Astrophysics of Galaxies
Galaxy mergers drive enhancements in ionization states
A. Le Reste and K. B. Mantha
Recent studies have suggested that
galaxy mergers may help drive the escape of ionizing
photons from
galaxies. However, the ionization properties of merging
galaxies have not yet been systematically studied across the full merger sequence in a large, well-defined sample. Here, we investigate the impact of mergers on the line ratio $\rm{O}_{32}$ tracing the ionization state and study its
evolution as a function of merger progression. We identify 7641
galaxy mergers with robust ($\rm{SNR}>3$) emission line fluxes from the Sloan Digital Sky Survey Data Release 17, using spectroscopic pair analysis and visual classifications from the participatory science experiment "
Cosmic Disco: Characterizing
Galaxy Collisions". We find a continuous increase in $\rm{O}_{32}$ as a function of merger progression traced by pair separation and visual merger stages, with median and 90th percentile peaking post-coalescence. $\rm{O}_{32}$ is significantly enhanced in mergers past the first pericenter passage as compared to a control sample of isolated
galaxies. We investigate the properties of
galaxy mergers with $\rm{O}_{32}>3$ and find that these are mainly low-mass ($\widetilde{\rm{M}_{*}}=6\times 10^{8}\,\rm{M}{_\odot}$) mergers close to coalescence. In this population, large $\rm{O}_{32}$ values are due to mergers driving a simultaneous increase in specific
star formation rate and decrease in
metallicity. Thus,
galaxy mergers enhance the ionization state of
galaxies and likely facilitate the escape of ionizing radiation from
galaxies, even at low
stellar masses. Finally, we infer that Green Pea
galaxies, a population characterized by high $\rm{O}_{32}$ , are low-mass
galaxy mergers at coalescence, a scenario that reconciles findings from environmental and interferometric 21cm studies.
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Cosmology and Nongalactic Astrophysics
Using SquiRels to Find LiMRs: A Model-Insensitive Approach to Cosmic Microwave Background Studies of Light but Massive Relics
Nicholas DePorzio, David Imig and Jessie Shelton
Light but Massive Relics (LiMRs), cosmological relics that are relativistic at some point in the observable early universe but are non-relativistic today, are a generic prediction of many theories of physics beyond the Standard Model, and are a target of high interest for current and upcoming cosmological surveys. The enormous variety of scenarios that can give rise to LiMRs also gives rise to a wide range of possible phase space distributions for these relics, making it valuable to have a model-agnostic quantification of LiMR signatures. Toward that end we identify three independent physical quantities that govern LiMRs' dominant effects on cosmological observables, and introduce a phenomenological family of "Squished Relics" (SquiRels) that allow us to efficiently and flexibly search for the imprint of LiMRs with different phase space distributions in data. Our primary focus here is on LiMRs that transition from radiation to matter during the
Cosmic Microwave Background epoch. Using this framework we explicitly demonstrate that current Planck observations are not sensitive to the shape of the LiMR's phase space distribution function, which allows us to provide a model-insensitive and readily reinterpretable limit on LiMRs that become non-relativistic at
redshifts z_{NR}<10^5. We further demonstrate that upcoming and future ground-based observatories will be able to distinguish LiMRs from massless dark radiation species, and could begin to provide information about the shape of its distribution.
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Astrophysics of Galaxies
The JADES Transient Survey II: Volumetric Supernova Rates out to z~5
Christa DeCoursey, Christian Vassallo, Louis-Gregory Strolger et al. (+27 more)
The JADES Transient Survey (JTS) identified 83
supernova (SN) candidates in the JADES Deep Field, a $\sim$25 arcmin$^2$ region with deep ($\sim$30 mag) multi-band, multi-epoch JWST/NIRCam coverage. We use this sample to derive the first volumetric core-collapse (CC) SN and Type Ia (SN Ia) rates in the $z$$\sim$2-5 range. Many of these SNe are photometrically classified from single-epoch photometry (i.e., single spectral energy distributions (SEDs)), so we simulate and classify $\sim$23,000 CC SN and SN Ia mock SEDs over 0.7$\leq$$z$$\leq$5 to quantify single-SED classification accuracy as a function of
redshift. We report consistent rates for two samples: (1) the full JTS sample, including single-SED classifications, and (2) the "gold" sample, restricted to sources classified spectroscopically or with multi-epoch light curves. In units of 10$^{-4}$ CC SNe yr$^{-1}$ Mpc$^{-3}$, the full sample CC SN rates are 6.2$^{+2.2}_{-1.7}$ at 2.06$\leq$$z$$<$2.78 and 4.1$^{+1.5}_{-1.1}$ at 2.78$\leq$$z$$\leq$5.06, broadly consistent with the expectations from the
galaxy luminosity-based measurements of the
cosmic star formation rate density. Our full sample rates tentatively exhibit the predicted decline beyond
cosmic noon, providing the first direct observational indication of this behavior. A companion paper, C. Vassallo et al., presents a more detailed comparison. We measure a full sample SN Ia rate of 0.3$^{+0.3}_{-0.2}$$\times$10$^{-4}$ SNe Ia yr$^{-1}$ Mpc$^{-3}$ at 1.92$\leq$$z$$<$3.60. Future high-$z$ SN surveys with JWST and the Roman Space
Telescope will expand these samples and provide more robust constraints on SN rates in the high-$z$ Universe.
