Showing new listings for Tuesday, 12 May 2026

Auto update Star Formation & Molecular Cloud papers at about 2:30am UTC (10:30am Beijing time) every weekday.

阅读 Usage.md了解如何使用此repo实现个性化的Arxiv论文推送

See Usage.md for instructions on how to personalize the repo.

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: 18papers

An Inverse-Compton-Boosted Cool Core Unifies Perseus's Radio and X-ray Halos

• Authors: Philip F. Hopkins, Emily M. Silich, Jack Sayers, Sam B. Ponnada, Isabel S. Sands

• Subjects: Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Cosmology and Nongalactic Astrophysics (astro-ph.CO); Astrophysics of Galaxies (astro-ph.GA)

• Arxiv link: https://arxiv.org/abs/2605.08349

• Pdf link: https://arxiv.org/pdf/2605.08349

• Abstract Perseus is the brightest X-ray strong cool-core (SCC) cluster, with a bright central radio and $\gamma$-ray source plus low-frequency radio mini and giant halos. It is the archetype of the cooling flow (CF) problem, with X-rays implying mass cooling rates orders-of-magnitude larger than observed in other channels. Recent work suggested that ancient ($\gtrsim$,Gyr-old) cosmic ray (CR) halos (ACRHs), injected by the central source, would produce thermal-like soft X-ray inverse-Compton (CR-IC) emission 'boosting' the CC and alleviating the CF problem. We examine Perseus and show that a simple model of CRs injected by NGC 1275 (+satellites) simultaneously accounts for the excess CF luminosity and minihalo. The models reproduce Perseus's soft X-ray surface brightness and X-ray inferred density/temperature/pressure/metallicity/cooling time/mass deposition rates; $\gamma$-ray spectra; extended hard X-rays; and radio surface brightness and spectral index data, from kpc-Mpc. These also reproduce independent constraints on magnetic field strengths and mass/potential models. The evolution of the minihalo spectral index and surface brightness are predicted by an aging population of CRs boosting the apparent SCC luminosity via CR-IC, and match well the observed hard X-ray slopes. The 'giant' low-frequency halo can be predicted by the sum of ACRHs around satellites distributed throughout the cluster, dominating diffuse synchrotron at $\gtrsim 100,$kpc. Re-acceleration is neither needed nor important in these models, and implied CR transport speeds are consistent with buoyant advection. Previous claims of upper limits to non-thermal X-rays and CR pressure relied on strong assumptions which are not valid at the CR energies of interest, e.g. a power-law spectrum of CRs. This could resolve many historical puzzles about Perseus, and makes new predictions for future observations.

Unmasking Stellar Feedback-Driven Bubbles: Identification and Properties Analysis

• Authors: Aaron Angress, Michael M. Foley, Sarah M. R. Jeffreson, Alyssa Goodman, Lars Hernquist

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

• Arxiv link: https://arxiv.org/abs/2605.08534

• Pdf link: https://arxiv.org/pdf/2605.08534

• Abstract The identification and tracking of stellar feedback-driven galaxy bubbles is an important topic in star formation and galactic structure research. However, current observational analysis of bubbles is limited in scope; information on bubble lifetime is inaccessible. Simulation data thus provides a unique opportunity to glean some of these characteristics at high resolution. We present an investigation into the characteristics and evolution of hot, ionized bubbles in the interstellar medium of a dwarf spiral (NGC300-like) galaxy. We calculate the average radius, lifetime, temperature, density, and spatial distribution of the simulated feedback-driven bubbles using Lagrangian gas parcels, and we examine the relationship between these characteristics and the local galactic environment. We find exponential distributions of bubble lifetime and size, and we find a positive correlation between bubble lifetime and galactocentric radius. Finally, we predict how the data would appear in H$\alpha$ tracers and compare the simulated values to observations. We find an additional positive correlation between the size of the bubbles and the galactocentric radius using their H$\alpha$ tracers.

