Astrophysics of Galaxies
Chemical composition and kinematics of ionised gas in low-mass star-forming galaxies with extremely high [OIII]/[OII] ratios
Y. I. Izotov, N. G. Guseva, D. Schaerer et al. (+1 more)
We present Very Large
Telescope/Xshooter spectrophotometric observations of eleven low-
redshift (z<0.085) compact
star-forming
galaxies (`high O32 sample'). These
galaxies are characterised by extremely high emission-line ratios [OIII]$\lambda$5007/[OII]3727, ranging from 11 to 42.
Galaxies with such high ratios are thought to be promising candidates for leaking large amounts of Lyman continuum radiation. They are characterized by low oxygen abundances 12+log(O/H)\,=7.5-8.0 and low
stellar masses M*~10^6-10^8 Msun. Strong emission lines of various ions in all spectra are used to derive helium and oxygen abundances, and N/O, Ne/O, S/O, Cl/O, Ar/O and Fe/O abundance ratios. We also derived macroscopic velocity dispersions sigma(lambda) from various emission lines of different ions. We find that sigma(4861) of the Hbeta emission line is increased with increasing
stellar mass and decreasing O32 ratio. On the other hand, sigma(lambda)/sigma(4861) ratios for various lines are close to 1. Exceptions are sigma(lambda)/sigma(4861) of two lines, HeII 4686 and HeI 10830, which are considerably higher than unity and of four lines, [OII] 3726,3729, [SII] 6717,6731, with sigma(lambda)/sigma(4861) lower than unity. The two former lines are likely produced in the inner parts of HII regions and are broadened by dynamical processes generated by massive
stars, and by radiative scattering in the case of the HeI 10830 emission line. Emission in the four latter lines is produced mainly in the outer and likely more quiet parts of HII regions.
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All authors Y. I. Izotov, N. G. Guseva, D. Schaerer, R. O. Amorin
High Energy Astrophysical Phenomena · Cross-listed from hep-ph
A High-Precision Statistical Analysis of the SN1987A Neutrino Temporal Distribution
Riccardo Maria Bozza, Vigilante di Risi, Veronica Oliviero et al. (+2 more)
The interpretation of the SN1987A
neutrino data remains limited by significant absolute timing uncertainties across independent detectors and a long-standing tension in the angular distributions. This work presents a high-precision statistical framework that resolves these issues by formalizing the mathematical distinction between intrinsic and relative timing offsets (ITOs and RTOs). By performing a simultaneous $\chi^2$-
alignment of the Kamiokande-II and Baksan data with the IMB clock, we systematically incorporate non-Gaussian statistical correlations, reducing the temporal uncertainty by two orders of magnitude to the sub-second level. The $\chi^2$-analysis shows that Baksan's absolute timestamps require an advancement of $30.4\,$s, while those of Kamiokande-II require a delay of about $6.4\,$s. Establishing this unified, high-precision timeline is critical to test the physical nature of the first Kamiokande-II event (K1), specifically whether its distinct angular features signal the onset of the
prompt neutronization burst. Previous literature often assumes that K1 originated from inverse beta decay (IBD) on qualitative grounds. By contrast, our multidimensional likelihood analysis incorporates energy, direction, and MSW
flavor-conversion effects to provide the first quantitative constraint on its origin. We find a likelihood ratio of 3-6 in favor of an
accretion-phase $\bar{\nu}_e$ origin over a neutronization-burst origin, thereby turning a traditional assumption into a statistically bounded physical inference. This framework provides the most stringent constraints to date on the chronology of SN1987A and establishes a precise methodology for future multimessenger observations of
Galactic supernovae.
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All authors Riccardo Maria Bozza, Vigilante di Risi, Veronica Oliviero, Giulia Ricciardi, Francesco Vissani
Cosmology and Nongalactic Astrophysics
Galaxy clusters in the LoTSS-DR3: Catalogues and detection pipeline for diffuse radio emission
C. Stuardi, G. Di Gennaro, A. Botteon et al. (+19 more)
The third data release of the LOFAR Two-metre Sky Survey provides an unprecedented view of the northern sky at 144 MHz. While compact sources can be efficiently identified with automated software packages, the detection of diffuse
radio emission associated with
galaxy clusters still requires dedicated processing and visual inspection. Given the scale of current and forthcoming
radio surveys, automated approaches based on artificial intelligence are becoming essential to the identification of the most interesting targets. We aim to develop an automated pipeline to construct a catalogue of
galaxy clusters hosting diffuse
radio emission from LoTSS-DR3 20arcsec images. The pipeline is designed to provide both the probability that a cluster hosts diffuse
radio emission and an interpretable image of its shape and morphology. We employed
Radio U-Net, a convolutional neural network optimised for image
segmentation (i.e. pixel-level identification) of diffuse
radio emission. To associate detected emission with individual clusters, we combined the network output with positional, mass, and
redshift information from four X-ray- and Sunyaev-Zeldovich-selected cluster catalogues, resulting in a merged sample of 3822 clusters covered by the LoTSS-DR3. We produced a pixel-level
segmentation map of the full LoTSS-DR3 and a quantitative indicator for the presence of diffuse emission in each cluster. This enables the selection of sub-samples with specific properties for targeted follow-up or statistical studies. As a demonstration of the first application, we identified a sub-sample of 357 clusters selected at the highest network accuracy (76%), and we showed some examples of newly detected systems. For the second, using a larger statistical sample, we verified that the detection fraction of diffuse
radio sources in the four catalogues increases with the mass and
redshift of the clusters. [Abridged]
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All authors C. Stuardi, G. Di Gennaro, A. Botteon, F. Braga, C. Gheller, F. Vazza, M. Balboni, N. Biava, A. Bonafede, M. Brüggen, G. Brunetti, R. Cassano, M. Cianfaglione, V. Cuciti, F. De Gasperin, F. Gastaldello, M.J. Hardcastle, M. Hoeft, H.J.A. Rottgering, N. Sanvitale, T. W. Shimwell, R.J. van Weeren
Solar and Stellar Astrophysics
First time delay observation between two mid-infrared channels in solar flare footpoints
Miguel Rojas-Quesada, Lyndsay Fletcher, Hugh Hudson et al. (+2 more)
The strong correlation between energy injection and mid-infrared (mid-IR) emission observed during
solar flares can be used to probe energy deposition throughout the chromosphere, since the IR tracks
prompt flare-induced changes in electron density. Despite its diagnostic value,
solar mid-IR observations are relatively recent, with sporadic campaigns over the last decade resulting in only a few recorded
flares. Earlier studies found time lags between mid-IR emissions from spatially resolved footpoints, offering clues about
flare energy transport. Building on this, we analyse the time lags between emissions at two wavelengths (5.2 micrometers and 8.2 micrometers) for each footpoint. Using a local cross-correlation function, we show for the first time that the 8.2 micrometers emission channel peaks 0.3 s-0.45 s before the 5.2 micrometer channel. We investigate the origin of this lag, obtaining infrared emission estimates using results from the RADYN radiation hydrodynamics code. The theoretical lag values fall within the range of the observed ones. Variations in opacity-primarily due to
flare-induced ionization-explain the wavelength-dependent temporal shift between emission maxima. In particular, longer wavelengths exhibit a smaller lag between the peak of energy injection and peak of intensity. These results contribute to a better understanding of how energy deposition during a
flare affects the chromospheric layers of the atmosphere. Future observations with higher temporal resolution could exploit measurements of these time lags to more fully characterize the dynamics of energy deposition during
solar flares, opening a new avenue for studying heating and energy transport processes in the
solar atmosphere.
