $N_2$ and $H_2$ as it has fewer degrees of freedom. Line broadening differences are small, collision-induced absorption (CIA) is not important in $He$-dominated atmospheres, and Rayleigh scattering by $He$ is weak. The combined impact of these effects is that $He$-dominated atmospheres provide more warming than $N_2$-dominated atmospheres but less than $H_2$-dominated atmospheres, for the same surface pressure. For surface pressures in the range 1-20 bar, the habitable zone for rocky
planets around M
dwarfs with $He$-dominated atmospheres is narrower than for $H_2$-dominated atmospheres. Nonetheless, due to their large scale height compared to $N_2$ or $CO_2$-dominated atmospheres, temperate $He$-dominated atmospheres are favorable targets for characterization via transit spectroscopy with JWST.
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All authors Viviane Kuss, Robin Wordsworth, Collin Cherubim, Jessica Cmiel
Astrophysics of Galaxies
First detection of ultra-fast outflows in a quiescent galaxy
Yerong Xu, Malgorzata Siudek, Victor Rodríguez Morales et al. (+7 more)
Outflows in active
galactic nuclei (AGN) are recognized as a fundamental mechanism driving the co-
evolution of supermassive black holes (SMBHs) and their host
galaxies. Although powerful
outflows are frequently detected in gas-rich, active
star-forming
galaxies, their existence and potential impact within gas-poor, quiescent
galaxies remain poorly understood. We report the first detection of a powerful ultra-fast
outflow (UFO) in a nearby quiescent
galaxy KUG 1208+386, providing a multiscale analysis of AGN winds from
nuclear to
galactic scales. We detect a
nuclear X-ray UFO with a velocity of $v_{out} \approx -0.07c$ and a kinetic power of $\dot{E}_{\rm UFO}=(0.8\mbox{--}6.5) \times 10^{43}$erg/s, sufficient to drive effective AGN feedback ($\dot{E}_{\rm UFO}/L_\mathrm{Edd}=(1\mbox{--}8)\%$) and far exceeding the
galactic [OIII]
outflow power $\sim 10^{40}$ erg/s. Host
galaxy analysis reveals a massive quiescent system (specific
star formation rate $\sim3\times10^{-12}\mathrm{yr}^{-1}$) that has been quenched $\sim$9 Gyr ago. The central AGN is obscured by a line-of-sight (LOS) column density of $\log (N_\mathrm{H}^\mathrm{LOS}/\mathrm{cm}^{-2})\sim23$ and the circumnuclear scattering material is Compton-thick $\log(N_\mathrm{H}^\mathrm{scatter}/\mathrm{cm}^{-2})=24.7^{+0.8}_{-0.5}$. The discovery of a
nuclear UFO in a long-quenched massive
galaxy challenges the paradigm that UFOs are exclusive to gas-rich,
star-forming systems, suggesting instead that they are governed by the local circumnuclear environments, rather than the global gas reservoir. Our results indicate that episodic, powerful winds can maintain the quiescent state of KUG 1208+386 over Gyr timescales, supporting a wind-driven `maintenance' mode of AGN feedback that is distinct from the classical jet mode.
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All authors Yerong Xu, Malgorzata Siudek, Victor Rodríguez Morales, Mar Mezcua, Hai-cheng Feng, Ciro Pinto, James N. Reeves, Stefano Bianchi, Valentina Braito, Luigi C. Gallo
Solar and Stellar Astrophysics
Nitrogen rises to the top: evidence of enhanced mixing in very massive stars
Pablo Marchant and Tomer Shenar
Recent observations of young
galaxies in the high-
redshift Universe reveal signs of early enrichment of nitrogen. Extremely massive
stars ($M \gtrsim 10^{2}-10^3\,M_\odot$) with strong
stellar winds have been proposed as a potential driver of this phenomenon. Here, we show that the observed fraction of nitrogen rich
stars with masses $\gtrsim 100M_\odot$ cannot be explained solely by mass loss, requiring significantly more efficient mixing beyond their convective cores than accounted in present evolutionary models. We compile a representative sample of 122
stars in the Tarantula Nebula of the Large Magellanic Cloud (LMC) with masses $M \gtrsim 30\,M_\odot$. Nearly all
stars with masses $M \gtrsim 100\,M_\odot$ exhibit strong nitrogen enrichment, by factors $\gtrsim 5-10$. We demonstrate that this trend cannot be reproduced by varying assumptions on binary fraction,
star formation history, or mass-loss rates within ranges predicted by current empirical and theoretical models. In contrast, enhanced core overshooting of $\alpha_\text{ov}\gtrsim 1$ can account for the observed enrichment, but leads to quasi-chemically homogeneous
evolution that is inconsistent with the observed Hertzsprung-Russell diagram. While the origin of this discrepancy remains unclear, our results, in combination with observational and theoretical constraints on mass-loss rates, suggest the presence of efficient early mixing operating during or shortly after the formation of very massive
stars. Such mixing models are currently not included in
stellar evolution models. These findings have immediate implications for the formation, radial expansion,
evolution, and final fates of
stars at the upper mass end, and provide a potential pathway to explaining the rapid nitrogen enrichment observed in the high-
redshift Universe.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Particle Cosmology: 1980-2000
Edward W. Kolb
A new field, Particle Cosmology, emerged at the interface of elementary particle physics and cosmology in the last two decades of the 20th century. In this chapter of the Proceedings of the 4th International Symposium on the History of Particle Physics, the Standard Model and Beyond I will review the development of Particle Cosmology in the period 1980-2000 centered on two events: a conference, Inner-Space/Outer-Space held at Fermilab in May 1984 \cite{kolb1986innerspace} and the 1994 Snowmass Summer Study Particle and
Nuclear Astrophysics in the Next Millennium \cite{kolb1995particle}.
