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Keyword list: ['star formation', 'star-forming', 'molecular cloud', 'interstellar medium', 'cloud', 'clump', 'core', 'filament', 'atomic gas', 'N-PDF']

Excluded: ['galaxies', 'galaxy cluster', ' AGN ', 'standard candle', 'X-ray binar', 'solar corona']

Today: 14papers

Mapping the Distorted Dark Matter Distribution of the LMC-SMC System Prior to Milky Way Infall with Basis Function Expansions

• Authors: Hayden R. Foote, Himansh Rathore, Gurtina Besla, Nicolás Garavito-Camargo, Ekta Patel, Michael S. Petersen, Martin D. Weinberg, Facundo A. Gómez, Chervin F. P. Laporte

• Subjects: Subjects: Astrophysics of Galaxies (astro-ph.GA)

• Arxiv link: https://arxiv.org/abs/2601.00946

• Pdf link: https://arxiv.org/pdf/2601.00946

• Abstract The SMC orbits within the LMC's dark matter (DM) halo in a $\sim$1:10 mass-ratio encounter. The LMC:Milky Way (MW) interaction is also $\sim$1:10, and is expected to perturb the MW's DM distribution. However, no framework exists to quantify the severity of these perturbations over multiple pericenters and longer periods of time, such as the LMC-SMC interaction history. We construct basis function expansions of a high-resolution N-body simulation of the Clouds interacting in isolation and analyze their DM distributions at an epoch approximating the time of infall to the MW. Our goal is to quantify how the Clouds distort each other's DM distributions without the MW. The LMC halo's response to the SMC includes a $\sim 20$ kpc-long dynamical friction wake and the displacement of the LMC's density center during each SMC pericenter, which produces two overdensities in the LMC halo (at $\sim$60 and $\sim$100 kpc) at MW infall. The SMC's tidal radius at infall is just $\sim4$ kpc, at which point the SMC has lost two-thirds of its initial DM mass to the LMC. The distortions to the Clouds' halos produce a highly asymmetric acceleration field. Accurate orbit integration in the LMC-SMC system must account for the time-dependent shapes of both halos. The SMC-induced perturbations in the LMC DM halo resemble the MW-LMC system, and persist over multiple SMC pericenters. We conclude that 1:10 satellite:host encounters induce characteristic deformations in both DM halos across all host mass scales, with implications for merger rates and tests of DM models.

thornado+Flash-X: A Hybrid DG-IMEX and Finite-Volume Framework for Neutrino-Radiation Hydrodynamics in Core-Collapse Supernovae

• Authors: Eirik Endeve, Vassilios Mewes, J. Austin Harris, M. Paul Laiu, Ran Chu, Steven A. Fromm, Anthony Mezzacappa, O. E. Bronson Messer, W. Raphael Hix, Stephen W. Bruenn, Eric J. Lentz, Klaus Weide, Christian Y. Cardall, Ann S. Almgren, Anshu Dubey, Sean M. Couch, Philipp Moesta, Donald E. Willcox

• Subjects: Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM); Computational Physics (physics.comp-ph)

• Arxiv link: https://arxiv.org/abs/2601.00976

• Pdf link: https://arxiv.org/pdf/2601.00976

• Abstract We present neutrino-transport algorithms implemented in the toolkit for high-order neutrino-radiation hydrodynamics (thornado) and their coupling to self-gravitating hydrodynamics within the adaptive mesh refinement (AMR)-based multiphysics simulation framework Flash-X. thornado, developed primarily for simulations of core-collapse supernovae (CCSNe), employs a spectral, six-species two-moment formulation with algebraic closure and special-relativistic observer corrections accurate to $O(v/c)$, and uses discontinuous Galerkin (DG) methods for phase-space discretization combined with implicit-explicit time stepping. A key development is a nonlinear neutrino-matter coupling algorithm based on nested fixed-point iteration with Anderson acceleration, enabling fully implicit treatment of collisional processes, including energy-coupling interactions such as neutrino-electron scattering and pair production. Coupling to finite-volume (FV) hydrodynamics is achieved with a hybrid DG-FV representation of the fluid variables and operator-split evolution in Flash-X. The implementation is verified using basic transport tests with idealized opacities and relaxation and deleptonization problems with tabulated microphysics. Spherically symmetric CCSN simulations demonstrate accuracy and robustness of the coupled scheme, including close agreement with the CCSN simulation code Chimera. An axisymmetric CCSN simulation further demonstrates the viability of DG-based neutrino transport for multidimensional supernova modeling within Flash-X. thornado's neutrino-transport solver is GPU-enabled using OpenMP offloading or OpenACC, and all CCSN applications included in this work use the GPU implementation. Together, these results establish a foundation for future enhancements in physics fidelity, numerical algorithms, and computational performance, for increasingly realistic large-scale CCSN simulations.