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All authors Miguel Rojas-Quesada, Lyndsay Fletcher, Hugh Hudson, Sargam M. Mulay, Paulo J. A. Simoes
High Energy Astrophysical Phenomena
Gravitational Lensing of Gravitational Waves from Astrophysical Sources: Theory, Detection, and Applications
Zhiwei Chen and Youjun Lu
Gravitational waves (GWs) from distant sources such as inspiralling and merging
stellar-mass compact binaries, intermediate-mass and supermassive-binary-black-hole can be gravitationally lensed by intervening objects, ranging from
stars and
primordial black holes to
galaxies and clusters. Depending on the GW wavelength relative to the lens scale,
lensing occurs in two regimes:
geometric optics, producing multiple images with time delays and magnifications, and wave optics, resulting in frequency-dependent waveform modulations. Lensed signals are identified via parameter overlap between event pairs or characteristic frequency-dependent modulations that distinguish them from unlensed signals. Detection rates depend on the
redshift and mass distributions of sources and lenses, with promising prospects for future observatories. Once confirmed, lensed GWs will be powerful probes of fundamental physics and cosmology: they can constrain dark matter,
lensing structures, the Hubble constant, and other cosmological parameters. In this review, we provide a concise overview of GW
lensing, covering the theoretical framework, predicted detection rates, search strategies, and applications. We conclude with prospects and future directions for observing and exploiting lensed astrophysical GW events.
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High Energy Astrophysical Phenomena
Early interaction signatures and an extended plateau phase in Type II SN 2020aze
B. Ailawadhi, R. Dastidar, K. Misra et al. (+27 more)
We present a photometric and spectroscopic analysis of the fast-declining Type II SN 2020aze, observed in optical bands from 2.2 to 137.4 days after explosion. The V-band light curve reaches a peak absolute magnitude of about minus 16.97$\pm$0.20 mag by 15 days, followed by a recombination phase with a decline rate of 2.04$\pm$0.13 mag per 100 days, lasting about 120 days. Early spectra (younger than 6 days) show a transient weak narrow emission line at 4687 Angstroms and a feature spanning 4400-4800 Angstroms, attributed to narrow and broad blue-shifted He II 4686, indicating interaction between the ejecta and dense circumstellar material. Comparison with spectral models suggests a red supergiant progenitor with a weak wind and a mass-loss rate of about 1e-3
solar masses per year. Semi-analytical light-curve modeling gives an initial radius of about 1100
solar radii, an ejecta mass of about 12
solar masses, an explosion energy of about 1.5e51 erg, and a progenitor mass of about 14
solar masses. These early interaction signatures, the steep decline, and the extended photospheric phase highlight the role of pre-
supernova mass loss and circumstellar interaction in shaping the diversity of Type II
supernovae.
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All authors B. Ailawadhi, R. Dastidar, K. Misra, S. Valenti, D. J. Sand, J. E. Andrews, J. P. Anderson, K. A. Bostroem, P. J. Brown, R. Cartier, T. W. Chen, Y. Dong, N. Dukiya, E. Padilla Gonzalez, M. Gromadzki, J. Haislip, D. Hiramatsu, D. A. Howell, C. Inserra, D. Janzen, S. W. Jha, V. Kouprianov, C. McCully, T. E. Müller-Bravo, C. Pellegrino, G. Pignata, D. E. Reichart, J. Sollerman, D. R. Young, L. Yadav
Cosmology and Nongalactic Astrophysics
Revisiting the Constancy of the Speed of Light: Galaxy Cluster Mass Bias Implications
R. F. L. Holanda, Marcelo Ferreira, Javier E. Gonzalez et al. (+1 more)
In recent years, improvements in
galaxy cluster observations have enabled a variety of tests of fundamental physics using these systems. In this work, we test the constancy of the speed of light, $c$, by combining X-ray gas mass fraction measurements from
galaxy clusters with SNe Ia luminosity distance measurements from Pantheon+. We adopt the SH0ES prior on $H_0$ and the $\Omega_b/\Omega_m$ ratio from
galaxy clustering observations, thereby minimizing the dependence of our analysis on any specific cosmological model. We explore different assumptions for the cluster mass calibration (mass bias), including CLASH, CCCP, and Planck-based estimates. We find no deviation from a constant $c$ when adopting CLASH or CCCP priors, while Planck-based calibration yields a mild tension, with the hypothesis of constant $c$ being only marginally consistent at the $2\sigma$ level, indicating a non-negligible sensitivity of the results to the adopted calibration scheme.