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Instrumentation and Methods for Astrophysics
"Perfect" spectra for ESO's HARPS spectrograph
Dinko Milaković, Guido Cupani, Bruce A. Bassett et al. (+2 more)
HARPERFECT is the first application of "spectral perfectionism" to a high-resolution echelle spectrograph, reconstructing 1D spectra from 2D detector data via a forward model built on a calibration
matrix consisting of point-spread function (PSF) shape, wavelength, and order trace, which were built entirely from
laser frequency comb (LFC) observations. HARPS cannot resolve individual LFC lines, so each of 21 148 identified lines directly samples the PSF. We modelled these with a bivariate Gaussian, determining the PSF shape on the detector, calibrating wavelength, and tracing orders more accurately than the standard HARPS pipeline. Applied to 52.5 hours of HARPS data on
quasar HE0515-4414, HARPERFECT gives S/N comparable to, though slightly lower than, the standard pipeline. Its value lies in an exact resolution
matrix and independent samples, properties standard extraction cannot guarantee for a non-separable PSF - a step toward better measurements of fundamental constants and
exoplanet atmospheres.
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All authors Dinko Milaković, Guido Cupani, Bruce A. Bassett, Stefano Cristiani, Luca Pasquini
High Energy Astrophysical Phenomena
Radio Observations of the Unusual Tidal Disruption Event AT 2022wtn: a Fast and Highly Energetic Outflow
Gavin Farley, Tanmoy Laskar, Noah Franz et al. (+11 more)
We present multi-epoch, multi-frequency
radio observations of the
tidal disruption event (TDE) AT 2022wtn, obtained with the Karl G. Jansky Very Large Array (VLA) and
Giant Metrewave
Radio Telescope (GMRT), spanning 97-866 days after optical detection. The peak
radio flux density increases until 300 days post optical discovery, flattens out for several hundred days, then begins to decrease at 534 days. Utilizing an updated equipartition analysis framework, we estimate several physical parameters of the event and the surrounding medium. We model AT 2022wtn with two different geometries: a spherical and a conical emitting region. The spherical
outflow model gives an expansion velocity of $v\approx0.21c$ and a kinetic energy of $\sim3.8\times10^{49}$ erg, and the conical
outflow model yields a higher energy ($\sim1.8\times10^{50}$) and velocity ($v\approx0.41c$) than the spherical case. After ruling out the possibility of a relativistic jet, we consider several potential origins for sub-relativistic
outflow regions in TDEs including unbound debris streams, collisionally-induced
outflows, an
accretion-driven wind, and an
outflow from an
accretion disk state transition, and find only an
accretion disk state transition
outflow to be consistent with the high energy and velocity found in our equipartition results. AT 2022wtn is a uniquely powerful non-relativistic
radio-emitting TDE, and joins a growing population that display a diverse range of
outflow properties.
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All authors Gavin Farley, Tanmoy Laskar, Noah Franz, Collin T. Christy, Coleman Rohde, A. J. Goodwin, Kate D. Alexander, Edo Berger, Yvette Cendes, Ryan Chornock, Tarraneh Eftekhari, Walter W. Golay, Wenbin Lu, Raffaella Margutti
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Natural Phantom Dark Energy from a $\mathbb{Z}_N$–Axion
Cédric Delaunay and Admir Greljo
We present a technically natural microscopic realization of apparent phantom dark energy based on an
axion coupled to $N$ copies of two-
flavor dark QCD related by a $\mathbb{Z}_N$ exchange
symmetry. The
symmetry exponentially suppresses the
axion vacuum potential, naturally generating the dark-energy scale, while reheating into a single dark sector induces a controlled breaking of $\mathbb{Z}_N$ that simultaneously restores the physical
axion periodicity, sets the dark-matter abundance, and drives the late-time dark-energy dynamics. The selected sector contains dark-pion dark matter, whose finite density initially traps the
axion away from its
vacuum minimum. As the Universe expands and the dark-pion density
redshifts away, the
axion is released and rolls on the reheating-induced
vacuum potential, generating an effective phantom crossing without tuned cancellations. We identify a viable parameter region that simultaneously reproduces the observed dark-matter relic abundance and dark-energy scale, satisfies cosmological and astrophysical constraints, and qualitatively reproduces the DESI preference for an evolving dark-energy equation of state.
