Sazuna/UAT_keywords huggingface dataset:
Cold Gas Infall onto a Brightest Group Galaxy via a Gas-rich Minor Merger. Dust and cold gas are not uncommon in nearby early-type galaxies (ETGs) and represent an important aspect of their evolution. However, their origin has been debated for decades. Potential sources include internal processes (e.g., mass loss from evolved stars), external mechanisms (e.g., minor mergers or cooling flows), or a combination of both. Gas-rich minor mergers have long been proposed as an important channel for cold gas fueling in both observations and simulations, but direct evidence of cold gas transportation via gas-rich minor mergers remains elusive, particularly in galaxy groups and clusters where environmental effects are prevalent. In this Letter, we present the first unambiguous case of direct cold gas transportation onto a brightest group galaxy (BGG) at z = 0.25, driven by an ongoing close-separation gas-rich minor merger with a mass ratio of ∼1:56. High-resolution JWST imaging reveals a heavily obscured, low-mass satellite that is barely visible at restframe optical wavelengths. Tidal stripping from this satellite deposits gas and dust onto the BGG, forming prominent ∼10 kpc dust lanes in situ. Cosmological simulations indicate that such interactions preferentially occur in gas-rich satellites undergoing their first infall in highly eccentric orbits. Our results highlight the pivotal role of gas-rich minor mergers in replenishing cold gas reservoirs and shaping the evolution of central ETGs in galaxy groups.

Keywords: Galaxy interactions, Galaxy mergers, Interstellar medium, Galaxy evolution, Galaxy groups
Bar-driven Shocks in NGC 1365 Revealed by the Most Luminous Extragalactic Class I Methanol Maser. We report the first detection of the 36.2 GHz (4−1 → 30 E) Class I methanol (CH3OH) maser in the central region of the barred spiral galaxy NGC 1365. This detection using the Australia Telescope Compact Array establishes NGC 1365 as the host of the most luminous extragalactic Class I methanol maser known, with a total isotropic luminosity of 19.3 L⊙. The maser emission is unambiguously localized to the southern arm of the circumnuclear starburst ring and exhibits a tight alignment with the bar-driven gas inflow lane. The striking absence of maser emission in the star formation and feedback-dominated northern arm reveals a fundamental bimodality within the ring. Combined with archival multiwavelength data, our results demonstrate that the maser traces low-velocity (∼25−30 km s−1), nondissociative molecular shocks in the southern arm, where the gas is cold, dense, and subject to a weak radiation field. This work directly resolves the long-standing ambiguity between bar-driven shocks and stellar feedback, establishing the 36.2 GHz maser as a unique and powerful shock-specific diagnostic for extragalactic studies. It provides a novel tool to spatially pinpoint shock fronts and to disentangle the roles of gravitational dynamics and radiative feedback in shaping the extreme environments of galactic nuclei.

Keywords: Star formation, Astrophysical masers, Circumgalactic medium, Extragalactic astronomy, Barred spiral galaxies
Observations of Transition from Imbalanced to Balanced Kinetic Alfvénic Turbulence. We report observations of solar wind turbulence derived from measurements by the Parker Solar Probe. Our findings reveal the emergence of finite magnetic helicity within the transition range of the turbulence, aligning with signatures of kinetic Alfvén waves (KAWs). Notably, as the wave scale transitions from superion to subion scales, the ratio between KAWs with opposite signs of magnetic helicity initially increases from approximately one to 6.5, before decreasing back to one. This observation provides, for the first time, compelling evidence for the transition from imbalanced to balanced kinetic Alfvénic turbulence.