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All authors R. F. L. Holanda, Marcelo Ferreira, Javier E. Gonzalez, S. H. Pereira
High Energy Astrophysical Phenomena
Vacuum polarization and cyclotron resonance effects on radiative transfer and plasma deceleration in subcritical X-ray pulsars
I. D. Markozov, A. Y. Potekhin, A. D. Kaminker et al. (+1 more)
We investigate the spectrum and polarization of radiation emerging from a subcritical X-ray
pulsar using self-consistent radiation-hydrodynamic simulations of an
accretion channel in a strong
magnetic field. The polarized radiative transfer in the channel above the hot spot is simulated for the two normal modes, taking into account resonant Compton scattering in a strongly magnetized
plasma and the effects of
vacuum polarization. We show that the deceleration of the accreting matter in the subcritical regime is mainly governed by resonant scattering. Our simulations provide the velocity profiles of the
plasma flow and demonstrate that
vacuum polarization dominates over
plasma birefringence, enhancing both the cyclotron spectral feature and the radiative deceleration of the
plasma. We also find that the energy of the cyclotron feature increases with
accretion luminosity, indicating a positive correlation consistent with previous observational results and theoretical interpretation.
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All authors I. D. Markozov, A. Y. Potekhin, A. D. Kaminker, A. A. Mushtukov
High Energy Astrophysical Phenomena
A comparative study of occurrence rates and nature of Ultraluminous X-ray sources in spiral and elliptical galaxies
C. M. Sariga, P. Shalima, D. Bhattacharya et al. (+1 more)
Ultraluminous X-ray sources (ULXs) are mostly extragalactic non-
nuclear point sources having X-ray luminosity exceeding the Eddington luminosity of 10 $M_\odot$ black hole i.e., $L_X \geq $ 10$^{39}$ erg ~s$^{-1}$. They are observed in all types of
galaxies; spirals, ellipticals and
dwarf irregulars. But the rate of occurrence of ULXs per
galaxy varies, some might host a single ULX, whereas some host a large number. In this work we attempt to identify possible differences in ULX properties between two extreme categories in spirals and ellipticals, i.e. ULXs occurring at a rate of one per
galaxy ($N=1$) and those occurring at larger rate. We adopt an effective scheme to generate flux limited, credible samples corresponding to the two groups in spirals and ellipticals. From this study, we infer the presence of a separate population of ULXs in the $N=1$ spiral group which contains a reasonable fraction of both soft and hard sources, while the remaining categories contain mostly harder sources. We also find six ULXs in $N=1$ ellipticals with globular cluster association. In addition, we identify few luminous candidates likely hosting massive accretors. This study provides crucial hints of a potential link between ULX types and their occurrence rates and host morphology, a finding that warrants validation via targeted observations and detailed spectral analysis of these sources.
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All authors C. M. Sariga, P. Shalima, D. Bhattacharya, Vivek K. Agrawal
High Energy Astrophysical Phenomena
Tearing of charged current layers
Maxim Lyutikov
Astrophysical current layers, e.g., in
pulsar winds, can be electrically charged, while the
plasma is charge-symmetric, $e^\pm$. Using PIC simulations, we investigate dynamics and plasmoid formation (tearing instability) in charged Harris-type and rotational current layers. Electrically charged current layers, initially in global force-balance, are electrostatically unstable: the resulting dynamics is an intricate interplay between electrostatic Bernstein waves (BWs) and the current tearing mode. Besides overall density and
magnetic field,
plasma temperature is an important factor. In the charged Harris sheet set-up, the quickly generated BW are trapped within the layers (internally reflected at the upper hybrid resonance). BWs quickly redistribute the charge modifying the initial stage of tearing, but without strongly affecting overall plasmoid growth; resulting plasmoids are mildly charged. In rotational current layers: (i) even initially overall uncharged configurations develop large fluctuations of charge density; (ii) overall dynamics depends on the initial overall temperature; (iii) for certain combination of parameters tearing rate is greatly increased in the charged case.
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Astrophysics of Galaxies
Phase-Space Crystallization in Galactic Globular Clusters: A Gaia-Based Metric and Implications for Technosignature Searches
Bo-Lun Huang, Zhen-Zhao Tao and Tong-Jie Zhang
We develop a model-independent framework to quantify phase-space "crystallization", the degree of ordered radial and kinematic substructure, in 79
Galactic globular clusters using the
Gaia EDR3-based membership catalogue of E. Vasiliev & H. Baumgardt (2021a). We construct a scalar crystallization index, C_index, by combining a radial inhomogeneity metric (z_rad) and a local, cluster-centric tangential-velocity metric (z_vel) standardized against empirical nulls. The population distribution is strongly non-Gaussian: most clusters are consistent with smooth,
equilibrium expectations, while a small high-C tail (C_index >= 2) identifies dynamically complex systems, including NGC 5139 (\omega Cen) and NGC 104 (47 Tuc). Correlation and fixed-N tests show that sample size affects detectability, but does not by itself explain all high-rank objects. Through synthetic injection tests in dynamically "quiet" control clusters, we demonstrate sensitivity to ultra-cold, shell-confined kinematic components, ruling out single-shell structures comprising more than a few to ~ 10-20% of core
stars in the best-sampled control clusters. We find no evidence, within the sensitivity of the adopted diagnostics, for phase-space structures that require explanations beyond known dynamical processes. However, C_index provides a useful tool for ranking clusters by dynamical extremeness, serving both as a diagnostic for internal complexity and as a quantitative metric for prioritizing follow-up dynamical or technosignature-oriented observations.