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High Energy Astrophysical Phenomena
A Self-Consistent Framework for Synchrotron Equipartition Analysis
Coleman Rohde, Tanmoy Laskar, Noah Franz et al. (+3 more)
Determining the energy, size, and velocity of synchrotron-emitting
outflows is essential for testing models of their formation and
evolution, but these quantities are often poorly constrained by observations alone. Equipartition analysis, therefore, provides a widely used framework for estimating these properties. Prior works have developed refinements to account for additional physical effects and other sources of energy (e.g., self-absorption, hot
protons, and deviations from strict equipartition); however, these corrections are typically applied independently of one another, resulting in internal inconsistencies. In this work, we derive a self-consistent equipartition framework that accounts for the interdependence of various correction factors for Newtonian
outflows and on- and off-axis relativistic jets. We implement our framework in an easy-to-use, publicly available code and apply it to study the
tidal disruption events ASASSN-19bt and AT2019dsg, fast X-ray transient EP240414a, and active
galactic nucleus J0231-0433. The interdependence of the corrections can increase energy estimates by a factor of ~5, suggesting that the energies of other synchrotron sources may be similarly underestimated in the literature. These results indicate that simultaneously incorporating these correction factors is essential for determining accurate
outflow properties and constraining launch mechanisms.
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All authors Coleman Rohde, Tanmoy Laskar, Noah Franz, Gavin Farley, Collin Christy, Kate D. Alexander
Earth and Planetary Astrophysics
Unveiling the Nature of C/2023 A3 (Tsuchinshan-ATLAS): A Multi-Technique Observational Approach
Goldy Ahuja, Shashikiran Ganesh, Aravind Krishnakumar et al. (+3 more)
Comet C/2023 A3 (Tsuchinshan-ATLAS) is a non-periodic dynamically new Oort cloud comet that was discovered independently by Purple Mountain Observatory in China and Asteroid Terrestrial-impact Last Alert System (ATLAS)
telescopes in South Africa. The comet passed perihelion at a distance of 0.39 AU on 27 September 2024. It was visible to the naked eye (the brightest since the comet C/1995 O1 (Hale-Bopp)) and was dubbed the great comet of 2024. In this work, we investigate the nature of this comet, which is moving in a
hyperbolic orbit (e > 1), by analysing its composition using various observational techniques and tracing its orbital
evolution through high-precision N-body simulations.
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All authors Goldy Ahuja, Shashikiran Ganesh, Aravind Krishnakumar, Devendra K. Sahu, Thirupathi Sivarani, Vikrant K. Agnihotri
Astrophysics of Galaxies
Joint constraints on gravity and stellar orbital anisotropy in massive galaxies
Wei Du, Liping Fu, Gong-Bo Zhao et al. (+5 more)
Strong gravitational
lensing combined with
stellar dynamics provides a complementary route for testing
gravity on kiloparsec scales and probing the internal structure of massive
galaxies. However, such studies remain limited by degeneracies among the mass-density profile,
stellar orbital anisotropy and external convergence, and by modelling assumptions, especially when only single-aperture velocity dispersions are available. Here we develop a hierarchical
Bayesian framework to disentangle
gravity and
stellar orbital anisotropy from other effects at the population level. By reconstructing the lens mass distribution with a flexible broken power-law model and propagating its posterior uncertainty into the predicted velocity dispersion, we obtain a likelihood for each lens in the plane of
stellar orbital anisotropy and an effective mismatch parameter. This parameter encapsulates projection bias, external convergence, cosmological distance ratios and deviations from general relativity via the post-Newtonian parameter $\gamma_{\rm PPN}$. Applying this framework to 121
galaxy-scale lenses, we find $\gamma_{\rm PPN}=1.027^{+0.099}_{-0.095}$, consistent with general relativity, and obtain $2\sigma$ evidence that the
stellar orbits of massive
galaxies have become more radially biased over the past $\sim6$ Gyr. Forecasts show that future samples of order $10^5$ lenses could enable sub-percent tests of
gravity, precise measurements of orbital-structure
evolution and complementary constraints on the cosmological matter-density parameter.
