Sazuna/UAT_keywords huggingface dataset:
The Leakage of Lyman-continuum Photons from a Major Merger at z ∼ 1. We report the detection of Lyman-continuum (LyC) photons from a massive interacting system at z = 1.097 in the Hubble Ultra Deep Field. The LyC detection is made in the far-ultraviolet F154W band of the UVIT telescope on board AstroSat. Both JWST and Hubble Space Telescope (HST) imaging of the system reveal signs that it is a likely merger. In particular, high-resolution imaging in the JWST bands reveals an infrared-luminous object within the system that is faint in the bluer HST bands. The ionized gas kinematics from the MUSE-UDF data supports the merger hypothesis. We estimate that the entire system is leaking more than 8% of its ionizing photons to the intergalactic medium. The spectral-energy-distribution-derived stellar masses of the two components indicate that this is a major merger with a mass ratio of 1.13 ± 0.37. This detection hints at the potential contribution of massive interacting systems at higher redshifts, when major mergers were more frequent, to the ionizing budget of the Universe.

Keywords: Ultraviolet astronomy, Reionization, Galaxy interactions
Force-free Wave Interaction in Magnetar Magnetospheres: Computational Modeling in Axisymmetry. Crustal quakes of highly magnetized neutron stars can disrupt their magnetospheres, triggering energetic phenomena like X-ray and fast radio bursts. Understanding plasma wave dynamics in these extreme environments is vital for predicting energy transport across scales to the radiation length. This study models relativistic plasma wave interaction in magnetar magnetospheres with force-free electrodynamics simulations. For propagation along curved magnetic field lines, we observe the continuous conversion of Alfvén waves to fast magnetosonic (FMS) waves. The conversion efficiency can be up to three times higher when counter-propagating Alfvén waves interact in the equatorial region. Alfvén waves generate FMS waves of twice their frequency during their first crossing of the magnetosphere. After the initial transient burst of FMS waves, Alfvén waves convert to FMS waves periodically, generating variations on timescales of the magnetospheric Alfvén wave crossing time. This decaying FMS wave tail carries a significant portion (half) of the total energy emitted. Plastic damping of "bouncing" Alfvén waves by the magnetar crust has minimal impact on the FMS efficiency. We discuss the implications of the identified wave phenomena for magnetar observations. Outgoing FMS waves can develop electric zones, potential sources of coherent radiation. Long wavelength FMS waves could generate FRBs through reconnection beyond the light cylinder.

Keywords: Magnetohydrodynamical simulations, Plasma astrophysics, Stellar magnetic fields, Magnetars, X-ray bursts, Radio transient sources
The Landscape of Thermal Transients from Supernovae Interacting with a Circumstellar Medium. The interaction of supernova ejecta with a surrounding circumstellar medium (CSM) generates a strong shock, which can convert ejecta kinetic energy into observable radiation. Given the diversity of potential CSM structures (arising from diverse mass-loss processes such as late-stage stellar outbursts, binary interaction, and winds), the resulting transients can display a wide range of light-curve morphologies. We provide a framework for classifying the transients arising from interaction with a spherical CSM shell. The light curves are decomposed into five consecutive phases, starting from the onset of interaction and extending through shock breakout and subsequent shock cooling. The relative prominence of each phase in the light curve is determined by two dimensionless quantities representing the CSM-to-ejecta mass ratio η, and the breakout parameter ξ. These two parameters define four light-curve morphology classes, where each class is characterized by the location of the shock breakout and the degree of deceleration as the shock sweeps up the CSM. We compile analytic scaling relations connecting the luminosity and duration of each light-curve phase to the physical parameters. We then run a grid of radiation hydrodynamics simulations for a wide range of ejecta and CSM parameters to numerically explore the landscape of interaction light curves, and to calibrate and confirm the analytic scalings. We connect our theoretical framework to several case studies of observed transients, highlighting the relevance in explaining slow-rising and superluminous supernovae, fast blue optical transients, and double-peaked light curves.