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Astrophysics of Galaxies
A statistical look on kinematic planes of satellite galaxies II: The physics behind their early formation in TNG50 MW/M31-like galaxies
Matías Gámez-Marín, Rosa Domínguez-Tenreiro, Isabel Santos-Santos et al. (+2 more)
We investigate the physical origin of kinematically persistent planes (KPPs) of satellite
galaxies in a sample of 190 Milky Way (MW)/M31-like host-satellite systems drawn from the TNG50 simulation. Building on the identification of 46 early KPPs in a previous work, we analyse their formation in the context of the high-
redshift evolution of the local
Cosmic Web by tracking the deformation of the so-called Lagrangian Volumes (LVs) surrounding each system. Using a reduced tensor-of-inertia analysis, we characterise the time
evolution of the principal directions of collapse and relate them to the clustering of satellite orbital poles. We find that in approximately 67% of KPPs satellite orbital poles align with the LV direction of strongest collapse, $\vec{e}_3$, while a smaller fraction ($\sim20\%$) align with the intermediate axis, $\vec{e}_2$;
alignments with the major axis are rare. These
alignments are statistically distinct from random expectations and reflect the confinement of satellites to planar configurations normal to the corresponding LV principal directions. We perform a kinematic analysis of satellite motion within KPPs, finding that vertical and radial motions relative to these KPPs decay early, leading to rotation-dominated, “disky” configurations. The characteristic timescales for satellites to settle onto a common orbital plane, for satellite orbital pole clustering, and for LV shape
evolution are found to be quasi-coeval, peaking at a Universe age T$_{\rm uni}\sim4$~Gyr, during the fast mass assembly phase of the host
halo. These results support a scenario in which early KPPs are fossil remnants of high-
redshift, anisotropic mass collapse driven by the local
Cosmic Web formation process in $\Lambda$CDM.
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All authors Matías Gámez-Marín, Rosa Domínguez-Tenreiro, Isabel Santos-Santos, Diego Sotillo-Ramos, Alexander Knebe
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Kaon Portal to Freeze-in Dark Matter
Motoi Endo and Takumu Yamanaka
We investigate freeze-in production of light dark matter through the
quark flavor-changing operator $(\bar{s}\gamma_\mu d)(\bar{\chi}\gamma^\mu\chi)$ in a low-reheating cosmology. For reheating temperatures below the QCD crossover, kaon decays and scatterings generate the dark matter abundance through $K\to\pi\chi\bar{\chi}$ and $K\pi\to\chi\bar{\chi}$. The same interaction induces the rare kaon decays $K^+\to\pi^+\chi\bar{\chi}$ and $K_L\to\pi^0\chi\bar{\chi}$. This links the freeze-in relic abundance to searches at NA62, KOTO, and KOTO II. We find that lower reheating temperatures require larger couplings to compensate for the Boltzmann-suppressed kaon abundance, making kaon-driven freeze-in dark matter testable at rare kaon decay experiments.
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Astrophysics of Galaxies
The multiple corrugations in the Galactic disk derived from the LAMOST and Gaia survey data
Jifei Wang, Zhuohan Li, Chengdong Li et al. (+6 more)
Large spectroscopic and astrometric surveys have revealed complex wave-like features in the Milky Way disk, suggesting that its kinematic and chemical structures are shaped by time-dependent perturbations. Recent studies have reported oscillatory patterns in the Rg-Vphi-VR space, hinting at a possible structural transition in the outer disk. We aim to characterise the transition between the inner and outer
Galactic thin disk and to investigate whether radial corrugations can provide a plausible physical interpretation of the observed features. We analysed two large
stellar samples from LAMOST DR8 and
Gaia DR3, combining spatial, kinematic, and chemical diagnostics. A simplified corrugation model consisting of two radial waves propagating in opposite directions was constructed and fitted to the observed VR pattern. We further validated the model using N-body simulations. Both LAMOST and
Gaia samples reproduce the previously reported wave-like pattern in the Rg-Vphi-VR plane. We identify a clear transition between the inner and outer disks via the variations in rotational velocity and
metallicities. The corrugation model naturally reproduces the periodic variation of VR with galactocentric radius, and the superposition of the inward and outward propagating modes gives rise to a comparable oscillatory pattern in both observations and simulations. Our modelling suggests that radial corrugations can provide a plausible interpretation of the observed kinematic signatures. The results highlight the complex, multi-perturber nature of the
Galactic disk and motivate further investigation with upcoming surveys.
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All authors Jifei Wang, Zhuohan Li, Chengdong Li, Yuqin Chen, Chengqun Yang, Zixi Guo, Zhou Fan, Hongrui Gu, Maoli Bu
Cosmology and Nongalactic Astrophysics
Axion-Like Particle Dark Matter Intensity Mapping: A New Probe via Cross-Correlation with Galaxy Surveys
Wen-Qing Guo
The particle nature of dark matter (DM) remains one of the most significant enigmas in modern cosmology.
Axion-like particles (ALPs), as well-motivated candidates for cold dark matter, can undergo radiative decay into
photon pairs, a process that is significantly enhanced in the presence of ambient radiation fields. In this work, we propose a novel probe of $\mu{\rm eV}$-scale ALP DM by cross-correlating
radio intensity mapping (IM) with the large-scale
galaxy distribution from the 2MASS
Redshift Survey (2MRS) in the local universe ($z\leq 0.1$). We develop a comprehensive theoretical framework that incorporates stimulated decay effects driven by both the
Cosmic Microwave Background (CMB) and a bottom-up modeled extragalactic
radio background (ERB). By
forecasting the sensitivity of the Square Kilometre Array (SKA) Phase 2, we demonstrate that this cross-correlation technique provides a promising and complementary approach to searching for ALP DM signals. This study establishes a new proof-of-concept for utilizing next-generation
radio telescopes to probe ALP dark matter on
cosmic scales.
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Solar and Stellar Astrophysics
Modeling of Coronal Mass Ejection Originated from a Sheared Arcade of Realistic Active-Region Scale and Its Propagation in the Heliosphere: Methodology
Chaowei Jiang, Xueshang Feng, Liping Yang et al. (+4 more)
Simulating coronal mass ejections (CMEs) from their origin in active regions (ARs) to their propagation to Earth remains challenging, particularly when aiming to resolve AR scales and employ realistic
magnetic field strengths without compromising computational efficiency. Here we present a methodology for end-to-end CME modeling that addresses these challenges. Three nested magnetohydrodynamic simulations are coupled to jointly cover the heliosphere from
solar surface to beyond $1.5$ au. A block-structured adaptive mesh refinement scheme is employed to achieve $\sim 700$ km resolution in the low corona, allowing AR scales to be resolved while maintaining the total grid count below $10^8$ across the entire computational domain. A semi-relativistic Boris correction combined with a relativistic mass-density factor is used to handle
magnetic field strengths up to $10^3$ G without prohibitively small time steps. Using this model, we simulate the emergence of a bipolar AR into the corona, the initiation of a CME by shearing of the AR core field and the subsequent
evolution. Our simulation captures its pre-eruption energy buildup, triggering by
magnetic reconnection, rapid acceleration, and propagation to 1 au and beyond. The simulated CME exhibits a three-part structure in synthetic coronagraph images and a
torus-shaped flux rope in the heliosphere, with synthetic in-situ observations showing shock formation, density compression, and a prolonged southward $B_z$ component at 1 au. The entire simulation requires about one day on a moderately sized cluster (e.g., $600$ processors), while the simulated CME takes three days to arrive at $1$ au, offering a lead time of two days if used for
forecasting.