The internal kinematics of local young stellar associations. Identifying correlations among age, expansion, rotation, and shear

• Authors: J. Olivares, N. Miret-Roig, P.A.B. Galli

• Subjects: Subjects: Astrophysics of Galaxies (astro-ph.GA); Solar and Stellar Astrophysics (astro-ph.SR)

• Arxiv link: https://arxiv.org/abs/2601.01006

• Pdf link: https://arxiv.org/pdf/2601.01006

• Abstract Context. The local (<200 pc away) young (<50 Myr old) stellar associations (LYSA) provide fundamental evidence for the study of the star formation process in the local neighbourhood. Aims. We aim at exploring robust statistical correlations in the internal kinematics of LYSAs and of these with age. Methods. We analyse a public data set containing the linear velocity field parameters and expansion ages of 18 LYSAs. We identify the most robust correlations using frequentist and Bayesian methods. Results. Among the 45 correlations, we identify only four that passed both frequentist and Bayesian criteria, with these four related to radial motions in the Galactic Z direction. We hypothesise several origins for these four correlations and identify the gravitational potential of the Galactic disk as the most likely driving element. It imprinted the observed motions in the parent molecular clouds, and once the stars were formed, it also damped these motions on a timescale shorter than the LYSAs' ages. Conclusions. The internal kinematics of local young stellar associations contain fundamental information about the star-formation process that is not fully addressed by star-formation theories, in particular, rotation and shear. Although the Galactic potential appears to be the driving force of these correlations, we urge the theoretical community to provide predictions about the internal motions of expansion, rotation, and shear of stellar associations.

Analysis of 14 Years of X-Ray Emission From SN 2011DH

• Authors: Elisa J. Gao, Vikram V. Dwarkadas

• Subjects: Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

• Arxiv link: https://arxiv.org/abs/2601.01365

• Pdf link: https://arxiv.org/pdf/2601.01365

• Abstract Ejecta from core-collapse supernovae interact with the circumstellar medium shed by the progenitor star, producing X-ray emission. Previous studies analyzed the X-ray spectrum of the Type IIb supernova SN 2011dh up to 500 days after explosion. Long-term monitoring of X-ray emission provides valuable constraints on supernova evolution and progenitor systems, yet such studies remain rare for Type IIb events due to limited data. Here we present the most comprehensive X-ray light curve of SN 2011dh to date, combining all available Chandra and XMM-Newton data with previously published and newly released Swift observations, extending coverage to 5100 days. We measure a luminosity decline proportional to t$^{-0.74 \pm 0.04}$ and infer a mass-loss rate of $(1.0-2.2) \times 10^{-6}$ solar masses per year for $v_w = 10$ km/s, or $(2.0-4.4) \times 10^{-6} $ solar masses per year for $v_w = 20$ km/s. These estimates agree with earlier results, supporting the interpretation that the X-ray emission has been dominated by an adiabatic reverse shock. The consistency of our late-time results with previous studies demonstrates that SN 2011dh has evolved steadily for nearly 14 years.

