Sazuna/UAT_keywords huggingface dataset:
Extended Star Formation in Luminous Infrared Galaxies at z ∼ 1 in the SMILES Field. Luminous infrared galaxies (LIRGs) and ultraluminous infrared galaxies (ULIRGs) in the local Universe are highly centrally concentrated in the mid-infrared (MIR) and substantially more likely than non-(U)LIRGs to be involved in mergers. At higher redshifts, images of radio emission, cold dust, and molecular gas have suggested that (U)LIRGs at cosmic noon and even earlier may be relatively less concentrated than their z ∼ 0 counterparts. Prior to the launch of the James Webb Space Telescope (JWST), quantifying the extent of obscured star formation in (U)LIRGs at z ∼ 1 was not possible due to the low spatial resolution of previous instruments in the MIR. With JWST's Mid-Infrared Instrument (MIRI), it is now possible. We use MIRI imaging to identify a sample of 24 LIRGs at 0.5 ≤ z ≤ 1.22 in the Systematic Mid-Infrared Legacy Extragalactic Survey and find that they are generally less centrally concentrated than their z ∼ 0 counterparts. Compared to high-mass star-forming galaxies that are not LIRGs, we find little evidence that LIRGs are more likely to be morphologically disturbed at rest-frame UV, optical, and near-infrared wavelengths at z ∼ 1. This also differs from the local counterparts where strong disturbances and major mergers are closely associated with LIRGs. These results support suggestions that smaller disturbances and perhaps even internal processes can trigger the collapse of gas clouds outside of galactic cores and cause very high levels of extended star formation at z ≳ 1.

Keywords: Star formation, Polycyclic aromatic hydrocarbons, Ultraluminous infrared galaxies, Luminous infrared galaxies
Inhomogeneous Stellar Mixing in the Final Hours before the Cassiopeia A Supernova. Understanding stars and their evolution is a key goal of astronomical research and has long been a focus of human interest. In recent years, theorists have paid much attention to the final interior processes within massive stars, as they can be essential for revealing neutrino-driven supernova mechanisms and other potential transients of massive star collapse. However, it is challenging to observe directly the last hours of a massive star before explosion, since it is the supernova event that triggers the start of intense observational study. Here, we report evidence for a final phase of stellar activity known as a "shell merger," an intense shell burning in which the O-burning shell swallows its outer C-/Ne-burning shell, deep within the progenitor's interior moments before the supernova explosion. In the violent convective layer created by the shell merger, Ne, which is abundant in the stellar O-rich layer, is burned as it is pulled inward, and Si, which is synthesized inside, is transported outward. The remnant still preserves some traces of such Ne-rich downflows and Si-rich upflows in the O-rich layer, suggesting that inhomogeneous shell-merger mixing began just hours (≲104 s) before its gravitational collapse. Our results provide the first observational evidence that the final stellar burning process rapidly alters the internal structure, leaving a pre-supernova asymmetry. This breaking of spherical symmetry facilitates the explosion of massive stars and influences various supernova and remnant characteristics, including explosion asymmetries and the neutron star's kick and spin.

Keywords: X-ray astronomy, Stellar structures, Core-collapse supernovae, Massive stars, Supernova remnants, Supernova dynamics
Predicting the Properties of the Fallback Rate from Tidal Disruption Events: Investigating the Maximum Gravity Model. A star destroyed by the tidal field of a supermassive black hole (SMBH) in a tidal disruption event (TDE) gives rise to a luminous flare. TDEs are being detected at an ever-increasing rate, motivating the need for accurate models of their lightcurves. The "maximum gravity" (MG) model posits that a star is completely destroyed when the tidal field of the SMBH exceeds the maximum self-gravitational field within the star,  gmax , and predicts the peak fallback rate  Ṁpeak  and the time to peak tpeak. Here we perform hydrodynamical simulations of the complete disruption of 24 stars with masses ranging from 0.2 to 5.0 M⊙, at different stages of their main sequence evolution, to test the predictions of this model. We find excellent agreement between the MG model predictions and our simulations for stars near the zero-age main sequence, while the predictions are less accurate (but still within ∼35%–50% of the simulation results) for highly evolved stars. We also generalize the MG model to incorporate the Paczyński–Wiita potential to assess the impact of strong-gravity effects, which are especially important for deep encounters that are required to completely destroy evolved and centrally concentrated stars, and find good agreement with recent works that include relativistic gravity. Our results demonstrate that this model provides accurate constraints on the peak timescale of TDE lightcurves and their correlation with black hole mass.