Keywords: Core-collapse supernovae, Late stellar evolution, Stellar mass loss, Radiative transfer, Shocks, Supernovae
AGN STORM 2. VIII. Investigating the Narrow Absorption Lines in Mrk 817 Using HST-COS Observations. We observed the Seyfert 1 galaxy Mrk 817 during an intensive multiwavelength reverberation mapping campaign for 16 months. Here, we examine the behavior of narrow UV absorption lines seen in the Hubble Space Telescope/Cosmic Origins Spectrograph spectra, both during the campaign and in other epochs extending over 14 yr. We conclude that, while the narrow absorption outflow system (at ‑3750 km s‑1 with FWHM = 177 km s‑1) responds to the variations of the UV continuum as modified by the X-ray obscurer, its total column density (log N H = 19.5  ‑0.13+0.61  cm‑2) did not change across all epochs. The adjusted ionization parameter (scaled with respect to the variations in the hydrogen-ionizing continuum flux) is log U H = ‑1.0  ‑0.3+0.1 . The outflow is located at a distance smaller than 38 pc from the central source, which implies a hydrogen density of n H &gt; 3000 cm‑3. The absorption outflow system only covers the continuum emission source and not the broad emission line region, which suggests that its transverse size is small (&lt; 1016 cm), with potential cloud geometries ranging from spherical to elongated along the line of sight. * Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. These observations are associated with program GO-16196, and archival data from programs 11505, 11524, and 17105.

Keywords: Seyfert galaxies, Active galaxies, Active galactic nuclei
Nonideal Magnetohydrodynamic Instabilities in Protoplanetary Disks: Vertical Modes and Reflection Asymmetry. Magnetized disk winds and wind-driven accretion are an essential and intensively studied dispersion mechanism of protoplanetary disks (PPDs). However, the stability of these mechanisms has yet to be adequately examined. This paper employs semi-analytic linear perturbation theories under nonideal magnetohydrodynamics, focusing on disk models whose magnetic diffusivities vary by a few orders of magnitude from the disk midplane to its surface. Linear modes are distinguished by their symmetry with respect to the midplane. These modes have qualitatively different growth rates: symmetric modes almost always decay, while at least one antisymmetric mode always has a positive growth rate. This growth rate decreases faster than the Keplerian angular velocity with cylindrical radius R in the disk and scales steeper than R ‑5/2 in the fiducial disk model. The growth of antisymmetric modes breaks the reflection symmetry across the disk equatorial plane, and may occur even in the absence of the Hall effect. In the disk regions where fully developed antisymmetric modes occur, accretion flows appear only on one side of the disk, while disk winds occur only on the other. This may explain the asymmetry of some observed PPD outflows.

Keywords: Accretion, Magnetohydrodynamics, Protoplanetary disks, Stellar accretion disks, Exoplanet formation
JWST NIRSpec Spectroscopy of the Remarkable Bright Galaxy GHZ2/GLASS-z12 at Redshift 12.34. We spectroscopically confirm the M UV = −20.5 mag galaxy GHZ2/GLASS-z12 to be at redshift z = 12.34. The source was selected via NIRCam photometry in GLASS-JWST Early Release Science data, providing the first evidence of a surprising abundance of bright galaxies at z ≳ 10. The NIRSpec PRISM spectrum shows detections of N IV, C IV, He II, O III, C III, O II, and Ne III lines and the first detection at high redshift of the O III Bowen fluorescence line at 3133 Å rest frame. The prominent C IV line with rest-frame equivalent width (EW) ≍ 46 Å puts GHZ2 in the category of extreme C IV emitters. GHZ2 displays UV lines with EWs that are only found in active galactic nuclei (AGNs) or composite objects at low/intermediate redshifts. The UV line-intensity ratios are compatible with both AGNs and star formation in a low-metallicity environment, with the low limit on the [Ne IV]/[N IV] ratio favoring a stellar origin of the ionizing photons. We discuss a possible scenario in which the high ionizing output is due to low-metallicity stars forming in a dense environment. We estimate a metallicity ≲0.1 Z/Z ⊙, a high ionization parameter log U &gt; −2, a N/O abundance 4─5 times the solar value, and a subsolar C/O ratio similar to the recently discovered class of nitrogen-enhanced objects. Considering its abundance patterns and the high stellar mass density (104 M ⊙ pc−2), GHZ2 is an ideal formation site for the progenitors of today's globular clusters. The remarkable brightness of GHZ2 makes it a "Rosetta stone" for understanding the physics of galaxy formation within just 360 Myr after the Big Bang.