Non-Parametric Equation of State Reveals Non-Conformal Behavior Beyond Neutron Star Densities

• Authors: Yong-Jia Huang, Shao-Peng Tang, Yi-Zhong Fan

• Subjects: Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); General Relativity and Quantum Cosmology (gr-qc); Nuclear Theory (nucl-th)

• Arxiv link: https://arxiv.org/abs/2605.08584

• Pdf link: https://arxiv.org/pdf/2605.08584

• Abstract We propose a non-parametric approach to construct the statistical equation of state (EOS) continuously from the nuclear crust to the asymptotic-freedom regime. Driven by the observationally required stiffening to support two-solar-mass neutron stars (NSs) with relatively small radii for low-mass NSs, this global thermodynamic constraint suggests a clear peak of squared sound speed ($c_s^2$) in massive NSs. To prevent overshooting perturbative QCD (pQCD) energy-density bounds, this early stiffening must be actively compensated by an extended density range of softening, with $c_s^2$ not approaching $1/3$ until $\sim!30,n_{\rm sat}$. Consistently, the trace anomaly $\Delta \equiv 1/3 - p/\epsilon$ becomes positive beyond NS densities and approaches the pQCD limit from above. This natural emergence of $\Delta > 0$ organically aligns with some anticipated microphysics, likely arising from the pressure dilution in a quark-hadron mixed phase, non-conformal pQCD corrections to quark-gluon interactions, or the symmetry-breaking effects of finite strange quark mass. By measuring the degree of this non-monotonic behavior in the posterior, we find evidence for a hadron-quark phase transition in the cores of the most massive neutron stars. This indicates that the non-perturbative quark matter is intrinsically soft, fundamentally distinguishing it from the stiff scenarios associated with the quark-star picture.

The evolution of C4H and c-C3H2 in molecular cores

• Authors: Yijia Liu, Junzhi Wang, Ningyu Tang, Yajiang Lu, Donghui Quan, Juan Li, Kai Yang, Shu Liu, Yuqiang Li, Siqi Zheng, Chao Ou

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

• Arxiv link: https://arxiv.org/abs/2605.08790

• Pdf link: https://arxiv.org/pdf/2605.08790

• Abstract Linear C4H and cyclic c-C3H2, as small unsaturated hydrocarbons, are the key precursors to complex organic molecules and are critical components of the interstellar medium. We present on-the-fly mapping observations of C4H 9-8 lines, c-C3H2 2-1, H13CO+ 1-0, and H42 toward a sample of 22 massive star-forming regions using the IRAM 30m telescope. Our aim is to further explore the evolution of these carbon-chain molecules by combining observational results obtained in cold cores. We employed H13CO+ 1-0 and H42 as tracers to probe the positions of molecular cloud cores and ionised hydrogen regions (HII regions), respectively. One chemical model in particular, which includes gas, dust grain surface, and icy mantle phases for C4H and c-C3H2 molecules, was used to make comparisons with observed abundances. From mapping observations targeting 31 regions across 22 sources, C4H 9-8 (J = 19/2-17/2) and C4H 9-8 (J = 17/2-15/2) were detected in only 17 regions, while H13CO+ 1-0 and c-C3H2 2-1 were successfully detected in all 31 regions. We find that the emission of C4H 9-8 and c-C3H2 2-1 is concentrated at the edges of H42 emission regions. The C4H/H13CO+ and c-C3H2/H13CO+ relative abundance ratios range from 0.17 to 1.77 and 1.42 to 6.69, respectively, with a median C4H/c-C3H2 ratio of 0.13. By combining the observational results of cold cores, we find that C4H/H13CO+ and c-C3H2/H13CO+ ratios show a strong decreasing trend as molecular cores evolve. The decreasing trends in C4H/H13CO+ and c-C3H2/H13CO+ ratios imply that small unsaturated hydrocarbons can be consumed and converted into other organic molecules during the evolution of molecular cores. The spatial concentration of C4H and c-C3H2 emission at the edges of H42 regions further supports their role as precursors in the chemical pathways that lead to complex organic molecules in the interstellar medium.