Keywords: Space plasmas, Solar wind, Plasma physics
A Protoplanet Candidate in the PDS 66 Disk Indicated by Silicon Sulfide Isotopologues. Despite observational progress in planet formation, the stage in which planetesimals grow into planets remains poorly understood. During this phase, protoplanets may develop gaseous envelopes that are warmer than the surrounding disk gas, potentially providing observable signatures through molecules otherwise depleted in cold regions. In this Letter, we report the detection of the silicon sulfide isotopologues 28SiS J = 16−15 and 30SiS J = 18−17 in the protoplanetary disk around PDS 66 (MP Mus) at a significance of ∼5σ−6σ, using the Atacama Large Millimeter/submillimeter Array. These constitute the second and first detections of 28SiS and 30SiS in a protoplanetary disk, respectively. The emission appears as a compact source at r = 60 au in the southwestern region of the disk, unresolved with a  ∼0.″5  beam, and shows a velocity consistent with Keplerian rotation, suggesting a protoplanetary origin. By modeling the line fluxes, we constrain the emitting radius to ∼0.5−4 au and estimate a SiS mass of 1022─1023 g, corresponding to at least ∼10% of the silicon contained in local dust grains. Because complete sublimation of a substantial fraction of dust grains by local processes is difficult to achieve, this result instead implies an accumulation of silicon from a larger region. We propose that a circumplanetary envelope surrounding a low-mass protoplanet, where pebble accretion and subsequent sublimation of grains may enhance gaseous silicon abundance with respect to observable dust grains around it, can account for the observed characteristics.

Keywords: Protoplanetary disks, Planet formation, Astrochemistry
Nonlinear Mode Conversion from a Large-amplitude Propagating Kink Wave to Longitudinal Oscillations in a Quiescent Prominence. In this Letter, we present the direct observations of a mode conversion from a large-amplitude transverse propagating kink wave to antiphase large-amplitude longitudinal oscillations (LALOs) in a quiescent prominence observed on 2014 February 25. This event was simultaneously recorded by the Solar Dynamics Observatory/Atmospheric Imaging Assembly and the Behind Solar Terrestrial Relation Observatory/Extreme Ultraviolet Imager. The transverse oscillation was triggered when a global extreme-ultraviolet wave associated with an X4.9 flare swept over the northern end of the prominence. For the first time, a clearly visible, coherent large-amplitude propagating kink wave was observed in the prominence, traveling southward along the prominence spine with a phase speed of ∼380 km s−1. The propagating wave reached its largest initial amplitude (∼15 Mm) and period (∼24 minutes) near the spine center. After one cycle of the transverse oscillation, antiphase LALOs were detected simultaneously near both ends of the prominence, exhibiting similar physical parameters (period ∼79 minutes, initial displacement amplitude ∼10 Mm, and velocity amplitude ∼12 km s−1). Their strict antiphase relation, supported by quantitative order-of-magnitude consistency, demonstrates that the LALOs were directly triggered by a nonlinear magnetic pressure gradient (ponderomotive effect) induced by the large-amplitude propagating kink wave. These results provide the first direct evidence of the large-amplitude transverse-to-longitudinal wave-mode conversion and reveal the nonlinear coupling mechanism in a prominence.

Keywords: Solar oscillations, Solar coronal waves, Solar filaments, Quiescent solar prominence
Emergence of a Lithium Dip in ∼35 Myr "Snake" Open Clusters. We report the discovery of a lithium dip (Li dip) in the stellar "Snake" (age = 35 ± 5 Myr), challenging the classical view that Li dips emerge only at ages ≳150 Myr. Using high-resolution spectra from GALAH Data Release 4 (R ∼ 28,000) for 211 member stars, we identify a clear depletion feature in a Teff range of 6200─6800 K with a depth of ∆A(Li) ≍ 0.40 dex. Our analysis reveals two key advances: the Li dip appears ≳100 Myr earlier than the previous observations, and within the dip temperature range, a significant correlation is found between rotational velocity and lithium depletion. Specifically, fast rotators ( vsini&gt;25  km s−1) exhibit stronger lithium depletion than slow rotators ( vsini&lt;25  km s−1). This trend suggests that faster rotators develop stronger rotational shear at the convective-radiative boundary, which enhances turbulent mixing and accelerates lithium destruction. It is also found that the lower temperature edge of the lithium plateau can reach as low as 5500 K for the young open clusters.

