Sazuna/UAT_keywords huggingface dataset:
Where is the Supervirial Gas? II. Insight from the Survey of Galactic Sightlines. Recent observations have revealed a supervirial temperature gas phase at log(T/K) ∼ 7 in the Milky Way, challenging existing galaxy formation models. This hot gas phase was discovered toward extragalactic absorption sightlines and blank-sky emission fields, both at high Galactic latitudes. The location of this hot component is unknown; is it in the extended circumgalactic medium (CGM) or in the interstellar medium (ISM) instead? We analyzed X-ray spectra from Chandra's High-Energy Transmission Grating observations of 27 Galactic X-ray binaries (XRBs) to investigate whether the hot gas component is present in the ISM. We searched for absorption lines of S XVI Kα, Si XIV Kα, and Ne X Kα, which are the telltale signatures of the hot gas and which have been detected toward extragalactic sightlines. Of the 27 targets, these lines were detected in the spectra of only 7, with two sources displaying broad line features likely intrinsic to the XRB systems. Additionally, most of the detected lines are time variable, reinforcing their likely association with the XRBs. Our results suggest that the supervirial temperature gas is not a widespread component of the ISM but may instead be located in extraplanar regions or the extended CGM, which aligns with some recent simulation results.

Keywords: X-ray astronomy, Galaxy evolution, Circumgalactic medium
A 3D Simulation of a Type II-P Supernova: From Core Bounce to beyond Shock Breakout. In order to better connect core-collapse supernova (CCSN) theory with its observational signatures, we have developed a simulation pipeline from the onset of the core collapse to beyond shock breakout from the stellar envelope. Using this framework, we present a 3D simulation study from 5 s to over 5 days following the evolution of a 17 M⊙ progenitor, exploding with ∼1051 erg of energy and ∼0.1 M⊙ of 56Ni ejecta. The early explosion is highly asymmetric, expanding most prominently along the southern hemisphere. This early asymmetry is preserved to shock breakout, ∼1 day later. Breakout itself evinces strong angle-dependence, with as much as 1 day delay in the shock breakout by direction. The nickel ejecta closely tail the forward shock, with velocities at the breakout as high as ∼7000 km s‑1. A delayed reverse shock forming at the H/He interface on hour timescales leads to the formation of Rayleigh–Taylor instabilities, fast-moving nickel bullets, and almost complete mixing of the metal core into the hydrogen envelope. For the first time, we illustrate the angle-dependent emergent broadband and bolometric light curves from simulations evolved in 3D in entirety, continuing through hydrodynamic shock breakout from a CCSN model of a massive stellar progenitor evolved with detailed, late-time neutrino microphysics and transport. Our case study of a single progenitor underscores that 3D simulations generically produce the cornucopia of observed asymmetries and features in CCSNe observations, while establishing the methodology to study this problem in breadth.

Keywords: Hydrodynamical simulations, Type II supernovae, Massive stars, Radiative transfer, Astrophysical fluid dynamics, Supernova dynamics
Tripling the Census of Dwarf AGN Candidates Using DESI Early Data. Using early data from the Dark Energy Spectroscopic Instrument (DESI) survey, we search for active galactic nuclei (AGN) signatures in 410,757 line-emitting galaxies. By employing the BPT emission-line ratio diagnostic diagram, we identify AGNs in 75,928/296,261 (≈25.6%) high-mass ( log(M⋆/M⊙)&gt;  9.5) and 2444/114,496 (≈2.1%) dwarf ( log(M⋆/M⊙)≤  9.5) galaxies. Of these AGN candidates, 4181 sources exhibit a broad Hα component, allowing us to estimate their BH masses via virial techniques. This study more than triples the census of dwarf AGNs and doubles the number of intermediate-mass black hole (MBH ≤ 106M⊙) candidates, spanning a broad discovery space in stellar mass (7  &lt;log(M⋆/M⊙)&lt;  12) and redshift (0.001 &lt;z &lt; 0.45). The observed AGN fraction in dwarf galaxies (≈2.1%) is nearly four times higher than prior estimates, primarily due to DESI's smaller fiber size, which enables the detection of lower-luminosity dwarf AGN candidates. We also extend the MBH–M⋆ scaling relation down to  log(M⋆/M⊙)≈  8.5 and  log(MBH/M⊙)≈  4.4, with our results aligning well with previous low-redshift studies. The large statistical sample of dwarf AGN candidates from current and future DESI releases will be invaluable for enhancing our understanding of galaxy evolution at the low-mass end of the galaxy mass function.

