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Physics Astrophysics

astro-ph Watch Astrophysics

Wednesday 6 May

Astrophysics of Galaxies

Investigating the Effects of Bars on Star Formation and Nuclear Activity of Galaxies Using DESI Survey Data

Jianfei Liu and Zhimin Zhou

We present a statistical analysis of the connections between galactic bars, star formation, and active galactic nucleus (AGN) activity using 33,201 disk galaxies (0.01 < z < 0.05) from DESI DR1 cross-matched with Galaxy Zoo DESI. Based on morphological classifications, we identify 3,508 strongly barred and 8,335 weakly barred systems. We find that barred galaxies exhibit a clear bimodal distribution in color-mass space: weak bars are preferentially found in bluer, lower-mass disks, whereas strong bars are more common in massive, redder systems. Strongly barred galaxies are on average more massive and metal-rich than unbarred systems. In addition, strong bars enhance central SFRs in low-mass galaxies but reduce sSFRs in massive systems, reflecting a dual role where bars initially trigger central star formation but eventually promote quenching by accelerating gas consumption. In terms of nuclear activity, barred galaxies display a higher incidence of AGN activity. The presence of a bar is also associated with an increased fraction of powerful AGN, with the highest proportions found in strongly barred systems. However, the correlations between AGN activity and detailed bar structural parameters are weak, suggesting that the link between bars and nuclear activity is indirect and regulated by multiple factors. Overall, our results support a scenario in which bars facilitate angular-momentum transport and gas inflow, thereby driving central star formation and fueling supermassive black hole accretion while operating alongside other processes that shape galaxy evolution.
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Cosmology and Nongalactic Astrophysics

Gravitational wave emission from nonspherical collapse in an early matter-dominated era using N-body simulations

Albert Escrivà, Tomohiro Harada, Kazunori Kohri et al. (+2 more)

We study the dynamics of the collapse of a nonspherical overdense patch during an early matter-dominated era and the associated production of gravitational waves (GWs) using a semirelativistic N-body framework that we develop. The collapsing patch is initialized through a Zel'dovich deformation of a homogeneous sphere and evolved in an Einstein–de Sitter background, while the emitted signal is computed directly from the numerical quadrupole evolution. We show that a reliable prediction of the signal requires a fully numerical treatment of the nonlinear collapse dynamics. In particular, fitting-based procedures and Zel'dovich-based estimates fail to capture the post-shell-crossing evolution and can over/under-estimate the emitted power of the GWs. After averaging over realizations weighted by the Doroshkevich and BBKS (peak theory) distributions, we find that the two spectra have similar shapes and remain within the same overall order of magnitude at the peak amplitude, although the BBKS result is systematically smaller. The dominant contribution arises from peaks of relatively modest height, around $\nu \simeq 3$, while a larger variance significantly enhances the signal. Finally, by varying the horizon mass and reheating temperature, we map the present-day GW spectra to the sensitivity bands of different classes of detectors. In this way, the signal can populate a broad range of frequencies, from pulsar timing arrays to very high-frequency experiments, showing that GWs from nonspherical collapse can provide a probe of the pre-BBN thermal history.
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All authors Albert Escrivà, Tomohiro Harada, Kazunori Kohri, Takahiro Terada, Chul-Moon Yoo

Earth and Planetary Astrophysics

Beyond the $\alpha$ model: scaling the wind-driven accretion rate in protoplanetary disks using systematic non-ideal magnetohydrodynamical simulations

Haruhi Enomoto, Shoji Mori and Satoshi Okuzumi

Magnetically driven mass accretion plays a key role in protoplanetary disk evolution and planet formation. However, the alpha prescription remains phenomenological, and how the accretion rate depends on basic disk quantities is still poorly understood. While local shearing-box simulations are computationally efficient, they suffer from a fundamental problem: the toroidal magnetic field generated by Keplerian shear accumulates within the computational domain, disrupting a field-line geometry consistent with global wind-driven accretion. In this study, we use the super-box-scale diffusion (SBD) scheme in non-ideal MHD shearing-box simulations. By damping the horizontally averaged horizontal magnetic fields, this scheme successfully mitigates the artificial field accumulation and maintains the field-line symmetry required for global wind-driven accretion for more than 500 orbital periods. Comparison with self-similar solutions supports the quantitative usefulness of the SBD method, showing good agreement in both the vertical structure and the plasma-beta dependence of the accretion rate. We then conduct a parameter survey using a magnetic diffusivity table, covering a wide range of disk radii, surface densities, magnetic field strengths, and dust-to-gas ratios. We demonstrate that the mass accretion rate follow power-law scaling relations in terms of three local disk properties: the midplane plasma beta, an effective ambipolar Elsasser number in ionized surface layers, and the thickness of the magnetically active layer. The scaling relations reproduce the numerical results to within a factor of 2-3 across the explored parameter space. The present scaling relations provide a framework for predicting the mass accretion rate from local disk physical quantities without invoking an alpha parameter.
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Solar and Stellar Astrophysics

Nonlinear steepening of a fast magnetoacoustic wave in the vicinity of a coronal magnetic null point

Yu Zhong, Valery M. Nakariakov, Mariana Cécere et al. (+1 more)

The interaction of a fast magnetoacoustic wave with a magnetic null point is studied in the context of the sympathetic flare phenomenon. Attention is paid to steepening the wave caused by the finite-amplitude effects in a non-uniform plasma environment. The null point is modelled by a potential magnetic configuration without a guiding field. The equilibrium plasma density and temperature are taken to be constant. The fast wave is excited by an impulsive point source outside the distance at which the local Alfvén and sound speeds are equal to each other. The incoming fast wave approaches the null point along the bisector of the magnetic configuration, i.e., across the local field. The fast-speed non-uniformity around the null point causes the refraction of the incident fast wave. However, the segment of the incoming wave, which approaches the null point is locally plane. The decrease in the fast speed towards the null point amplifies the nonlinear deformation of the incoming wave. Hence, the fast wave can become subject to nonlinear dissipation at a distance from the null point and not reach it.
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All authors Yu Zhong, Valery M. Nakariakov, Mariana Cécere, Andrea Costa