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All authors Chaowei Jiang, Xueshang Feng, Liping Yang, Huichao Li, Jinhan Guo, Pingbing Zuo, Yi Wang
Earth and Planetary Astrophysics
Jovian Zonal Winds Revealed from Cassini/VIMS Observations
Shenghan Ma, Yuming Wang, Tao Li et al. (+3 more)
Understanding Jupiter's zonal winds is crucial to unraveling the dynamics of its atmosphere. Over the last decades, multiple data sources and techniques have been used to study zonal winds in Jupiter. Here, we develop a correlation-based method for the near-infrared data from the Cassini spacecraft to investigate zonal winds at different altitudes. The new method uses Jupiter's rotation to scan the
planet as it rotates, allowing
retrieval of winds from the analysis of light-curves of specific pixels over the Jovian disc. The method allows the
retrieval of winds at multiple wavelengths from the Cassini/VIMS spectral data despite the low spatial resolution and the non-uniform cadence of the data. By applying this method to two VIMS data cubes acquired on 15 January 2001 at 09:42 UT and 16 January 2001 at 03:22 UT, we reveal the zonal winds at five main latitudes using information from three different wavebands, as well as the wind vertical structure at the equator, showing significant vertical wind shear in the troposphere. The vertical wind shear we derived is weaker than as reported in previous studies, highlighting the intricate interactions among multiple dynamical processes in Jupiter's atmosphere and reflecting the complexity of its atmospheric circulation. Despite the uncertainty due to the low spatial/temporal resolution and non-uniform cadence of the Cassini/VIMS-IR spectral data, the new method established in this study maximizes the value of the Cassini/VIMS in understanding Jupiter's zonal winds. Further observations are essential to explore the underlying mechanisms in Jupiter's atmosphere.
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All authors Shenghan Ma, Yuming Wang, Tao Li, Quanhao Zhang, Jiajia Liu, Ruobing Zheng
Solar and Stellar Astrophysics
Investigating the Relationship Between Physical Properties and Spatial Irregularities at Coronal Hole Boundaries
Nawin Ngampoopun, David M. Long, Lucie M. Green et al. (+5 more)
Coronal hole boundaries are the interfaces between closed and open
magnetic field regions in the
solar atmosphere. Many fundamental processes take place at these regions, including
magnetic reconnection that is responsible for
solar wind release and restructuring of the
solar magnetic field. In this paper, we present a case study in which we investigate the physical properties of the boundary of a large low-latitude coronal hole. Differential Emission Measure analysis is used to derive the
plasma properties of these regions. We also apply correlation dimension mapping analysis to measure the irregularities of the coronal hole boundary. We find that the leading boundary of this coronal hole has a slightly higher average
plasma temperature, is associated with a stronger and more unipolar
magnetic field, and has a smoother boundary line than the trailing counterpart. These differences are hypothesised to be direct consequences of the local
magnetic field configurations of the coronal hole boundary: the leading boundary corresponds to large, well-organised coronal loops, and the trailing boundary corresponds to more dispersed, randomly orientated small
magnetic bipoles. Hence, we suggest that the surrounding
magnetic field structure and the nature of
magnetic reconnection influence the properties of coronal hole boundaries.
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All authors Nawin Ngampoopun, David M. Long, Lucie M. Green, Stephanie L. Yardley, Alexander W. James, Emily I. Mason, Stephan G. Heinemann, Vadim M. Uritsky
High Energy Astrophysical Phenomena · Cross-listed from hep-ph
Massive hybrid stars within the extended three-flavor quark-meson diquark model
Jens O. Andersen, Manuel Linares and Mathias P. Nødtvedt
We discuss the properties of the extended three-
flavor quark-
meson diquark (EQMD) model as a renormalizable low-energy effective model for QCD. The effective degrees of freedom are
quarks, scalar- and pseudoscalar
mesons, diquarks, vector- and axial-vector
mesons. We calculate the equation of state (EoS) in the mean-field approximation at $T=0$ imposing charge neutrality for electric and color charges. We match the EoS with a low-density
nuclear equation of state. We discuss how the choice of parameters in the model affects the EoS and thereby the mass-radius for hybrid
stars. We show that it is possible to construct hybrid
stars whose masses and radii are in agreement with recent astrophysical observations and perturbative QCD (pQCD). The addition of vector and axial vector
mesons to the
quark-
meson diquark is essential, since it makes the EoS sufficiently stiff for intermediate densities. Our results suggest that
stars with a mass larger than $M\sim2M_{\odot}$ have a
quark core with a central density $n_B\geq 3.9n_{\rm sat}$, where $n_{\rm sat}\approx0.165$fm$^{-3}$ is the saturation density. The speed of sound has a double-peak structure and relaxes to the conformal limit from above for large
baryon chemical potentials $\mu_B$. This structure is caused by the decrease in the mass of the $s$
quark as $\mu_B$ increases.