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All authors Christa DeCoursey, Christian Vassallo, Louis-Gregory Strolger, Justin D. R. Pierel, Eiichi Egami, Seppo Mattila, Armin Rest, David A. Coulter, Andrew J. Bunker, Alex J. Cameron, James M. DerKacy, Daniel J. Eisenstein, Michael Engesser, Ori D. Fox, Sebastian Gomez, Massimo Griggio, Kevin Hainline, Ryan Hausen, Zhiyuan Ji, Benjamin D. Johnson, Roberto Maiolino, Takashi J. Moriya, Brant Robertson, Koji Shukawa, Matthew R. Siebert, Fengwu Sun, Sandro Tacchella, Christina C. Williams, Christopher N. A. Willmer, Yossef Zenati
Earth and Planetary Astrophysics
Biosignature detectability on transiting habitable worlds with ELT/ANDES
E. Kurzawa-Ferrandez, A. Bello-Arufe and R. Hu
The search for life beyond the
Solar System is at a turning point, transitioning from theoretical predictions to observations enabled by next-generation observatories. The Extremely Large
Telescope (ELT) will host the ArmazoNes high Dispersion Echelle Spectrograph (ANDES), optimized for visible-to-near-infrared high-resolution spectroscopy. We present a simulation–detection pipeline and evaluate the detectability of CO$_2$, H$_2$O, and the biosignature gases O$_2$ and CH$_4$ in high-resolution transmission spectroscopy of transiting habitable-zone rocky
planets with ANDES. Assuming cloud-free, modern Earth-like atmospheres, we model transmission spectra using noise estimates from the ANDES Exposure Time Calculator, based on the latest preliminary instrument design in seeing-limited mode. We introduce a novel
Bayesian cross-correlation function (CCF) framework that incorporates molecule-specific kernels and a new autoregressive model to account for correlations in the CCF. We apply our framework to 18 known potentially habitable transiting
exoplanets and estimate the number of transits required for a decisive detection ($\log_{10} B \ge 2.0$). We find that H$_2$O is the most accessible species, with potential detections in 10-19 transits for the TRAPPIST-1
planets and 30 transits for LHS 1140 b. CO$_2$, CH$_4$, and O$_2$ are more difficult to detect, requiring approximately 1.5, 3, and 4 times as many transits as H$_2$O. These estimates are lower limits that assume favorable observing conditions, perfect detrending, and the absence of systematics, yet still imply large observing campaigns. Alternative approaches, such as reflected-light high-dispersion coronagraphy of nearby nontransiting
planets, may offer a promising complementary route for biosignature searches.
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Astrophysics of Galaxies
The onset of stellar bars at Cosmic Noon. Bar-driven quenching and AGN co-evolution in a mature disc galaxy
Luca Costantin, Lorenzo Morelli, Cristina Cabello et al. (+15 more)
Observations with the JWST revealed an unexpected abundance of barred
galaxies at
Cosmic Noon. However, the physical properties of these early bars are almost unconstrained, as it is their impact in the structural
evolution of high-z disc
galaxies. In this work, we derived the
stellar populations of EGS-24154, a barred spiral
galaxy at $z=1.17$. First, we investigated the role of the
stellar bar in the early assembly history and structural
evolution of the
galaxy. Second, we studied the properties of the interstellar medium to shed light on the interplay with the central supermassive black hole. We analysed medium-resolution NIRSpec/IFS data of EGS-24154 through full-spectral fitting and derived light and mass-weighted ages and
metallicities. We then reconstructed the spatially-resolved SFH, derived the ionizing mechanisms of the interstellar medium analysing several emission lines, characterized the dynamics of EGS-24154, and constrained the properties of a biconical
outflow launched by the AGN. EGS-24154 is a
baryon-dominated, gas-rich disc
galaxy, which grew more than 90% of its
stellar mass when the Universe was ~2 Gyr old. We found that the
stellar population of the bar started to form at $z\sim5$, compatibly to the time when the
stellar disc started to assemble. We observed a
star formation desert in the bar region, which is responsible for quenching
star formation over several Gyr. We then interpreted that the feedback from the AGN prevented the growth of central mass concentration, allowing the
stellar bar to grow in size and strength. In this first study of spatially-resolved
stellar populations of a barred disc
galaxy at $z>1$, we demonstrated how
stellar bars are key drivers of the early structural and dynamical
evolution of disc
galaxies. In particular, our results call for a revision of most models of disc and bar formation in early
baryon-dominated, gas-rich disc
galaxies.
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All authors Luca Costantin, Lorenzo Morelli, Cristina Cabello, Virginia Cuomo, Michele Perna, J. Alfonso L. Aguerri, Mahmood Roshan, Edoardo Borsato, Enrico Maria Corsini, Adriana de Lorenzo-Cáceres, Francesco D'Eugenio, Daniele Gasparri, Asiyeh Habibi, Taehyun Kim, Yun Hee Lee, Jairo Méndez-Abreu, Alessandro Pizzella, Bruno Rodríguez Del Pino
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Stochastic Tsunamis: Diffuse Scalar Background from Black Hole Formation
Arturo de Giorgi and Joerg Jaeckel
Massive astrophysical objects can source huge static configurations of a scalar field. When such an object ends up forming a black hole, for instance, via a core-collapse
supernova, the scalar field loses its source abruptly; then the static configuration becomes dynamical and propagates away in a burst, a "scalar tsunami". These bursts accumulate over cosmological history, forming a relic
stochastic diffuse scalar background peaked in the $1-10^3~\text{Hz}$ range. We propose this as a novel mechanism for the generation of such a background, compute its spectrum, and compare it with the sensitivity of future experiments. We show how this extends the experimental sensitivity to scalar masses $m_\phi\lesssim 10^{-13}~\text{eV}$, ten orders of magnitude larger than those accessible via individual transient events previously considered.
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Astrophysics of Galaxies
Andrea Caputo, Giovanni Maria Tomaselli and Chris Hamilton
We develop a general Fokker-Planck framework describing the dynamical
evolution of Keplerian binaries subjected to
stochastic perturbations. The formalism provides an algorithmic way to obtain the Fokker-Planck drift and
diffusion coefficients of any set of orbital variables given the statistics of the perturbations. We apply the method to three physically distinct regimes: adiabatic
tidal perturbations, white-noise
tidal perturbations, and impulsive encounters with a third body of arbitrary density profile. In each regime we provide explicit drift and
diffusion coefficients for all six orbital elements, derive the associated
evolution timescale, and obtain analytic steady-state distribution functions. Our results extend previous treatments by including the
evolution of the binary's orientation, retaining the complete tensor structure of
tidal correlators, treating non-pointlike perturbers, and resolving the exact geometry of impulsive encounters. The latter correction leads to a steady-state eccentricity distribution that is slightly sub-thermal. We also show how these equations can be applied directly in several astrophysical scenarios, including binaries perturbed by dark matter subhaloes, ultralight dark matter, and the interstellar medium. This work delivers both a complete mathematical framework and a practical toolkit for
stochastic binary
evolution, providing ready-to-evaluate equations to be applied directly to binary population data.