Classifying Core-Collapse Supernova Gravitational Waves using Supervised Contrastive Learning

• Authors: Ao-Bo Wang, Yong Yuan, Hao Cai, Xi-Long Fan

• Subjects: Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

• Arxiv link: https://arxiv.org/abs/2601.01376

• Pdf link: https://arxiv.org/pdf/2601.01376

• Abstract The detection and reconstruction of gravitational waves from core-collapse supernovae (CCSN) present significant challenges due to the highly stochastic nature of the signals and the complexity of detector noise. In this work, we introduce a deep learning framework utilizing a ResNet-50 encoder pre-trained via supervised contrastive learning to classify CCSN signals and distinguish them from instrumental noise artifacts. Our approach explicitly optimizes the feature space to maximize intra-class compactness and inter-class separability. Using a simulated four-detector network (LIGO Hanford, LIGO Livingston, Virgo, and KAGRA) and realistic datasets injecting magnetorotational and neutrino-driven waveforms, we demonstrate that the contrastive learning paradigm establishes a superior metric structure within the embedding space, significantly enhancing detection efficiency. At a false positive rate of $10^{-4}$, our method achieves a true positive rate (TPR) of nearly $100%$ for both rotational and neutrino-driven signals within a distance range of $10$--$200$~kpc, while maintaining a TPR of approximately $80%$ at $1200$~kpc. In contrast, traditional end-to-end methods yield a TPR below $20%$ for rotational signals at distances $\geq 200$~kpc, and fail to exceed $60%$ for neutrino-driven signals even at a close proximity of $10$~kpc.

Turbulence driving in a star-forming Milky-Way-type galaxy

• Authors: Isabella A. Gerrard, Christoph Federrath

• Subjects: Subjects: Astrophysics of Galaxies (astro-ph.GA); Instrumentation and Methods for Astrophysics (astro-ph.IM); Solar and Stellar Astrophysics (astro-ph.SR)

• Arxiv link: https://arxiv.org/abs/2601.01427

• Pdf link: https://arxiv.org/pdf/2601.01427

• Abstract The life-cycle, structure, and dynamics of the interstellar medium (ISM) is regulated by turbulence. Complex physical processes, including supernova (SN) explosions, shear, and gravitational collapse, drive and maintain turbulence, but it is still an open question what turbulence driving mode is primarily excited by these different mechanisms. The turbulence driving parameter, b, can be used to quantify the ratio of solenoidal to compressive modes in the acceleration field that drives the turbulence. Compressive driving is characterised by b ~ 1, while purely solenoidal driving gives b ~ 0.3. To quantify the turbulence in the galactic ISM, we investigate the time evolution of b, as well as the turbulent Mach number, and plasma beta (thermal-to-magnetic pressure ratio), and its correlation with star formation in the magnetised warm neutral medium (WNM) of the TIGRESS shearing-box simulations of a kpc-sized patch of a Milky-Way-like galaxy, over a 100 Myr time period (~ half an orbital time). In this simulation the turbulence is driven by a combination of shear, gravitational collapse, and star formation feedback in the form of radiation and SNe. We find that the turbulence driving parameter fluctuates in time between b ~ 0.4 and b ~ 1. We find a time-dependent correlation of b with star formation activity, such that high star formation rates follow about one turbulent turnover time (~ 10 Myr) after phases of highly compressive driving (b > 0.5). About 20 Myr after the peak in star formation, type-B SN feedback drives up the WNM fraction and turbulent Mach numbers, and reduces plasma beta and the driving to b ~ 0.4-0.5.

Spheroidal core-mantle particle absorption, scattering, and polarisation in the long-wavelength limit

• Authors: Ant Jones, Nathalie Ysard

• Subjects: Subjects: Astrophysics of Galaxies (astro-ph.GA); Optics (physics.optics)

• Arxiv link: https://arxiv.org/abs/2601.01515

• Pdf link: https://arxiv.org/pdf/2601.01515

• Abstract The numerical calculation of optical properties (extinction, absorption, scattering and polarisation efficiencies) is often time-consuming for non-spherical and inhomogeneous particles. Where possible analytical methods are therefore to be preferred. We provide an analytical tool to derive the optical properties of mantled spheroidal particles, of arbitrary axis ratio, in the long wavelength limit (a << lambda), where the mantle form may be confocal, co-axial or of constant depth with respect to the particle core. We have developed an analytical approach to spheroidal core/mantle particle optical property calculations. The analytical method compares well with DDSCAT numerical calculations and, under limited circumstances, with those made using the Bruggemann effective medium theory (EMT).The analytical method presented here provides a useful tool to explore the optical and polarisation properties of core/mantle spheroidal particles at long wavelengths (lambda >~ 8mu) and is simpler and faster to implement than corresponding numerical methods. We caution against the use of EMT methods in approximating the optical properties of core/mantle particles.

