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Physics Astrophysics

astro-ph Watch Astrophysics

Friday 20 March

High Energy Astrophysical Phenomena

Early emission characterization of TDE 2025aarm

Andrea Simongini, Maria Kherlakian, Alicia López-Oramas et al. (+2 more)

In this Letter, we present early emission data analysis of the tidal disruption event TDE 2025aarm, including optical, UV and X-ray data. At a redshift of z = 0.01368, TDE 2025aarm is the second closest TDE ever discovered, offering an unprecedented opportunity to study such phenomena in great details. We observed TDE 2025aarm in optical with the Liverpool Telescope for a total of three epochs, and complemented our dataset with ancillary spectroscopic and photometric data. The early optical spectra are characterized by a blue-continuum and helium, hydrogen and possibly Bowen lines typical of H+He events. The optical light curves peak at M_g ~ -18.68 mag and are well described by fallback of a M_star ~ 0.16 M_sun star onto a M_BH ~ 2x10^{7}M_sun black hole. We report Swift-XRT detection in the 0.3-10 keV range, with a total flux of F_X ~ 1.42x10^{-14} erg cm^{-2} s^{-1}, fitted by a black-body with k_BT ~ 0.39 keV. This makes TDE~2025aarm a new event among optical/UV bright TDEs detected in soft X-rays. Our analysis suggests that the early emission from TDE 2025aarm is powered by circularization shocks, and that the delayed accretion scenario best describes the observed features.
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All authors Andrea Simongini, Maria Kherlakian, Alicia López-Oramas, Josefa Becerra, Davide Cerasole

Earth and Planetary Astrophysics · Cross-listed from math.DS

Cislunar State and Uncertainty Propagation via the Modified Generalized Equinoctial Orbital Elements

Maaninee Gupta and Kyle J. DeMars

The complex cislunar dynamical environment poses challenges for spacecraft navigation and Space Domain Awareness (SDA) operations, where the knowledge of current and future spacecraft states is essential. Conventional Gaussian-based approaches for SDA degrade under the nonlinearities that manifest in this regime. To accurately model the underlying dynamics and characterize uncertainty, this work explores the Modified Generalized Equinoctial Orbital Elements under high-fidelity propagation for cislunar applications. The Henze-Zirkler test for multivariate normality is leveraged to evaluate uncertainty evolution across a range of orbits, demonstrating improved preservation of Gaussian behavior in cislunar space.
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Solar and Stellar Astrophysics

Evidence of Long-Lived Powerful Gyrosynchrotron Radio Emission in the Close Binary FF UMa

Ruijie Gao, Jun Yang, Yang Gao et al. (+7 more)

RS Canum Venaticorum (RS CVn) close binaries, characterized by tidal locking, rapid rotations, and strong magnetic fields, are ideal laboratories for high-resolution radio observations to probe emission processes, magnetic field configurations, and interaction activity. Despite their importance, only a few RS CVn sources have been explored by polarimetric observations of very long baseline interferometry (VLBI). To expand the effort, we have analyzed the existing Very Long Baseline Array (VLBA) astrometric data for the RS CVn binary FF Ursae Majoris (FF UMa). In the 5GHz VLBA experiments conducted between 2021 and 2024, both total intensity and circularly polarized emission were clearly detected at six of seven epochs. The consistently high brightness temperatures (10^7 K) and the moderate fractional circular polarization (10%-30%) over about three years indicate that the radio emission is mainly produced by gyrosynchrotron radiation from mildly relativistic electrons in the highly-ordered magnetic field. The radio luminosities are also comparable to those of previously studied powerful RS CVn binaries and show a significant anti-correlation with fractional circular polarization. A mean centroid offset of 13.4 +/- 3.1 solar radii between the Stokes I and V emission was found across multiple epochs, indicating a possible additional contribution from the secondary star via a magnetically active corona, a giant magnetic loop, or significant interaction activity with the primary star in the quiescent state.
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All authors Ruijie Gao, Jun Yang, Yang Gao, Jingdong Zhang, Bo Zhang, Wen Chen, Xiaohui Sun, Guannan Gao, Zhibin Dai, Tobia D. Carozzi

Earth and Planetary Astrophysics

A Century of Radial Velocity and Astrometric Monitoring of 70 Oph AB: New PFS Data and Constraints on Planetary Companions

Yiting Li, Michael R. Meyer, Skylar D'Angiolillo et al. (+29 more)

At a distance of 5.1 pc, the 70 Oph AB binary star system is one of the most favorable targets for future direct imaging and astrometry missions surveying mature, terrestrial planets. We present new radial velocities (RVs) obtained with the Planet Finder Spectrograph (PFS) on the 6.5\,m Magellan II Clay Telescope in Chile. We collected 499 measurements of 70 Oph A and 334 measurements of 70 Oph B during 2023–2025. Combining these data with decades of archival RVs and astrometry, we derive an updated orbital solution for the binary and dynamical masses of $0.88 \pm 0.004\,M_\odot$ and $0.73 \pm 0.003\,M_\odot$ for the primary and secondary components, respectively. We find that the long-term RV variability of both components is consistent with stellar activity modulated by rotation periods, and we detect no coherent planetary signals in either component. We place upper limits on any planets orbiting in the plane of the binary. The 27 yr RV baseline for 70 Oph A excludes Jupiter-mass planets interior to 5 au and reaches a sensitivity of $0.3\,M_{\rm Jup}$ at 1 au or $0.5\,M_{\rm Jup}$ at 2 au. For 70 Oph B, with PFS data we rule out planets more massive than $0.25$–$0.3\,M_{\rm Jup}$ inside 0.5 au. We show that stable S-type orbits around 70 Oph A extend to $\sim2.5$ au, covering the habitable zone. Thus, Saturn-mass planets or smaller on stable orbits in the habitable zone of 70 Oph A are allowed. Overall, our results provide important guidance for future planet searches around this stellar system.
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All authors Yiting Li, Michael R. Meyer, Skylar D'Angiolillo, Stephen R. Kane, R. Paul Butler, Stephen A. Shectman, Eric E. Mamajek, Johanna Teske, Jack Lubin, Paul Robertson, Jessie L. Christiansen, Howard Isaacson, Caleb K. Harada, Bradford Holden, William D. Cochran, Michael Endl, Jennifer Burt, Juliette Becker, Alyssa Jankowski, Peter Tuthill, Catherine A. Clark, Rachael M. Roettenbacher, Eric Nielsen, Eduardo Bendek, Armen Tokadjian, William Roberson, Kaitlin M. Kratter, Edwin Bergin, Dave Osip, Jeffrey D. Crane, Alex Davis, Gautam Vasisht

Earth and Planetary Astrophysics

Retrieving the Red Edge on Earth-like Planets with Heterogeneous Clouds and Surfaces