Astrophysics of Galaxies

A CNN–Transformer Denoiser for low-$S/N$ Galaxy Spectra: Stellar Population Recovery in Synthetic Tests

Suk Kim, Joon Hyeop Lee and Soo-Chang Rey

Stellar population measurements in integral field unit surveys are often limited by low signal-to-noise ratios (S/N) in low-surface-brightness spaxels. Using controlled synthetic experiments, we test whether deep-learning-based denoising can recover stellar population information without spatial binning. We introduce the Enhanced U-Net Transformer (EUT), a one-dimensional CNN-Transformer model trained on 90,000 synthetic spectra constructed from MILES simple stellar population models following Lee et al. (2023). Wavelength-dependent noise is injected on the fly to emulate SAMI-like data with S/N = 5-20, measured in a 4484.77-4573.12 Angstrom continuum window. On an independent test set of 10,000 spectra, EUT reduces the full-spectrum RMS residual by about 96.5 percent at S/N = 5 and about 94 percent at S/N = 20, with recovery rates of at least 99.8 percent. In fixed windows around Ca II H, Hdelta, Hbeta, Fe I 4383, Mg b, and Na D, residuals decrease by more than about 88 percent while preserving line-profile structure. In downstream pPXF fitting, the RMS scatter in recovered mass-weighted age decreases from about 0.41 to 0.25 dex at S/N = 5 and from about 0.32 to 0.22 dex at S/N = 10. For mass-weighted metallicity, [M/H], the scatter decreases from about 0.45 to 0.36 dex and from about 0.32 to 0.28 dex, respectively. At S/N = 20, denoised and noisy inputs give consistent results within the synthetic-test uncertainties. These experiments suggest that hybrid CNN-Transformer denoisers can improve low-S/N spectra for stellar population studies, although validation with observed spectra is still required.
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Earth and Planetary Astrophysics

Modeling Volcanic Plume Heights Across Exoplanet Atmospheres: Insights from TRAPPIST-1

Prabal Saxena and Thomas Fauchez

Explosive volcanic eruptions play a fundamental role in the evolution and observability of rocky exoplanets, serving as a key mechanism for injecting volatiles into planetary atmospheres and potentially modifying their climate and composition. This process may be particularly important for close-in exoplanets where tidal forcing can drive substantial internal heating, analogous to (but often exceeding) Io's volcanism. In this work, we adapt and extend a classic 1D volcanic plume model originally developed in IDL by Glaze and Baloga for Venus and Mars applications, and port it into a flexible, open Python framework suitable for exoplanet studies. The model explicitly couples vent thermodynamics, buoyant entrainment, and vertically varying static stability to predict plume rise, neutral-buoyancy height, and overshoot for a wide range of planetary and atmospheric conditions. We first benchmark the Python implementation against the original IDL code and analytic scaling laws to ensure adequate momentum budgets and strict mass conservation. We then apply the model to a suite of exoplanet-relevant background states, including CO2-rich atmospheres under strong irradiation and diverse surface conditions. A systematic sensitivity analysis explores how plume height depends on surface gravity, bulk atmospheric composition (and mean molecular weight), background temperature and stratification, vent overpressure, and volatile loading. We identify regions of parameter space where plumes routinely penetrate to low-pressure levels, maximizing their potential detectability in transmission or emission. These results provide a physically grounded framework for predicting whether and how volcanic emissions might be detected on rocky exoplanets, including-but not limited to-those experiencing strong tidal heating.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-th

New Exponential and Polynomial $\xi$-attractors

Renata Kallosh and Andrei Linde

We introduce a new family of cosmological attractors with non-minimal coupling of gravity and non-canonical kinetic terms. In the Einstein frame, these models transform into a class of exponential and polynomial attractors with the spectral index $n_{s}$ spanning a broad range $1-2/N \leq n_{s} < 1-1/N$, and $r$ can decrease to zero in the limit $\xi \to \infty$. This is sufficient to match any combination of Planck, BICEP/Keck, ACT, SPT, and DESI data. We present a supergravity implementation of these models.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph

Landscape of Spontaneous CP Violation

Yuichiro Nakai

Spontaneous CP violation (SCPV) provides a promising solution to the strong CP problem, explaining the smallness of the QCD $\theta$-angle while generating the Cabibbo-Kobayashi-Maskawa (CKM) phase. In the present work, we review and discuss the realization of SCPV in the supersymmetric framework, which addresses critical issues such as the naturalness of the scale of SCPV and the presence of problematic higher dimensional operators and radiative corrections spoiling the mechanism. It is explicitly shown that SCPV is realized along flat directions and stabilized through supersymmetry-breaking effects and a non-perturbative dynamics, predicting light SCPV sector particles feebly coupled to the Standard Model particles. Furthermore, we discuss the issue of baryon asymmetric Universe in the SCPV framework and point out that the Affleck-Dine mechanism can successfully generate the observed baryon asymmetry with a low reheating temperature compatible with the gravitino dark matter. Our framework predicts a nonzero neutron electric dipole moment which is within the reach of near-future experiments.
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Tuesday 5 May

Instrumentation and Methods for Astrophysics · Cross-listed from eess.SP

Neural Posterior Estimation of Terrain Parameters from Radar Sounder Data

Jordy Dal Corso, Annalena Kofler, Marco Cortellazzi et al. (+2 more)

Radar sounders are electromagnetic instruments that can probe deep into the subsurface of Earth and other planetary bodies by processing the echo of transmitted radar waves. Conventional approaches for analyzing such data rely on approximate assumptions and often produce point estimates that ignore parameter correlations as well as galactic and measurement noise. We propose a simulation-based inference approach to terrain parameter inversion from radar sounder data, where synthetic observations from a GPU-based simulator are used to train a neural network-based density estimator for neural posterior estimation (NPE). By explicitly conditioning on reference surface assumptions, the proposed framework allows systematic evaluation of posterior robustness to reference surface variability. We demonstrate that our NPE model is well calibrated on simulated data and transferable to real Mars radar profiles, where we analyze terrain parameters using literature-informed reference values.
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All authors Jordy Dal Corso, Annalena Kofler, Marco Cortellazzi, Lorenzo Bruzzone, Bernhard Schölkopf