Keywords: AGN host galaxies, Intermediate-mass black holes, Dwarf galaxies
Diverse Rotation Curves of Galaxies in a Simulated Universe: The Observed Dependence on Stellar Mass and Morphology Reproduced. We use the IllustrisTNG cosmological hydrodynamical simulation to study the rotation curves of galaxies in the local universe. To do that, we first select the galaxies with 9.4 &lt;   &lt; 11.5 to make a sample comparable to that of SDSS/MaNGA observations. We then construct the 2D line-of-sight velocity map and conduct the fit to determine the rotational velocity and the slope of the rotation curve in the outer region (Rt &lt; r &lt; 3 × rhalf,*). The outer slopes of the simulated galaxies show diverse patterns that are dependent on morphology and stellar mass. The outer slope increases as galaxies are more disky, and decreases as galaxies are more massive, except for the very massive early-type galaxies. The outer slope of the rotation curves shows a correlation with the dark matter fraction, slightly better than for the gas mass fraction. Our study demonstrates that the observed dependence of galaxy rotation curves on morphology and stellar mass can be successfully reproduced in cosmological simulations, and provides a hint that dark matter plays an important role in shaping the rotation curve. The sample of simulated galaxies in this study could serve as an important test bed for the subsequent study tracing galaxies back in time, enabling a deeper understanding of the physical origin behind the diverse rotation curves.

Keywords: Galaxy dark matter halos, Hydrodynamical simulations, Galaxy properties, Galaxy dynamics, Galaxy rotation curves
Luminous Type II Short-plateau SN 2023ufx: Asymmetric Explosion of a Partially Stripped Massive Progenitor. We present supernova (SN) 2023ufx, a unique Type IIP SN with the shortest known plateau duration (tPT ∼ 47 days), a luminous V-band peak (MV = −18.42 ± 0.08 mag), and a rapid early decline rate (s1 = 3.47 ± 0.09 mag (50 days)−1). By comparing observed photometry to a hydrodynamic MESA+STELLA model grid, we constrain the progenitor to be a massive red supergiant with MZAMS ∼ 19─25 M⊙. Independent comparisons with nebular spectral models also suggest an initial He-core mass of ∼6 M⊙, and thus a massive progenitor. For a Type IIP, SN 2023ufx produced an unusually high amount of nickel (56Ni) ∼0.14 ± 0.02 M⊙, during the explosion. We find that the short plateau duration in SN 2023ufx can be explained with the presence of a small hydrogen envelope (  ∼ 1.2 M⊙), suggesting partial stripping of the progenitor. About ∼0.09 M⊙ of circumstellar material through mass loss from late-time stellar evolution of the progenitor is needed to fit the early time (≲10 days) pseudo-bolometric light curve. Nebular line diagnostics of broad and multipeak components of [O I] λλ6300, 6364, Hα, and [Ca II] λλ7291, 7323 suggest that the explosion of SN 2023ufx could be inherently asymmetric, preferentially ejecting material along our line of sight.

Keywords: Red supergiant stars, Core-collapse supernovae, Type II supernovae, Stellar mass loss, Circumstellar matter
A Data-driven M Dwarf Model and Detailed Abundances for ∼17,000 M Dwarfs in SDSS-V. The cool temperatures of M dwarf atmospheres enable complex molecular chemistry, making robust characterization of M dwarf compositions a long-standing challenge. Recent modifications to spectral synthesis pipelines have enabled more accurate modeling of M dwarf atmospheres, but these methods are too slow for characterizing more than a handful of stars at a time. Data-driven methods such as The Cannon are viable alternatives, and can harness the information content of many M dwarfs from large spectroscopic surveys. Here, we train The Cannon on M dwarfs with FGK binary companions from the Sloan Digital Sky Survey-V/Milky Way Mapper (SDSS-V/MWM), with spectra from the Apache Point Observatory Galactic Evolution Experiment. The FGK-M pairs are assumed to be chemically homogeneous and span ‑0.56 &lt; [Fe/H] &lt; 0.31 dex. The resulting model is capable of inferring M dwarf Teff and elemental abundances for Fe, Mg, Al, Si, C, N, O, Ca, Ti, Cr, and Ni with median uncertainties of 13 K and 0.018–0.029 dex, respectively. We test the model by verifying that it reproduces the reported abundance values of M dwarfs in open clusters and benchmark M dwarf data sets, as well as the expected metallicity trends from stellar evolution. We apply the model to 16,590 M dwarfs in SDSS-V/MWM and provide their detailed abundances in our accompanying catalog.