Zachary Burr, Mario Damiano, Vincent Kofman et al. (+2 more)

The detection and characterization of potentially habitable exoplanets is one of the chief goals of astrophysics for the coming decades. Imaging in reflected light is well suited for characterizing Earth-like planets, as much can be learned about these planets in this wavelength range (i.e., ~0.3-2 {\mu}m). Several studies have been conducted to determine the abilities and limitations of reflectance spectroscopy, but most previous studies assumed a homogeneous atmospheric and surface composition. Here we investigate how heterogeneities in the atmosphere and surface of an Earth-like planet impact retrieval results. We extend the ExoReL retrieval framework to include a step function for retrieving wavelength varying surface albedo. We then use it to retrieve on visible-to-near-infrared spectra of realistic 3D Earth models with different surface features in view and varying cloud types/distributions synthesized with the Planetary Spectrum Generator. Including the ability to fit for wavelength dependent albedo mitigates degeneracies that arise when using 1D models to analyze 3D planets, and we recover an Earth-like planet in all cases. We detect surface albedo steps at ~0.7 and ~1.1 {\mu}m despite clouds, both when significant lands are in view and when the spectra are averaged to account for a longer integration time. Our findings support the application of the vegetation red edge as a biosignature in the context of the Habitable Worlds Observatory. This study highlights the importance of considering a range of-particularly wavelength-dependent-surface albedos when using reflectance spectroscopy to characterize Earth-like exoplanets.
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All authors Zachary Burr, Mario Damiano, Vincent Kofman, Renyu Hu, Geronimo L. Villanueva

Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph

Can QCD Axions Survive the Cosmological Constant Problem?

Carsten van de Bruck, C.P. Burgess and Adam Smith

Mechanisms that dynamically relax the vacuum energy offer a concrete way to approach the cosmological constant problem, but because relaxation is not confined to the vacuum energy alone it can have consequences for the rest of low-energy physics. We explore this issue using the recently proposed 'yoga' relaxation models as an explicit framework and show how relaxation differentially suppresses 'slow' physics relative to a characteristic timescale set by the mass of the relaxon. It therefore need not alter e.g. Higgs & collider physics but can dramatically change how light scalar fields participate in cosmology. We revisit the QCD axion in this setting and show that the suppression of the axion's vacuum potential reshapes its behaviour on cosmological timescales while leaving fast, high-energy processes unaffected. The result is to alter the axion mass-coupling relation away from the standard QCD band, driving it into a regime already ruled out by observational constraints. In particular, suppression of the vacuum axion potential allows the QCD matter-induced potential to dominate even for matter densities relevant to cosmology and everyday matter, potentially driving the axion away from the CP-conserving minimum for QCD-motivated parameters. We conclude that conventional QCD axions are unlikely to remain viable in their standard form within vacuum-energy relaxation frameworks.
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Astrophysics of Galaxies

Unveiling large-scale rotational motions in the intragroup medium at z~1 through gravitational-arc tomography

Cédric Ledoux, Fernanda Muñoz-Olivares, L. Felipe Barrientos et al. (+8 more)

We present the first spatially resolved characterisation of the cool intragroup medium (IGrM) in a spectroscopically confirmed galaxy group at z=1.167. Using 30 independent sightlines towards the gravitationally lensed galaxy SGAS J0033+02, we combine background light from an extended gravitational arc and various sources in the field to map the distribution and kinematics of diffuse, metal-enriched gas pertaining to the group. We detect prominent MgII, FeII, CaII, and MgI absorption extending up to 62 kpc from a massive star-forming spiral galaxy and its interacting companion. Together with four other members, these form a compact group with a virial radius of 313 kpc. Down-the-barrel, blueshifted absorption indicates outflows. The distribution and two-dimensional kinematics of this gas suggest the influence of tidal stripping and star formation-driven winds. Intervening absorption across the field partly traces internal galaxy motions. A simple superposition of individual discs cannot reproduce the velocity field at large impact parameters or in counter-rotating regions, while a global IGrM halo with a rotational velocity of ~130 km/s provides a good match. Beyond individual galaxy envelopes, the data are consistent with a group-scale structure that co-rotates in concert with the galaxies. Assuming dynamical equilibrium, we estimate a total (cool+warm+hot) gas mass of 1.3-2.5x10^11 Msol, with large systematic uncertainties, corresponding to approximately 50% of all baryons, within one-quarter of the group's virial radius. These results point to a multiphase IGrM in which cool (~10^4 K) clouds are embedded within a dynamically coherent, group-wide halo. The gas appears gravitationally bound to the group rather than reaccreting onto individual galaxies.
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All authors Cédric Ledoux, Fernanda Muñoz-Olivares, L. Felipe Barrientos, Nicolas Tejos, Trystyn Berg, Felipe Corro-Guerra, Evelyn Johnston, Guillaume Mahler, Jorge González-López, Joaquín Hernández-Guajardo, Pasquier Noterdaeme

Earth and Planetary Astrophysics

Three-body Mean Motion Resonance Chains as a Delivery Mechanism for White Dwarf Pollution

Jeremy Wood Natalie Cummins

In this work, we used numerical integration of the 4-body problem to study 3-body resonance chains (two planets and an asteroid in the innermost orbit) as a possible mechanism for white dwarf pollution. Two 3-body resonance chains were selected for study: the 6:3:2 and the 4:2:1. Asteroids in both a dynamically colder initial orbit in the 6:3:2 resonance and hotter initial orbits in both resonances were studied. An asteroid had up to a 1.08% chance of being delivered to the stellar Roche Limit of the white dwarf. This probability was strongly linearly correlated with the mass of the inner planet but was not correlated with the mass of the outer planet for both colder and hotter orbits. Average dynamical lifetimes ranged from 23 kyr to 1137 kyr for the dynamically colder orbit and from 12.9 kyr to 89.2 kyr and 10.8 kyr to 793.4 kyr for the dynamically hotter orbits in the 6:3:2 and 4:2:1 resonances, respectively. Average dynamical lifetime was exponentially anticorrelated with the outer planet mass and usually with the inner planet mass except in one case. The hotter 4:2:1 resonance delivered 1.1 times more asteroids to the stellar Roche Limit than the hotter 6:3:2 resonance. The hotter 6:3:2 resonance delivered 1.2 times more asteroids to the stellar Roche Limit than the colder 6:3:2 resonance. A typical accretion rate for a white dwarf star of 10^8 grams s^-1 could be explained by the accretion of an equivalent mass of one of our simulated asteroids every 13.8 Myr.
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Instrumentation and Methods for Astrophysics

Monte Carlo conformal prediction for quantifying uncertainty in radio galaxy classification under ambiguous ground truth

Alex Walls, James Barry, Devina Mohan et al. (+1 more)