When Magnetic Fields Sculpt the Sky: The Riegel-Crutcher cloud in optical polarization

• Authors: Gabriel A. P. Franco, Mayara Gomides, Zhi-Yun Li, Fabio P. Santos, Farideh S. Tabatabaei

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

• Arxiv link: https://arxiv.org/abs/2605.08823

• Pdf link: https://arxiv.org/pdf/2605.08823

• Abstract Filamentary structures are ubiquitous in the interstellar medium, yet the extent to which magnetic fields influence the morphology of cold atomic gas remains an open question. The nearby Riegel-Crutcher cloud, composed of long and narrow H I filaments observed in self-absorption, provides a critical test case. We present the most extensive optical polarimetric survey of this region to date, comprising more than 90,000 high signal-to-noise stellar polarization measurements combined with Gaia DR3 data. Using stellar polarization, extinction estimates, and archival Na I absorption data, we locate the cloud at a distance of $150 \pm 15$ pc, consistent with that of the Pipe Nebula. The plane-of-sky magnetic field traced by optical starlight polarization closely matches that inferred independently from Planck 353 GHz dust-emission polarization, revealing a coherent large-scale magnetic field across the region. A Rolling Hough Transform analysis shows that the H I filaments are tightly aligned with this field orientation. Together, these results provide strong observational evidence that the structure of the cold neutral medium in the Riegel-Crutcher cloud is closely linked to a highly ordered magnetic field. This level of coherence supports a scenario in which magnetic fields play a dynamically important role in shaping the cloud structure, and suggests that the Riegel-Crutcher cloud is part of a larger magnetized complex influencing gas flows in the solar neighborhood.

Exploring Enceladus's Interior Structure Using Electromagnetic Induction

• Authors: Alexander Grayver, Joachim Saur

• Subjects: Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Geophysics (physics.geo-ph); Space Physics (physics.space-ph)

• Arxiv link: https://arxiv.org/abs/2605.09052

• Pdf link: https://arxiv.org/pdf/2605.09052

• Abstract Electromagnetic (EM) sounding can constrain the electrical structure of Enceladus and, in turn, the salinity of its ocean and the porosity, fluid content, and thermal state of its hydrothermally active core. Here, we assess the feasibility of EM sounding at Enceladus using both global (orbiter) and local (lander) EM induction transfer functions. We provide a physical framework for modeling EM induction for 1-D and 3-D subsurface conductivity models and discuss how transfer functions can be estimated from global or local measurements of the magnetic and electric fields. We simulate 3-D induction effects arising from variations in ice-shell thickness. The magnitude of these effects in the magnetic field correlates with the ice-shell thickness at the surface and is strongly dependent on the ocean's conductivity. These magnetic variations, if observed, would favor a moderately to highly conductive ocean, providing lower bounds on salinity and volatile content. The absence of these effects indicates a thicker, more homogeneous ice shell and/or a lower-conductivity ocean. Given plausible magnitudes, a polar-orbiting mission with low-altitude measurements will be required to detect these effects. In summary, an orbiter will constrain global ocean conductivity using long-period induction and possibly map the ice thickness variations. The detailed EM sounding of both the hydrosphere and the core can be achieved by a lander-based broadband EM sounding at periods $\approx 10^1-10^5$ s to probe ocean salinity and thickness, as well as core properties including porosity, fluid content, and temperature.

Characterizing the Scale Height and Filamentary Structure of Radiatively Cooled MADs

• Authors: Akshay Singh (1), Damien Begue (1), Asaf Pe'er (1) ((1) Bar-Ilan University)