Keywords: M dwarf stars, Stellar abundances, High resolution spectroscopy
On the Average Ultraviolet Emission-line Spectra of High-redshift Galaxies: Hot and Cold, Carbon-poor, Nitrogen Modest, and Oozing Ionizing Photons. We determine the spectroscopic properties of ≃1000 ostensibly star-forming galaxies at redshifts (z = 4–10) using prism spectroscopy from JWST/NIRSpec. With rest-wavelength coverage between Lyα and [S II] in the optical, we stack spectra as a function of nebular conditions, and compare UV spectral properties with stellar age. This reveals UV lines of N III], N IV], C III], C IV, He II, and O III] in the average high-z galaxy. All of the UV lines are more intense in younger starbursts. We measure electron temperatures from the collisionally excited [O III] line ratios, finding Te = 18,000–22,000 K for the O++ regions. We also detect a significant nebular Balmer jump, from which we estimate only Te = 8000–13,000 K. Accounting for typical temperature offsets between zones bearing doubly and singly ionized oxygen, these two temperatures remain discrepant by around 40%. We use the [O III] temperatures to estimate abundances of carbon, nitrogen, and oxygen. We find that log(C/O) is consistently ≃ ‑1, with no evolution of C/O with metallicity or stellar age. The average spectra are mildly enhanced in nitrogen, with higher N/O than low-z starbursts, but are less enhanced than samples of recently reported, high-z, extreme galaxies that show N III] and N IV] emission in the UV. Whatever processes produce the N-enhancement in the individual galaxies must also be ongoing, at lower levels, in the median galaxy in the early Universe. The strongest starbursts are a source of significant ionizing emission: ionizing photon production efficiencies reach 1025.7 Hz erg‑1, and show multiple signatures of high Lyman continuum escape, including Mg II escape fractions nearing 100%, significant deficits in [S II] emission, high degrees of ionization, and blue UV colors.

Keywords: Starburst galaxies, Galaxy spectroscopy, High-redshift galaxies
Measurement and Modeling of Polarized Atmosphere at the South Pole with SPT-3G. We present the detection and characterization of fluctuations in linearly polarized emission from the atmosphere above the South Pole. These measurements make use of data from the SPT-3G receiver on the South Pole Telescope in three frequency bands centered at 95, 150, and 220 GHz. We use the cross-correlation between detectors to produce an unbiased estimate of the power in Stokes I, Q, and U parameters on large angular scales. Our results are consistent with the polarized signal being produced by the combination of Rayleigh scattering of thermal radiation from the ground and thermal emission from a population of horizontally aligned ice crystals with an anisotropic distribution described by Kolmogorov turbulence. The measured spatial scaling, frequency scaling, and elevation dependence of the polarized emission are explained by this model. Polarized atmospheric emission has the potential to significantly impact observations on the large angular scales being targeted by searches for inflationary B-mode CMB polarization. We present the distribution of measured angular power spectrum amplitudes in Stokes Q and I for 4 yr of Austral winter observations, which can be used to simulate the impact of atmospheric polarization and intensity fluctuations at the South Pole on a specified experiment and observation strategy. We present a mitigation strategy that involves both downweighting significantly contaminated observations and subtracting a polarized atmospheric signal from the 150 GHz band maps. In observations with the SPT-3G instrument, the polarized atmospheric signal is a well-understood and subdominant contribution to the measured noise after implementing the mitigation strategies described here.