Dramatically increasing data volumes are forcing astronomers to adopt automated methods for the identification and classification of astronomical objects. Although deep-learning models are often well-suited to this task, obtaining a measure of uncertainty on their predictions is challenging. Here we consider the suitability of Monte Carlo conformal prediction (MCCP) set size and confidence as measures of model uncertainty for the astronomical classification of radio galaxies. We demonstrate this approach using model predictions from a pre-trained radio galaxy foundation model, fine-tuned on a smaller set of labelled radio galaxies. We calibrate the MCCP by obtaining annotator-derived soft label distributions, i.e. probability distributions over classes instead of single class assignments, for each of these labelled radio galaxies and compare the resulting set sizes and confidence scores to predictive entropy measures for each galaxy obtained using a supervised Bayesian deep-learning model trained using Hamiltonian Monte Carlo (HMC). The comparison reveals only a weak correlation between the measures.
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All authors Alex Walls, James Barry, Devina Mohan, Anna M. M. Scaife

Solar and Stellar Astrophysics

High-resolution mid-IR spectroscopy of SVS 13-A with EXES/SOFIA: The surprisingly high CH$_3$OH/H$_2$O ratio in the planet-forming zone of a solar mass protostar

Curtis DeWitt, Marta De Simone, Eleonora Bianchi et al. (+8 more)

Water and methanol are key components of interstellar ices and gas in star- and planet-forming regions, but direct observations of water in low-mass protostars are challenging due to atmospheric absorption. We present high-resolution (R = 70,500) mid-infrared spectroscopy of the Class I protostar SVS13-A with EXES on board SOFIA at 26 $\mu$m, targeting both H$_2$O and CH$_3$OH absorption lines. Several lines of each species are detected, tracing warm gas with rotational temperatures of $\sim$140–170 K. Remarkably, the methanol column density is a factor of $\sim$4 higher than that of water, well above typical interstellar ice ratios ($<$10%). Comparison with previous millimeter observations indicates that absorption and emission probe distinct regions, with the mid-IR lines likely tracing cooler gas along the line of sight. The surprising observed CH$_3$OH/H$_2$O ratio may reflect selective sublimation due to the distribution of binding energies or ice stratification in the inner envelope. These observations probe the inner regions of the protostar, where planets are expected to form and inherit the chemical composition of their natal environment, providing a direct link between ice sublimation and gas-phase chemistry. Our results represent the first high-spectral-resolution mid-infrared view of both water and methanol toward a low-mass protostar, offering a unique window into the chemical composition of the innermost envelope and planet-forming region, and highlighting the diagnostic power of high-resolution mid-infrared spectroscopy to uncover hidden chemical layers and the ice-to-gas transition in embedded protostars.
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All authors Curtis DeWitt, Marta De Simone, Eleonora Bianchi, Cecilia Ceccarelli, Claudio Codella, Sarah Nickerson, Keeyoon Sung, Albert Rimola, Vittorio Bariosco, Piero Uliengo, Naseem Rangwala

Earth and Planetary Astrophysics

The Arc in the DX Cha Circumbinary System: Evidence For a Retrograde Circumbinary Disk

Cheng Chen, Daniela Paz Iglesias, James M. Miley et al. (+1 more)

Observations of the binary system DX Cha (HD 104237) reveal a compact, asymmetric ring structure with a radius of 0.43\,au. This ring is just outside the binary orbit, which has semi-major axis $a_{\rm b} = 0.22$\,au and eccentricity $e_{\rm b} = 0.665$; placing the ring at $\approx 1.2$ times the binary apocenter distance. The inner regions of circumbinary disks, $\approx 2-3\,a_{\rm b}$, are typically evacuated by strong gravitational torques from the binary, resulting in a deep gap between the binary and the disk. Accordingly, previous numerical simulations of DX Cha have found an eccentric inner cavity with almost no material inside $\approx 1$\,au, and we find similar results when making the same assumption that the circumbinary disk orbits in the same direction as the binary. However, the disk can exist much closer to the binary if it is retrograde. For DX Cha we find that the inner edge of a retrograde disk occurs at $\approx 2a_{\rm b}$, and moreover takes the form of one or two arcs, in agreement with observations. We therefore suggest that the circumbinary disk in the DX Cha system could be orbiting retrograde to the binary star system in the center. We conclude that compact circumbinary disks observed in young stellar systems are important targets for future observations; if the disks are prograde then their properties are likely to be significantly different from current estimates, while if they are retrograde then this will have profound implications for our understanding of star and planet formation.
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All authors Cheng Chen, Daniela Paz Iglesias, James M. Miley, C.J. Nixon

Earth and Planetary Astrophysics

Observations of Exocomets

Judith Korth, Azib Norazman, Raphäel Bendahan-West et al. (+6 more)

Active small bodies in extrasolar systems, the extrasolar analogues of Solar System comets, provide insights into the orbital evolution and physical processes shaping planetary systems. Since the discovery of exocomets around $\beta$ Pictoris, these small, icy bodies have shown the potential to become key probes for understanding planetary formation and migration. This review presents an overview of current observational techniques used to detect exocomets, focusing on individual systems and large-scale searches. We discuss photometric methods that identify exocomet transits through asymmetric light curves and spectroscopic techniques revealing cometary gases via time-variable absorption lines. Despite progress, significant open questions remain regarding the physical properties, occurrence rates, and similarities between exocomets and their Solar System counterparts. This review explores future opportunities in observational exocomet research, highlighting advancements required to further our understanding of these active small bodies and their role in the context of planetary system evolution.
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All authors Judith Korth, Azib Norazman, Raphäel Bendahan-West, Grant Kennedy, Cristina Madurga Favieres, Daniela Iglesias, Olena Shubina, Siyi Xu, Nathan X. Roth

Solar and Stellar Astrophysics

Connection-angle dependence of proton anisotropy in ground-level enhancement events

Alessandro Bruno and Silvia Dalla

Ground Level Enhancements (GLEs) probe the earliest, highest-energy solar energetic particles and thus provide a unique window onto particle release and transport from the low corona to 1 AU. We present a uniform, event-resolved analysis of the early anisotropy for ten well-observed GLEs, combining consistently reconstructed neutron-monitor pitch-angle distributions (PADs) with Parker-spiral footpoint mapping. We find a clear, monotonic decline of initial anisotropy with increasing magnetic connection angle: well-connected events exhibit strong, persistent forward-directed beams, while poorly connected events show systematically weaker and more rapidly decaying anisotropies. This relationship holds across a wide range of flare classes and CME speeds, demonstrating that magnetic connectivity and interplanetary transport, rather than eruption magnitude, dominate the directional properties of the earliest relativistic arrivals at Earth. A principal component analysis was applied to time-resolved spectral and angular parameters to separate source-driven changes from transport effects. By explicitly identifying and removing secondary sunward (back-scattered) components-attributable to scattering and reflection from solar-wind structures and transient interplanetary features-from the PAD fits, we isolate the intrinsic relaxation of the primary forward beam and show that apparent departures from simple exponential decay are frequently attributable to reflected or delayed populations rather than prolonged source injection. The empirical anisotropy–connection-angle relation reported here provides an event-resolved, quantitative benchmark that constrains focused-transport and shock-acceleration models and offers immediate operational value: rapid footpoint estimates can meaningfully limit expected initial beaming and directional radiation risk.
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High Energy Astrophysical Phenomena