Keywords: Black hole physics, Supermassive black holes, Hydrodynamics, Tidal disruption, Astrophysical black holes
Deep Neural Networks for Modeling Astrophysical Nuclear Reacting Flows. In astrophysical simulations, nuclear reacting flows pose computational challenges due to the stiffness of reaction networks. We introduce neural network-based surrogate models using the DeePODE framework to enhance simulation efficiency while maintaining accuracy and robustness. Our method replaces conventional stiff ordinary differential equation (ODE) solvers with deep learning models trained through evolutionary Monte Carlo sampling from zero-dimensional simulation data, ensuring generalization across varied thermonuclear and hydrodynamic conditions. Tested on 3-species and 13-species reaction networks, the models achieve ≲1% accuracy relative to semi-implicit numerical solutions and deliver a ∼2.6× speedup on CPUs. A temperature-thresholded deployment strategy ensures stability in extreme conditions, sustaining neural network utilization above 75% in multidimensional simulations. These data-driven surrogates effectively mitigate stiffness constraints, offering a scalable approach for high-fidelity modeling of astrophysical nuclear reacting flows.

Keywords: Hydrodynamical simulations, Computational methods, Nuclear astrophysics, Neural networks
Assessing Robustness and Bias in 1D Retrievals of 3D Global Circulation Models at High Spectral Resolution: A WASP-76 b Simulation Case Study in Emission. High-resolution spectroscopy (HRS) of exoplanet atmospheres has successfully detected many chemical species and is quickly moving toward detailed characterization of the chemical abundances and dynamics. HRS is highly sensitive to the line shape and position; thus, it can detect three-dimensional (3D) effects such as winds, rotation, and spatial variation of atmospheric conditions. At the same time, retrieval frameworks are increasingly deployed to constrain chemical abundances, pressure–temperature (P–T) structures, orbital parameters, and rotational broadening. To explore the multidimensional parameter space, we need computationally fast models, which are consequently mostly one-dimensional (1D). However, this approach risks introducing interpretation bias since the planet's true nature is 3D. We investigate the robustness of this methodology at high spectral resolution by running 1D retrievals on simulated observations in emission within an observational framework using 3D global circulation models of the quintessential HJ WASP-76 b. We find that the retrieval broadly recovers conditions present in the atmosphere, but that the retrieved P–T and chemical profiles are not a homogeneous average of all spatial and phase-dependent information. Instead, they are most sensitive to spatial regions with large thermal gradients, which do not necessarily coincide with the strongest emitting regions. Our results further suggest that the choice of parameterization for the P–T and chemical profiles, as well as Doppler offsets among opacity sources, impact the retrieval results. These factors should be carefully considered in future retrieval analyses.

Keywords: High resolution spectroscopy, Exoplanet atmospheric composition , Astronomical simulations, Exoplanet atmospheric structure
Orbital and Physical Properties of the Pleiades Binary 27 Tau (Atlas). We report new spectroscopic and interferometric observations of the Pleiades binary star Atlas, which played an important role nearly 3 decades ago in settling the debate over the distance to the cluster from ground-based and space-based determinations. We use the new measurements, together with other published and archival astrometric observations, to improve the determination of the 291 day orbit and the distance to Atlas (136.2 ± 1.4 pc). We also derive the main properties of the components, including their absolute masses (5.04 ± 0.17 M⊙ and 3.64 ± 0.12 M⊙), sizes, effective temperatures, projected rotational velocities, and chemical compositions. We find that the more evolved primary star is rotationally distorted, and we are able to estimate its oblateness and the approximate orientation of its spin axis from the interferometric observations. The spin axis may well be aligned with the orbital axis. Models of stellar evolution from the Modules for Experiments in Stellar Astrophysics (or MESA) that account for rotation provide a good match to all of the primary's global properties, and point to an initial angular rotation rate on the zero-age main sequence of about 55% of the breakup velocity. The current location of the star in the Hertzsprung–Russell diagram is near the very end of the hydrogen-burning main sequence, at an age of about 105 Myr, according to these models. Our spectroscopic analysis of the more slowly rotating secondary indicates that it is a helium-weak star, with other chemical anomalies.