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Cosmology and Nongalactic Astrophysics
The Limitations of Cosmological Collider Analyses
Oliver H. E. Philcox
Massive fields exchanged during inflation source cosmological
collider features in the correlators of
primordial curvature fluctuations. While their structure is fixed by the
symmetries of inflation, the amplitude of such signatures is a priori unknown, though bounded by physical principles such as unitarity. We assess the observational viability of the scalar cosmological
collider by combining precise numerical predictions derived using CosmoFlow with observational data from Planck bispectrum reconstructions. Working in the limit of weak quadratic mixing between the Goldstone and scalar sectors (as assumed by all previous searches), we find that perturbativity restricts the
collider signals to be unobservably small, except for double- and triple-exchange configurations at low masses. Larger bispectra can be generated by increasing the mixing to non-perturbative (but still
unitary) values: however, this distorts the signal, damping its amplitude and shifting the
collider oscillations. Furthermore, strong mixing breaks the factorization of the bispectrum into a free amplitude and a fixed shape, and complicates both theoretical predictions and observational searches. Despite the challenges, we argue that strong mixing analyses are necessary to obtain meaningful constraints on the scalar cosmological
collider from current and upcoming
datasets.
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Astrophysics of Galaxies
A Universal Distribution of Dark Matter in Milky Way-like galaxies and How to Infer It
Sam Cheng-Tse Huang, Matthew R. Buckley, Justin I. Read et al. (+1 more)
The phase-space density of dark matter within the Milky Way is a key quantity that encodes information about the nature of the dark sector. The local phase-space density is also required to properly interpret the results of dark matter direct detection experiments. However, there are at present few observational constraints. In this paper, we show that a simple coordinate transformation reveals a near-universal DM phase-space distribution function among three independent suites of cosmological simulations of Milky Way-mass
galaxies. We provide evidence for this with plots of kinematic features as well as machine learning-based classifiers that are sensitive to all of the correlations in the full multivariate phase space. Deviations from universality are found only at extremes of
galactic radius and/or velocity, and in one simulation that has a prominent accreted dark disc. We further show that the parameters for the coordinate transformation can be inferred from metal poor
stars ($\log_{10}[{\rm Fe}/{\rm H}]< -2$). These
stars also contain signatures of the dark disk, allowing the existence of such a structure to be inferred from observation. Finally, we construct a model of this universal phase-space distribution using a normalizing flow, trained on the standardized phase-space across simulations. We will apply our method to survey data from
Gaia and SDSS in a forthcoming work.
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All authors Sam Cheng-Tse Huang, Matthew R. Buckley, Justin I. Read, David Shih
Earth and Planetary Astrophysics
Modeling the Evolution of Protoplanetary Disks: Two Pathways from Gravitational Instability to MHD Wind-Driven Accretion
Yang Ni, Wenrui Xu and Xue-Ning Bai
The global
evolution of protoplanetary disks sets the initial conditions for
planet formation. However, most models focus on individual evolutionary phases, with idealized initial conditions and oversimplified prescriptions for angular momentum transport and thermodynamics. We present a more realistic semi-two-dimensional ($1+1$D) model incorporating gravitational instability (GI), magnetohydrodynamic (MHD) winds, magneto-rotational instability (MRI),
stellar irradiation, self-shadowing, and radiation transport. The radial distribution of large-scale
magnetic flux drives two different pathways of disk
evolution. When the vertical field is spatially uniform, a puffed-up, MRI-heated inner rim shadows the disk beyond it, sustaining a massive, gravitationally unstable region for $\sim 1$ Myr and, for several Myr, a compact ($\lesssim 10$ AU), cold ($\sim10$ K), low-
turbulence ($\alpha_\mathrm{SS}\sim10^{-4}$), high-density ($\Sigma\gtrsim300\,\mathrm{g\,cm^{-2}}$), optically thick reservoir, so that the disk mass inferred from mm-continuum emission can be greatly underestimated. When the field instead scales with midplane gas pressure, it drives stronger transport in the inner disk and eventually strips the shadow, leaving an extended, flared disk whose observable mass closely traces the true mass. Our results connect GI-dominated Class~0/I disks to MHD wind-driven Class~II disks, and point to three broader conclusions: (i) disk physics is strongly inhomogeneous in space and time, so constant-$\alpha$ treatments miss essential physics; (ii) thermodynamics plays an active role, with self-shadowing simultaneously preserving GI and weakening MHD winds; and (iii) the distribution of large-scale
magnetic flux is the key uncertainty, closely linked to whether the shadow is maintained. The two pathways align, respectively, with observations of compact, shadowed disks and extended, irradiated disks.
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Earth and Planetary Astrophysics
Probing the Innermost Region of the V883 Ori Disk Using ALMA Band 1 Methanol Line Observations
Yoshihide Yamato, Shota Notsu, Rui Zhuang et al. (+2 more)
The snowlines of major volatiles in protoplanetary disks play a pivotal role in
dust evolutions and volatile delivery to nascent planetary systems. In this paper, we report the Atacama Large Millimeter/submillimeter Array Band 1 ($\approx7.5\,\mathrm{mm}$) observations of methanol (CH$_3$OH) emission lines in the disk around the FU-Ori type
star V883 Ori, where
accretion outburst heats the disk and the majority of ices has sublimated. We detect three CH$_3$OH emission lines at an angular resolution of $\approx0.\!\!^{\prime\prime}2$. The stacked CH$_3$OH image exhibits a centrally-peaked morphology in contrast to the previous (sub-)mm observations that show a central depression. By fitting radially-resolved line profiles, we derive the radial intensity profile of the CH$_3$OH emission where we find a steep increase at $\lesssim40\,\mathrm{au}$. The column density of CH$_3$OH reaches at least $\sim10^{19}\mathrm{-}10^{20}\,\mathrm{cm^{-2}}$ at $\sim10\,\mathrm{au}$. This provides direct evidence that a significant amount of warm gaseous methanol is present in the innermost region of the disk where its emission has been suppressed in previous (sub-)mm observations due to the optically thick
dust emission. The steep increase in the intensity profile may indicate that the CH$_3$OH snowline in the midplane is located at $\sim30\mathrm{-}55\,\mathrm{au}$, or that the CH$_3$OH emission traces the temperature structure given that the emission is likely optically thick. Our results demonstrate the capability and significance of (sub-)cm observations in probing the innermost opaque region of disks, paving the way for the future observations with upcoming facilities.