High-energy neutrino flux from SN2024ggi: constraints from semi-analytic modeling of its post-explosive emission

M. Buccheri, S. P. Cosentino and M. L. Pumo

Hydrogen-rich supernovae can efficiently accelerate particles when the expanding ejecta interact with the surrounding circumstellar medium (CSM), producing high-energy (TeV–PeV) neutrinos. In this work we investigate the nearby SN~2024ggi, whose proximity and clear signatures of ejecta–CSM interaction make it a promising candidate for studying high-energy ($\nu$) emission. We apply a new semi-analytical model that consistently links the electromagnetic and neutrino emission components, allowing us to constrain the main explosion parameters, including the kinetic energy, ejecta mass, progenitor radius, and nickel yield. The predicted high-energy ($\nu$) fluence at Earth peaks at TeV energies and remains below the sensitivity of current detectors. However, the modeling establishes a robust framework for interpreting future signals from nearby interacting supernovae and fine-tuning observational strategies for next-generation multi-messenger facilities such as IceCube-Gen2 and KM3NeT/ARCA.
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Cosmology and Nongalactic Astrophysics

On the cosmology dependence of the cluster weak-lensing mass bias

S. Bocquet, A. Fumagalli, C. T. Davies et al. (+3 more)

Measurements of the shear induced by weak gravitational lensing around galaxy cluster lines of sight are the gold standard for calibrating cluster observable-mass relations, thereby enabling a robust and precise inference of cosmological parameters. The weak-lensing mass bias is the systematic offset between the true halo mass and the mass that is inferred from the lensing data using an imperfect model for the halo mass distribution. We study the impact of cosmology on the lensing mass bias to inform future cosmological analyses of galaxy clusters. We create synthetic lensing shear maps for 115,920 projections of clusters with $M_{200\mathrm c}>1.56\times10^{14}\,h^{-1}M_\odot$ in a suite of Magneticum simulations. The simulation boxes are $896\,h^{-1}$Mpc on a side and are set up with 15 different combinations of the cosmological parameters $\Omega_\mathrm{m}$, $\Omega_\mathrm{b}$, $\sigma_8$, and $H_0$. Assuming a Navarro-Frenk-White profile, we extract weak-lensing mass measurements and quantify their bias $b_\mathrm{WL}$ with respect to the true halo mass. To investigate the impact of baryonic effects, we perform the analysis on gravity-only simulations and on their full-physics hydrodynamical counterparts. We confirm that assuming a fixed halo concentration or a fixed concentration-mass relation leads to cosmology-dependent changes of the mass bias. We report changes of up to $\Delta\ln b_\mathrm{WL}=0.030$ with respect to the bias obtained at the fiducial WMAP7 cosmology. Adopting a model for the concentration that also depends on cosmology absorbs the changes in halo profiles and we recover essentially constant values for the mass bias. Our analysis of hydrodynamical simulations suggests that future, more accurate models will also need to explicitly account for the strength of baryonic effects.
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All authors S. Bocquet, A. Fumagalli, C. T. Davies, K. Dolag, S. Grandis, J. J. Mohr

High Energy Astrophysical Phenomena

VHE gamma-ray intranight variability from BL Lacertae during the extreme flaring state of 2022