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All authors Wei Du, Liping Fu, Gong-Bo Zhao, Yiping Shu, Shuo Yuan, Zuhui Fan, Huanyuan Shan, Chenggang Shu
Astrophysics of Galaxies
CRexit observed: probing cosmic ray transport in the circumgalactic medium with absorption line spectra
Matthias Weber, Timon Thomas, Christoph Pfrommer et al. (+1 more)
Cosmic rays (CRs) likely provide dynamically important non-thermal pressure support in the circumgalactic medium (CGM), but how their transport physics shapes observable absorption signatures remains uncertain. We investigate whether absorption-line diagnostics can distinguish between different CR transport regimes in CR-pressure-dominated
halos. Using high-resolution simulations, we generate synthetic spectra along large ensembles of sightlines and measure column densities, equivalent widths, covering fractions (CFs), velocity widths, abundance ratios, and stacked absorption profiles for ions tracing cool, warm, and hot gas. We find that the effective CR transport speed strongly regulates the multiphase structure of the CGM. Efficient CR transport enhances the formation of cool ($T\sim10^4$ K) and warm ($T\sim10^5$ K) gas, leading to deeper and broader absorption lines of low- and intermediate-ionization species. The two-moment CR transport model produces the strongest MgII and SiII absorption and reaches MgII CFs consistent with the range inferred for
star-forming
galaxies. In contrast, slow CR transport underproduces cool, low-ionization gas and yields substantially weaker absorption. We also find that the origin of CIV-bearing gas changes with CR transport: slow transport mainly produces extended warm
halo gas, whereas efficient transport shifts much of the CIV absorption into mixing layers around cool clouds. The high-ionization tracer OVI responds more weakly, indicating that CR transport primarily regulates the cool condensed phase and its interfaces rather than the volume-filling hot
halo. These findings suggest that absorption-line measurements of cool and transition-phase gas can provide valuable constraints on the effective transport of CRs through the CGM.
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All authors Matthias Weber, Timon Thomas, Christoph Pfrommer, Tanya Urrutia
Cosmology and Nongalactic Astrophysics
Effect of post-recombination accretion on primordial binary black hole mergers within virialized dark matter halos
A. Konovalov and K. Postnov
Gravitational waves from binary black hole mergers remain among primary sources for ground-based and space
laser interferometers.
Primordial binary black holes (PBHs) can form binaries in the early Universe or at the matter-dominated stage in virialized dark matter
halos at
redshifts $z\sim 7-15$. We study enhancement of
primordial binary PBH merger rate in virialized dark matter
halos due to
baryon accretion in the post-recombination epoch within two
accretion models onto individual PBH – Bondi-Hoyle-Littleton (BHL) and Park-Ricotti (PR), representing two extreme cases of the
accretion efficiency. We calculate modification of the initial PBH mass function and their fractional contribution to dark matter. A significant enhancement in the binary PBH merger rate is found for the late three-body channel, which was previously treated as subdominant. In the case of delayed virialization onset at $z<10$, merger rates of dynamically formed PBH binaries are limited by the existing LVK binary BH detections. An increased merger frequency is revealed for PBH binaries with highly asymmetric mass ratios. We also calculate expected detection rates of binary PBH mergers for the TianQin space-based gravitational-wave interferometer and show them to be optimistic in the BHL
accretion case even for very low initial PBH abundances $f\sim 10^{-6}$.
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High Energy Astrophysical Phenomena
The Generalization Gap in Machine Learning EoS Inference from Core-Collapse Supernova Gravitational Waves
Ayan Mitra
Core-collapse
supernova gravitational waves may carry information about the dense matter equation of state (EoS), which describes the relation between pressure, density, temperature, and composition. This work tests a crucial question for physical inference: can a machine learning model trained on a finite simulation catalogue predict EoS parameters for an EoS family that was absent during training? Under standard random cross-validation, a LightGBM regressor appears highly successful, yielding $R^2=(0.70,0.67,0.60)$ for the
nuclear incompressibility,
symmetry energy, and slope parameter $(K_0,J,L)$. However, under Leave-One-EoS-Out (LOEO) validation, where all waveforms from a single EoS are withheld, the model fails, yielding mean absolute errors of $(44.57,3.19,30.54)$ MeV and negative pooled $R^2$ scores, performing worse than a baseline mean predictor. This generalisation gap persists across linear models, random forests, neural networks, and gradient-boosted trees. Restricting inputs to physical features (bounce amplitude, bounce width, peak frequency) reduces template leakage, the memorisation of related templates shared across random splits, but does not restore reliable EoS extrapolation. In contrast, a progenitor mass case study shows that classification generalises to unseen rotation speeds, while continuous mass regression compresses predictions towards the catalogue interior. These results demonstrate that while machine learning successfully interpolates within current waveform catalogues, this does not imply robust physical inference for unseen EoS models. Future pipelines should adopt leave-family-out validation, wider simulation coverage, and physics-aware inference frameworks.