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All authors Yoshihide Yamato, Shota Notsu, Rui Zhuang, Yuri Aikawa, Nami Sakai
Earth and Planetary Astrophysics · Cross-listed from math-ph
Expansion of the planetary Hamiltonian for small eccentricities and inclinations: a vector formalism
Federico Mogavero
We revisit the classical expansion of the planetary
Hamiltonian for small eccentricities and mutual inclinations of the orbits, presenting a derivation based entirely on vector formalism. We demonstrate that the secular part of the disturbing function, as well as any other
Fourier harmonic, can be expressed in terms of scalar products of vectors lying in the system's invariant plane. Furthermore, we show how to express any such term using the angular momentum and eccentricity vectors of the orbits.
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Cosmology and Nongalactic Astrophysics
Signatures of $10-10^4\,{\rm M}_{\odot}$ Dark Matter halos in LISA via Stochastic Diffraction
Han Gil Choi, Juan Urrutia and Miguel Zumalacárregui
Cold Dark Matter predicts a population of low-mass
halos which are sensitive to its fundamental nature and the
primordial power spectrum, yet remain undetected. Although elusive, their discovery may be possible thanks to wave-optics
lensing of gravitational waves (GWs) by the superposition of many
halos along the line of sight. We study the statistical properties of
stochastic diffractive
lensing, which imprints correlated fluctuations on the amplitude and phase of the original waveform. The
stochastic distortions can be described by an orthogonal basis that captures the dominant ”tones” associated with the dark matter properties, or dark timbre, which is not degenerate with binary source parameters. LISA is most sensitive to
halos of $O(10\text{--}10^4\,M_\odot)$, and because the imprint recurs in every source, stacking $\sim(50,500)$ loud binaries could confirm them at the $(2,5)\sigma$ level ($\sim0.2$ to $\gtrsim4\sigma$ for realistic merger rates and different concentration estimations). The per-event signal is only $O(10^{-3})$ in cold dark matter, demanding major advances in waveform accuracy and data analysis. Even short of that reach,
stochastic diffraction places stringent bounds on models that enhance small-scale structure, such as
axion miniclusters and
primordial black holes.
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Solar and Stellar Astrophysics
Direct Measurement of Diffusion Coefficients: Evidence for Diffusive Stochastic Heating in Collisionless Plasmas
Tamar Ervin, Trevor A. Bowen, Alfred Mallet et al. (+7 more)
Open questions in collisionless
plasma dissipation can be addressed using space-based observations in different astrophysical environments, with implications for both astrophysical and laboratory
plasma systems. We study a low-$\beta$, highly imbalanced, sub-Alfvénic stream observed by Parker
Solar Probe (PSP) to identify and distinguish between signatures of
stochastic heating (SH) and resonant heating (RH) by parallel ion cyclotron waves (ICWs). Prior work studying this stream (Bowen et al., 2025) showed that the SH rate, accounting for intermittency, matched the amplitude of the local energy transfer (LET) rate while the RH rate did not. This comparison relied on a number of assumptions regarding the nature of the diffusive process, and the calculation of the LET rate. We introduce a novel technique of inverting the
proton guiding center equation to empirically measure velocity-space
diffusion coefficients using three-dimensional
proton velocity distribution functions (VDFs), from the ion electrostatic analyzer (SPANi) on PSP. Measured
diffusion coefficients are used to determine phase-space heating rates, leading to a calculation of a fully kinetic heating rate independent of assumptions made in prior work. We show that scale-dependent analytic expressions for SH via non-coherent fluctuations match the empirical measurements from PSP data, provided that we account for intermittency in the heating calculation. In contrast, the derived heating rates for SH that accounts for the effects of the helicity barrier, and heating rates for RH via $\parallel$-ICWs do not peak in the same region of velocity-space as the empirical measurements, nor reach the required magnitude. Our approach provides novel methodology to uniquely identify and constrain heating processes in collisionless
plasmas, and shows evidence of a Fokker-Planck like diffusive process in the near-Sun
solar wind.
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All authors Tamar Ervin, Trevor A. Bowen, Alfred Mallet, Philip A. Isenberg, Kristopher G. Klein, Stuart D. Bale, Benjamin D. G. Chandran, Roberto Livi, Ali Rahmati, Davin E. Larson
Cosmology and Nongalactic Astrophysics
Constraints on Ultra-Light Axions from the DESI DR1 Full Shape, Planck and ACT
Francesco Verdiani, Emanuele Castorina, Ennio Salvioni et al. (+2 more)
We present updated bounds on ultra-light
axions (ULAs) as a subcomponent of dark matter, derived from the full-shape analysis of the DESI Data Release 1
galaxy power spectra combined with
Cosmic Microwave Background (CMB) data from ACT and Planck. We focus on the mass window $10^{-32}\,\mathrm{eV}\leq m_a \leq 10^{-24}\,\mathrm{eV}$, employing state-of-the-art analysis methods rooted in the Effective Field Theory of Large Scale Structure. For the smallest masses, our joint analysis with DESI improves over CMB-only constraints by more than a factor of 2, establishing the most stringent limits to date. For instance, for $m_a \sim 10^{-29}\,\mathrm{eV}$ ULAs are constrained to be a fraction as small as $0.3\%$ of the total matter energy density. The DESI Luminous Red
Galaxy sample shows a mild preference for an ULA subcomponent with $m_a \approx 10^{-26}\,\mathrm{eV}$, mirroring previous hints from BOSS, but this preference vanishes upon combination with CMB data. Probing the largest masses, $m_a\gtrsim10^{-25}\,\mathrm{eV}$, in future studies will benefit from extending the data analysis to smaller scales, both for
galaxy clustering and CMB
lensing, but will also require concurrent improvements in the theoretical modeling.