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

• Arxiv link: https://arxiv.org/abs/2605.09326

• Pdf link: https://arxiv.org/pdf/2605.09326

• Abstract Radiative cooling can strongly influence the structure and dynamics of black hole accretion disks. Here, we perform general relativistic magnetohydrodynamic (GR-MHD) simulations of magnetically arrested disks (MADs) around a non-spinning black hole. Radiative cooling is consistently included in the simulations and its intensity is scaled by the mass accretion rate ranging from $10^{-7}$ to $10^{-4} \dot{M}_{\mathrm{Edd}}$. Considering synchrotron and bremsstrahlung emission, we quantify how radiative losses modify the disk structure and the accretion dynamics. In the inner MAD disk regions, accumulation of magnetic field regulates gas accretion, enforcing the gas into a discrete interchange-driven filamentary structure. We identify, both analytically and numerically, a transition mass accretion rate above which radiative cooling becomes faster than the heating, which is assumed to occur via local coupling to the magnetic field. Above this mass accretion rate, cooling substantially reduces the gas thermal pressure, leading to considerably thinner and denser accretion filaments, and a substantial increase in radiative efficiency, relative to lower accretion rates. We show that under these conditions, conventional measures of the disk scale height become misleading in MAD flows. We therefore introduce an alternative definition based on the polar position of the density maximum, which more robustly characterizes the filamentary structure of the disks in the presence of strong magnetic fields and cooling.

Physical characterization and modeling of candidate Hyper-Compact HII Regions

• Authors: I. T. Rodríguez-Esnard, S. Kurtz, J. D. Pandian, J. Franco, A. Sánchez-Monge, M. A. Trinidad, V. Migenes

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

• Arxiv link: https://arxiv.org/abs/2605.09412

• Pdf link: https://arxiv.org/pdf/2605.09412

• Abstract Hypercompact HII regions (HC) are regions of ionized gas associated with the early stages of high-mass star formation. With the aim of better understanding their characteristics, we studied five candidate HC HII regions. Here, we present observations with the Jansky Very Large Array (VLA) at 2 and 6 cm, with angular resolutions in the range of $\sim$1 -- 3\arcsec and report the images of the detected sources and the measured parameters. In addition, we explore several possible scenarios, considering the regions as both uniform and non-uniform spheres, and as winds, both spherical and collimated. In most cases, the sources were unresolved, but by applying the models, we estimate that their sizes vary in a range of 0.3 to 3.7 mpc while their electron densities are in the range of $1.3 \times 10^{5}$ to $2.4 \times 10^{6}$ cm$^{-3}$, indicating that most sources are consistent with small, weak UC HII regions, although a few remain viable candidates for HC HII regions, with G40.28$-$0.22 as the strongest case. We do not rule out the possibility that some sources are jets or stellar winds.

Simulating Star Formation and Star Cluster Assembly in the Aquila Rift Using Archival Observations

• Authors: Jeremy Karam, Michiko S. Fujii, Rachel Friesen, Alison Sills

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

• Arxiv link: https://arxiv.org/abs/2605.09837

• Pdf link: https://arxiv.org/pdf/2605.09837

• Abstract We simulate star formation and star cluster assembly inside a molecular cloud with parameters we derive directly from observations of the Aquila Rift. We model the evolution of stars and gas together while resolving close encounters between stars, the formation of new stars, and stellar feedback to follow cluster formation up to the expulsion of the surrounding gas. We find that star formation takes place in clumps spaced unevenly along Serpens South and that these clumps accrete surrounding gas to grow and form new stars. Gas flows along the filament promote the merger of these clumps into a star cluster inside the Serpens South filament. The imprints of these mergers are seen in the dynamics of the Serpens South cluster in the form of velocity space anisotropies, cluster rotation, and cluster expansion. Before gas is removed from the simulation, the Serpens South cluster merges with the nearby cluster W40 non-monolithically resulting in a fractal cluster at the end of the simulation. The dynamics inherited from the mergers throughout the simulation are still seen in the final bound stellar system after the gas has been removed. We compare these results with recent observations of Milky Way clusters to comment on their formation histories. We also study how our results change when lowering the mass resolution of our simulation and removing observations of dense gas tracers from our initial condition setup. Each of the three simulations result in different final cluster configurations pointing towards the importance of gas in cluster assembly.