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Cosmology and Nongalactic Astrophysics
Catching the Cosmic Sign Flip: Background and Growth Tests of Smooth Sign Switching Lambda_s CDM
Ayan Mitra
Recent
baryon acoustic oscillation (BAO) measurements from the Dark Energy Spectroscopic Instrument (DESI), in combination with CMB and
supernova data, show a mild preference for dynamical dark energy over flat $\Lambda$CDM. They can also drive the best-fit effective
neutrino mass to unphysical negative values, motivating models that mimic this effect through late-time expansion physics. The sign-switching cosmological constant ($\Lambda_s$CDM) model addresses this by introducing an AdS-like negative
vacuum energy density at high
redshifts ($z > z^\dagger$) that transitions to a dS-like positive density at low
redshifts. While original fits assumed a discontinuous step function transition, we generalise the dynamics using a smooth
hyperbolic tangent parametrisation, $\Lambda(z) \propto \tanh[\Delta(z^\dagger - z)]$. We constrain the transition
redshift $z^\dagger$ and smoothness parameter $\Delta$ using background distance data from DES-SN5YR (with Dovekie recalibration) and DESI 2024 BAO. We further incorporate a compact
redshift space distortion (RSD) $f\sigma_8$ compilation. The joint data do not prefer the smooth sign-switching model over flat $\Lambda$CDM, yielding nearly identical $\chi^2_{\text{min}}$ values, while information criteria penalise the additional parameters. The transition smoothness remains unconstrained and dominated by the prior volume ($\Delta = 24.75^{+17.42}_{-17.48}$), indicating that current data cannot distinguish between a sharp transition and a smooth dynamical crossover. This work does not directly constrain the physical sum of
neutrino masses $\sum m_\nu$; rather, it shows that current late-time background and growth data alone cannot resolve the transition details. We discuss the implications of this null detection and present projections for next-generation surveys.
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Cosmology and Nongalactic Astrophysics
Machine Learning Closure Audits for LSST Photometric Supernova Cosmology
Ayan Mitra
Modern and next generation
supernova cosmology analyses rely on end to end simulations to train photometric classifiers, characterise selection effects, validate light curve models, and calibrate distance bias corrections. Standard closure tests based on global Hubble diagram summaries can miss multivariate structure that remains in post correction residuals. We introduce a supervised machine learning closure audit that tests whether measured observables can predict the bias corrected Hubble residuals $\Delta\mu$. We apply the audit to LSST Type Ia
supernova simulations from two independent analyses: the M23 mock data sets of Mitra et al. (2023), with spectroscopic
redshift and photometric
redshift samples, and the predominantly photometric LSST like M25 simulation of Mitra et al. (2025). Standard one dimensional
Redshift binned diagnostics explain <1% of the residual variance ($R^2 < 0.01$), suggesting apparent closure. In contrast, out of fold LightGBM models recover up to 98.2% of the variance in the simulated residuals ($R^2 = 0.982$), revealing structured residual predictability. Applying the same audit directly to the real Dark Energy Survey 5 Year (DES 5YR) spectroscopic sample yields a held out $R^2 = 0.725$. SHAP feature attribution rankings are highly consistent between independently trained M25 and DES models (Spearman $\rho = 0.802$), with apparent magnitudes, signal to noise ratios, and
redshift dominating the shared predictive hierarchy. The resulting scorecard provides a diagnostic protocol for comparing mock ensembles and real observations, identifying residual non closure before cosmological parameters are unblinded.
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Solar and Stellar Astrophysics
A Momentum-Regulated Model For Star Formation Efficiency in Giant Molecular Clouds
Erik Bertram
We present a minimal analytic framework to investigate the
star formation efficiency per free-fall time, $\epsilon_{\rm ff}$, in
giant molecular clouds (GMCs), focusing on the origin of the observed clustering around $\epsilon_{\rm ff} \sim 0.01$. We model the time
evolution of the turbulent velocity dispersion through a momentum balance between
stellar feedback and turbulent dissipation, and show that this generically leads to a stable low-efficiency
equilibrium with only weak dependence on global cloud properties. We extend the framework by including a phenomenological contribution from
gravity-driven
turbulence and find that both feedback- and
gravity-driven motions converge to similar
equilibrium states under typical GMC conditions. The efficiency can be expressed as the ratio between a gravitational velocity scale and an effective feedback velocity scale, providing a physically transparent interpretation of self-regulated
star formation. The model provides a simple, physically motivated interpretation of observed gas-
star formation scaling relations, including a Schmidt-like scaling at cloud scales and a Kennicutt-like scaling when averaged over cloud populations. Comparison with observed GMC properties shows agreement within a factor of a few and highlights the weak sensitivity of $\epsilon_{\rm ff}$ to cloud parameters. Despite its simplicity, the framework captures the leading-order interplay between
turbulence,
gravity, and feedback, and provides a physically transparent explanation for the origin and robustness of low
star formation efficiencies in GMCs.
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Earth and Planetary Astrophysics · Cross-listed from stat.ME
Modality Analysis via Spacing with the Dimodal Software Libraries
Greg Kreider
Spacing, the difference between consecutive order statistics, has two features that reflect the modality of the data. Consistent, stable values occur around modes while local increases mark the transitions between them. These features not only signal multi-modality, they also locate modes and anti-modes. Dimodal is an R package for detecting and evaluating these situations. It includes parametric feature models and bootstrap tests for spacing smoothed by low-pass filtering, non-parametric runs and permutation tests for the interval spacing, and a fusion of changepoints in the raw spacing. We introduce the analysis, describe the package, its implementation and performance, and apply it to identifying Kirkwood gaps in the asteroid belt. We also present ports of the software, with DimodalCPy a command-line program written in C with a Python interface.