Keywords: Cosmology, Atmospheric effects, Cosmic microwave background radiation, Millimeter astronomy
Unsupervised Machine Learning for Classifying CHIME Fast Radio Bursts and Investigating Empirical Relations. Fast radio bursts (FRBs) are highly energetic millisecond-duration astrophysical phenomena typically categorized as repeaters or nonrepeaters. However, observational limitations may result in misclassifications, potentially leading to a higher proportion of repeaters than currently identified. In this study, we leverage unsupervised machine learning techniques to classify FRBs using data from the CHIME/FRB catalogs, including both the first catalog and a recent repeater catalog. By employing Uniform Manifold Approximation and Projection for dimensionality reduction and clustering algorithms (k-means and Hierarchical Density-Based Spatial Clustering of Applications with Noise), we successfully segregate repeaters and nonrepeaters into distinct clusters, identifying over 100 potential repeater candidates. Our analysis reveals several empirical relations within the clusters, including the  ,  , and r–γ correlations, where Δtsc, Δtrw, TB, r, and γ represent the scattering time, rest-frame width, brightness temperature, spectral running, and spectral index, respectively. The Chow test results reveal that while some repeaters and nonrepeaters share similar empirical relationships, the overall distinctions between the two groups remain significant, reinforcing the classification of FRBs into repeaters and nonrepeaters. These findings provide new insights into the physical properties and emission mechanisms of FRBs. This study demonstrates the effectiveness of unsupervised learning in classifying FRBs and identifying potential repeaters, paving the way for more precise investigations into their origins and applications in cosmology. Future improvements in observational data and machine learning methodologies are expected to further enhance our understanding of FRBs.

Keywords: Dimensionality reduction, Clustering, Classification, Radio transient sources
The Roman Microlensing Survey: Confirmation or Refutation of Gas Giant Exoplanet Formation Theories. Exoplanet research has moved from the discovery of new classes of planets toward creating a census of exoplanet population demographics across the spectrum of exoplanet and host star masses. This census will constrain possible exoplanet formation and evolution theories. Direct imaging and ground-based microlensing surveys excel at detecting long-period exoplanets. The Roman Space Telescope microlensing survey (RMS) will help complete the census by possibly discovering hundreds of long-period and free-floating exoplanets. Long-period gas giants are difficult to form by the classic core-accretion mechanism, whereas the gas disk gravitational instability (GDGI) mechanism can form gas giants at distances of 10 au and beyond for AFGKM host stars. The Enzo 2.6 adaptive mesh refinement three-dimensional hydrodynamics code is used to model the formation of gas giant protoplanets by GDGI around solar-mass protostars, for future comparison with the RMS, which will provide convincing evidence about whether GDGI is needed to explain exoplanet demographics. Previous Enzo models have shown that a robust GDGI is able to form enough gas giants in a single system to result in the ejection of a significant fraction within ∼2000 yr, a likely source of free-floating exoplanets. The present models investigate the GDGI outcomes for a larger range of initial protoplanetary disk masses and outer disk temperatures than in the previous work of A. P. Boss, resulting in the formation of abundant substellar companions with masses in the range of ∼0.1 to ∼100 MJup on orbits ranging from ∼3 to ∼30 au.

Keywords: Astrometric exoplanet detection, Exoplanet formation, Gravitational instability, Extrasolar gaseous giant planets
Quenching and Recovery of Persistent X-Ray Emission during a Superburst in 4U 1820–30. We report the superburst from 4U 1820–30 in 2021 observed by the Monitor of All-sky X-ray Image and Neutron star Interior Composition Explorer (NICER). During the tail of the superburst, we found that the NICER light curve unexpectedly increased from 1080 to 2204 counts s‑1 over 6.89 hr. From the time-resolved superburst spectra, we estimated the burst decay time of ≈2.5 hr, the ignition column depth of ≈0.3 × 1012 g cm‑2, the energy release per unit mass of ≈2.4 × 1017 erg g‑1, the fluence of ≈4.1 × 10‑4 erg cm‑2, and the total energy release of ≈3.5 × 1042 erg. Notably, we found a gradual increase in the Comptonization flux from 8.9 × 10‑10 erg s‑1 cm‑2 to the preburst level during the superburst. This increase can be interpreted as a consequence of superburst radiation depleting the inner accretion disk, leading to a near-complete quenching of the persistent emission. As the burst radiation decayed, the inner accretion disk gradually returned to its preburst state, as evidenced by the best-fit spectral parameters. Additionally, we observed a prominent absorption line that exhibited a gravitational redshift, shifting from 4.15 to 3.62 keV during the recovery phase of persistent emission. This absorption feature likely originates from the inner accretion disk rather than from burst emission on the neutron star (NS) surface. The observed changes in the absorption line energy suggest that the inner disk approached the NS to a distance as close as ≈17 km.