Cracks in the Standard Cosmological Model: Anomalies, Tensions, and Hints of New Physics

• Authors: Eleonora Di Valentino

• Subjects: Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

• Arxiv link: https://arxiv.org/abs/2601.01525

• Pdf link: https://arxiv.org/pdf/2601.01525

• Abstract Cosmology has entered an era of unprecedented precision, yet increasing accuracy has revealed cracks in the standard $\Lambda$CDM paradigm. Although the model remains highly successful when confronted with individual datasets, joint analyses expose a network of tensions involving the Hubble constant, CMB lensing, curvature, neutrino masses, and the nature of dark energy. In this contribution to the 3rd General Meeting of the COST Action COSMIC WISPers (CA21106), within the context of Working Group~2, we critically assess these discrepancies, emphasizing the role of model assumptions, parameter degeneracies, and dataset consistency. We review proposed early- and late-time solutions, discuss how recent DESI BAO results alter the viability of late-time extensions, and explore interacting dark-sector scenarios. Our analysis highlights the need for caution in interpreting cosmological measurements and underscores the importance of internal consistency among cosmological probes before claiming percent-level accuracy or invoking new physics.

Inferring physical parameters of solar filaments from simultaneous longitudinal and transverse oscillations

• Authors: Upasna Baweja, Vaibhav Pant, Iñigo Arregui, M. Saleem Khan

• Subjects: Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

• Arxiv link: https://arxiv.org/abs/2601.01730

• Pdf link: https://arxiv.org/pdf/2601.01730

• Abstract Context. Different modes of oscillations are frequently observed in solar prominences/filaments, and prominence seismology helps estimate important physical parameters like the magnetic field strength. Although the simultaneous detection of longitudinal and transverse oscillations in the same filament is not common, such rare observations provide a unique opportunity to constrain the physical parameters of interest. Aims. In this study, we aim to estimate the physical parameters of prominences undergoing simultaneous longitudinal and transverse oscillations. Methods. We apply Bayesian seismology techniques to observations of longitudinal and transverse filament oscillations to infer the magnetic field strength, the length, and the number of twists in the flux tube holding the prominence plasma. We first use the observations of longitudinal oscillations and the pendulum model to infer the posterior probability density for the magnetic field strength. The obtained marginal posterior of the magnetic field, combined with the observations of the transverse oscillations, is then used to estimate the probable values of the length of the magnetic flux tube that supports the filament material using Bayesian inference. This estimated length is used to compute the number of twists in the flux tube. Results. For the prominences under study, we find that the length of the flux tubes supporting the quiescent prominences can be very large (from 100 to 1000 Mm) and the number of twists in the flux tube are not more than three. Conclusions. Our results demonstrate that Bayesian analysis offers valuable methods to perform parameter inference in the context of prominence seismology.

Exploring the interplay between molecular and ionized gas in HII regions

• Authors: S. Khan, A. M. Jacob, M. R. Rugel, J. S. Urquhart, S. Neupane, F. Wyrowski, A. Brunthaler, J. D. Pandian, Y. Gong, I. Barlach Christensen, K. M. Menten

• Subjects: Subjects: Astrophysics of Galaxies (astro-ph.GA)