RAYTHEIA: A high-performance ray-tracing algorithm for three-dimensional direction-dependent equations in astronomical simulations

• Authors: Zhengping Zhu, Thomas G. Bisbas, Xuefei Tang, Brandt A.L. Gaches, Tianwei Zhang, Huaxi Chen

• Subjects: Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM)

• Arxiv link: https://arxiv.org/abs/2605.09882

• Pdf link: https://arxiv.org/pdf/2605.09882

• Abstract We present RAYTHEIA, a high-performance reverse ray-tracing algorithm designed to efficiently solve three-dimensional direction-dependent equations in astronomical simulations. The algorithm uses a dual-grid framework in which the native simulation mesh -- serving as the source grid for ray emission -- and an adaptive mesh refinement (AMR) Cartesian contribution grid are constructed for efficient ray-walking and contribution accumulation. The core of the algorithm integrates a leaf-only linear-octree data structure to reduce memory overhead, the digital differential analyzer (DDA) traversal method to efficiently determine the ray-walking path, Morton Code indexing to fast leaf cell lookup during traversal, and the slab method to analytically compute the path length. Furthermore, RAYTHEIA employs a hybrid (MPI/OpenMP) distributed parallel framework with a chunk-to-chunk communication strategy, achieving exceptional, near-ideal linear speed-up ratio and delivering high-end performance. We integrate RAYTHEIA with the 3D-PDR code to solve the complex chemistry and radiation transfer in photodissociation regions (PDRs). This allowed the modelling of three-dimensional PDR chemistry in a turbulent, star-forming cloud at an unprecedented resolution of $512^3$ grid cells. The algorithm demonstrates accuracy and convergence even at low angular resolutions. We further showcase the capabilities of RAYTHEIA by producing high-resolution synthetic emission maps of key diagnostic lines of a star-forming region capturing physical effects such as [O I] $63\mu$m self-absorption, measuring the [C I]-bright but CO-dark molecular gas, and deriving a CO-to-H$_2$ conversion factor in agreement with observations.

On the Problem of Prognostication of Bright Kreutz Sungrazers

• Authors: Zdenek Sekanina

• Subjects: Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

• Arxiv link: https://arxiv.org/abs/2605.09938

• Pdf link: https://arxiv.org/pdf/2605.09938

• Abstract Tidal fragmentation at perihelion and nontidal fragmentation elsewhere cause the orbital distribution of Kreutz sungrazers of all sizes to be extremely complicated and highly nonuniform. Among the features are (largely fortuitous) clusters of bright (naked-eye) objects and clumps of dwarf objects (often closely genetically related, as their detection primarily by the SOHO coronagraphs suggests) on the one hand; and both spectacular and less brilliant sibling sungrazers, whose perihelion times are scattered over centuries, on the other hand. Investigation of four fragment nuclei of the Great September Comet of 1882, the products of a perihelion breakup of the comet's original nucleus, showed that their orbital periods followed a distinct pattern, which likewise applied to other tidally split sungrazers and was characterized by a specific value of the second difference of parameter u_frg of neighboring fragments' centers of mass. The algorithm has a potential for the prognostication of bright Kreutz sungrazers over the rest of the 21st century and beyond. However, because of its as yet unverified empirical character, the utmost caution should be exercised when applying the procedure.

Astrophysical signatures of Kerr-Bertotti-Robinson black holes in a cloud of strings: ISCO, microquasar QPOs, and Bondi-Hoyle-Lyttleton accretion