Keywords: Stellar abundances, Young star clusters, Lithium stars, Open star clusters, Star clusters
Fading into Darkness: A Weak Mass Ejection and Low-efficiency Fallback Accompanying Black Hole Formation in M31-2014-DS1. Stellar-mass black holes (BHs) can form from the near-complete collapse of massive stars, causing them to abruptly disappear. The star M31-2014-DS1 in the Andromeda galaxy was reported to exhibit such a disappearance between 2014 and 2022, with properties consistent with the failed explosion of an ≍12─13 M⊙ yellow supergiant leading to the formation of an ≍5 M⊙ BH. We present mid-infrared (MIR) observations of the remnant obtained with the James Webb Space Telescope (JWST) and X-ray observations from the Chandra X-ray Observatory in 2024. The JWST Mid-infrared Instrument/NIRSpec data reveal an extremely red source, showing strong blueshifted absorption from molecular gas (CO, CO2, H2O, SO2) and deep silicate dust features. Modeling the dust continuum confirms continued bolometric fading of the central source to  log(L/L⊙)≍3.88  (≍7%─8% of the progenitor luminosity), surrounded by a dust shell spanning ≍40─200 au. Modeling of the molecular gas indicates ∼0.1 M⊙ of gas expanding at ≍100 km s−1 near the inner edge of the dust shell. No X-ray source is detected down to a luminosity limit of LX ≲ 1.5 × 1035 erg s−1. We show that the panchromatic observations are explained by (i) a low-energy (≍1046 erg) ejection of the outer H-rich progenitor envelope and (ii) a fading central BH powered by inefficient (∼0.1% in mass) accretion of loosely bound fallback material. The analysis robustly establishes the bolometric fading of M31-2014-DS1 following its &gt;30 yr archival record of constant optical/infrared brightness, and provides the first cohesive insights into BH formation via low-energy explosions and long-term fallback.

Keywords: Black holes, Core-collapse supernovae, Massive stars, Circumstellar dust, Supernova dynamics
Evidence for a Peak at ∼0.3 in the Eccentricity Distribution of Typical Super-Jovian Exoplanets. In this study, we compute completeness-corrected occurrence rates of giant exoplanets as a function of mass, semimajor axis, and eccentricity, using the approximately uniform California Legacy Survey sample of radial velocity-discovered planets published in L. J. Rosenthal et al. We recover the previously detected rise in occurrence with semimajor axis for both lower- and higher-mass subsets of the population out to ∼5 au. When restricting to planets with semimajor axes between 0.1 and 4.5 au (roughly speaking, the "peak" of giant planet occurrence), we find evidence for distinct eccentricity distributions for each of two mass subpopulations. Most strikingly, we observe a peak in the eccentricity distribution of super-Jovian planets (3─20 MJ) at 0.3, which is apparent using two different parameterizations of the eccentricity distribution model. A hierarchical histogram model reveals that ∼92% of posterior samples indicate an elevated occurrence rate of super-Jupiters with modest eccentricities (0.2─0.4) compared to lower or higher eccentricities (i.e., evidence for a moderate eccentricity "peak"), and 99% of samples indicate super-Jupiters with modest eccentricities are more common than those with lower eccentricities (i.e., evidence that moderate eccentricities are more common than low eccentricities). We use a truncated Gaussian model fit to pinpoint the location of the super-Jupiter eccentricity peak with more precision, finding a maximum a posteriori peak location of e = 0.3. This low but elevated characteristic eccentricity could be the result of dynamically hot histories, perhaps involving a giant impacts phase. All analysis code for this project is publicly available on Zenodo (doi: 10.5281/zenodo.18089157) and GitHub: github.com/sblunt/eccentricities.

Keywords: Exoplanet dynamics
Shock-like Magnetic Enhancements Generated by Kelvin─Helmholtz Instability above Weakly Magnetized Bodies. Shock-like magnetic field structures above weakly magnetized bodies such as the Moon have been reported for more than half a century and represent a key long-standing feature of their solar-wind interactions. Yet their physical origin has remained without a satisfactory explanation, particularly regarding their steepened profiles and high-altitude extension. Here we show that a long-overlooked nonlinear branch of the Kelvin─Helmholtz instability (KHI) naturally produces these localized external magnetic enhancements. Using magnetohydrodynamic simulations constrained by Lunar Prospector (LP) observations, we demonstrate that velocity shear at the solar-wind─crustal-anomaly interface can trigger a KHI whose nonlinear evolution generates outward-propagating fast-mode shocks that are distinct from the familiar vortex-type KHI waves. These KHI-driven shocks reproduce the LP-observed amplitude and morphology of lunar magnetic enhancements extending hundreds of kilometers above the surface. Two distinct nonlinear KHI regimes, one shock-dominated and one vortex-dominated, together provide a unified framework that explains both the morphological diversity and the wide range of amplitudes of localized magnetic enhancements observed above the Moon and can be applied to other weakly magnetized bodies, revealing a previously unrecognized mechanism governing solar-wind interactions with crustal magnetic anomalies across the solar system.