K. Abe, S. Abe, A. Abhishek et al. (+297 more)

BL Lacertae (BL Lac), the archetypal blazar of its subclass and one of the most studied blazars in the last decades, has undergone a series of major multi-wavelength outbursts since 2020, resulting in its highest recorded $\gamma$-ray flare to date between September and November 2022 together with those from August 2021 and October 2024. We characterised the $\gamma$-ray and multi-wavelength emission and spectral energy distribution (SED) of BL Lac, as well as their evolution during the major and extended $\gamma$-ray and multi-wavelength flare that occurred between September and November 2022. We evaluated the variability of the flare, focusing on the nights of October 20 and November 13, when clear intranight very-high-energy (VHE, $E>100$ GeV) $\gamma$-ray variability was observed. We modelled the $\gamma$-ray and broadband SEDs during periods of stable emission identified with a Bayesian block analysis and interpreted the flare's evolution in terms of the variability in the relativistic particles and the jet's physical parameters. The VHE emission shows an average flux of 0.23 Crab Units (C.U.) above 200 GeV and a variability amplitude of more than a factor ten. We observe intranight flux-doubling variations as fast as $\sim$8 minutes during the nights of October 20 and November 13, 2022 with maximum fluxes of 4.4 C.U. above 100 GeV and 2.8 C.U. above 200 GeV. The spectral analysis reveals a transition of the X-ray emission from the high- to the low-energy SED peak and a shift of the $\gamma$-ray peak towards higher energies. We interpret the broadband emission within a leptonic two-zone model in which intranight variability is explained as magnetic reconnection in a compact region closely oriented with the line of sight while variations in the relativistic electron distributions and the injection of freshly accelerated particles explain the weekly scale variations.
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All authors K. Abe, S. Abe, A. Abhishek, F. Acero, A. Aguasca-Cabot, I. Agudo, C. Alispach, D. Ambrosino, F. Ambrosino, L. A. Antonelli, C. Aramo, A. Arbet-Engels, C. Arcaro, T. T. H. Arnesen, P. Aubert, A. Baktash, M. Balbo, A. Bamba, A. Baquero Larriva, U. Barres de Almeida, J. A. Barrio, L. Barrios Jiménez, I. Batkovic, J. Baxter, J. Becerra González, J. Bernete, A. Berti, E. Bissaldi, O. Blanch, G. Bonnoli, P. Bordas, A. Briscioli, G. Brunelli, J. Buces, A. Bulgarelli, I. Burelli, L. Burmistrov, M. Cardillo, S. Caroff, A. Carosi, R. Carraro, F. Cassol, D. Cerasole, A. Cerviño Cortínez, Y. Chai, G. Chon, L. Chytka, G. M. Cicciari, J. L. Contreras, J. Cortina, H. Costantini, M. Croisonnier, M. Dalchenko, G. D'Amico, P. Da Vela, F. Dazzi, A. De Angelis, M. de Bony de Lavergne, R. Del Burgo, C. Delgado, J. Delgado Mengual, D. della Volpe, B. De Lotto, L. Del Peral, R. de Menezes, G. De Palma, V. de Souza, C. Díaz, L. Di Bella, A. Di Piano, F. Di Pierro, R. Di Tria, L. Di Venere, D. Dominis Prester, A. Donini, D. Dorner, L. Eisenberger, D. Elsässer, G. Emery, L. Feligioni, F. Ferrarotto, A. Fiasson, L. Foffano, Y. Fukazawa, S. Gallozzi, R. Garcia López, S. Garcia Soto, C. Gasbarra, D. Gasparrini, J. Giesbrecht Paiva, N. Giglietto, F. Giordano, N. Godinovic, T. Gradetzke, R. Grau, J. Green, G. Grolleron, S. Gunji, P. Günther, J. Hackfeld, D. Hadasch, M. Hashizume, T. Hassan, K. Hayashi, L. Heckmann, M. Heller, J. Herrera Llorente, N. Hiroshima, D. Hoffmann, D. Horns, J. Houles, D. Hrupec, R. Imazawa, T. Inada, S. Inoue, K. Ioka, M. Iori, T. Itokawa, A. Iuliano, J. Jahanvi, I. Jimenez Martinez, J. Jimenez Quiles, I. Jorge Rodrigo, J. Jurysek, M. Kagaya, V. Karas, H. Katagiri, D. Kerszberg, T. Kiyomoto, Y. Kobayashi, K. Kohri, P. Kornecki, H. Kubo, J. Kushida, B. Lacave, M. Lainez, A. Lamastra, L. Lemoigne, M. Linhoff, S. Lombardi, F. Longo, R. López-Coto, A. López-Oramas, S. Loporchio, J. Lozano Bahilo, F. Lucarelli, H. Luciani, P. L. Luque-Escamilla, M. Makariev, M. Mallamaci, D. Mandat, K. Mannheim, F. Marini, M. Mariotti, P. Marquez, G. Marsella, J. Martí, O. Martinez, G. Martínez, M. Martínez, M. Massa, D. Mazin, J. Méndez-Gallego, S. Menon, E. Mestre Guillen, D. Miceli, T. Miener, J. M. Miranda, M. Molero Gonzalez, E. Molina, T. Montaruli, A. Moralejo, A. Morselli, V. Moya, A. L. Müller, H. Muraishi, S. Nagataki, T. Nakamori, A. Neronov, D. Nieto Castaño, M. Nievas Rosillo, L. Nikolic, K. Noda, V. Novotny, S. Nozaki, M. Ohishi, Y. Ohtani, A. Okumura, R. Orito, L. Orsini, J. Otero-Santos, P. Ottanelli, M. Palatiello, G. Panebianco, D. Paneque, R. Paoletti, J. M. Paredes, M. Pech, M. Pecimotika, M. Peresano, F. Perrotta, F. Pfeifle, M. Pihet, G. Pirola, C. Plard, F. Podobnik, M. Polo, C. Pozo-Gonzaléz, E. Prandini, S. Rainò, R. Rando, W. Rhode, M. Ribó, G. Rodriguez Fernandez, M. D. Rodríguez Frías, A. Roy, A. Ruina, E. Ruiz-Velasco, T. Saito, S. Sakurai, D. A. Sanchez, H. Sano, E. Santos Moura, T. Šarić, Y. Sato, F. G. Saturni, V. Savchenko, F. Schiavone, F. Schussler, T. Schweizer, M. Seglar Arroyo, G. Silvestri, A. Simongini, J. Sitarek, V. Sliusar, I. Sofia, J. Strišković, M. Strzys, Y. Suda, A. Sunny, H. Tajima, M. Takahashi, R. Takeishi, S. J. Tanaka, D. Tateishi, T. Tavernier, P. Temnikov, Y. Terada, K. Terauchi, T. Terzic, M. Teshima, M. Tluczykont, T. Tomura, D. F. Torres, F. Tramonti, P. Travnicek, G. Tripodo, A. Tutone, M. Vacula, M. Vázquez Acosta, G. Verna, I. Viale, A. Viana, A. Vigliano, C. F. Vigorito, E. Visentin, V. Vitale, G. Voutsinas, I. Vovk, T. Vuillaume, R. Walter, T. Yamamoto, R. Yamazaki, Y. Yao, T. Yoshida, T. Yoshikoshi, W. Zhang, N. Zywucka, the CTAO-LST collaboration, F. Aceituno, J. A. Acosta-Pulido, V. Casanova, J. Escudero Pedrosa, V. Fallah Ramazani, J. Jormanainen, S. Jorstad, G. Keating, P. M. Kouch, M. Gurwell, A. Lähteenmäki, E. Lindfors, A. Marscher, D. Morcuende, I. Myserlis, K. Nilsson, C. A. Ortega Hunter, R. Rao, A. Sota, M. Tornikoski, H. Zhang

High Energy Astrophysical Phenomena

A Complete X-ray View of Supernova Remnant W28 with Einstein Probe: Spatial Distribution of Parameters and Origin of the Thermal-Composite Morphology

Yi-Heng Chi, Ping Zhou, Yang Chen et al. (+6 more)

It has been an unsolved question what leads a supernova remnant (SNR) to a thermal composite rather than a typical shell-like morphology, and what causes recombining plasma inside it. With the 13-ks observation of the Following-up X-ray Telescope onboard the Einstein Probe, we give an overall X-ray picture of W28, one of the prototypical thermal composite SNRs. The observation revealed a shell-like structure west of W28 in radio, optical, and X-ray images, which may revise the known extent of the SNR to $72'\times45'$. Spectral analysis explicitly maps that the special relationship where the plasma experiences recombination in the interior of the remnant, spatially coincident with H$\alpha$ emissions, while in the other regions, the plasma is ionization-dominated. We found that W28 is generally isobaric from its center to the newly discovered shell, and it is even isothermal with a temperature of $\sim0.6$-0.7 keV in the center before the cooling of the plasma. Saturated thermal conduction and cloud evaporation may cool down the plasma within $\sim3$ kyr, the estimated recombination timescale. We revised the SNR dynamical age to $\sim8$ kyr, much younger than previous estimates. The complex structure and complex ionization state distribution may suggest that centrally filled and shell-like morphologies coexist in W28. This state may depend on the environment in which the SNR evolves.
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All authors Yi-Heng Chi, Ping Zhou, Yang Chen, Lei Sun, Chengkui Li, Shumei Jia, Yong Chen, Chong Ge, Weimin Yuan

Solar and Stellar Astrophysics

Constraints on the $^{12}$C$(\alpha, \gamma)^{16}$O and $^{16}$O+$^{16}$O Reaction Rates from Binary Black Holes Detected via Gravitational Wave Signals

Wenyu Xin, Xiaokun Hou, Xianfei Zhang et al. (+2 more)