• Authors: Faizuddin Ahmed, Orhan Donmez, Ahmad Al-Badawi, Izzet Sakalli

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

• Arxiv link: https://arxiv.org/abs/2605.10214

• Pdf link: https://arxiv.org/pdf/2605.10214

• Abstract We study test-particle dynamics in the equatorial plane of a Kerr-Bertotti-Robinson black hole (BH) immersed in a cloud of strings (CS), with mass M , rotation a, magnetic parameter B, and string parameter {\alpha}. Using the Hamilton formalism we recover the effective potential Ueff and the conditions for circular motion, and we compute the specific energy E and specific angular momentum L together with the radial, vertical, and azimuthal epicyclic frequencies {\nu}r , {\nu}{\theta} , {\nu}{\phi}. Going beyond the analytic setup, we provide the first numerical mapping of the innermost stable circular orbit (ISCO) for this background and tabulate rISCO, EISCO, LISCO, and the accretion efficiency {\eta} = 1 - EISCO for both co- and counter-rotating motion across a wide (a, B, {\alpha}) grid. The CS parameter pushes the ISCO outward and raises {\eta} from 0.057 in Schwarzschild to above 0.25 for {\alpha} = 0.30 at a = 0.9. We then connect the model with observed twin-peak high-frequency quasi-periodic oscillations (QPOs) in three microquasars (GRO J1655-40, XTE J1550-564, GRS 1915+105) using the relativistic-precession (RP) model and find {chi}^2-minimum fits with {\alpha} < 0.13. A general-relativistic hydrodynamical (GRH) study of Bondi-Hoyle-Lyttleton (BHL) accretion completes the picture: the CS contribution sustains shock-cone instabilities, redistributes power-spectral-density (PSD) peaks, and produces low-frequency QPO-like components that distinguish KBR+CS from pure Kerr or KBR.

Dynamic Competition of Fast and Collisional Neutrino Flavor Instabilities with Collisional Damping in Spatially Inhomogeneous Systems

• Authors: Shota Takahashi, Hiroki Nagakura, Masamichi Zaizen, Chinami Kato, Jiabao Liu

• Subjects: Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); High Energy Physics - Phenomenology (hep-ph)

• Arxiv link: https://arxiv.org/abs/2605.10435

• Pdf link: https://arxiv.org/pdf/2605.10435

• Abstract Neutrino flavor evolution in dense astrophysical environments such as core-collapse supernova (CCSN) is influenced by collective effects. While the Fast Flavor Instability (FFI) and the Collisional Flavor Instability (CFI) are recognized as key drivers of rapid flavor conversion, their non-linear competition with collisional damping in spatially varying environments remains poorly understood. Motivated by recent findings that FFI and resonance-like CFI co-occur in the post-bounce phase in CCSN, we scrutinize their dynamic competitions and asymptotic states. To this end, we perform numerical simulations of the quantum kinetic neutrino transport, incorporating both spatial advection and the collision terms. We demonstrate that the interplay between these coexisting neutrino flavor instabilities and collisions leads to rich dynamics. Rather than merely inducing simple decoherence, collisional damping can substantially alter the overall dynamics of collective flavor oscillations, driving the system through complex evolutionary pathways. In all cases where flavor instability develops, we find that the system converges to the same flavor-equilibrated asymptotic state, despite the diversity of intermediate dynamics. Our results suggest that this dynamic competition could alter the widely accepted picture of collisionless FFI, highlighting the need to incorporate realistic collisional effects into studies of flavor conversions in CCSN models.

Co-evolution of the Milky Way high- and low-α sequences with chemical evolution models

• Authors: V. Grisoni, E. Spitoni, F. Matteucci

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

• Arxiv link: https://arxiv.org/abs/2605.10596

• Pdf link: https://arxiv.org/pdf/2605.10596

• Abstract Observational data have revealed a clear dichotomy in the [{\alpha}/Fe] vs. [Fe/H] diagram of the Milky Way thick and thin disc stars. Many recent studies have shown evidences of a co-evolution phase between the high- and low-{\alpha} disc sequences as well as the presence of very old low-{\alpha} stars. We aim to revise the parallel chemical evolution model that assumes two parallel histories of star formation for the two discs, by considering a pre-enriched delayed second infall episode in our revised scenario. By means of our chemical evolution models, we aim to explore the effects of a phase of co-evolution and the presence of old low-{\alpha} stars, as recently observed. We consider a new version of the parallel scenario for the Milky Way thick and thin disc formation, which consists into two distinct infall episodes of slightly pre-enriched gas. The gas is considered to be extragalactic but possibly contaminated by chemically enriched gas of a massive dwarf galaxy as Gaia-Enceladus, which merged with the Milky Way at least 10 Gyrs ago. Moreover, we test in our model observationally derived star formation histories of kinematically selected thick and thin discs, suggesting that the star formation is triggered by the passages of the Sagittarius galaxy. Our models can well explain the [{\alpha}/Fe] vs. [Fe/H] diagram from APOGEE DR17. Our revised chemical evolution model with a pre-enriched and delayed (roughly 1 Gyr) second infall episode, explains not only the abundance patterns of high- and low-{\alpha} stars but also stellar age distributions for the selected observational sample. We predict a short co-evolution period in between the two phases and we can explain the observed old low-{\alpha} stars, but still further data for precise stellar ages would be needed to put more stringent constraints on their physical nature.