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All authors Francesco Verdiani, Emanuele Castorina, Ennio Salvioni, Emiliano Sefusatti, Matteo Viel
Astrophysics of Galaxies
Electron Density of Ionized Gas Outflows: Insights from the MaNGA Survey
Andrew Weldon, Casey Papovich, Justin Spilker et al. (+1 more)
We investigate the properties of ionized gas
outflows in nearby
star-forming
galaxies from the final Data Release of the Mapping Nearby
Galaxies at Apache Point Observatory (MaNGA) Survey. Using spatially resolved spectroscopy, we search for signatures of ionized
outflows within physically motivated
outflow apertures. We find significant evidence for additional broad H$\alpha$, [N II]$\lambda\lambda$6550,6584, and [S II]$\lambda\lambda$6718,6733 emission-line components in 115
galaxies, $\sim$3% of
star-forming MaNGA
galaxies. Our analysis suggests that
outflow electron densities ($n_{\text{e, out}}$), mass-loss rates, and mass-loading factors are related to both the properties of the regions that launch and global
galactic properties. In particular, we find correlations between $n_{\text{e, out}}$ and both the enclosed ($-$3.4$\sigma$) and global ($-$2.4$\sigma$)
star-formation-rate surface densities, such that lower surface density regions tend to drive denser ionized gas
outflows. We find several $>$$2\sigma$ correlations between the mass-loading factor and
galactic properties using individual $n_{\text{e, out}}$ estimates, while more significant correlations ($>$$3\sigma$) only emerge when $n_{\text{e, out}}$ is fixed to the median value of the sample. Combining with literature $n_{\text{e, out}}$ measurements out to $z \sim 1.9$, $n_{\text{e, out}}$ exhibits no significant
redshift evolution, in contrast to the strong
evolution observed for gas electron densities of the interstellar medium (ISM). Ionized
outflows remain denser than the ISM by a factor of $\sim$8.5 at $z \sim 0$ and $\sim$1.6 at $z \sim 1.9$. These results provide new constraints for feedback models and highlight the need for high-resolution IFU observations and synthetic line diagnostics from simulations to investigate the connection between
outflow properties and local ISM conditions.
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All authors Andrew Weldon, Casey Papovich, Justin Spilker, Robert C. Kennicutt Jr
Instrumentation and Methods for Astrophysics
Ardua: Unveiling the Baryon Cycle from Stars to the Cosmic Web
Carlos J. Vargas, Caroline Kilbourne, Haeun Chung et al. (+29 more)
The circumgalactic medium (CGM) – the multiphase gas reservoirs surrounding
galaxies – remains the least understood component of the
baryon cycle governing
galaxy growth, despite its central role in the Astro2020 Decadal Survey's priorities. Existing constraints come almost exclusively from pencil-beam absorption spectroscopy, leaving the spatial structure, kinematics, and phase interactions of CGM gas fundamentally unmapped. We present Ardua, a mission concept for NASA's ASTRA Initiative that combines wide-field far-ultraviolet spectroscopy with a Line Emission Mapper (LEM)-derived X-ray microcalorimeter instrument to obtain the first comprehensive emission maps spanning the full CGM temperature range, including cool neutral gas, ionized warm-hot phase gas, and the volume-filling hot corona. By observing more than 50 nearby
galaxies comprehensively in the UV and X-ray, Ardua will test competing
galaxy formation models, resolve multiphase gas flows and feedback-driven
outflows, and extend
baryon-cycle science to the intergalactic medium and the environments of
exoplanet-hosting
stars. Beyond its core CGM/IGM program, Ardua's wide-field, high-sensitivity instruments are designed to serve as a flexible community resource, supporting guest-investigator science across astrophysics. No planned or approved mission is designed to deliver this combined UV/X-ray survey capability.
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All authors Carlos J. Vargas, Caroline Kilbourne, Haeun Chung, Erika Hamden, Ralph Kraft, Joseph N. Burchett, Lauren Corlies, Claude-André Faucher-Giguère, Kevin France, Keri Hoadley, Briana Indahl, Dong-Woo Kim, Varsha Kulkarni, Jiangtao Li, Nicole Melso, Drew Miles, Nikole M. Nielsen, Anna Ogorzalek, Ben Oppenheimer, Frits Paerels, Daniel Patnaude, Molly Peeples, Frederick S. Porter, David Schiminovich, Malgorzata Sobolewska, Ming Sun, Todd Tripp, Jason Tumlinson, Sarah Tuttle, Jessica Werk, Ka-Wah Wong, John ZuHone
Cosmology and Nongalactic Astrophysics
Reconstructing the kinematics of Laniakea using Type Ia Supernovae
Francesco Sorrenti, Erick Pastén and Leonardo Giani
We develop a kinematic framework that relates the monopole, dipole, and quadrupole of the luminosity distance to an ellipsoidal peculiar velocity field describing the dynamics of the Laniakea supercluster. By properly accounting for the transformations between the CMB and Laniakea reference frames and selecting Type Ia
supernovae within the volume associated with the superstructure, we show that luminosity distance multipoles encode the expansion and shear of the local velocity field. This allows the ellipsoidal kinematics of Laniakea to be inferred directly from
supernova observations. Our results provide a physically motivated interpretation of luminosity distance anisotropies within the volume dynamically dominated by Laniakea as signatures of its large-scale kinematics. The framework developed here suggests that future
supernova observations can enable the independent reconstruction of large-scale structures in the local Universe
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Cosmology and Nongalactic Astrophysics
Anisotropic Dirac-Born-Infeld Inflation with Non-Vacuum Initial States: Primordial Perturbations, Non-Gaussianity, and Observational Constraints
Narges Rashidi and Maryam Roushan
We investigate linear and nonlinear
primordial perturbations in an anisotropic Dirac-Born-Infeld (DBI) inflationary model with a non-
vacuum initial state. Using the Arnowitt-Deser- Misner (ADM) formalism, we expand the action up to second and third order in the
curvature perturbation and derive the corresponding scalar and tensor power spectra, as well as the bispectrum and the equilateral non-linearity parameter \(f_{NL}^{\mathrm{equil}}\). The effects of anisotropic corrections and non-Bunch-Davies (non-BD) initial conditions are incorporated through the slow-roll sector and Bogoliubov coefficients. For the numerical analysis, we consider an intermediate expansion scenario together with a phenomenological ansatz for the excited-state occupation number \(N_k\). By comparing the model predictions with recent observational
datasets, including Planck2018 TT, TE, EE + lowE +
lensing + BK18 + BAO and DESI+CMB+DESY5 data, we identify observationally viable regions in the parameter space of the model. Our analysis indicates that the anisotropic DBI scenario with non-
vacuum initial conditions can remain compatible with current constraints on the scalar spectral index, tensor-to-scalar ratio, and equilateral non-Gaussianity for suitable ranges of the anisotropy parameter \(c\) and the initial-state parameter \(N_{k,0}\).