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Solar and Stellar Astrophysics
ATOMIUM: Inner circumstellar envelopes of oxygen-rich AGB stars as revealed by highly excited SiO lines
B. Pimpanuwat, S. Etoka, M. D. Gray et al. (+14 more)
Silicon monoxide (SiO) traces the physical conditions and dynamics in the circumstellar envelopes (CSEs) of AGB
stars. We present high-resolution ALMA Band 6 observations of highly excited SiO emission in 14 oxygen-rich AGB
stars. We cover transitions from v = 0 to v = 8, including first detections of 28SiO v = 3, 4, 8, J = 6-5, 29SiO v = 6, J = 6-5, and 30SiO v = 4, 5, J = 6-5, some of which are masers. The v = 8 transition is the highest v-state observed in an AGB
star yet. Masers in v = 0 are detected clearly in V PsA and IRC+10011 and tentatively in T Mic. R Hya exhibits the richest SiO spectrum. SiO J = 6-5 absorption is seen in R Aql, R Hya, S Pav, and T Mic, with features indicative of both infalls and
outflows, and tentative detection of 28SiO v = 8, J = 6-5 absorption is found towards S Pav and R Aql. Highly excited SiO emission is often distributed in arcs or clumps with velocity gradients; components in R Hya and U Her align with predicted shock fronts. Detection rates show no significant difference between low and high mass-loss rate
stars, although line overlap may affect some intensities. Maser detections appear uncorrelated with pulsation period or phase. The radius enclosing 90 per cent of compact SiO emission shows a tentative correlation with mass-loss rate. These results highlight the role of mass loss and CSE geometry in shaping high-excitation SiO emission.
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All authors B. Pimpanuwat, S. Etoka, M. D. Gray, A. M. S. Richards, A. Baudry, F. Herpin, T. Danilovich, L. Decin, M. O. Lewis, I. El Mellah, C. A. Gottlieb, Y. Mori, H. S. P. Müller, R. Sahai, K. T. Wong, J. A. Yates, A. Zijlstra
High Energy Astrophysical Phenomena
An Insight-HXMT View of the Evolution of the Type-C Quasiperiodic Oscillation during the Flaring State of Swift J1727.8-1613
Min Wei, Xiang Ma, Liang Zhang et al. (+16 more)
We present a detailed analysis of the
evolution of type-C quasiperiodic oscillations (QPOs) observed during the flaring state of the recently discovered black hole X-ray binary Swift J1727.8-1613, utilizing data from the Insight Hard X-ray Modulation
Telescope. By examining the relation between the QPO fractional rms amplitude and QPO frequency across various energy bands, we discover that the behavior significantly differs between these energy bands. Below 10 keV, the QPO fractional rms generally decreases with increasing QPO frequency, whereas above 10 keV, the QPO fractional rms remains relatively stable with frequency. Additionally, we report, for the first time, the detection of a common break at around 4 Hz in the relation between QPO fractional rms and frequency in both the 2-4 and 50-100 keV energy bands. We also find that the
evolution of all the spectral parameters alters its behavior at around 4 Hz, with the changes in all parameters becoming flatter. This suggests a significant change in the geometry of the
accretion flow. We attribute the observed break to the overall changes in the spectrum.
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All authors Min Wei, Xiang Ma, Liang Zhang, Xiang-Hua Li, Ming-Yu Ge, Lian Tao, Jin-Lu Qu, Shuang-Nan Zhang, Shu Zhang, Li-Ming Song, Rui-Can Ma, Zi-Xu Yang, Yue Huang, Pan-Ping Li, Jia-Ying Cao, Shu-Jie Zhao, Qing-Chang Zhao, Yun-Xiang Xiao, Guo-Li Huang
Solar and Stellar Astrophysics
IY Lyr: A Thick-Disk first-overtone RR Lyrae Star with a Possible Neutron Star Companion
Linjia Li, Shengbang Qian, Ildar Asfandiyarov et al. (+10 more)
IY Lyr, historically misclassified as an eclipsing binary, has been previously identified as a first-overtone RR Lyrae
star (RRc
star). Using multiband photometry (All-Sky Automated Survey for
Supernovae, Zwicky Transient Facility, TESS, and our BVRI data), Large Sky Area Multi-Object Fiber Spectroscopic
Telescope spectroscopy, and
Gaia astrometry, we investigate its pulsation, binarity, and
Galactic population. From O-C analysis, we detect a long-term period decrease and a light-travel time effect with an orbital period of 3.94 $\pm$ 0.09 years, eccentricity of 0.46 $\pm$ 0.15, and a mass function of 0.65 $\pm$ 0.14 M$_{\odot}$. The companion is independently supported by radial velocity residuals and
Gaia proper motions. Combined constraints yield an orbital inclination of 94.2$^{\circ}$ $\pm$ 1.1$^{\circ}$ and a companion mass of 1.37 $\pm$ 0.19 M$_{\odot}$. Chemical abundances ([Fe/H] $\simeq$ -1.0 $\pm$ 0.1, [$\alpha$/Fe] $\simeq$ +0.27 $\pm$ 0.03, Xiang et al. 2019) and dynamics ($L_{\rm z}$ $\simeq$ 1287 $\pm$ 35 kpc km s$^{-1}$, $Z_{\rm max}$ $\simeq$ 1.17 $\pm$ 0.10 kpc) identify IY Lyr as likely an old, high-$\alpha$, thick-disk
star. The companion mass lies at the peak of the
neutron star mass distribution, and the system's age excludes a main-sequence
star; we conclude the companion is most likely a typical
neutron star, although a massive white
dwarf near the Chandrasekhar limit cannot be ruled out. IY Lyr is among the few RRc binaries with a compact companion supported by multiple methods, and it has important implications for thick-disk binary
evolution and
neutron star formation.