Cosmology and Nongalactic Astrophysics

Neutrino Flavor Transformation in Collapsing Supermassive Objects

Kyle S. Kehrer, George M. Fuller, Ian Padilla-Gay et al. (+1 more)

The collapse of supermassive stars (SMSs, $M\gtrsim10^4\,M_\odot$) to black holes is accompanied by a prodigious flux of neutrinos of all flavors. These are produced thermally via $e^\pm$ annihilations, mostly in the core and just before gravitational trapped surface formation. There, the ratio of fluxes for $\nu_e\bar{\nu}_e$-pairs to $\nu_{\mu}\bar{\nu}_{\mu}/\nu_{\tau}\bar{\nu}_{\tau}$-pairs is $\sim$\,5-to-1. This is because at SMS temperature scales, $\nu_e\bar{\nu}_e$ pairs have both charged and neutral current production channels, whereas $\nu_{\mu}\bar{\nu}_{\mu}/\nu_{\tau}\bar{\nu}_{\tau}$-pairs only have neutral current production channels. We point out that the typical energies of these neutrinos, and the run of density in collapsing radiation-dominated supermassive configurations, leads to Mikheyev-Smirnov-Wolfenstein (MSW) resonances inside these objects for the atmospheric neutrino mass splitting scale, $\Delta m^2_\mathrm{atm.}\sim2.4\times10^{-3}$ eV$^2$. In the normal neutrino mass hierarchy, adiabatic flavor transformation through the MSW resonances would then swap the fluxes $\nu_e\leftrightharpoons\nu_{\mu,\tau}$, whereas, in the inverted neutrino mass hierarchy, the anti-neutrino fluxes are swapped, $\bar{\nu}_e\leftrightharpoons\bar{\nu}_{\mu,\tau}$. We also examine the prospects for collective neutrino flavor oscillations in these environments. Implications for flavor oscillation's effects on neutrino energy deposition and neutrino-induced nucleosynthesis in the SMS's outer layers are examined, as are prospects for detections of SMS collapses through various means.
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All authors Kyle S. Kehrer, George M. Fuller, Ian Padilla-Gay, Chad T. Kishimoto

Astrophysics of Galaxies · Cross-listed from physics.space-ph

Transport of electrons in tangled magnetic fields

Daniel Verscharen, Natasha Jeffrey, Anton Artemyev et al. (+6 more)

Cosmic magnetic fields are typically inhomogeneous and often highly tangled due to large-scale plasma flows, turbulence, and instabilities. If the variations in the magnetic field occur on scales that are large compared to the gyro-radius of the plasma electrons, the electrons are primarily confined to gyro-centre trajectories along the field lines. Therefore, in-situ electron measurements help us map out the connectivity of the magnetic field in space plasmas. Gyro-centre drifts, wave-particle interactions, trapping, and cross-field diffusion are processes related to field inhomogeneities and fluctuations; they have the potential to modify or even disrupt the transport of electrons along field lines. We introduce the basic principles of electron transport in tangled magnetic fields and review the creation of tangled fields through turbulence and instabilities as well as the modulation of parallel electron transport through kinetic instabilities. We then describe trapping and de-trapping effects in inhomogeneous magnetic fields, as well as electron diffusion and energisation across the magnetic field. The transport of electrons in tangled fields results from a complex interplay of plasma processes that occur on a broad range of scales. A combination of in-situ plasma measurements, remote-sensing plasma observations, and plasma theory and simulations is required to resolve this contemporary challenge to the fields of heliophysics and astrophysics.
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All authors Daniel Verscharen, Natasha Jeffrey, Anton Artemyev, Jesse T. Coburn, Matthew W. Kunz, Oreste Pezzi, Mario Riquelme, Ida Svenningsson, Lynn B. Wilson III

Solar and Stellar Astrophysics · Cross-listed from physics.plasm-ph

Three dimensional, spherically polarized magnetic fields

Anna Tenerani and Marco Velli

Turbulence in the solar wind is characterized by Alfvénic fluctuations that exhibit spherical polarization, a geometric condition resulting in the nearly constant magnitude of the magnetic field. This property persists even during the largest field fluctuations, sometimes leading to local polarity reversals known as switchbacks. A longstanding question is whether three-dimensional smooth magnetic fields can simultaneously satisfy the constant-$|{\bf B}|$ constraint, and how such fields can be constructed analytically or numerically. Here we propose a new numerical method that allows to construct a magnetic field that is exactly spherically polarized, reproducing key features of solar wind fluctuations. Using this framework, we find evidence that discontinuities are unavoidable for generic three-dimensional configurations. Fundamentally, this implies that field rotations cannot maintain exactly constant $|{\bf B}|$ in an arbitrarily large spatial domain. Rather, field rotations with constant magnitude can exist in limited regions of space. We argue that these finite spatial domains are separated by discontinuities where a local departure from constant $|{\bf B}|$ is expected. These results provide insights into the structure of solar wind turbulence and more generally into the nature of nonlinear magnetic fluctuations in plasmas.
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Solar and Stellar Astrophysics

Ensemble modeling of Coronal Mass Ejection dynamics and forecasts at 1 AU with a semi-analytic flux-rope model