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Earth and Planetary Astrophysics
Ice Deposition Fronts In Porous Bodies From Transient Heating Events In a Protoplanetary Disk
Stephen Li, Alice C. Quillen, Adam E. Rubinstein et al. (+2 more)
Using a 1D mass and heat transport model, we numerically integrate heat flow and gas transport in a porous body exposed to a transient heating event while embedded in a protoplanetary disk. When small icy grains are heated, volatiles sublimate, enriching the disk with volatile gases. When a porous body enters this heated, volatile-rich environment, volatile gases diffuse throughout the cool, porous body and deposit ice where the partial pressure of a volatile exceeds its vapor pressure. We simulate sublimation and deposition fronts of water, carbon dioxide, and carbon monoxide. Our simulations show that an ice deposition front forms and moves deeper into the porous body as the body warms. The amount of nebular gas deposited in an initially dry body is usually extremely low; however, in an initially icy body, an ice deposition front contains locally sublimated volatiles. In this case, the front can increase the ice volume fraction (by a factor of 2) in a thin layer below the surface. We find that the propagation speed, propagation strength, and final depth of an ice deposition front primarily depend on pore size. We propose that nebular heating events can alter the subsurface morphology and physical properties of porous icy objects embedded in a protoplanetary disk.
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All authors Stephen Li, Alice C. Quillen, Adam E. Rubinstein, Dominique Segura-Cox, Kevin Righter
Instrumentation and Methods for Astrophysics
WALOP-South: a four camera one shot imaging polarimeter for the PASIPHAE survey. Paper III – PSF modelling
Indrajit Paul, Kishan Deka, Tuhin Ghosh et al. (+22 more)
The two WALOP instruments, built for the PASIPHAE survey, will measure the linear polarization of large numbers of
stars in the
Galactic polar regions in the SDSS-$r$ band. They are designed with a wide field-of-view, enabling measurement of the Stokes parameters $I$, $q$, and $u$ for multiple
stars simultaneously within a $35^\prime \times 35^\prime$ region of sky for WALOP-South and $30^\prime \times 30^\prime$ region for WALOP-North. In this paper, we present a polar shapelet-based PSF photometry framework for well-sampled
stellar point sources applicable to WALOP-type wide-field polarimeters. Polar shapelets are a set of orthogonal basis functions, constructed from Gauss-Hermite or Gauss-Laguerre
polynomials, that are well-suited to modelling localized PSF in a compact and efficient way. We developed an efficient PSF modelling method that uses polar shapelets as basis functions to reconstruct the spatial variation of the PSF shape across the CCD using Zemax-simulated images of one of the WALOP instruments, and show that a limited number of shapelet coefficients are sufficient to capture this variation consistently across different CCD locations. To simulate realistic
star images, we introduce random sub-pixel shifts in the
star centroids in the Zemax-simulated images, and account for this using a two-step iterative method that alternately estimates the PSF model and the sub-pixel centroid shift. Applying PSF photometry to the target faint
stars, we demonstrate that the photometric accuracy of approximately 0.15% is achievable, and that the reconstructed PSF model can be incorporated into the photometry across different seeing conditions, meeting the polarimetric science requirements of the PASIPHAE survey.
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All authors Indrajit Paul, Kishan Deka, Tuhin Ghosh, Siddharth Maharana, A. N. Ramaprakash, Ramya M. Anche, Artem Basyrov, Dmitry Blinov, Hans Kritian Eriksen, Eirik Gjerløw, John A. Kypriotakis, Sebastian Kiehlmann, Ioannis Liodakis, Nikolaos Mandarakas, Georgia V. Panopoulou, Vasiliki Pavlidou, Timothy J. Pearson, Vincent Pelgrims, Stephen B. Potter, Anthony C. S. Readhead, Raphael Skalidis, Trygve Leithe Svalheim, Konstantinos Tassis, Namita Uppal, Ingunn K. Wehus
Solar and Stellar Astrophysics
Time-Resolved Connection between Starspots and Flares in Nearby Young Solar-type Stars Observed by TESS
Daijiro Hitotsuyanagi, Hiroto Yamada, Daisuke Yamashiki et al. (+3 more)
Superflares are energetic explosions on
stellar surface with energies of 10^33-10^36 erg, significantly exceeding those of typical
solar flares. While previous studies have suggested that these events are driven by
magnetic energy stored in large starspots, the detailed time-resolved relationship between starspot area and
flare activity on individual
stars has remained unclear. In this paper, we investigate the time
evolution of
magnetic activity on three representative young
solar-type
stars (EK Draconis, DS Tucanae A, and V889 Herculis) using $\sim$7 years of photometric data from the Transiting
Exoplanet Survey Satellite (TESS). We automatically detected
stellar flares and derived the
flare frequency, starspot area, and rotational period for each TESS sector covering ~27 days. As a result, we found that the
flare frequency and starspot area vary significantly across sectors, although we could not identify any activity-cycle-like pattern. There is a positive correlation between the starspot area and
flare occurrence frequency for all three targets and the power-law dependence is consistent among the
stars. This result supports the physical picture that superflares on young
solar-type
stars are powered by
magnetic energy stored in large starspots, analogous to
solar flares, and that the energy release rate changes as the total stored
magnetic energy varies. Furthermore, from the analysis of EK Draconis, we find a possible dependence of starspot area on rotation period, which may suggest that large starspots preferentially form at mid-latitudes. These findings demonstrate that the
magnetic activity mechanisms established for the Sun extend to the extreme
magnetic activity observed on young active
stars.