• Arxiv link: https://arxiv.org/abs/2601.01748

• Pdf link: https://arxiv.org/pdf/2601.01748

• Abstract We aim to constrain the kinetic temperature and H$2$ volume density of massive star-forming clumps associated with HII regions using multiple para-H$2$CO transitions. In addition, we investigate the interplay between ionized gas, molecular gas, and dust to probe how massive stars influence their parental clumps. We observed the $J{K_aK_c}$ transitions of para-H2CO (within its J = 3-2 and 4-3 states) with the Atacama Pathfinder EXperiment (APEX) 12 m submillimeter telescope using the nFLASH230 and SEPIA345 receivers towards a sample of 61 HII regions. Spectral line parameters are derived via multi-component Gaussian fitting, which was then used to constrain the physical conditions determined using PyRADEX, a non-local thermodynamic equilibrium (LTE) radiative transfer code in combination with Markov Chain Monte Carlo (MCMC) analysis. The non-LTE analysis yielded kinetic temperatures ($T{kin}$) ranging from 33.7 K to 265 K and H2 densities (n(H$_2$)) between 0.8 X $10^4$ to 1.05 X $10^7$ cm$^{-3}$, providing a detailed characterization of the dense molecular gas contained in these clumps. In addition to the para-H$_2$CO emission arising from the targeted clump a large fraction (57%) of the sources exhibit multiple para-H$2$CO components, with the secondary components being characterized by higher $T{kin}$ and broader linewidths. Investigating the nature of the secondary component revealed its association with supersonic non-thermal motions and turbulent gas. When comparing the physical properties of the molecular gas and dust components with those of the ionizing gas, we find that parameters directly linked to the central high-mass star such as bolometric luminosity and Lyman continuum photon rate, show stronger and more systematic correlations. Emphasizing the role of the central star in governing the interplay between the molecular and ionized gas.(Abridged)

Unveiling Fiber Networks and Core Formation in the DR21 South Filament

• Authors: Kai Yang, Keping Qiu, Xing Pan

• Subjects: Subjects: Astrophysics of Galaxies (astro-ph.GA)

• Arxiv link: https://arxiv.org/abs/2601.01974

• Pdf link: https://arxiv.org/pdf/2601.01974

• Abstract We present high-resolution ($\sim$1000 AU) 3 mm observations with the NOrthern Extended Millimeter Array toward the DR21 South Filament, aiming to reveal its internal fragmentation and search for deeply embedded star-forming activities. Both the continuum and molecular line emissions align well with the filament axis traced by the low-resolution ($\sim$18$^{\prime\prime}$) column density map. The 3 mm continuum, CS (2$-$1), and HCO$^+$ (1$-$0) emissions reveal continuous and diffuse structures with measured FWHM widths of 0.054, 0.029, and 0.030 pc, respectively. In contrast, the H$^{13}$CO$^+$ (1$-$0) emission appears more clumpy and localized. The non-thermal motion in the filament is predominantly subsonic to transonic. We detect 13 dense cores in NH$2$D (1${11}-1_{01}$), three of which coincide with continuum peaks; virial analysis suggests most are gravitationally bound. Using a friend-of-friend algorithm, we identify 32, 34, and 22 velocity-coherent fibers from the CS, HCO$^+$, and H$^{13}$CO$^+$ data, respectively. Compared to fibers traced by CS and HCO$^+$, H$^{13}$CO$^+$ fibers are more frequently associated with NH$_2$D cold cores and exhibit higher average mass-per-unit-length values. Differences among CS, HCO$^+$, and H$^{13}$CO$^+$ emissions likely arise from variations in effective critical densities. These results are consistent with a hierarchical structure, in which the 3.6-pc DR21SF contains velocity-coherent fibers and gravitationally bound dense cores.

A phoenix rises from the ashes: WOH G64 is still a red supergiant, for now

• Authors: Jacco Th. van Loon (Keele University, UK), Keiichi Ohnaka (Universidad Andres Bello, Chile)

• Subjects: Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

• Arxiv link: https://arxiv.org/abs/2601.02057

• Pdf link: https://arxiv.org/pdf/2601.02057

• Abstract For a long time, WOH G64 was known as the most extreme red supergiant outside our Galaxy. However, in a matter of years it has faded, its pulsations have become suppressed and the spectrum has become dominated by emission lines from ionised gas, a far cry from the Mira-like pulsation and late M-type spectrum it used to display. Around the same time, a hot dust cloud was discovered using the VLT interferometer. WOH G64 has been claimed to have turned into a yellow hypergiant, which could signal a pre-supernova post-red supergiant evolution. Here we present spectra of WOH G64 obtained with the Southern African Large Telescope (SALT) between November 2024 and December 2025. Molecular absorption bands from TiO are seen at all times. This implies that WOH G64 is currently a red supergiant, and may never have ceased to be. However, the shallow, resolved bands and possible detection of VO hint at a highly extended atmosphere. The continuum appears to be varying, while the line emission shows a different behaviour, suggesting two separate components in the system. Meanwhile, atomic absorption lines are deepening. This places important constraints on scenarios for the dramatic events that are unfolding.