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Astrophysics of Galaxies
The nature of Cloud-9: a compact core embedded in a diffuse envelope
Ruilei Zhou, Ming Zhu, Chuan-Peng Zhang et al. (+1 more)
We present new HI observations of Cloud-9 with the Five-hundred-meter Aperture Spherical
Telescope (FAST), measuringvtotal flux of 0.35 +- 0.03 Jy km/s. Combined with Very Large Array (VLA) data, the HI shows a two-component structure: a compact, kinematically quiescent core and an extended envelope. The outer component exhibits a coherent velocity gradientvof ~25 km/s across ~7 kpc. The position-velocity structure does not support rotation; instead, the gradient is consistent with ordered large-scale motion, induced by environmental interaction with M94. The coexistence of a compact, kinematically quiescent core and an extended structured envelope is difficult to reconcile with a unbound or purely gaseous system. While the extended component is more naturally interpreted as environmentally shaped gas, the compact core suggests gravitational confinement beyond that provided by the observed baryonic content, without requiring strict long-term dynamical
equilibrium. Deep optical limits further rule out a significant
stellar component. Taken together, our results indicate that Cloud-9 is most naturally interpreted as a dark matter-dominated system undergoing environmental interaction. The observed morphology and kinematics are consistent with a stripped RELHIC scenario, in which a compact gas-rich core is embedded within an extended envelope shaped by ram-pressure interaction with the circumgalactic medium of M94.
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All authors Ruilei Zhou, Ming Zhu, Chuan-Peng Zhang, Jinlong Xu
Earth and Planetary Astrophysics
Mitigating Charge Migration in JWST NIRISS Reveals That KELT-7 b is a Metal-enriched Ultra-hot Jupiter Orbiting a Young Metal-rich Star
Stephen P. Schmidt, Erin M. May, Joshua D. Lothringer et al. (+19 more)
We present the first panchromatic JWST transmission spectrum of an ultra-hot Jupiter, combining NIRISS and NIRSpec observations to constrain KELT-7\,b's atmospheric properties. We show evidence for charge migration in our NIRISS SOSS observation between 1–1.5~$\mu$m, a wavelength range crucial to test for enhanced H$^-$ previously inferred from HST WFC3/IR G141 observations. We mitigate charge migration by fitting the ramp after extracting 1D
stellar spectra at the group level. This “late-ramp-fit” method accurately calculates KELT-7\,b's transmission spectrum between 1–1.5~$\mu$m at higher signal-to-noise. Using the transit-derived
stellar mean density during
stellar property inference reveals that KELT-7 is a $640\pm100$ Myr-old, $[\text{Fe}/\text{H}]=0.46\pm0.02$
star. Combined with NIRSpec and re-reduced WFC3/UVIS G280 data, our free
retrieval analysis shows strong evidence for H$_2$O, CO$_2$, and TiO among high-temperature species, but not H$^-$ or clouds. Unaccounted-for systematics may therefore bias longer-wavelength WFC3/IR G141 transit depths shallower. Our free
retrieval, two
equilibrium retrievals, and self-consistent grid fit all prefer a high
metallicity but find discrepant C/O ratios. Agglomerated together, we constrain a super-
stellar $\text{M/H}=92^{+24}_{-23}\times$~
Solar and C/O~$\leq0.9$, suggesting enhanced metal
accretion in the later stages of KELT-7\,b's formation. Our GCMs explain the observed lack of limb asymmetry with superrotating jet-driven efficient horizontal mixing. The stark contrast between our panchromatic analysis and prior analyses on subsets of these data demonstrates the value of broad wavelength coverage for the comprehensive study of
exoplanet atmospheres.
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All authors Stephen P. Schmidt, Erin M. May, Joshua D. Lothringer, Patrick McCreery, Mei Ting Mak, Myles Pope, Harry Baskett, Sagnick Mukherjee, David K. Sing, Katherine A. Bennett, Arika Egan, Guangwei Fu, Daniel P. Thorngren, Duncan A. Christie, Carlos Gascón, Le-Chris Wang, Lakeisha M. Ramos Rosado, Nathan J. Mayne, Natalie H. Allen, Zafar Rustamkulov, Mercedes López-Morales, Kevin C. Schlaufman
High Energy Astrophysical Phenomena · Cross-listed from gr-qc
Joule-Thomson Effect and Geodesic Structure of Charged AdS Black Holes in f(R,T) Coupled with Nonlinear Electrodynamics
Shyamalee Bora, Dhruba Jyoti Gogoi and Pralay Kumar Karmakar
We herein study both the Joule-Thomson (JT) expansion process and the geodesic properties of a charged anti-de Sitter (AdS) black hole arising in modified
gravity with nonlinear electrodynamic (NLED) sources. Our thermodynamic study reveals that the black hole charge has the most pronounced impact on the JT behaviour. The nonlinear electromagnetic sector together with the modified
gravity parameters introduces further corrections to the inversion temperature and the associated cooling characteristics. At astrophysically relevant distances, the geometry closely reproduces expected outcomes.