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All authors Daijiro Hitotsuyanagi, Hiroto Yamada, Daisuke Yamashiki, Kazuma Ishihara, Yosuke Yamashiki, Kosuke Namekata
Cosmology and Nongalactic Astrophysics
Anisotropic separate universe : Long-wavelength perturbations and conserved quantities
Daiki Saito and Atsushi Naruko
We investigate the long-wavelength
evolution of linear perturbations in a homogeneous and anisotropic background with a scalar field coupled to a vector field. Using the spatial gradient expansion in the uniform-$\mathcal{N}$ gauge in which the number of $e$-folds is unperturbed, we derive the complete set of superhorizon solutions and establish their correspondence with infinitesimal variations of the homogeneous anisotropic background. This extends the separate-universe picture, previously known for isotropic FLRW cosmology, to anisotropic spacetimes despite the mixing of scalar, vector, and tensor perturbations induced by broken rotational
symmetry. We show that the long-wavelength equations form a self-consistent system and identify a conserved quantity that generalizes the conserved Wronskian of isotropic cosmology. Unlike the isotropic case, the superhorizon modes sourcing the
curvature perturbation are governed by three independent conserved channels associated with the scalar field, the background shear, and the gauge-field tilt, together with an additional dynamical shear contribution originating from the anisotropic geometry. This reveals that the
evolution of
curvature perturbations around anisotropic background is intrinsically richer than in isotropic multi-field models. Our formulation provides a practical prescription for computing the final
curvature perturbation directly from horizon-crossing fluctuations, thereby establishing the anisotropic generalization of the $\delta N$ formalism. We further derive an explicit relation between
curvature perturbations and
primordial gravitational waves, demonstrating how anisotropic expansion couples scalar and tensor sectors on superhorizon scales. Our framework provides a practical basis for predicting statistical anisotropies in
primordial scalar and tensor perturbations.
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Cosmology and Nongalactic Astrophysics
Breaking the Dark Sector Degeneracy with Nonparametric Expansion–Growth Reconstruction
Changyu You, Rong-Gen Cai and Tao Yang
The dark energy equation of state (EoS) and a possible dark-sector interaction are degenerate at the level of background expansion: the same expansion history may be interpreted as time-varying dark energy, energy exchange with dark matter, or a mixture of both. We introduce a data-driven, nonparametric expansion–growth framework that breaks this degeneracy by simultaneously reconstructing the dark energy EoS and the dark-sector coupling. Allowing the interacting matter density to evolve freely, we incorporate the coupling into the linear matter perturbation equation and reconstruct the expansion and growth histories using Gaussian processes, with hyperparameters marginalized in a
Bayesian treatment. Applying this method to Pantheon+,
cosmic chronometers, BAO measurements including DESI DR2, and
redshift-space-distortion data, we infer both $w_{\rm de}(z)$ and the interaction history over $0\lesssim z\lesssim 2$, without assuming either a parametric EoS or a prescribed interaction form. We find no statistically significant evidence for either a nonzero interaction or dark energy dynamics: the reconstructed coupling and dark energy EoS remain consistent with the $\Lambda$CDM limit. Our results establish an expansion–growth consistency test for coupled dark-sector physics and provide a model-independent route to distinguish genuine dark energy dynamics from effective dark-sector energy exchange.
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High Energy Astrophysical Phenomena
HAMCOR: A physics-driven Hamiltonian framework for inferring AGN coronal geometry from X-ray reverberation lags
Fabio Buffoli
We present HAMCOR (
Hamiltonian-based AGN Multi-constraint CORonal inference framework), a geometry-agnostic method for inferring the X-ray coronal structure of accreting black holes using reverberation-lag measurements. Unlike conventional template-fitting approaches, HAMCOR reframes coronal geometry inference as the ground-state selection of a physical
Hamiltonian. The corona is represented as a discrete emissivity distribution over a cylindrical grid, and its geometry emerges from five competing physical constraints:
magnetic coherence, lag consistency, illumination consistency, pair-production stability, and energy budget feasibility. Minimisation is performed via projected gradient descent with Armijo backtracking line search on the probability simplex. We validate HAMCOR on three synthetic geometries (lamppost, column, ring) using the same grid as the real-data fits, recovering spatial correlations rho = 0.24, 0.50, 0.12 and fractional lag errors below 24 per cent. A hyperparameter sensitivity analysis confirms robustness over more than one order of magnitude in the coupling constants. We apply HAMCOR to five sources spanning seven orders of magnitude in black hole mass: four AGN observed with XMM-Newton (Mrk 335, 1H 0707-495, IRAS 13224-3809, MCG-6-30-15) and the
stellar-mass black hole binary Cyg X-1 (M_bh = 14.8 M_sun), recovering consistent extended disc-corona geometries across the full mass range. We further present a multi-epoch analysis of Mrk 335 across five XMM-Newton observations (2006-2019), revealing that the coronal centroid remains stable at (R_c, z_c) ~ (6.3, 0.5) r_g across flux states spanning a factor of ~15 in reverberation lag amplitude, arguing against a collapsing or expanding lamppost. Schwarzschild-Shapiro delay corrections amount to ~79 per cent of the flat-spacetime lag on average; the recovered spatial morphology is robust to this correction.
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Cosmology and Nongalactic Astrophysics · Cross-listed from physics.hist-ph
Cosmology: 100 years after A. A. Friedmann
A. F. Zakharov
A. A. Friedmann (04.06.1888 – 16.09.1925) proposed the first physical cosmological models in 1920s. Despite the fact that Friedmann's works were very famous soon after their publication, the study of dynamic models of the Universe in the USSR was actually banned in the 30s - 50s of the last century, and Soviet philosophers and propagandists wrote that models of the evolving Universe were invented by Lemaitre on the demand of the Roman Pope, because according to Soviet philosophers such the birth of the universe is very similar to the divine creation of the world described in the Bible. Thus, in the USSR, Friedman's works were in oblivion in since 1930s until 1960s.