S. Stamkos, S. Patsourakos, A. Vourlidas et al. (+1 more)

This study quantifies how uncertainty in physically meaningful coronal mass ejection (CME) and solar-wind inputs propagates into forecast-relevant diagnostics from eruption to 1 AU. We use a semi-analytic erupting flux rope (EFR) model to simulate CME initiation and Sun-to-1 AU propagation under Lorentz, gravitational, and drag forces, driven by a prescribed time-dependent poloidal-flux injection. Relative to the original EFR formulation, we include sheath and pile-up effects through an effective mass and update the drag term for CME solar-wind coupling. The model is embedded in a Monte Carlo framework with truncated-normal sampling of key eruption and background solar-wind inputs. Across six CME events, the ensembles show event-dependent dispersion in the 1 AU diagnostics. For +/- 20% input sampling, all spreads are 1-sigma ensemble standard deviations. The time-of-arrival spread is 2.4-7.7 h and is mainly controlled by the poloidal-flux injection history, upstream wind speed, and drag coefficient. The leading-edge speed spread is 28-53 km/s and is primarily controlled by background-flow properties. Magnetic-field diagnostics show two regimes: the sheath field is relatively tightly distributed, with a spread of 1-3.5 nT and sensitivity to upstream wind, size, and expansion scaling, whereas the internal flux-rope field has a larger spread of 1-7.6 nT and is governed mainly by eruption-driving and flux-content parameters. The impact-duration spread is 2.4-6.3 h and is controlled mostly by geometric size and expansion scaling, with additional sensitivity to the driving timescale. These results establish a quantitative link between EFR input uncertainties and the resulting spread in CME arrival and impact diagnostics, identifying the physical parameters that most strongly limit forecast precision at 1 AU.
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All authors S. Stamkos, S. Patsourakos, A. Vourlidas, E. Paouris

High Energy Astrophysical Phenomena

Sensitivity of the As-Built Askaryan Radio Array to Ultra-High Energy Neutrinos

ARA Collaboration: N. Alden, S. Ali, P. Allison et al. (+70 more)

The Askaryan Radio Array (ARA) is an ultra-high energy (UHE) neutrino observatory designed to detect the impulsive radio waves produced by relativistic particle cascades in the Antarctic glacial ice. Using a significantly enhanced simulation pipeline, which adds data-driven detector simulations and fully incorporates secondary particle production, we calculate the trigger-level acceptance of the entire array. We compare the resulting trigger-level sensitivity to constraints on the UHE neutrino flux from other detectors. Given its exposure from 2013 to 2023, we find that ARA achieves a world-leading sensitivity above about $10^{19}$ eV, depending on the details of the event selection used in a search. Moreover, we find that up to 13 neutrinos are predicted to have been observed in this period at trigger-level, assuming the most optimistic neutrino flux models. We show that observations of secondary particles account for up to 30% of the total acceptance starting at $10^{19}$ eV, and we explore the potential signatures and implications of both multi-pulse (from direct and refracted pulses and/or from secondary particle interactions) and multi-station events. Finally, we comment on the implications of this study for the design of next-generation UHE neutrino experiments, in particular IceCube-Gen2 Radio.
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All authors ARA Collaboration: N. Alden, S. Ali, P. Allison, J.J. Beatty, D.Z. Besson, A. Bishop, P. Chen, Y.C. Chen, Y.-C. Chen, S. Chiche, B.A. Clark, A. Connolly, K. Couberly, L. Cremonesi, A. Cummings, P. Dasgupta, R. Debolt, S. de Kockere, K.D. de Vries, C. Deaconu, M.A. DuVernois, J. Flaherty, E. Friedman, R. Gaior, P. Giri, J. Hanson, N. Harty, K.D. Hoffman, M.-H. Huang, K. Hughes, A. Ishihara, A. Karle, J.L. Kelley, K.-C. Kim, M.-C. Kim, I. Kravchenko, R. Krebs, C.Y. Kuo, U.A. Latif, C.H. Liu, T.C. Liu, W. Luszczak, A. Machtay, M.S. Muzio, J. Nam, R.J. Nichol, A. Novikov, A. Nozdrina, E. Oberla, C.W. Pai, Y. Pan, C. Pfendner, N. Punsuebsay, J. Roth, A. Salcedo-Gomez, D. Seckel, M.F.H. Seikh, Y.-S. Shiao, J. Stethem, S.C. Su, S. Toscano, J. Torres, J. Touart, N. van Eijndhoven, A. Vieregg, M. Vilarino Fostier, M.-Z. Wang, S.-H. Wang, P. Windischhofer, S.A. Wissel, C. Xie, S. Yoshida, R. Young

Solar and Stellar Astrophysics

Modeling Flare Continuum Emission Observed by Hinode/EIS: Instrument Calibration and Element Composition Results

Peter R. Young and Biswajit Mondal

Continuum emission from a solar flare observed with the Extreme ultraviolet Imaging Spectrometer (EIS) on board the Hinode satellite is used to obtain the radiometric calibration of the instrument. The flare had a GOES class of M8, and peaked at 23:59 UT on 2024 September 30. The continuum is modeled by computing a differential emission measure curve using EIS emission lines and atomic data from the CHIANTI database. The ratio of the observed continuum to model continuum yields effective area curves for the instrument. The new curves confirm earlier findings that the EIS long-wavelength channel has degraded by a factor two compared to the short-wavelength channel. However, no evidence is found for the fine-scale structure in the effective area curves that has been presented by previous authors. In order to reproduce both the emission line intensities and the continuum, it is found that the plasma must be depleted in elements with low first ionization potentials (FIPs), i.e., the so-called inverse FIP-effect. In particular, the Fe/H relative abundance is found to be a factor 0.57 below the photospheric value at a temperature of 10 MK. This is confirmed by analysis of soft X-ray spectra from the Solar X-ray Monitor on Chandrayaan-2, which yields an Fe/H FIP bias of 0.55 averaged over the entire flare.
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Cosmology and Nongalactic Astrophysics

Taming Additive Systematics via Redshift-Bin-Optimized Star-Galaxy Separation

Noah Weaverdyck, David Schlegel, Anand Raichoor et al. (+1 more)