Gravitational-wave observations of binary black hole (BH) mergers provide a novel avenue for testing massive-star evolution and the resulting BH mass spectrum. Recent population analyses under the hierarchical-merger hypothesis have offered evidence for the BH mass gap and inferred its lower edge to $\sim 44 - 68$ M$_\odot$. Motivated by these findings, we compute low-metallicity ($Z=10^{-5}$) helium star models with MESA and systematically explore the effect of uncertainties in the $^{12}$C$(\alpha, \gamma)^{16}$O and $^{16}$O+$^{16}$O reaction rates on the final fate. Varying the $^{12}$C$(\alpha, \gamma)^{16}$O reaction rate by $-3 \sigma$ to $+3\sigma$, we find that the predicted BH mass gap shifts from $\sim104 - 184$ M$_\odot$ to $\sim45 - 135$ M$_\odot$. In contrast, scaling the $^{16}$O+$^{16}$O reaction rate by global factors of 0.1, 1, and 10 has only a modest effect on the lower edge of the BH mass gap (less than 5 M$_\odot$), and shifts the upper edge by more than 10 M$_\odot$. Using the predictions of our models together with the literature estimates for the lower edge of the BH mass gap, we constrain the astrophysical S factor of $^{12}$C$(\alpha, \gamma)^{16}$O reaction at 300 keV of $S_{300} \simeq$ 137.6 - 263.4 keV barn.
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All authors Wenyu Xin, Xiaokun Hou, Xianfei Zhang, Shaolan Bi, Gang Zhao

Cosmology and Nongalactic Astrophysics

Quasar photometric redshifts beyond the spectroscopic coverage: Uncertainty models and redshift distributions in the Kilo-Degree Survey DR5

Kacper Drabicki, Szymon J. Nakoneczny and Maciej Bilicki

Photometric redshifts (photo-$z$) and their distributions underpin cosmology with photometric quasars, tracers in angular clustering and cross-correlations. Progress requires trustworthy uncertainties, especially beyond the spectroscopic training set. We compare how machine-learning frameworks estimate quasar photo-$z$ uncertainties and reconstruct the redshift distribution $n(z)$ under controlled data-quality shifts. Using Kilo-Degree Survey DR5 photometry and DESI DR1 spectroscopic quasars, we train artificial neural networks (ANNs), Mixture Density Networks (MDNs) and Bayesian Neural Networks (BNNs) with Gaussian-mixture outputs, plus a self-organizing map (SOM) as a direct $n(z)$ estimator. We evaluate them on four subsets, with and without magnitude extrapolation and missing bands, through the negative log-likelihood, probability integral transform, point-estimate accuracy and the bias of binned $n(z)$ moments; degeneracies are sought by clustering the predicted PDFs. At least two mixture components are essential: a single Gaussian is miscalibrated and produces more catastrophic outliers than the ANN. No model performs best everywhere. On well-covered data the five-component MDN, three-component BNN and SOM reconstruct $n(z)$ almost perfectly; under faint extrapolation the BNN gives the best likelihoods, while in the hardest faint-plus-missing regime the single Gaussian becomes the best-calibrated. For point estimates and tomographic binning, uncertainty models outperform the ANN, while the SOM fails out-of-distribution. PDF clustering exposes distinct colour-redshift degeneracies likely to grow for fainter samples. The best model is thus regime- and application-dependent: multi-component MDNs or BNNs are needed for clean binning and are the only intrinsically calibrated choice on a well-covered golden sample, a first step towards a full comparison of quasar photo-$z$ pipelines.
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High Energy Astrophysical Phenomena · Cross-listed from nucl-th

A dual description of quarks and baryons: Quarkyonic matter within a relativistic quark model

Tsuyoshi Miyatsu, Myung-Ki Cheoun and Koichi Saito

We investigate quarkyonic matter within a relativistic quark model by combining the dual quarkyonic picture with the quark-meson coupling (QMC) model. Using relativistic gaussian quark wavefunctions for the nucleon, we construct the quarkyonic QMC (QQMC) model and study the properties of symmetric nuclear matter and pure neutron matter. We find that the quark saturation density depends sensitively on the nucleon size parameter and that nuclear interactions quantitatively modify the high-density behavior of the equation of state (EoS) and the sound velocity. In particular, the QQMC model yields an earlier onset of quark saturation than the noninteracting gaussian quarkyonic (GQ) model, indicating that nuclear interactions enhance the stiffening of the EoS in the quarkyonic regime.
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High Energy Astrophysical Phenomena

The characteristics of variability of AGNs based on the structure function

Xuan Wei, Jie Tang and Yu Tao

Variability is one of the classic features of active galactic nuclei (AGNs). The normalized structure function was applied to distinguish variability samples from OVRO, ASAS-SN and Fermi. A power-law function model was selected to fit the structure functions of samples of three bands. We present the available samples of three bands, and by integrating two parameters, we obtain ideal discrimination results for three bands. Meanwhile, the differences between BL Lacs and FSRQs of Fermi and non-Fermi samples are well verified. The results show that the improved structure function can effectively distinguish samples of radio, optical, and gamma-ray. Additionally, BL Lacs and FSRQs in both Fermi and non-Fermi samples can be distinguished. The conclusion obtained through the distinction of structural functions in different bands supports that the variability in the three bands are caused by different physical mechanisms respectively: the samples in the optical band are radio quiet AGNs, and their variability is mainly caused by the fluctuations of the accretion disk, and the samples of radio band and gamma-ray band are radio loud AGNs whose variability is mainly caused by relativistic jet radiation. This conclusion conforms to the unified standard interpretation of variability about AGNs. Using these two parameters, we verify that there is no fundamental difference between Fermi and non-Fermi BL Lacs, while significant differences exist between FSRQs. However, the power exponent of the two can well distinguish BL Lacs.
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Cosmology and Nongalactic Astrophysics

Recovery of 21 cm BAO: a configuration-space correlation function analysis

Zhongyue Zhang, Kwan Chuen Chan, Santiago Avila et al. (+1 more)

Intensity mapping (IM) represents an innovative and potent probe to cosmology. One of its prime applications is to measure the Baryonic Acoustic Oscillations (BAO) in the late universe. We study the BAO measurement by IM in configuration space using simulations, focusing on the impact of the telescope beam and foreground removal effects, which are modeled by a Gaussian beam and radial power suppression, respectively. Three types of correlation functions are applied to measure BAO, including the radial correlation function, multipole correlation function, and wedge correlation function. We check our pipeline against a set of IM mock catalogs, finding good agreement with the numerical results. We use the mock catalogs to look for the parameter choices that optimize the BAO constraint for the correlation function estimators. With the optimal settings, our pipeline is utilized to forecast the BAO constraint for the 21 cm IM experiments: BINGO, MeerKAT, and SKA-mid. Despite our simple beam and foreground removal effect treatments, our analyses could offer a useful guide to strengthen the constraining power of these experiments. We find that for the low-redshift experiments BINGO and MeerKAT, the wedge correlation function achieves the tightest constraint for both the transverse and radial BAO. For SKA-mid, the radial correlation function and multipole correlation function deliver the tightest constraint for the radial and transverse BAO, respectively.
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All authors Zhongyue Zhang, Kwan Chuen Chan, Santiago Avila, Bernhard Vos-Gines

Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc

Casimir-Induced Quintessence in Dark Dimension

Tomoki Katayama, Hiroki Matsui, Yuri Michinobu et al. (+3 more)

We investigate a concrete realization of the Dark Dimension scenario, where a single large extra dimension is set at sub-millimeter scales. In this framework, the Casimir energy of bulk fields accounts for the observed dark energy. Working in a 5-dimensional setup with the Standard Model confined to a 4-dimensional brane, we derive the effective action for the radion. We demonstrate that a minimal model comprising only gravity and three right-handed bulk neutrinos typically yields a negative radion potential. To realize a positive vacuum energy, we consider some extensions with additional bulk degrees of freedom. These extensions generate a sufficiently flat positive potential that allows the radion to behave as a quintessence field, evolving slowly at the sub-eV scale. Finally, we analyze the evolution of the dark-energy equation-of-state parameter and show that our model is consistent with recent DESI BAO measurements, including the distance ratios $D_H/r_d$ and $D_M/r_d$.
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All authors Tomoki Katayama, Hiroki Matsui, Yuri Michinobu, Fumiya Okamatsu, Yutaka Sakamura, Takahiro Terada

Solar and Stellar Astrophysics

The dusty envelopes of asymptotic giant branch stars with ultraviolet excesses

Jaime Alonso-Hernández, Carmen Sánchez Contreras, Raghvendra Sahai et al. (+1 more)

Aims. In a first study, we characterised the properties of the gas component in the circumstellar envelopes surrounding a sample of 29 AGB stars with UV excesses. Now we intend to complement this information with an analysis of the dust component and compare the estimated parameters with those previously inferred from larger samples of AGB stars. Methods. We modelled the spectral energy distributions of the sample using dust radiative transfer models. In some cases, we complemented the analysis with Herschel/PACS radial surface brightness profiles. Results. We derived mass-loss rates and gas-to-dust ratios, which are in the typical ranges for AGB stars. We found that the stellar and mass-loss parameters follow similar trends than those presented in the literature. There is an anticorrelation between the gas-to-dust ratio and the UV emission, although it is weaker than its correlations with pulsation and mass-loss. We also estimated the dust attenuation produced by the dust at UV wavelengths and describe its effects on the intrinsic UV emission. Conclusions. Stellar and mass-loss parameters of UV emitting AGB stars follow similar trends as found for larger samples of AGB stars. High-angular resolution observations are required to explore the dust forming regions and identify the presence of stellar companions. Circumstellar dust attenuation might play a dominant role in the observed UV emission, and needs to be accounted to estimate the intrinsic UV emission.
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All authors Jaime Alonso-Hernández, Carmen Sánchez Contreras, Raghvendra Sahai, Jorge Sanz-Forcada

Earth and Planetary Astrophysics

Three outstanding physical questions for K2-18 b and other temperate sub-Neptunes

Shang-Min Tsai, Piero Ferrari, Mats Kuipers et al. (+7 more)

Recent transmission spectra of the temperate sub-Neptune K2-18 b obtained with JWST have attracted significant attention. Debates have quickly arisen over the interpretation of the spectral data, particularly the recent MIRI observation where dimethyl sulfide (DMS) and dimethyl disulfide (DMDS) are claimed. Here we revisit K2-18 b as a case study to examine several key questions that are also broadly relevant to the temperate sub-Neptune population: i) Can the low water abundance be reconciled with water clouds driven by orbital eccentricity? ii) Are the observed and non-observed atmospheric compositions mutually consistent? iii) Is it kinetically possible to produce DMS under sub-Neptune conditions? To address these questions, we couple climate and photochemical models to obtain self-consistent climate-photochemistry states for K2-18 b with a moderate orbital eccentricity of 0.2, as suggested by radial-velocity measurements. In addition, we present new laboratory measurements of DMS and DMDS infrared opacities by HFML-FELIX and compile updated C$_2$H$_6$ (ethane) opacities that include weak overtone bands. Our results support the interpretation of a sub-Neptune scenario without invoking DMS, and we do not find strong evidence for a water-rich interior.
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All authors Shang-Min Tsai, Piero Ferrari, Mats Kuipers, Jacob Lustig-Yaeger, Arnav Agrawal, Sean Jordan, Bart Oostenrijk, Laura Pille, Edward W. Schwieterman, Laurens B. F. M. Waters

Astrophysics of Galaxies

FATHOMER survey: III. Preliminary HI galaxy identification results

Shuanghao Shu, Yichao Li, Wenxiu Yang et al. (+6 more)

We present the HI galaxy observation results of the FATHOMER (FAst neuTral HydrOgen intensity Mapping ExpeRiment), a pilot drift scan survey by the Five-hundred-meter Aperture Spherical radio Telescope (FAST). The survey comprises 28 hours of observations over 7 nights in 2021, covering a $60\, \deg^2$ sky area in the frequency range 1.05-1.45 GHz. The HI galaxies are identified using both a matched-filtering algorithm and the SoFiA source-finding pipeline, which yield consistent detections. We derive the velocity width ($W_{50}$), flux density, and HI mass for detected galaxies. A total of 702 galaxies are identified with HI mass above $10^{6.2}\,{M_\odot}$, signal-to-noise ratio greater than 5, and redshift $z < 0.09$. Among these, 331 are previously known from the ALFALFA survey. Of the newly detected sources, 9 have spectroscopic confirmation from SDSS, 285 are matched to SDSS or DESI photometric data, and 77 lack optical counterparts–possible candidates for dark or faint galaxies. Comparison with ALFALFA shows that FAST enables detection of galaxies at higher redshifts and with lower HI fluxes, despite the radio frequency interference (RFI) and partial data masking. A preliminary HI mass function analysis reveals a higher characteristic mass and steeper low-mass slope than ALFALFA, indicating FAST's enhanced sensitivity to massive and distant HI systems. These results demonstrate FAST's strong potential for future deep HI surveys and highlight the importance of improved RFI mitigation and completeness correction.
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All authors Shuanghao Shu, Yichao Li, Wenxiu Yang, Jiaxin Wang, Wenkai Hu, Furen Deng, Shifan Zuo, Yougang Wang, Xuelei Chen