Spectral signatures of bright grains determine chromospheric heating

• Authors: Elias R. Udnæs, Tiago M.D. Pereira

• Subjects: Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

• Arxiv link: https://arxiv.org/abs/2601.02191

• Pdf link: https://arxiv.org/pdf/2601.02191

• Abstract Chromospheric heating is an important ingredient in the energy budget of the solar atmosphere, which is challenging to quantify from observations. By using 3D radiative magnetohydrodynamic simulations of the solar atmosphere combined with non-LTE spectral synthesis, we estimated chromospheric heating from synthetic spectra and studied the spectral and temporal signatures of heating events. We performed k-means clustering on the Mg II h, Ca II H, and Ca II 8542 Å lines to identify representative profiles associated with elevated chromospheric heating and studied their atmospheric stratification. We find that locations with the strongest chromospheric heating show spectral signatures with strong emission. Profiles with strong emission in the blue wing of the lines (blue grains) are created by upward-propagating shock waves and have an order of magnitude higher heating in the chromosphere than the ambient heating. Profiles with strong emission in the red wing (red grains) also display heating that is an order of magnitude stronger than the baseline, but these spectra do not show a characteristic atmospheric stratification. Spectra classified as blue grains have a consistent temporal evolution, which is an oscillating sawtooth pattern in the line core and emission in the blue wing. However, spectra classified as red grains did not show a consistent temporal signature: Red wing emission from the simulations can appear spontaneously or be associated with an oscillation. While red and blue grain profiles account for around 3% of our synthetic spectra, they account for more than 12% of the total chromospheric heating in these simulations. By comparing two quiet Sun simulations, we find that the prevalence of bright grains is influenced by the magnetic field configuration, with a unipolar configuration showing fewer bright grains and consequently a lower share of heating from such events.

The Polarization and Magnetic Field of the Radio Arc as Observed by ALMA at 100 GHz

• Authors: Nora Salem, Dylan M. Paré, Paulo Cortes, Mark R. Morris, Valentin J. M. Le Gouellec

• Subjects: Subjects: Astrophysics of Galaxies (astro-ph.GA)

• Arxiv link: https://arxiv.org/abs/2601.02297

• Pdf link: https://arxiv.org/pdf/2601.02297

• Abstract The unique Galactic Center non-thermal filaments (NTFs) have been a focus of investigations for over 40 years. The most prominent manifestation of the NTFs is a bundle of parallel filaments known as the Radio Arc. Radio polarimetric observations made with the Very Large Array (VLA) at 10 GHz have revealed an alternating magnetic field pattern in the Radio Arc that could either be a result of multiple field systems being encountered along the line of sight or an intrinsic feature of the Radio Arc. These VLA observations were not able to distinguish between these possibilities due to the large rotation measures encountered towards the source. We present ALMA 100 GHz observations of the Radio Arc that are not impacted by significant Faraday effects. The observations reported here represent both the first time that ALMA has been used to study the NTFs and the first time 100 GHz polarimetric observations have been conducted on the Radio Arc. We find a uniformly rotated magnetic field with respect to the NTF filament orientation, with the angle of rotation being constant along the length of each filament. However, we find a systematically different magnetic field orientation in different Radio Arc filaments. We use this field pattern to update our understanding of the line-of-sight structures local to the Radio Arc. We find that the magnetic field inferred from our ALMA observations is likely a result either of confusion from multiple magnetic field systems or because the polarization is centrally concentrated within the NTF filaments.

by olozhika (Xing Yuchen).

2026-01-06