Contamination from stars in the galaxy samples of large-scale structure surveys can bias cosmological constraints if not tightly controlled. This is especially true for lens samples used for galaxy clustering and galaxy-galaxy lensing probes, where contamination is a primary source of additive systematics. We propose an improved approach to star-galaxy separation and an optimal weighting scheme to jointly mitigate additive and multiplicative contamination of the density field at the map level. Our star-galaxy separation approach exploits the fact that photometric galaxy samples used for cosmological inference populate different regions of color-space than the full photometric dataset on which star-galaxy cuts are typically applied, and therefore optimizes star-galaxy separation for the galaxy samples in each redshift bin. This serves as a complementary approach to morphological star-galaxy separators, which can have complicated dependencies on PSF and blending systematics. We demonstrate the method using the Dark Energy Survey Y3 MagLim lens sample, for which we obtain forced NIR unWISE photometry via cross-matching with DECaLS DR9 to define redshift-bin-optimized color cuts. We identify and remove residual stellar contamination in the DES Y3 lens sample, which varies strongly across redshift bins ($1.3-5.5\%$) and across the footprint.
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All authors Noah Weaverdyck, David Schlegel, Anand Raichoor, Ignacio Sevilla-Noarbe

Earth and Planetary Astrophysics

Impact of Climate States and Seasons on Future Exo-Earth Observations

Kyle Batra, Stephanie Olson and Vincent Kofman

Many planetary parameters impact the climate state of Earth-like exoplanets and could vary significantly from those on Earth. However, some of these parameters may be impossible to observe, causing ambiguity in determining exoplanet climate and characterizing their atmospheric features. We explore how distinct planetary climate states impact their reflectance spectra to reduce uncertainty in the interpretation of future direct imaging observations, such as with the Habitable Worlds Observatory. We find that worlds with the same atmospheric composition but distinct climate states have notable differences in apparent albedos and feature detectability. An additional consequence is that the exposure time required to detect atmospheric features and biosignatures, such as O$_2$, will depend on climate state, with icier worlds being more favorable for biosignature detection while ice-limited worlds may be more habitable. We find that clouds improve the strength and detectability of atmospheric features in reflected light, especially for ice-limited low albedo worlds. We find temporal variation in the strength of spectra at different seasons on high obliquity worlds, causing the required time to resolve atmospheric features to vary between the equinoxes and solstices. This abiogenic seasonality could be detectable through repeated direct imaging observations and may help inform the planetary climate state, especially in combination with constraints on inclination and mass. Our work elevates the importance of astrometry performed concurrently with direct imaging for characterizing climate state and planetary habitability of exoplanets. Interpretation of future spectroscopic observations must also account for temporal variations created by obliquity when searching for biosignatures.
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High Energy Astrophysical Phenomena

Multiwavelength Characterization of a New Magnetic Cataclysmic Variable 2CXO J050740.7-091337

Ilkham Galiullin, Vladislav Dodon, Antonio C. Rodriguez et al. (+2 more)

We report the discovery and characterization of a new cataclysmic variable (CV), 2CXO J050740.7-091337 (hereafter 2CXO J0507), identified using the X-ray main sequence through a cross-match between the Chandra Source Catalogue 2.1 and Gaia DR3. Optical spectroscopic follow-up with Keck I/LRIS reveals prominent cyclotron humps and Balmer emission lines, indicating a strongly magnetized white dwarf with a magnetic field strength of $B \approx 30$ MG. Analysis of Chandra and XMM-Newton archival data shows an X-ray luminosity of $L_X = (5.18 \pm 0.88) \times 10^{30}$ erg s$^{-1}$ (0.3-10 keV). The X-ray spectrum is well approximated by a thermal plasma emission model with a temperature of $kT = 7.95^{+3.84}_{-1.85}$ keV, showing no soft excess or intrinsic absorption. 2CXO J0507 exhibits long-term optical variability by $\approx2$ mag (ranging $\approx18-20$ mag) in Zwicky Transient Facility and Asteroid Terrestrial-impact Last Alert System photometric data. Both X-ray and optical modulation suggest an orbital period of 2.34 hr. These properties indicate that 2CXO J0507 is a magnetic CV, most closely resembling a polar. As 2CXO J0507 sits close to the faint limit of current optical time-domain surveys, it serves as a representative example of the large population of faint, magnetic CVs expected to be systematically identified by the Rubin Observatory.
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All authors Ilkham Galiullin, Vladislav Dodon, Antonio C. Rodriguez, Paula Szkody, Askar Sibgatullin

Astrophysics of Galaxies

Matter Clustering in Astrid: Reduced Baryonic Suppression from Realistic Black Hole Dynamics

Yanhui Yang, Simeon Bird, Yihao Zhou et al. (+4 more)

Baryonic feedback from active galactic nuclei (AGN) is often invoked as a major source of suppression in the matter power spectrum, with implications for precision cosmology and the $S_8$ tension. We present Astrid-DMO, the dark matter-only counterpart to the large-volume Astrid hydrodynamical simulation, and measure baryonic effects through $P_{\rm hydro}(k)/P_{\rm DMO}(k)$. We find no significant suppression at $z=0$ and mild suppression at $z=0.2$, weaker than in other state-of-the-art simulations. Using controlled small-volume runs, we identify a key driver of this discrepancy: the treatment of black hole (BH) dynamics. The widely used BH repositioning scheme artificially enhances BH mergers and boosts kinetic AGN feedback (e.g., by a factor of $2$ at $z=1.5$), leading to overly strong suppression. By contrast, a more physical dynamical friction model reduces feedback efficiency and weakens clustering suppression. Consequently, reconciling large-scale structure measurements with cosmic microwave background (CMB)-inferred $\Lambda$CDM cosmology, while matching observed halo gas fractions, becomes more challenging. Although strengthening AGN feedback can increase suppression, in our model this induces tensions with the observed galaxy stellar mass and AGN luminosity functions. These results sharpen the need for novel mechanisms that can efficiently eject gas from halos without compromising other galaxy properties.
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All authors Yanhui Yang, Simeon Bird, Yihao Zhou, Tiziana Di Matteo, Rupert Croft, Yueying Ni, Nianyi Chen

Solar and Stellar Astrophysics

Orbital motion and dynamical mass of the complex periodic variable binary system 2MASS J05082729-2101444