Earth and Planetary Astrophysics

Smoothed Particle Hydrodynamics in pkdgrav3 for Shock Physics Simulations. II. Shear Strength

Thomas Meier, Christian Reinhardt, Martin Jutzi et al. (+2 more)

Material strength effects have been recently shown to be significant in giant impacts even at scales of planetary collisions. Despite this, their effects are often neglected in numerical giant impact simulations. We present an implementation of a basic strength model (pressure dependent shear strength) in the massively parallel smoothed particle hydrodynamics code pkdgrav3. The model includes elastic deviatoric stresses, plasticity with pressure-dependent yield strength, and thermal softening, and is fully integrated into the GPU-accelerated framework introduced in Paper I, preserving its scalability and performance characteristics. We validate the implementation against laboratory experiments of granular cliff collapse and our simulation results are in excellent agreement. We then determine the catastrophic disruption threshold, $Q_{RD}^*$, over a wide mass range of the colliding bodies using simulations performed both with and without material strength. Consistent with prior work, we find that strength substantially increases $Q_{RD}^*$ in the low-mass regime, while convergence toward the fluid limit occurs only near $R_{C1} \sim 10^7$ m ($\sim 0.7,M_\oplus$), well above the often assumed $\sim 100$ km size limit. Entropy production and remnant morphology likewise remain sensitive to rheology at intermediate masses. Performance measurements show that including strength introduces only modest computational overhead while maintaining favorable scaling, thereby enabling realistic solid mechanics in large-scale impact simulations.
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All authors Thomas Meier, Christian Reinhardt, Martin Jutzi, Douglas Potter, Joachim Stadel

High Energy Astrophysical Phenomena

The FAST Galactic Plane Pulsar Snapshot Survey. IX. Timing Three Binary Pulsars with Wide Orbits and Low Orbital Eccentricities

Z. L. Yang, J. L. Han, W. Q. Su et al. (+11 more)

Current pulsar timing models face challenges when applied to binary pulsars with wide orbits and low orbital eccentricities. The conventional DD model accurately characterizes the orbits of such systems, but it suffers from strong correlations between the time of periastron passage ($T_0$) and the longitude of periastron ($\omega$). The ELL1 model avoids these parameter correlations, yet fails due to the limitations of its first-order low-eccentricity approximation. Recent enhancements to the ELL1 model (dubbed ELL1+ model) have incorporated higher-order terms but retain the low-eccentricity approximation. In this study, we propose a further improved model, ELL1R, which eliminates reliance on the low-eccentricity approximation through rigorous calculation of the Römer delay. This modification can avoid strong parameter correlations in the DD model, and it can be used in systems with mild eccentricity $0.01\lesssim e\lesssim0.1$ where the ELL1+ model can not. Using the ELL1R model, we present the first phase-coherent timing solutions for three binary pulsars: PSR~J1851–0108 (orbital period: 228 days), PSR~J1910+0423 (886 days), and PSR~J1923+2022 (777 days). Validation against the DD and ELL1+ models confirms that ELL1R yields consistent timing results while integrating the advantages of the two models. Our analysis further indicates that all three pulsars are mildly recycled. The companions of PSRs J1910+0423 and J1923+2022 are likely white dwarfs, whereas the nature of PSR J1851–0108's companion remains unknown.
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All authors Z. L. Yang, J. L. Han, W. Q. Su, C. Wang, J. P. Yuan, T. Wang, Yi Yan, J. Xu, W. C. Jing, P. F. Wang, N. N. Cai, D. J. Zhou, X. J. Chen, D. Zhao

Astrophysics of Galaxies

The radial velocity stability for reference sources in the MWISP CO survey

Lixia Yuan, Ji Yang, Min Fang et al. (+3 more)

To assess the velocity stability of CO spectral lines in the Milky Way Imaging Scroll Painting (MWISP) survey, we employ a cross-correlation method to measure velocity shifts across $\sim$ 10,000 CO spectra from six reference sources observed over the ten-year duration of the survey. The standard deviations ($\sigma$) of these measured velocity shifts range from 0.03 to 0.23 km s$^{-1}$ for their $^{12}$CO lines and 0.03 to 0.16 km s$^{-1}$ for $^{13}$CO lines. We find that larger shifts are associated with broader linewidths, more pronounced differences between monthly and long-term variations, and a stronger correlation between velocity shifts of $^{12}$CO and $^{13}$CO lines. By examining the relation of velocity shifts with the Azimuth-Elevation of the telescope, as well as the velocity fields of these extended sources, we find that the velocity shifts exhibit systematic changes across different Azimuth-Elevation ranges. The patterns and amplitudes of these changes vary among sources and are closely linked to the extended velocity fields of sources. This indicates that the increased velocity shifts are primarily caused by pointing errors, which are more sensitive to reference sources with higher velocity gradients. We also provide high signal-to-noise, velocity-aligned template spectra for reference sources.
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All authors Lixia Yuan, Ji Yang, Min Fang, Shaobo Zhang, Dengrong Lu, Jixian Sun

Cosmology and Nongalactic Astrophysics

Morphological Signatures of Gravitational Evolution, Redshift-Space Distortions, and Massive Neutrinos in Large-Scale Structure

Priya Goyal, Stephen Appleby, Pravabati Chingangbam et al. (+1 more)

We investigate the morphological properties of large-scale structure in the Universe and the physical processes that modify the excursion-set morphology of the three-dimensional matter density field. Using the Quijote N-body simulation suite, we study how an initially Gaussian random matter density field is altered by non-linear gravitational evolution, redshift-space distortions, and massive neutrino free-streaming. To quantify these effects, we employ a comprehensive set of morphological descriptors, including Minkowski Functionals, Betti numbers, Minkowski Tensors, and local measures of the size and shape of connected components and cavities. We find that gravitational evolution, on quasi-linear scales $R_G \sim 10 h^{-1} \mathrm{Mpc}$, strongly skews the one-point distribution and slightly smooths the field via the merging of critical points, with a more pronounced effect for minima and wall saddle points than for peaks. Redshift-space distortions produce the strongest morphological signal, generating pronounced anisotropies that are robustly captured by Minkowski Tensors and local shape measures, arising from both coherent large-scale flows and non-linear Finger-of-God effects. In contrast, massive neutrinos induce an approximately isotropic suppression of small-scale structure, slightly reducing the amplitudes of the Minkowski Functionals while leaving individual shape measures largely unchanged. We further explore the sensitivity of these statistics to variations in cosmological parameters $\Omega_m$, $n_s$, and $\sigma_8$, finding that they probe strongly degenerate combinations of $\Omega_m$ and $n_s$, while also exhibiting sensitivity to $\sigma_8$ through the non-Gaussianity of the evolved density field.
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All authors Priya Goyal, Stephen Appleby, Pravabati Chingangbam, Changbom Park