Keywords: Primordial galaxies, High-redshift galaxies
Performance of the HAWC Observatory and TeV Gamma-Ray Measurements of the Crab Nebula with Improved Extensive Air Shower Reconstruction Algorithms. The High-Altitude Water Cherenkov (HAWC) Gamma-Ray Observatory, located on the side of the Sierra Negra volcano in Mexico, has been fully operational since 2015. The HAWC collaboration has recently significantly improved their extensive air shower reconstruction algorithms, which has notably advanced the observatory performance. The energy resolution for primary gamma rays with energies below 1 TeV was improved by including a noise-suppression algorithm. Corrections have also been made to systematic errors in direction fitting related to the detector and shower plane inclinations,  O(0.°1)  biases in highly inclined showers, and enhancements to the core reconstruction. The angular resolution for gamma rays approaching the HAWC array from large zenith angles (&gt;37°) has improved by a factor of 4 at the highest energies (&gt;70 TeV) as compared to previous reconstructions. The inclusion of a lateral distribution function fit to the extensive air shower footprint on the array to separate gamma-ray primaries from cosmic-ray ones based on the resulting χ 2 values improved the background rejection performance at all inclinations. At large zenith angles, the improvement in significance is a factor of 4 compared to previous HAWC publications. These enhancements have been verified by observing the Crab Nebula, which is an overhead source for the HAWC Observatory. We show that the sensitivity to Crab-like point sources (E ‑2.63) with locations overhead to 30° zenith is comparable to or less than 10% of the Crab Nebula's flux between 2 and 50 TeV. Thanks to these improvements, HAWC can now detect more sources, including the Galactic center.

Keywords: Gamma-ray detectors, Gamma-rays, High energy astrophysics
The Orbit and Mass of the Cepheid AW Per. The Cepheid AW Per is a component in a multiple system with a long-period orbit. The radial velocities of Griffin cover the 38 yr orbit well. An extensive program of interferometry with the Center for High Angular Resolution Astronomy array is reported here, from which the long-period orbit is determined. In addition, a Hubble Space Telescope high-resolution spectrum in the ultraviolet demonstrates that the companion is itself a binary with nearly equal-mass components. These data combined with a distance from Gaia provide a mass of the Cepheid (primary) of M 1 = 6.79 ± 0.85 M ⊙. The combined mass of the secondary is M S = 8.79 ± 0.50 M ⊙. The accuracy of the mass will be improved after the fourth Gaia data release, expected in approximately two years. ∗ Based on observations with the NASA/ESA Hubble Space Telescope obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555.

Keywords: Multiple stars, Cepheid variable stars, Stellar evolution, Stellar masses
Interstellar Glycolaldehyde, Methyl Formate, and Acetic Acid. II. Chemical Modeling of the Bimodal Abundance Pattern in NGC 6334I. Gas-phase abundance ratios between C2H4O2 isomers methyl formate (MF), glycolaldehyde (GA), and acetic acid (AA) are typically on the order of 100:10:1 in star-forming regions. However, an unexplained divergence from this neat relationship was recently observed toward a collection of sources in the massive protocluster NGC 6334I; some sources exhibited extreme MF:GA ratios, producing a bimodal behavior between different sources, while the MF:AA ratio remained stable. Here, we use a three-phase gas-grain hot-core chemical model to study the effects of a large parameter space on the simulated C2H4O2 abundances. A combination of high gas densities and long timescales during ice-mantle desorption (∼125─160 K) appears to be the physical cause of the high MF:GA ratios. The main chemical mechanism for GA destruction occurring under these conditions is the rapid adsorption and reaction of atomic H with GA on the ice surfaces before it has time to desorb. The different binding energies of MF and GA on water ice are crucial to the selectivity of the surface destruction mechanism; individual MF molecules rapidly escape the surface when exposed by water loss, while GA lingers and is destroyed by H. Moderately elevated cosmic-ray ionization rates can increase absolute levels of "complex organic molecule" (COM) production in the ices and increase the MF:GA ratio, but extreme values are destructive for gas-phase COMs. We speculate that the high densities required for extreme MF:GA ratios could be evidence of COM emission dominated by COMs desorbing within a circumstellar disk.