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All authors Linjia Li, Shengbang Qian, Ildar Asfandiyarov, Azizbek Matekov, Liying Zhu, Boonrucksar Soonthornthum, Evelina Gaynullina, Alina Khalikova, Jiajia He, Fangbin Meng, Huiting Zhang, Jiangjiao Wang, Xiangdong Shi
Cosmology and Nongalactic Astrophysics
From Scalar $H_0$ to $E(z)$: A Reformulation of the Hubble Tension
Seokcheon Lee
The Hubble tension is usually expressed as a discrepancy between the low H_0 inferred from Planck CMB data within base \LambdaCDM and the higher value obtained from late-time distance-ladder measurements. This scalar comparison compresses distinct inference problems into one derived parameter: Planck CMB, DESI DR2 BAO, and Pantheon+SH0ES constrain physical densities and acoustic scales, ruler-normalized distances, and calibrated luminosity-distance relations, respectively. We reformulate the comparison in terms of the dimensionless expansion history E(z)=H(z)/H_0. This does not remove the absolute-scale discrepancy, but separates the normalization encoded in $H_0$ from the
redshift-dependent shape of the expansion history. Within a common flat-\LambdaCDM framework, each probe posterior is mapped onto posterior-implied E(z) histories. Since the reconstructed values E(z_k) are strongly correlated across
redshift, we quantify the global mismatch with a covariance-subspace history displacement S_{hist}, alongside pointwise
redshift differences. The histories are not identical, but the discrepancies are moderate: the pointwise significance is typically 1-2\sigma, while S_{hist} simeq 1.65 for DESI DR2 and S_{hist} \simeq 2.55 for Pantheon+SH0ES relative to Planck. With two retained covariance eigenmodes, these correspond to two-sided one-dimensional Gaussian equivalents of approximately 1.1\sigma and 2.1\sigma, both below the conventional \simeq 4.9\sigma Planck-SH0ES scalar-H_0 discrepancy.
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Cosmology and Nongalactic Astrophysics
Bayesian leave-one-out cross-validation for astrophysical model comparison using gravitational-wave background data
Shreyas Tiruvaskar and Chris Gordon
Previous work showed that ultralight-dark-matter
solitons can provide dynamical friction for supermassive black-hole binaries, suppressing low-frequency power in the
pulsar-timing-array gravitational-wave background and constraining the particle mass and effective ultralight-dark-matter fraction. Here we extend that analysis by comparing the predictive performance of four models: simplified and realistic ultralight-dark-matter implementations, a phenomenological environmental-hardening model, and a gravitational-wave-only model. We use
Bayesian leave-one-out cross-validation on the five lowest
pulsar-timing-array frequency bins. The phenomenological model gives the largest expected log predictive density, but its advantage over the other models is not large compared with the estimated standard errors. The current data therefore do not decisively prefer one model overall. The clearest pairwise result is within the ultralight-dark-matter framework: the simplified model outperforms the realistic implementation in all five frequency bins. Current
pulsar-timing-array data are therefore compatible with ultralight-dark-matter-induced low-frequency suppression, but do not yet distinguish ultralight-dark-matter significantly from more generic environmental descriptions of supermassive-black-hole-binary
evolution.
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Astrophysics of Galaxies
Detection of an Extended Ly$\alpha$ Halo around a $\textit{z}=6.64$ Broad Absorption Line Quasar with the Keck Cosmic Web Imager
Raymond P. Remigio, Aaron J. Barth, Feige Wang et al. (+6 more)
We present the first results from a program searching for extended Ly$\alpha$
halos around high
redshift ($ z \gtrsim 6.5$)
quasars using the red channel of the Keck
Cosmic Web Imager (KCWI). Our observations reveal a Ly$\alpha$
halo extending to $\simeq11$ pkpc around the $z=6.64$ broad absorption line
quasar J0910$-$0414. The Ly$\alpha$ velocity field displays a rotation-like gradient, and the gas velocity dispersion is consistent with gravitationally dominated motion ($\sigma_{\mathrm{Ly\alpha}}<300$ km s$^{-1}$). Comparison with the $[\mathrm{C\;II}]$ kinematics of the host
galaxy core from ALMA observations shows that the Ly$\alpha$-emitting gas extends over a much larger region, shows distinct kinematics, and has a smaller velocity dispersion ($\sigma_{\mathrm{Ly\alpha}} \simeq 0.6\sigma_{\mathrm{[C\;II]}}$). The Ly$\alpha$ spectral region of the
quasar is largely obscured by a deep $\mathrm{N\;V}$ absorption trough, and as a result, roughly $55\%$ of the total Ly$\alpha$ flux is from the extended
halo. These observations demonstrate the potential of KCWI for probing the cool gas reservoir that fuels the growth of
quasars and their hosts in the epoch of reionization.
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All authors Raymond P. Remigio, Aaron J. Barth, Feige Wang, Jinyi Yang, Joseph F. Hennawi, Ryan J. Cooke, Eduardo Banados, Xiaohui Fan, Emanuele Paolo Farina
Solar and Stellar Astrophysics
Microwave Polar Brightening and Its Connection to Polar Coronal Holes
Rohan Bose, Anshu Kumari, Vaibhav Pant et al. (+3 more)
Polar brightening (PB) observed at microwave frequencies serves as an important probe to study the thermal and
magnetic properties in the Sun's polar regions. Building on earlier studies that linked microwave PB to polar faculae, small-scale loops, and the polar coronal holes (PCHs), we present a comprehensive analysis of the long-term behaviour of 17 GHz microwave PB and its relation to polar
magnetic field and coronal hole
evolution. Using daily Nobeyama Radioheliograph observations spanning 1992 to 2018, we quantify microwave PB peak temperature variations and compare them with the temporal
evolution of PCH area extracted from SDO/AIA-based SPoCA coronal hole catalogues during the period 2010-2018. We also examine the correspondence between microwave PB and the polar
magnetic field to assess the nature of their association. Our results show a strong correlation between microwave PB peak temperature and PCH area, as well as with the polar
magnetic-field strength. In addition, we found that regions of enhanced microwave emission are frequently associated with small-scale loop structures, consistent with Coronal Bright Points (CBPs), which are often associated with the eruption of jets. Overall, this study aims to investigate the impact of coronal holes, polar
magnetic fields, and small-scale polar activity on polar brightening observed at 17 GHz and its long-term
evolution.