Keywords: Space plasmas, Magnetohydrodynamics, Mars, Lunar magnetic fields, Solar wind, The Moon, Shocks, Planetary magnetospheres
The Energy─Duration Relationship in Astrophysical Self-organized Criticality Systems. Scaling laws in astrophysical systems that involve energy, geometry, and spatiotemporal evolution provide the theoretical framework for physical models of energy dissipation processes. A leading model is the standard fractal-diffusive self-organized criticality (FD-SOC) model, which is built on four fundamental assumptions: (i) the dimensionality d = 3, (ii) the fractal dimension DV = d − 1/2 = 2.5, (iii) classical diffusion L ∝ T(1/2), and (iv) the proportionality of the dissipated energy to the fractal volume, E ∝ V. Based on these assumptions, the FD-SOC model predicts a scaling law of T ∝ Ek ∝ E(4/5) = E0.8. On the observational side, we find only one case (out of the nine analyzed cases) that is consistent with the FD-SOC model, namely, the scaling law of T ∝ E0.86±0.03 by A. Araujo &amp; A. Valio. The other eight cases have scaling law coefficients clustered around values of k ≍ 0.3−0.4, which possibly can be explained by nonstandard SOC models, i.e., k = 2/(βDV), in terms of linear expansion β = 2 and/or Euclidean dimension DV = 3. The relatively low values of time duration ranges may also indicate possible truncation biases.

Keywords: Solar gamma-ray emission, Gamma-ray bursts
The Maximum Offsets of Binary Neutron Star Mergers from Host Galaxies. We analytically derive, and illustrate with a population synthesis model, the maximum offset of binary neutron star mergers ejected from their host galaxies. This approximate maximum offset is 300 kpc  ×(vesc/500kms−1)−7 , where vesc is the escape velocity from the host galaxy. Massive hosts with high escape velocities are unlikely to yield very large offsets. This maximum offset should inform the host associations of mergers that are not coincident with galaxies. We also discuss potential correlations between offsets and system masses, and possibly the duration of the gamma-ray burst accompanying the merger.

Keywords: Neutron stars, Gamma-ray bursts
The Maximum Mass Ratio of Hierarchical Binary Black Hole Mergers May Cause the q─χ<SUB>eff</SUB> Correlation. Regardless of their initial spins, the merger of two roughly equal mass black holes (BHs) produces a remnant BH of dimensionless spin 0.69. Such remnants can merge with other BHs in dense stellar environments and produce hierarchical mergers. Analyzing the latest catalog binary black hole (BBH) mergers from the LIGO─Virgo─KAGRA detectors, we identify a subpopulation with primary spins consistent with such hierarchical mergers. Consistent with astrophysical expectations for mergers of second-generation BHs with first-generation BHs, we find that this subpopulation has mass ratios below  0.59−0.23+0.18 . We also infer that 19%─88% of the BBH population below this mass ratio is consistent with belonging to the hierarchically merged population. Our results offer a natural explanation for the narrowing of the effective inspiral spin distribution with mass ratio observed in other studies.

Keywords: Globular star clusters, High energy astrophysics, Gravitational wave sources
Indications of Rapid Dust Formation in the Inner Region of a Protoplanetary Disk. We report a significant increase in mid-infrared emission ≤10 μm in a transitional disk. The 2024 JWST/MIRI observation of the disk around CVSO 1942 reveals flux increase by a factor of 2 at λ ≤10 μm, compared to the near-photospheric flux level observed with Spitzer's Infrared Spectrograph (IRS) in 2005. No significant change in flux at ≳15 μm is detected in the spectra. Comparing the MIRI/MRS spectrum and NEOWISE photometry, we found that this ≤10 μm flux increase occurs on a timescale of 2 weeks and is consistent with the presence of warm (1400 K), optically thick, large (≳1 μm) dust grains near the dust sublimation radius. We propose that this rapid dust appearance may indicate in situ dust formation, possibly from planetesimal collisions in the inner disk.