Keywords: Abundance ratios, Chemical abundances, Astrochemistry, Star formation, Interstellar medium, Complex organic molecules
Comparisons between Resolved Star Formation Rate and Gas Tracers in the Strongly Lensed Galaxy SDSS J0901+1814 at Cosmic Noon. We report new radio observations of SDSS J090122.37+181432.3, a strongly lensed star-forming galaxy at z = 2.26. We image 1.4 GHz (L-band) and 3 GHz (S-band) continuum using the Very Large Array (VLA) and 1.2 mm (band 6) continuum with Atacama Large Millimeter/submillimeter Array, in addition to the CO(7–6) and C I(3 P 2→3 P 1) lines, all at ≲1.″7 resolution. Based on the VLA integrated flux densities, we decompose the radio spectrum into its free–free (FF) and nonthermal components. The infrared–radio correlation parameter  qTIR=2.65‑0.31+0.24  is consistent with expectations for star-forming galaxies. We obtain radio continuum-derived star formation rates (SFRs) that are free of dust extinction, finding  620‑220+280M⊙yr‑1 ,  230‑160+570M⊙yr‑1 , and  280‑120+460M⊙yr‑1  from the FF emission, nonthermal emission, and when accounting for both emission processes, respectively, in agreement with previous results. We estimate the gas mass from the C I(3 P 2→3 P 1) line as M gas = (1.2 ± 0.2) × 1011 M ☉, which is consistent with prior CO(1–0)-derived gas masses. Using our new IR and radio continuum data to map the SFR, we assess the dependence of the Schmidt–Kennicutt relation on choices of SFR and gas tracer for ∼kpc scales. The different SFR tracers yield different slopes, with the IR being the steepest, potentially due to highly obscured star formation in J0901. The radio continuum maps have the lowest slopes and overall fidelity for mapping the SFR, despite producing consistent total SFRs. We also find that the Schmidt–Kennicutt relation slope is flattest when using CO(7–6) or C I(3 P 2→3 P 1) to trace gas mass, suggesting that those transitions are not suitable for tracing the bulk molecular gas in galaxies like J0901.

Keywords: Radio continuum emission, Molecular gas, Star formation, High-redshift galaxies
CLOUDFLEX: A Flexible Parametric Model for the Small-scale Structure of the Circumgalactic Medium. We present CLOUDFLEX, an open-source tool for predicting absorption-line signatures of cool gas in galaxy halos with small-scale structure. Motivated by analyses of ∼104 K material in hydrodynamical simulations of turbulent, multiphase media, we model cool gas structures as complexes of cloudlets sampled from a power-law distribution of mass  ∝mcl−α  with velocities drawn from a turbulent velocity field. The user may specify α, the lower limit of the cloudlet mass distribution ( mcl,min ), and several other parameters that set the mass, size, and velocity distribution of the complex. This permits investigation of the relation between these parameters and absorption-line observables. As a proof-of-concept, we calculate the Mg II λ2796 absorption induced by the cloudlets in background quasi-stellar object (QSO) spectra. We demonstrate that, at fixed metallicity, the covering fraction of sight lines with equivalent widths W 2796 &lt; 0.3 Å increases significantly with decreasing  mcl,min , cloudlet number density (n cl), and complex size. We then use this framework to predict the halo-scale W 2796 distribution around ∼L * galaxies. We show that the observed incidences of W 2796 &gt; 0.3 Å sight lines with impact parameters 10 kpc &lt; R ⊥ &lt; 50 kpc in projected QSO─galaxy studies are consistent with our model over much of parameter space. However, they are underpredicted by models with  mcl,min≥100M⊙  and n cl ≥ 0.03 cm−3, in keeping with a picture in which the inner cool circumgalactic medium (CGM) is dominated by numerous low-mass cloudlets (m cl ≲ 100M ⊙) with a volume filling factor ≲1%. When used to model absorption-line data sets built from multi-sight line and/or spatially extended background probes, CLOUDFLEX enables detailed constraints on the size and velocity distributions of structures comprising the photoionized CGM.