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High Energy Astrophysical Phenomena
Tidal deformation and strain accumulation of solid compact stars
Hongxiang Shen, Yong Gao, Hong-Bo Li et al. (+1 more)
The
tidal deformability of compact
stars encodes the equation of state of dense matter, and gravitational-wave observations such as GW170817 have begun to constrain it under the assumption of a fluid interior. Yet whether the interior of
pulsar-like compact
stars is fluid or solid remains largely untested, despite the distinct
tidal responses the two states predict. In this work, based on the strangeon-
star model, we develop a framework for modeling
tidal deformation in solid compact
stars. Adopting a shear modulus of $\mu = 10^{34}\,\mathrm{erg}\,\mathrm{cm}^{-3}$, we find a relative difference of approximately $40\%$ in
tidal deformability between solid and fluid strangeon
stars of $1.4\,M_\odot$, corresponding to a $\sim 10\%$ deviation from the universal I–Love relation. We further model the accumulation of internal strain during binary inspiral and find that it peaks near the
stellar center. When the gravitational-wave frequency reaches several hundred $\rm Hz$, large-scale fracturing occurs and can release up to $\sim 10^{46}\,\mathrm{erg}$ of elastic energy, sufficient to power short $\gamma$-ray-burst precursors. This solid-to-fluid transition alters the
tidal response and imprints on the waveform and phase of the emitted gravitational radiation. Combined with the precursor electromagnetic emission, these gravitational-wave signatures offer a multi-messenger avenue to test the solid nature of
pulsar-like compact
stars.
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All authors Hongxiang Shen, Yong Gao, Hong-Bo Li, Ren-Xin Xu
Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc
A way to constrain a graviton mass from astronomical observations
Alexander F. Zakharov, Predrag Jovanovic, Dusko Borka et al. (+1 more)
Along with a whole range of alternative theories of
gravity, variants of the massive theory of
gravity, i.e. the theory of
gravity, in which the graviton has mass, have been actively discussed in recent years. Theorists have proposed versions of massive
gravity theories that address the shortcomings of early versions of such theories. Astrophysicists and experimental physicists have been discussing limitations on the graviton mass from various astronomical observations. In particular, in the first LIGO paper, where the discovery of gravitational waves from binary black holes was reported, a limit on the mass of the graviton was obtained from the analysis of the profile of the gravitational wave signal. In the paper graviton mass constraints were obtained by analyzing the trajectory of a bright
star in the vicinity of the center of our
Galaxy, using observations from the
GRAVITY and Keck groups. Briefly other astronomical ways to limit a graviton mass were discussed.
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All authors Alexander F. Zakharov, Predrag Jovanovic, Dusko Borka, Vesna Borka Jovanovic
Astrophysics of Galaxies · Cross-listed from physics.plasm-ph
Collisionless whistler heat-flux instability in ultra-high-$\beta$ plasmas
Rhisiart Davies, Prakriti Pal Choudhury and Archie F. A. Bott
Kinetic instabilities, notably the whistler heat-flux instability (WHFI), are known to suppress thermal transport significantly in the moderate- to high-$\beta$
plasmas relevant to many astrophysical systems. This paper explores WHFI-regulated heat transport in a new regime: ultra-high-$\beta$
plasmas with $\beta_{e} \gtrsim L_{\mathrm{T}}/\rho_e$. Extrapolating previous theories of the WHFI to ultra-high-$\beta$
plasmas, we propose that the
magnetic energy in unstable whistler fluctuations becomes comparable to that of the background
magnetic field at saturation. We corroborate this hypothesis using 1D3V and 2D3V kinetic simulations using the particle-in-
cell code OSIRIS. We find that, in ultra-high-$\beta$
plasmas, the heat flux is localised and no longer regulated primarily by resonant pitch-angle scattering of electrons; instead, thermal energy is transported predominantly by advection at the whistler phase velocity. Heat-flux suppression is observed in 1D3V and 2D3V simulations; however, we show that the saturation of the WHFI and the regulation of heat flux are sensitive to dimensionality in the ultra-high-$\beta$ regime. The amplitude and phase velocity of the heat-flux-regulating whistler waves scale differently with $\beta_e$, yielding parallel heat fluxes, normalised to the free-streaming value, of $q_{e\parallel} / q_\mathrm{fs} \approx 4.7 \beta_{e}^{-1}$ and $q_{e\parallel} / q_\mathrm{fs} \approx 0.3 \beta_{e}^{-1/2}$ in 2D3V and 1D3V simulations, respectively. We perform 2D3V simulations with background
magnetic fields inclined to the temperature gradient, showing perpendicular heat transport remains negligible. We develop a heuristic theory from kinetic equations that explains these phenomena. Our work extends our understanding of how the WHFI modifies thermal transport to regimes applicable to high-energy-density physics and the reionised intergalactic medium.
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Solar and Stellar Astrophysics
STARSFLUX: an all-sky catalogue of absolute spectro-photometric calibrators from 0.3 to 30 $\mu$m
Violeta Gámez Rosas, Michiel Hogerheijde, Roy van Boekel et al. (+10 more)
Obtaining accurate fluxes for faint sources from the ground at near- and mid-infrared wavelengths is challenging because of rapidly varying atmospheric absorption, and is often limited by the lack of a nearby spectro-photometric calibrator. We present the
STellar Absolute Reference Spectroscopic Flux Library (STARSFLUX), an all-sky catalogue of 64,484 calibrator spectra spanning 0.3–30 $\mu$m, based on the Mid-infrared
stellar Diameters and Fluxes compilation Catalogue (MDFC). STARSFLUX combines
Gaia DR3
stellar parameters, multi-band photometry from space- and ground-based surveys, and synthetic NewEra PHOENIX atmosphere models. For each
star, we fit the observed SED with an interpolated model spectrum, angular diameter, and extinction to produce an absolutely flux-calibrated spectrum. The derived angular diameters can also be used to calibrate interferometric observations. We validate the catalogue using three independent tests. First, STARSFLUX angular radii agree closely with
Gaia DR3 radii, with a median $|\Delta R|/R_{\rm Gaia,DR3} \simeq 4.8$ per cent. Second, integrated L-band (2.8–4.2 $\mu$m) fluxes for 12
stars in common with the Cohen infrared standards agree with Cohen values with a mean absolute percentage difference of $4.7 \pm 2.6$ per cent. Third, comparison with
Gaia DR3 BP/RP spectra shows that the near-UV/visible/near-IR absolute spectro-photometric fluxes agree to approximately 3 per cent. The FITS spectra are available at https://home.strw.leidenuniv.nl/~gamez/ and will be submitted to VizieR.
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All authors Violeta Gámez Rosas, Michiel Hogerheijde, Roy van Boekel, Jozsef Varga, Walter Jaffe, Alexis Matter, Peter H. Hauschildt, Leonard Burtscher, James Leftley, Bruno Lopez, Florentin Millour, Romain G. Petrov, Harikumar N