Gas Phase Distribution in the Neutral ISM: A Comparison between Observation and Numerical Simulation

• Authors: Atanu Koley

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

• Arxiv link: https://arxiv.org/abs/2605.10711

• Pdf link: https://arxiv.org/pdf/2605.10711

• Abstract The neutral hydrogen (Hi) 21-cm line serves as a powerful tracer of the neutral interstellar medium (ISM). Thermal stability analysis suggests that the neutral ISM is bistable in nature, consisting of the cold neutral medium (CNM) embedded within the warm neutral medium (WNM), both in approximate thermal pressure equilibrium. When turbulence is incorporated into the numerical simulations, a third thermally unstable medium (UNM) emerges between the CNM and the WNM. Although observational studies support the existence of this intermediate phase, a clear empirical correlation between the fraction of the UNM gas and the strength of the turbulence remains elusive. In this study, we investigate the various phases of neutral ISM using Hi 21-cm emission-absorption spectra from the publicly available GWA and LAB surveys and compare it with TIGRESS-NCR and TIGRESS-CLASSIC numerical simulations. From our observational modeling, we find that 19.8% of the gas reside in the CNM phase, 32.5% in the UNM phase, and 47.8% in the WNM phase, assuming phase boundaries defined by spin temperature: T_s < 250 K for the CNM, 250 K < T_s < 5000 K for the UNM, and T_s > 5000 K for the WNM. These results are entirely in agreement with the TIGRESS-NCR numerical simulation. We further expect that deep, sensitive absorption studies with the Square Kilometre Array (SKA) or the Next Generation Very Large Array (ngVLA) or existing Upgraded Giant Metrewave Radio Telescope (uGMRT) capable of robustly detecting WNM clouds in absorption will place more tighter observational constraints on the fraction of the gas in three different phases of the neutral ISM.

Characterizing Pulsar Distances Using HI Kinematics

• Authors: S. Romero-Ruiz, S.K. Ocker

• Subjects: Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Astrophysics of Galaxies (astro-ph.GA)

• Arxiv link: https://arxiv.org/abs/2605.10881

• Pdf link: https://arxiv.org/pdf/2605.10881

• Abstract Distance measurements are fundamental to radio pulsars' use as astrophysical probes of General Relativity and the interstellar medium. One of the primary methods for determining pulsar distances is HI kinematics, which leverages the radial velocities of HI absorption and emission features detected along pulsar lines-of-sight. This method necessarily assumes a model for Galactic rotation, our knowledge of which continues to evolve in both accuracy and precision. In this research note, we derive kinematic distances for 66 pulsars with archival HI radial velocity measurements using a state-of-the-art Galactic rotation curve. The results and software are provided in an online repository. Our kinematic distances differ by $&lt;1\sigma$ from published parallaxes for nearly all pulsars in the sample that have both types of distance measurement available. Comparison to the NE2025 Galactic electron density model shows general consistency between measured and predicted distances.

Can We Distinguish the Source Region Location of Filament/Prominence Eruptions from the Sun-as-a-star H$α$ Spectrum?