Keywords: Astrophysical fluid dynamics, Galaxy evolution, Circumgalactic medium
iSHELL K-band Survey of Class I and Flat Spectrum Sources: Magnetic Field Measurements in the Protostellar Phase. We perform the first magnetic field strength survey of Class I and Flat Spectrum (FS) sources using K-band observations with iSHELL. We obtained new observations of 42 Class I and FS sources and additionally included 10 sources from the archive. We detect photospheric lines in 44 of the sources, in addition to Brγ, H2, and CO emission in several objects. We model the photospheric absorption lines of 32 Class I and FS sources and measure their magnetic field strengths, K-band temperatures, gravities, projected rotational velocities, and infrared veiling values. We put the physical properties of Class I and FS sources in context by comparing them to the values derived for a sample of Class II sources. We find that (a) the average magnetic field strength of Class I and FS sources = 2.0 ± 0.15 kG is consistent with the average magnetic field strength of Class II sources = 1.8 ± 0.15 kG, and (b) the average gravity of Class I and FS objects  logg=3.43±0.07  is lower than the average gravity of Class II sources  logg=3.75±0.04 , although there is significant overlap between both gravity distributions. Furthermore, using stellar evolutionary models, we deduce that Class I and FS sources have a median age of ∼0.6 Myr, and are, as a group, younger than the Class II stars with a median age of ∼3 Myr. Our results confirm that Class I and FS sources host strong magnetic fields on their photospheres. Thus, it is likely that these sources accrete disk material through a magnetosphere similar to the more evolved T Tauri stars.

Keywords: High resolution spectroscopy, Stellar magnetic fields, T Tauri stars, Pre-main sequence stars, Protostars
BP3M: Bayesian Positions, Parallaxes, and Proper Motions Derived from the Hubble Space Telescope and Gaia Data. We present a hierarchical Bayesian pipeline, BP3M, that measures positions, parallaxes, and proper motions (PMs) for cross-matched sources between Hubble Space Telescope (HST) images and Gaia—even for sparse fields (N * &lt; 10 per image)—expanding from the recent GaiaHub tool. This technique uses Gaia-measured astrometry as priors to predict the locations of sources in HST images, and is therefore able to put the HST images onto a global reference frame without the use of background galaxies/QSOs. Testing our publicly available code in the Fornax and Draco dwarf spheroidal galaxies, we measure PMs that are a median of 8–13 times more precise than Gaia DR3 alone for 20.5 &lt; G &lt; 21 mag. We are able to explore the effect of observation strategies on BP3M astrometry using synthetic data, finding an optimal strategy to improve parallax and position precision at no cost to the PM uncertainty. Using 1619 HST images in the sparse COSMOS field (median nine Gaia sources per HST image), we measure BP3M PMs for 2640 unique sources in the 16 &lt; G &lt; 21.5 mag range, 25% of which have no Gaia PMs; the median BP3M PM uncertainty for 20.25 &lt; G &lt; 20.75 mag sources is 0.44 mas yr‑1 compared to 1.03 mas yr‑1 from Gaia, while the median BP3M PM uncertainty for sources without Gaia-measured PMs (20.75 &lt; G &lt; 21.5 mag) is 1.16 mas yr‑1. The statistics that underpin the BP3M pipeline are a generalized way of combining position measurements from different images, epochs, and telescopes, which allows information to be shared between surveys and archives to achieve higher astrometric precision than that from each catalog alone.

Keywords: Stellar kinematics, Dwarf galaxies, Astrostatistics, Milky Way stellar halo, Proper motions, Milky Way Galaxy
Direct Method to Compute Doppler Beaming Factors in Binary Stars. The Doppler beaming effect, induced by the reflex motion of stars, introduces flux modulations and serves as an efficient method to photometrically determine mass functions for a large number of close binary systems, particularly those involving compact objects. In order to convert observed beaming-flux variations into a radial-velocity curve, precise determination of the beaming factor is essential. Previously, this factor was calculated as a constant, assuming a power-law profile for stellar spectra. In this study, we present a novel approach to directly compute this factor. Our new method not only simplifies the computation, especially for blue bands and cool stars, but also enables us to evaluate whether the relationship between beaming flux and radial velocity can be accurately described as linear. We develop a Python code and compute a comprehensive beaming-factor table for commonly used filter systems covering main-sequence, subgiant, and giant stars, as well as hot subdwarf and white dwarf stars. Both the code and our table are archived and publicly available on Zenodo: doi:10.5281/zenodo.13049419.

Keywords: Radial velocity, Computational methods, Binary stars