S. Curiel, G. N. Ortiz-León, V. J. S. Béjar et al. (+22 more)

We used very long baseline interferometry to constrain the orbit of the binary system 2MASS J05082729-2101444. We observed the system with the VLBA in three epochs at a frequency of 4.85 GHz, which provides an angular resolution of about 3 mas. We combined the three radio astrometric observations, 119 RVs (60 VIS and 59 NIR) obtained with the CARMENES high-resolution spectrograph over a period of 8.1 years, and a relative astrometric measurement of an archival H-band Keck NIRC adaptive optics image to fit the orbital motion of the binary system. The VLBA observations resolved the binary system and show emission from both stellar components, with similar flux-density levels (0.34-0.67 mJy), and showing slight temporal flux variations. The emission appears quiescent, with no significant circular polarization, and with no flare events. We obtained an orbital motion fit of the binary system, which shows an eccentric orbit (e = 0.71), an orbital period of 2.19 yr, and a semimajor axis of 26.964 mas (1.3 au). The VLBA observations made it possible to resolve the binary system and identify both stars as radio-loud sources. The combined fit shows that 2M0508-21 is an M-dwarf binary with a total dynamical mass of $0.459\pm0.007$ M$_{\odot}$, assuming Gaia's parallax. This mass is slightly higher than those estimated from the luminosity and theoretical evolutionary models. The upper limit of the circular polarization at 4.85 GHz ($\lesssim$10%), the persistence of the quiescent emission, and the relatively low brightness temperatures are consistent with a gyro-synchrotron or synchrotron origin of the radio emission. Further VLBA observations are needed to obtain the individual masses of the stars, as well as to verify Gaia's parallax of the system. A complete characterization of the system will help improve evolutionary models for young objects at the substellar boundary.
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All authors S. Curiel, G. N. Ortiz-León, V. J. S. Béjar, D. Viganò, J. M. Girart, S. Kaur, Y. Shan, F. Murgas, M. Zechmeister, P. J. Amado, J. A. Caballero, Th. Henning, E. Ilin, D. Montes, J. C. Morales, Ó. Morata, M. Pérez-Torres, A. Quirrenbach, A. Reiners, I. Ribas, Á. Sánchez-Monge, A. Schweitzer, J. I. Vico Linares, M., R. Zapatero Osorio

Instrumentation and Methods for Astrophysics

Overview of the New Hubble Spectroscopic Legacy Archive

Ravi Sankrit, John Debes, Matthew Burger et al. (+34 more)

The new Hubble Spectroscopic Legacy Archive (HSLA) provides coadded spectra of individual targets that have been observed with the Cosmic Origins Spectrograph (COS) and the Space Telescope Imaging Spectrograph (STIS) over their operating lifetime. HSLA uses data available in the Mikulski Archive for Space Telescopes (MAST). It automatically produces coadds whenever new data become publicly available or when there is newly recalibrated data. HSLA defines individual targets by their associated coordinates, accounting for proper motions, and uses SIMBAD, NED and the Phase II observing proposals to obtain astronomical classifications for each object. Coadded spectra are produced for each observing mode. In the case of COS far-ultraviolet observations there is one coadded spectrum for each lifetime position (LP). Additionally, a spectrum spanning the entire wavelength range covered by the observations is produced by abutting the spectra from a selection of individual modes. For each individual target, HSLA also provides a human-readable metadata file with key information that can be used in searches or for further exploration of the data. The HSLA project also makes the code used for coadding spectra publicly available along with several other tools (using Jupyter notebooks) for custom coaddition required in special cases. In this report we will describe the main components of HSLA and provide a brief description of how the data and metadata can be accessed.
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All authors Ravi Sankrit, John Debes, Matthew Burger, Van Dixon, Anna Payne, Leonardo Dos Santos, Thomas Wevers, Travis Fischer, Peter Forshay, Svea Hernandez, Robert Jedrzejewski, Rich Kidwell, Lauren Miller, Marc Rafelski, David Rodriguez, Robert Swaters, Dan Welty, Sara Anderson, Thomas Bair, Joleen Carlberg, Brian Charlow, Andrew Cortese, Tracy Ellis, Ben Falk, Scott Fleming, Elaine Frazer, Syed Gilani, Alec Hirschauer, Talya Kelley, Tim Kimball, Jennifer Kotler, Adrian Lucy, Sunita Malla, Christopher Rahmani, Fred Romelfanger, Kate Rowlands, Lisa Sherbert

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

Emergent gravity from nonlinear perturbation of spherical accretion with variable adiabatic index

Rohit Ghosh, Souvik Ghose, Biplab Raychaudhuri et al. (+2 more)

The main aim of the present work is to demonstrate that the analogue gravity phenomena are not an artifact of linear perturbation, rather gravity-like effects emerge through the non linear higher order perturbation of transonic fluid as well. To establish that fact, a spherically accreting astrophysical system has been considered where the hydrodynamic accretion with a relativistic, multi-component equation of state with position dependent adiabatic index onto compact astrophysical objects has been considered. By extending the acoustic metric formalism beyond the linear regime, it has been shown that the aforementioned perturbations satisfy a covariant wave equation in an effective acoustic spacetime with non-linear corrections, making the analogue geometry dynamical. As a consequence, the acoustic horizon can shift (inward or outward), depending on the relative amplitudes of density, temperature, and mass accretion-rate fluctuations. This provides a more realistic framework to investigate the dynamics of the non-linear analogue spacetime in astrophysically relevant accretion flows.
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All authors Rohit Ghosh, Souvik Ghose, Biplab Raychaudhuri, Apashanka Das, Tapas K. Das

High Energy Astrophysical Phenomena

On the spin dependence of the emergent gravity phenomena as observed in axially symmetric black hole accretion with spatially varying adiabatic index

Kalyanbrata Pal, Souvik Ghose, Ripon Sk et al. (+2 more)