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Cosmology and Nongalactic Astrophysics
Impact and measurability of linear relativistic effects in galaxy surveys
Robin Y. Wen, Henry S. Grasshorn Gebhardt and Olivier Doré
The three-dimensional
galaxy power spectrum is a powerful probe of
primordial non-Gaussianity (PNG) and additional general relativistic (GR) effects on large scales, which can be constrained by current and upcoming large-scale structure surveys. In this work, we forecast the measurability of local PNG and linear-order relativistic effects in the spherical
Fourier-Bessel (SFB) power spectrum for DESI, Euclid, and SPHEREx surveys. A Chebyshev-decomposition scheme is employed to accelerate the multi-tracer SFB power-spectrum calculations. Fisher forecasts establish baseline constraints and test the sensitivity of $f_{\rm NL}$ constraints to SFB mode cuts and to the marginalization over
primordial cosmological parameters, while simulated
Bayesian inference is used to quantify the impact and measurability of relativistic effects. We find that neglecting GR effects can bias $f_{\rm NL}$ constraints at the $1$-$3\sigma$ level for Euclid and SPHEREx. The degeneracy between GR and PNG terms is strongly tracer dependent, with the degradation of $\sigma(f_{\rm NL})$ ranging from a few percent to nearly a factor of two when the GR amplitudes are varied.
Lensing can be detected at high significance for several tracers, while multi-tracer analyses substantially improve the measurability of the Doppler term. Assuming GR, we show that relativistic clustering partially breaks the exact $b_\phi f_{\rm NL}$ product degeneracy present in Newtonian linear power-spectrum analyses, although the resulting $b_\phi$ constraints remain weak for the survey configurations considered. The joint PNG-GR inference consistently propagates uncertainty in $b_\phi$ into the marginalized $f_{\rm NL}$ constraint. This firmly establishes the path toward extracting cosmological information from ultra-large-scale
galaxy clustering.
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Cosmology and Nongalactic Astrophysics
Primordial Physics in the Nonlinear Universe: Towards particle constraints using the Weak lensing, Thermal SZ, and X-ray fields
Dhayaa Anbajagane
Primordial non-Gaussianities (PNGs) are a broad class of features in the initial density field that are connected to the particle physics of the early Universe. Measuring the amplitude of these features directly constrains fundamental physics from these earliest epochs and lends insight into energy scales that cannot be probed with terrestrial experiments. Using a new class of simulation methods, we propagate these signatures to their impact on the formation of non-linear structure and quantify the constraining power in non-Gaussian summary statistics of weak
lensing, thermal Sunyaev Zeldovich (tSZ), and X-ray surveys. We use semi-analytic
baryon models that consistently include astrophysical effects across all these observables, and use foreground modeling approaches that explicitly fold in correlations between the various components. We find that the tSZ and X-ray fields have significant information about PNGs, and additionally can help self-calibrate a broad set of nuisance parameters/models by breaking parameter degeneracies. Using the second and third moments of the
lensing, tSZ, and X-ray fields, we find a factor of 2 improvement in PNG constraints relative to using
lensing alone. Larger improvements are expected when including more scales and other complementary summary statistics. Our multi-wavelength map maker can be found at https://github.com/DhayaaAnbajagane/Vaanam. The simulations and software pipelines used in this analysis are publicly available.
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Earth and Planetary Astrophysics
Extreme Debris Disks: Insights into Violent Collisions in Planet Formation and Destruction
Kate Y. L. Su, Attila Moor, Agnes Kospal et al. (+7 more)
Debris disks are dusty structures around mature
stars, primarily identified by infrared excesses in the
stellar spectra. A subset, known as extreme debris disks (EDDs), exhibits
stochastic infrared variability, believed to result from large-scale violent collisions that contribute to the formation or destruction of rocky planetary bodies. We analyze JWST and Spitzer mid-infrared spectra for 21 EDDs to investigate the connection between impact-produced
dust mineralogy and the age and dynamical state of these systems during various stages of
planet formation and
evolution. Our findings indicate that EDDs contain significantly more optically thin, small
dust grains compared to those typically seen in protoplanetary and debris disks. Predominantly submicron in size, these grains are thermally altered, as shown by their high levels of silica and crystalline silicate composition. Along with
stochastic infrared variability, these features define EDDs as a subclass of debris systems where
dust is generated from large collisions between Moon- and Mars-sized bodies. Our results not only provide diagnostic information about the physical conditions of violent events during terrestrial
planet formation, aiding in differentiating the complex outcomes of these impacts, but also offer a potential marker for identifying planetary systems experiencing dynamical instability.