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All authors Rohan Bose, Anshu Kumari, Vaibhav Pant, Srinjana Routh, Divya Paliwal, M. V. Sunil Krishna
Solar and Stellar Astrophysics
Helium emission from Balmer-dominated shocks in Type Ia supernova remnants provides constraints to their progenitor systems
Priyam Das, Ivo Rolf Seitenzahl, Parviz Ghavamian et al. (+4 more)
Balmer-dominated shocks in Type Ia
supernova remnants offer powerful probes into collisionless shock physics and hints towards
supernova progenitor environments. Prior studies focused on the hydrogen Balmer lines, which manifest as a superposition of broad and narrow emission lines. Using integral-field spectroscopy with MUSE, we discovered broad and narrow helium emission lines from Balmer-dominated filaments of three Type Ia
supernovae remnants in the Large Magellanic Cloud: SNR 0509-67.5, SNR 0519-69.0 and N103B. We detect broad and narrow He~i 5876~Å~,7065~Å\ emission in SNR 0519 and N103B and He ii 8236~Å\ in SNR 0519. In SNR 0509 we detect narrow He~i 5015~Å, 6678~Å, 7065~Å\ and 7281~Å, with only 7065~Å~ exhibiting a broad component. The detection of narrow He\,ii challenges existing shock models, where such emission is not expected, and may indicate either incomplete ion-ion equilibration behind the shock or an origin in shock precursors. For SNR 0509 and N103B, the neutral He/H line ratios indicate enhanced helium abundances, whereas SNR 0519 is consistent with the
primordial He/H value. We therefore propose helium emission in Balmer-dominated shocks as a new diagnostic of shock physics and Type Ia
supernova circumstellar environments. Although our modeling is primarily a proof of concept, it demonstrates the possibility to infer the total He-to-H abundance ratio, with dominant uncertainties arising from the assumed initial ionization fractions. Despite the uncertainties, we demonstrate that narrow helium lines can serve as effective probes of circumstellar conditions and progenitor
evolution when analysed alongside reliable constraints on the preshock neutral H/He abundance ratio.
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All authors Priyam Das, Ivo Rolf Seitenzahl, Parviz Ghavamian, Ashley Jade Ruiter, J. Martin Laming, Simon J. Murphy, Cillian O'Donnel
Astrophysics of Galaxies
Differences between emission and absorption tracers of spatially resolved outflows in clumpy z ~ 0.1 star-forming galaxies
Antonia Fernández-Figueroa, Glenn G Kacprzak, Deanne B Fisher et al. (+2 more)
We present spatially resolved Keck/LRIS spectroscopy of three clumpy
star-forming
galaxies at $z\sim0.1$, comparing
outflow properties traced by H$\alpha$ and Mg II emission with those probed by Mg II and Na I D absorption.
Outflow velocities measured using Mg II absorption ($\langle v_{\rm out} \rangle = -560 \pm 30$~\kms) are consistently higher than those traced by H$\alpha$ emission ($\langle v_{\rm out} \rangle = -124 \pm 3$~\kms) across $\sim$5 kpc$^{2}$ regions. Despite this offset, the correlation between $v_{\rm out}$ and
galaxy properties, such as SFR and $\Sigma_{\rm SFR}$, show similar slopes for both tracers, with Mg II absorption systematically offset by $\sim 0.4$ dex. In two
galaxies, Mg II emission is also detected, yielding velocities consistent with H$\alpha$. In one
galaxy we also detect
outflows in Na I D absorption and find similar velocities as Mg II in absorption, which leads to a $\sim$0.4 dex higher Na I D
outflow velocities compared to those measured in emission. Our spatially resolved results are consistent with those found for
galactic-scale measurements, implying the
outflow relationships are similar from the sales of $\sim$1-2 kpc to global measurements. Combined with literature measurements, these results suggest that the offset in velocities is driven not by ionisation state, but rather by the systematics associated to how absorption and emission measures trace the gas density.
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All authors Antonia Fernández-Figueroa, Glenn G Kacprzak, Deanne B Fisher, Magdalena Hamel-Bravo, Karl Glazebrook
Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc
Adaptive ray tracing, image diagnostics, and photon ring signatures of rotating dark-matter-dressed black holes
Mohsen Fathi
We study the optical appearance of rotating black holes embedded in dark matter environments using a phenomenological ray tracing framework. Rather than focusing on a single geometry, we compare two effective rotating backgrounds obtained from static dark matter sourced seed metrics: a regular Einasto-type black hole and a cored-NFW black hole. Kerr is used as the reference spacetime. We construct observer-screen images by numerical backward ray tracing and analyse the horizon structure, shadow boundary,
lensing bands, transfer maps, and synthetic intensity distributions produced by a common semi-analytic
accretion prescription. We also introduce simple image-level diagnostics, an angular-size confrontation with M87* and Sgr A*, and simplified visibility-amplitude diagnostics. These additions are not intended as an EHT fit, but as a controlled way to identify which observables are most affected by the dark matter dressing. For the representative parameters considered here, the Einasto-supported geometry remains very close to Kerr, while the cored-NFW case produces a stronger redistribution of the image, with larger centroid displacement, stronger brightness asymmetry, an outward shift of the characteristic bright-ring scale, and a visible change in the normalized visibility amplitude. The results indicate that rotating dark-matter-dressed backgrounds can produce systematic image-domain and
Fourier-domain deviations that are partially degenerate with
spin, inclination, and emission modelling. The framework is lightweight and extensible, and provides a first step toward future GRRT and GRMHD studies of rotating black holes in dark matter environments.
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Astrophysics of Galaxies
The formation of the C-19 progenitor: a primordial cluster heated by gas expulsion
Zhen Wang, Long Wang, Zhen Yuan et al. (+1 more)
The extremely metal-poor nature of the C-19 stream indicates that its progenitor was a
primordial stellar system born in the very early Universe. Current observations show that it has a small
metallicity dispersion (0.18 at the 95% confidence level), which is the signature of a globular cluster origin, while at the same time displaying an unusually large velocity dispersion ($\sim10$ km/s) typical of
dwarf galaxies. To reconcile this conflicting observational evidence, previous simulations have focused on potential interactions with dark matter subhalos, which can efficiently make a cluster stream dynamically hot. In this work, we explore internal dynamical processes in
star cluster formation, focusing on initial conditions shaped by gas expulsion and a top-heavy initial mass function. We find that the large observed velocity dispersion and broad stream morphology can be reproduced by a cluster that underwent severe gas expulsion and expansion during its birth phase, which is potentially a typical formation scenario of extremely metal-poor
star clusters. A top-heavy IMF and binaries can also increase the velocity dispersion. The formation of C-19 may involve a combination of these effects.
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All authors Zhen Wang, Long Wang, Zhen Yuan, Jiang Chang