The present work addresses an axisymmetrically accreting black hole system from three perspectives: the astrophysical, the dynamical systems, and the emergent gravity standpoint. Steady-state equations governing low angular momentum axially symmetric accretion under a pseudo-Kerr potential are formulated for a multi-species flow with a spatially varying adiabatic index. The resulting transonic solutions are shown to be multi-transonic and may accommodate a stationary shock. Critical points are classified via perturbative dynamical systems methods, and linear stability analysis confirms that the stationary solutions remain stable under radial perturbation. The ensuing acoustic geometry harbours acoustic black holes at the sonic points and an acoustic white hole at the shock location, whose causal structure is constructed via the Carter–Penrose diagram. The surface gravity associated with each acoustic horizon is computed using a generalized expression that accounts for the spatial variation of the local sound speed.
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All authors Kalyanbrata Pal, Souvik Ghose, Ripon Sk, Arpan Krishna Mitra, Tapas K. Das

High Energy Astrophysical Phenomena · Cross-listed from hep-ph

Proton-Proton to Antinucleon Cross Sections for Cosmic Ray Applications

Mariaelena Boglione, Mattia di Mauro, Fiorenza Donato et al. (+3 more)

We present predictions of inclusive antiproton and antineutron production cross sections in proton-proton collisions relevant to primary and secondary antiproton production in cosmic ray interactions with interstellar matter. Our predictions are based on collinear factorisation in Quantum Chromodynamics and are accurate to next-to-leading order in the perturbative expansion of the strong coupling. We assess the relevance of cross sections measured at collider experiments, such as NA49 at the CERN SPS and ALICE at the LHC, to the kinetic energy ranges accessed by cosmic ray detectors. We characterise the associated uncertainties due to the input parton distribution and fragmentation functions, and to missing higher orders. We critically examine the ~30% excess of antineutron over antiproton production in proton-proton collisions preliminarily reported by the NA49 experiment by combining our predictions with a data-driven model. Our results do not support the NA49 finding, and point to a mild excess of a few percent. We finally show that the NA49 result could only be reconciled with our framework by invoking sizeable differences between antiproton and antineutron production in the poorly constrained region of small transverse momenta of the produced hadron.
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All authors Mariaelena Boglione, Mattia di Mauro, Fiorenza Donato, Emanuele R. Nocera, Jennifer Rittenhouse West, Andrea Signori

Earth and Planetary Astrophysics

TOI-159 b: an eccentric hot-Jupiter planet around a young, pulsating $\gamma$ Doradus star

G. Mantovan, A. Llancaqueo Albornoz, A. Psaridi et al. (+16 more)

Fast-rotating hot stars are challenging targets for exoplanet searches due to rotational broadening and stellar variability. Moreover, hot stars often exhibit pulsations, an additional source of scatter in both photometric and spectroscopic series. Because of these challenges, such stars remain a relatively unexplored environment for planetary architecture and evolution studies. In this study, we present the confirmation and preliminary atmospheric characterisation of a giant planet orbiting a young ($\approx$ 150 Myr), pulsating $\gamma$ Doradus star. TOI-159 b ($P_{\rm orb} \simeq 3.7$ d, $R_{\rm p} \simeq 1.6~R_{\rm J}$, $M_{\rm p} \simeq 3.5 M_{\rm J}$) is an S-type planet in a close binary system and is the hottest ($T_{\rm eq} \simeq 1900$ K) hot Jupiter with a significant eccentricity ($e = 0.24 \pm 0.04$) ever detected. Our joint modelling of radial velocities (HARPS and CORALIE), transits (TESS), and spectro-photometry (IMACS) allows us to detect its Keplerian signal at high significance ($13 \sigma$), place strong constraints on its eccentricity ($6 \sigma$), disentangle the stellar rotational modulation and pulsation periods, and generate a low-resolution transmission spectrum, on which we conduct an exploratory analysis to constrain the presence of a planetary atmosphere using combined star-planet retrievals. Whilst our spectrum appears to display some modulation, the data is too coarse to allow for any conclusive detections at this stage. Higher-resolution observations are needed to confirm or refute these features and, if genuine, determine whether they originate from contamination from the star or a planetary atmosphere.
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All authors G. Mantovan, A. Llancaqueo Albornoz, A. Psaridi, A. Thompson, T. Zingales, V. Nascimbeni, S. Villanova, G. Piotto, K. A. Collins, J. Serna, L. Malavolta, K. Stassun, F. Bouchy, C. C. Cortes, P. Evans, T. Gan, M. Lendl, M. B. Lund, D. Nardiello

Astrophysics of Galaxies

The galaxy-halo connection and the dynamical evolution of a giant disc in a massive node of the Cosmic Web at z~3

G. Quadri, S. Cantalupo, C. Bacchini et al. (+9 more)

Recent JWST observations revealed the surprising presence of a giant and massive disc galaxy in a Cosmic Web node at z$\sim3$. This galaxy, named the Big Wheel, has a size almost three times larger than expected for typical disc galaxies at the same redshift and similar stellar masses. Constraining the origin and formation history of the Big Wheel requires knowledge of its dark matter halo properties, which are difficult to derive from JWST observations alone. Here, we investigate the dark matter halo of the Big Wheel and provide further constraints on the galaxy baryonic content, combining a physically motivated dynamical model with deep ALMA kinematical data. By using priors based on JWST photometric data and CO kinematics, we infer a dark matter halo mass of $\log (M_{h}/M_{\odot})= 12.11^{+0.29}_{-0.17}$ and a stellar mass of $\log(M_{\star}/M_{\odot})=11.00^{+0.11}_{-0.12}$, leading to a stellar-to-halo mass (SHM) ratio of $M_\star/M_h=0.06^{+0.04}_{-0.03}$. This value is significantly higher than expected from state-of-the-art empirical SHM relations. This implies that the Big Wheel may have assembled its stellar content in a much more efficient way with respect to the general galaxy population at z$\sim3$. Combined with its morphological properties, our results suggest that the Big Wheel had a tranquil recent formation history, with probably no major mergers, violent disc instabilities, or strong ejective feedback. We perform a numerical simulation of an idealised galaxy and let it evolve adiabatically for $2.5$ Gyr to demonstrate that it does not develop gravitational instabilities during its evolution that could alter its resemblance to the observed one. Although systems alike the Big Wheel are arguably rare, our results offer new constraints on the contribution of accretion and feedback to the formation history of the most massive discs within high-redshift Cosmic Web nodes.
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All authors G. Quadri, S. Cantalupo, C. Bacchini, A. Pensabene, A. Lupi, G. Pezzulli, W. Wang, M. Galbiati, T. Lazeyras, N. Ledos, H. Mao, A. Travascio