• Authors: Junyi Zhang, Yijun Hou, Xiaofeng Liu, Ting Li, Shihao Rao, Ye Qiu, HuiPing Jin, Yingjie Cai, Yangrui Chen, Chuan Li

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

• Arxiv link: https://arxiv.org/abs/2605.10891

• Pdf link: https://arxiv.org/pdf/2605.10891

• Abstract Solar filament/prominence eruptions can significantly perturb geospace when originating from favorable source locations and directions. While stellar analogs have been recently reported, the disk locations and magnetic environments of their source regions remain spatially unresolved on other stars. To bridge this gap, we investigate the typical Sun-as-a-star H$\alpha$ temporal spectral characteristics of solar filament/prominence eruptions with different source region locations (on-disk vs. limb, active region vs. quiet-Sun region). It is revealed that limb eruptions are characterized by blueshifted/redshifted emission caused by the bright off-limb erupting structures, whereas on-disk eruptions may show blueshifted absorptions due to the dark erupting filaments. Among the limb eruptions, front-side limb eruptions usually display line center emission before the blueshifted/redshifted emission, while far-side limb eruptions show the opposite sequence. Moreover, the magnetic environment at source also shapes the spectral characteristics. On-disk filament eruptions from active region exhibit much more intense flare-ribbon-dominated line center emission features compared with those from quiet-Sun region. Limb active region eruptions often show single-wing emissions, whereas large-scale quiet-Sun region (quiescent) prominence eruptions frequently display expansion-induced emission in both wings followed by line center absorption due to the disappearance of bright prominence. These distinct Sun-as-a-star H$\alpha$ spectral characteristics, dependent on eruption location, provide a diagnostic basis for inferring source regions of stellar filament/prominence eruptions from spatially unresolved H$\alpha$ spectra.

Electromagnetic Follow-up of the Sub-Solar Mass Gravitational Wave Candidate S251112cm: Kilonova Constraints and a Coincident IIb Supernova

• Authors: Xander J. Hall, Tomas Ahumada, Julius Gassert, Antonella Palmese, Brian D. Metzger, Mansi M. Kasliwal, Mattia Bulla, Daniel Gruen, Robert Stein, Christoffer Fremling, Shreya Anand, Igor Andreoni, Malte Busmann, Tomás Cabrera, Ryan Christinzio, James Freeburn, Ignacio Magaña Hernandez, Lei Hu, Brendan O'Connor, Ji-an Jiang, Zhengyan Liu, Wen Zhao, Eric C. Bellm, David Cook, Michael W. Coughlin, Richard Dekany, Matthew Graham, Russ R. Laher

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

• Arxiv link: https://arxiv.org/abs/2605.10940

• Pdf link: https://arxiv.org/pdf/2605.10940

• Abstract On November 12th, 2025 the LIGO--Virgo--KAGRA (LVK) collaboration reported gravitational waves (GWs) from a compact object merger candidate (S251112cm) with at least one sub-solar mass component. Using the Dark Energy Camera (DECam), the Fraunhofer Telescope at Wendelstein Observatory (FTW), and the Zwicky Transient Facility (ZTF), we surveyed $56%$ of the GW localization region beginning $2.4$hours after the GW alert. We find no kilonova (KN) counterpart, and use radiative-transfer models to rule out $42%$ (ZTF), $68%$ (DECam), and $92%$ (FTW) of the KN models as possible emission from this GW candidate. Within the recently proposed disk-fragmentation (``superkilonova'') model for generating sub-solar mass neutron star mergers from stellar core-collapse, the delay between the supernova explosion time and the GW merger time is estimated to be less than a few days. Searching this time window prior to the GW event, we identify and spectroscopically classify a IIb supernova (SN2025adtq), with a spatial association odds ratio of $\log_{10}\mathcal{I} \approx 4.8$, a chance coincidence probability of ${\sim}2$--$9%$, and an estimated explosion time ${\sim}2$ days prior to S251112cm. SN2025adtq is the second TypeIIb supernova found in spatial and temporal coincidence with a sub-solar mass GW candidate, following the previously reported S250818k/SN~2025ulz association; jointly, we measure an odds ratio that favors the association hypothesis over the null, however, when conditioned on finding a coincident supernova by chance, the odds ratio disfavors association. Together, these results provide suggestive but inconclusive evidence for the superkilonova formation channel.

by olozhika (Xing Yuchen).

2026-05-12