Keywords: Stellar accretion disks, T Tauri stars, Dust continuum emission, Protoplanetary disks
An Excited Dark Matter Solution to the MeV Galactic Center Excesses. Recent reanalyses of COMPTEL data reveal a ∼2 MeV continuum excess whose spatial distribution closely matches the 511 keV line observed by INTEGRAL/SPI (SPectrometer on INTEGRAL), pointing to a common population of low-energy Galactic positrons that is difficult to explain with known astrophysical sources or standard thermal dark matter (DM). We show that a minimal Excited DM scenario provides a unified explanation of these signals. In this framework, a DM particle χ is inelastically upscattered into an excited state χ*, which de-excites via χ* → χe+e−, injecting few-MeV positrons. These positrons reproduce the observed 511 keV morphology and generate the MeV continuum through in-flight annihilation. Using a full cosmic-ray propagation treatment, we obtain remarkable consistency for mχ ≃ 1.5 TeV with a mass splitting  ∆m=mχ*−mχ≃4  MeV, and an inelastic geometric scattering cross section σmr ≃ (3─4) × 10−23 cm2. The same positrons yield a substantial, approximately radially flat contribution to the anomalous ionization observed in the Central Molecular Zone.

Keywords: Particle astrophysics, Dark matter, High energy astrophysics
IRS 9: The Case for a Dynamically Ejected Star from the Galactic Center. Measuring stellar motions at the Milky Way's Galactic center (GC) provides unique insight into the dynamical processes within galactic nuclei. We present proper-motion measurements for 23 SiO-maser-emitting stars within 45″ of SgrA*, including four previously reported to have velocities exceeding their local escape velocities (i.e., they are "locally unbound" from the GC). Derived from 14 epochs of Hubble Space Telescope WFC3-IR observations (2010─2023), our measurements have a median precision of 0.038 mas yr−1—up to ∼100x more precise than previous constraints for some sources. By combining these proper motions with published radial velocities, we derive updated 3D velocities for the masers and find that only one is locally unbound (IRS 9; v3d = 370 ± 1.2 km s−1). Orbit integrations place the first constraints on the orbit of IRS 9, which is bound to the GC at larger radii with rperi ≥ 0.100 ± 0.005 pc and rapo ≥ 5.25 ± 0.18 pc. IRS 9's high velocity relative to stars at similar radii in the Nuclear Star Cluster makes it a candidate to have experienced a strong dynamical interaction in order to place it on its orbit. We explore the Hills mechanism as a possible origin, but binary evaporation and ejection velocity limits indicate that IRS 9 is unlikely to have experienced such an event in the past 0.4 Myr (the timescale constrained by the orbit integrations). Alternative mechanisms to produce IRS 9 include binary supernova disruption, two-body interactions, and stellar collisions. Identifying additional stars like IRS 9 will be essential for understanding these various dynamical processes.

Keywords: Stellar kinematics, Galactic center, Astrometry, Proper motions
Evidence for the Merger Hypothesis in V4332 Sgr: A Low <SUP>12</SUP>C/<SUP>13</SUP>C Ratio and Multiple Outbursts. Following the detections of the first extragalactic "luminous red nova" (LRN) M31RV in 1989, and its first Galactic counterpart V4332 Sgr in 1994, there have been many discoveries of similar, or closely related, objects. They are important because they bridge the luminosity gap between the brightest novae and supernovae, a largely unexplored parameter space. The cause of eruptions in LRNe is still unclear, a stellar merger being the most favored mechanism. However, barring V1309 Sco, there has been no direct evidence for a merger in the other objects. Here we present strong evidence that V4332 Sgr was a merger event. High-resolution infrared observations of the CO fundamental band show an unusually small 12C/13C ratio of 3.5 ± 1. This indicates that a violent event had occurred, whose effects penetrated deep enough to allow the CNO cycle processed 13C in the inner H burning shell to be brought to the surface. We rule out planetary ingestion and propose that the eruption was due to a merger between V4332 Sgr and a companion star. It is shown that V4332 Sgr was likely surrounded by an edge-on disk before its eruption. If this disk was a flattened common envelope containing V4332 Sgr and a companion star, then a merger scenario would not be inconsistent. Furthermore, it is also shown that V4332 Sgr had multiple outbursts, previously unreported but an important piece of information, since multiple outbursts are a trait shared by many LRNe.

Keywords: Infrared astronomy, Novae, Stellar mergers