Solar and Stellar Astrophysics

The Tale of a Hungry Subgiant and Its Brown Dwarf: Interior Radiative Damping Dominates the Tidal Evolution of TOI-5882

Ritvik Sai Narayan, Melinda Soares-Furtado and Richard H.D. Townsend

We present a self-consistent tidal evolution framework that couples binary evolution from MESA to the full linear tidal response from GYRE-tides. Applying this framework to TOI-5882, a subgiant hosting a short-period brown dwarf, we show that interior radiative damping dominates the system's tidal evolution, with the classical equilibrium tidal model significantly underestimating the star's angular momentum evolution by several orders of magnitude. Consequently, our combined framework predicts a 2-6 fold reduction in the engulfment timescale, accelerating the companion's inspiral by roughly 25-110 Myr. By modeling angular momentum transport through the star as it evolves, we demonstrate that the early inspiral is driven by the non-resonant dissipation of internal gravity waves, before transitioning into a regime dominated by resonance crossings as the system approaches Roche-lobe overflow. We highlight the necessity of reframing the historical dichotomy between equilibrium and dynamical tides and instead propose categorizing tidal interactions around their dissipation mechanisms: radiatively damped tides, driven by radiative diffusion, and viscously damped tides, driven by turbulent viscosity. Our framework is broadly applicable to the tidal modeling of a wide class of star-companion systems, from binary stars to hot Jupiters, in a self-consistent and computationally feasible manner.
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Astrophysics of Galaxies

Galactic Amnesia: The Information Washout of the Milky Way Merger History

Lina Necib, Dylan Folsom, Elliot Y. Davies et al. (+2 more)

The merger history of a galaxy leaves imprints on its present-day stellar chemodynamics, yet dynamical processes progressively erase this record. We ask: how far back in time, and from which observables, can a galaxy's assembly history still be recovered? We provide a quantitative framework to address this question, using Mutual Information normalized by Shannon entropy to measure how much present-day stellar chemodynamics retains about each past merger's stellar mass $M_\star$ and infall time $t_{\rm infall}$. This framework is applied to TNG50 Milky Way – like galaxies, with comparison to FIRE-2. We find that the gravitational potential and total energy are the most informative and longest-lived tracers of merger properties, highlighting the need for accurately measuring the Milky Way's potential. The information carried by the radial velocity decays to the noise floor within $\sim$5 Gyr, angular momentum carries low information overall with a mass-dependent decay, and chemical abundances retain a flat, low information floor. Information washout depends on three key factors: (1) radial position – stars in the inner galaxy lose information faster due to shorter orbital times; (2) infall time – old mergers are largely phase-mixed; and (3) merger mass – larger mergers sink to the bottom of the potential well via dynamical friction, inducing violent relaxation that erases dynamical information. At each galactocentric radius, we map the observational horizon in the $(M_\star,\; t_{\rm infall})$ plane beyond which past mergers can no longer be recovered from that observable. By recasting merger reconstruction into this quantitative, observable-by-observable map of what is and is not recoverable, our results provide a foundation for interpreting chemodynamical signatures of past mergers and for guiding surveys and modeling toward the observables that maximize merger information recovery.
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All authors Lina Necib, Dylan Folsom, Elliot Y. Davies, Nathaniel Starkman, Andreas Thoyas

Instrumentation and Methods for Astrophysics

Shaping the future of Global Interferometric Arrays: Imaging Strong Gravity and Magnetic Fields

Venkatessh Ramakrishnan, Violette Impellizzeri, Chi-Kwan Chan et al. (+6 more)

The observational validation of General Relativity (GR) has been propelled in recent years by recent breakthroughs in Very Long Baseline Interferometry (VLBI) augmented by ALMA. We explore ALMA2040 opportunities to transform these studies through greatly improved sensitivity and a multi-frequency approach. The focus will be on placing most stringent constraints on GR and alternative theories in the strong-gravity regime, and on understanding the formation and launching of relativistic jets.
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All authors Venkatessh Ramakrishnan, Violette Impellizzeri, Chi-Kwan Chan, Mariafelicia De Laurentis, Thomas Krichbaum, Andrei Lobanov, Laurent Loinard, Freek Roelofs, Eduardo Ros Hannah R. Stacey

Astrophysics of Galaxies

A Multi-parameter Fuzzy Set Framework for Classifying Red, Blue, and Green Valley Galaxies

Amit Mondal and Biswajit Pandey

We present a data-driven fuzzy set framework for classifying galaxies into the red sequence, blue cloud, and green-valley populations using multiple observables from the Sloan Digital Sky Survey (SDSS DR18). Unlike traditional methods based on hard boundaries in colour or stellar mass, our approach assigns continuous membership degrees using sigmoidal functions derived from bimodal galaxy properties, including $(u-r)$ colour, specific star formation rate (sSFR), and $D4000$. Membership functions are constructed via Gaussian mixture modeling and combined using a conservative fuzzy minimum operator. Applying this method to a volume-limited sample of 88,579 galaxies, we compare with the empirical classification of \citet{schawinski14}. The fuzzy approach reduces contamination in the red and green-valley populations and yields more physically consistent distributions of star formation and morphology. Red galaxies show a unimodal low-sSFR distribution, while green-valley galaxies exhibit clearer signatures of morphological evolution. We also examine the dependence of active galactic nucleus (AGN) fraction on stellar mass and find no significant differences between methods, indicating robust global AGN trends. However, clustering analysis reveals subtle differences: fuzzy-classified red galaxies show enhanced large-scale clustering, suggesting a stronger association with highly biased dark matter halos. These results demonstrate that fuzzy classification provides a flexible, physically motivated alternative to hard-cut methods, enabling a more accurate and interpretable view of galaxy populations and their evolution.
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