Keywords: Low-mass x-ray binary stars, Neutron stars, X-ray bursters
Signature of Strange Star as the Central Engine of GRB 240529A. GRB 240529A is a long-duration gamma-ray burst (GRB) whose light curve of prompt emission is composed of a triple-episode structure, separated by quiescent gaps of tens to hundreds of seconds. More interestingly, its X-ray light curve of afterglow exhibits two plateau emissions, namely, an internal plateau emission that is smoothly connected with a ∼t‑0.1 segment and followed by a ∼t‑2 power-law decay. The three episodes in the prompt emission, together with two plateau emissions in X-ray, are unique in the Swift era. They are very difficult to explain with the standard internal/external shock model by invoking a black hole central engine. However, it could be consistent with the prediction of a supramassive magnetar as the central engine, the physical process of phase transition from a magnetar to a strange star, as well as the cooling and spin-down of the strange star. In this paper, we propose that the first- and second-episode emissions in the prompt gamma ray of GRB 240529A are from the jet emission of a massive star collapsing into a supramassive magnetar and the reactivity of the central engine, respectively. Then, the third-episode emission of the prompt is attributed to the phase transition from a magnetar to a strange star. Finally, the first and second plateau emissions of the X-ray afterglow are powered by the cooling and spin-down of the strange star, respectively. The observational data of each component of GRB 240529A are roughly coincident with the estimations of the above physical picture.

Keywords: Gamma-ray bursts
The Initial-to-final Mass Relation of White Dwarfs in Intermediate-separation Binaries. We examine the applicability of the initial-to-final mass relation (IFMR) for white dwarfs (WDs) in intermediate-separation binary systems (∼1 au), using astrometric binaries identified in open clusters from Gaia DR3. A careful analysis of the astrometric orbits and spectral energy distributions isolates 33 main-sequence (MS) stars with highly likely WD companions. By combining cluster age estimates, dynamically measured WD masses, and, where available, WD cooling temperatures, we derive progenitor masses for 26 WD candidates. Our analysis suggests the presence of two distinct WD populations: (i) low-mass WDs, likely shaped by binary interactions during the progenitor's red giant phase; and (ii) "spender" WDs, which experienced higher-than-expected mass loss and have progenitor masses above the IFMR predictions. The rest of the candidates, referred to as the "others," represent systems with inconclusive formation mechanisms. We suggest that at least some of these systems might be hierarchical triples, where the companion to the MS is a double WD or a double-WD merger product. However, follow-up studies are required to determine the nature of each case. These results highlight significant deviations from the IFMR derived for isolated WDs, emphasizing the role of binary evolution. Follow-up observations, particularly in the far-ultraviolet, are crucial for refining these findings and advancing our understanding of mass transfer processes and binary evolution pathways.

Keywords: Binary stars, White dwarf stars, Astrometric binary stars, Open star clusters, Stellar evolution
Application of Resolved Low-J Multi-CO Line Modeling with RADEX to Constrain the Molecular Gas Properties in the Starburst M82. The distribution and physical conditions of molecular gas are closely linked to star formation and the subsequent evolution of galaxies. Emission from carbon monoxide (CO) and its isotopologues traces the bulk of molecular gas and provides constraints on the physical conditions through their line ratios. However, a comprehensive understanding of how the particular choice of line modeling approach impacts derived molecular properties remains incomplete. Here, we study the nearby starburst galaxy M82, known for its intense star formation and molecular emission, using the large set of available multi-CO line observations. We present high-resolution (∼85 pc) emission of seven CO isotopologue lines, including 12CO, 13CO, and C18O from the J = 1–0, 2–1, and 3–2 transitions. Using RADEX for radiative transfer modeling, we analyze M82's molecular properties with (i) a one-zone model and (ii) a variable density model, comparing observed and simulated emissions via a minimum χ2 analysis. We find that inferred gas conditions—kinetic temperature and density—are consistent across models, with minimal statistical differences. However, due to their low critical densities (&lt;104 cm‑3), low-J CO isotopologue lines do not effectively probe higher-density gas prevalent in starburst environments like that of M82. Our results further imply that this limitation extends to high-redshift (z ⪆ 1) galaxies with similar conditions, where low-J CO lines are inadequate for density constraints. Future studies of extreme star-forming regions like M82 will require higher-J CO lines or alternative molecular tracers with higher critical densities.

Keywords: Starburst galaxies, Molecular gas, Molecular spectroscopy, Millimeter-wave spectroscopy, Star formation, Interstellar medium