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All authors Kate Y. L. Su, Attila Moor, Agnes Kospal, George H. Rieke, Antranik A. Sefilian, Renu Malhotra, Ilaria Pascucci, Alan P. Jackson, Peter Abraham, Nicholas P. Ballering
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-th
Evidence for renormalized instantons in real-time simulations of vacuum decay
Emilie Hertig, Alexander C. Jenkins, Hiranya V. Peiris et al. (+2 more)
While
vacuum decay is traditionally described by Euclidean instanton methods,
lattice simulations enable real-time modeling of dynamical observables relevant to cosmology and upcoming cold-atom analog experiments. We investigate the relationship between these approaches by extracting ensemble-averaged bubble profiles from zero-temperature simulations of a relativistic scalar field. Our observed profiles differ markedly from the bare Coleman bounce and classical thermal predictions. However, we find that instanton solutions in an appropriately renormalized potential reproduce both the measured profiles and their dependence on the UV cutoff, and predict decay rates consistent with simulations across the parameter range considered. The fact that a single renormalized Euclidean object captures these independent observables provides strong evidence that renormalization accounts for the discrepancy between the two formalisms, and establishes a quantitative link between instanton predictions,
lattice simulations, and forthcoming empirical tests of
vacuum decay.
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All authors Emilie Hertig, Alexander C. Jenkins, Hiranya V. Peiris, Andrew Pontzen, Matthew C. Johnson
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-th
Classical conformal invariance and superhorizon dynamics in de Sitter
Maria Cristina Fiore and Andrea F. Sanfilippo
Soft de Sitter Effective Theory is a well-motivated candidate for the correct effective late-time description of equal-time correlation functions in de Sitter space. In this work, we study its application to theories that enjoy classical conformal invariance, using the conformally-coupled $\phi^4$-theory as a toy model. While
quantum effects generate non-trivial late-time dynamics in such models, we argue that it is not described by the standard construction of the effective theory as discussed thus far in the literature. We show that the tree-level matching of the trispectrum onto the effective theory does not fit into the expected power-counting scheme, and we contrast it with the matching of the tree-level bispectrum in the conformally-coupled $\phi^3$-theory, where it works consistently. We then propose a prescription to identify the leading superhorizon degrees of freedom in such theories, which should serve as the starting point for the construction of their late-time effective description. The interpretation of logarithms of the form $\log(-k\eta)$ in this context is briefly discussed.
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High Energy Astrophysical Phenomena · Cross-listed from gr-qc
Foundations of Direct Waves in Schwarzschild Ringdown
Sizheng Ma and Hai-Yang Wang
Recent studies have identified a new component in black-hole ringdown from merging binaries, termed the direct wave. This component was argued to be tied to the dynamical source
evolution near the black-hole horizon, and thus to encode horizon information. Yet a firm theoretical foundation for the direct wave has been lacking. Here we fill this gap by deriving direct waves from first principles in Schwarzschild spacetime, using the causal structure of the Green's function. We show that the direct wave does not vanish and is governed by the near-horizon source dynamics. Our results establish a theoretical basis for direct waves as a probe of near-horizon dynamics, complementary to quasinormal modes.
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Instrumentation and Methods for Astrophysics
Efficient Optimal Image Reconstruction for the Nancy Grace Roman Space Telescope and Beyond: I. First Results with Effortless
Kaili Cao
The forthcoming Nancy Grace Roman Space
Telescope will revolutionize astrophysics by generating huge amounts of data of unprecedented quality. To properly address the data deluge and fully realize its potential, analysis tools that are both efficient and optimal are needed. Effortless (previously known as Fast Imcom) is a new
algorithm for linear image reconstruction. Like its predecessor Imcom, it offers control over point spread functions in output images; by avoiding laborious calculations, it is tens of times faster and has a smaller
memory footprint. In this paper, I apply Effortless to simulated Roman images and present promising first results. With ideal point sources, I illustrate that a single image reconstructed by Effortless, combined with the post-measurement calibration procedure described in a companion paper, can lead to better measurements than a set of $\sim 6$ images coadded by Imcom. While both
algorithms were originally designed for weak gravitational
lensing cosmology, Effortless can benefit studies of static features and dynamic aspects of the Universe alike. Moreover, the efficiency and interpretability of Effortless provides new possibilities for further reducing errors in measurements. The implementation of Effortless is detailed in the companion paper.
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Astrophysics of Galaxies
A redshift of z=3.20 for the bright arc in eMACSJ2229.9-0808: Comment on Wagner & Falco (2026) "Hamilton's Object revisited: A challenging source redshift of a strong lensing configuration"
Ian Smail, Johan Richard, Harald Ebeling et al. (+1 more)
We re-analyse near-infrared and optical spectroscopy from the Subaru, Gemini, and Keck
telescopes of the bright gravitational arc seen in the z=0.62 X-ray cluster eMACSJ2229.9-0808. The 22 strongest spectral features we identify uniquely determine the
redshift of the
galaxy as z=3.20, as previously reported by Ebeling et al. (2025), not z=0.82 as claimed by Wagner & Falco (2026).
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All authors Ian Smail, Johan Richard, Harald Ebeling, A.C. Edge