Keywords: Fundamental parameters of stars, Stellar evolutionary models, Spectroscopic binary stars, Astrometric binary stars, Radial velocity, Stellar rotation
DELVE-DEEP Survey: The Faint Satellite System of NGC 55. We report the first comprehensive census of the satellite dwarf galaxies around NGC 55 (2.1 Mpc) as a part of the DECam Local Volume Exploration DEEP (DELVE-DEEP) survey. NGC 55 is one of four isolated, Magellanic analogs in the Local Volume around which DELVE-DEEP aims to identify faint dwarfs and other substructures. We employ two complementary detection methods: one targets fully resolved dwarf galaxies by identifying them as stellar overdensities, while the other focuses on semiresolved dwarf galaxies, detecting them through shredded unresolved light components. As shown through extensive tests with injected galaxies, our search is sensitive to candidates down to MV ≲ −6.6 and surface brightness μ ≲ 28.5 mag arcsec2, and ∼80% complete down to MV ≲ −7.8. We do not report any new confirmed satellites beyond two previously known systems, ESO 294─010 and NGC 55-dw1. We construct the satellite luminosity function of NGC 55 and find it to be consistent with the predictions from cosmological simulations. As one of the first complete luminosity functions for a Magellanic analog, our results provide a glimpse of the constraints on low-mass-host satellite populations that will be further explored by upcoming surveys, such as the Vera C. Rubin Observatory's Legacy Survey of Space and Time.

Keywords: Luminosity function, Dwarf galaxies, Galaxy evolution, Dwarf spheroidal galaxies, Galaxies
Minimum-entropy Constraints on Galactic Potentials. A tracer sample in a gravitational potential, starting from a generic initial condition, phase-mixes toward a stationary state. This evolution is accompanied by an entropy increase, and the final state is characterized by a distribution function (DF) that depends only on integrals of motion (Jeans' theorem). We present a method to constrain a gravitational potential assuming a stationary (phase mixed) sample by minimizing the entropy that the sample would have if it were allowed to phase-mix in trial potentials. This method avoids modeling the DF and is applicable to any sets of integrals. We provide expressions for the entropy of DFs depending on energy, f(E), energy and angular momentum, f(E, L), or three actions, f(J), and investigate the bias and statistical uncertainties in their estimates. We show that the method correctly recovers the parameters for spherical and axisymmetric potentials. We also present a methodology to characterize the posterior probability distribution of the parameters with an approximate Bayesian computation, indicating a pathway for application to observational data. Using 104 tracers with 10%(20%) uncertainties in the 6D coordinates, we recover the flattening parameter q of an axisymmetric potential with σq/q ∼ 5%(10%). The python module for the entropy estimators, tropygal, is made publicly available.

Keywords: Milky Way dark matter halo, Galaxy dynamics, Milky Way dynamics, Dark matter, Milky Way Galaxy, Milky Way mass
Forward and Reverse Shock Emission from Relativistic Jets with Arbitrary Angular and Stratified Radial Profiles. Gamma-ray bursts are expected to be generated by structured jets, whose profiles significantly impact their afterglow emission. Previously, we developed a numerical code jetsimpy, to model the afterglow of jets with arbitrary angular profiles. In this study, we extend the code to incorporate a stratified radial profile, enabling it to model jets with arbitrary axisymmetric two-dimensional structures. The radial profile leads to the formation of a reverse shock. We modeled the shock system using an energy conservation prescription, which differs from the pressure balance approach. This leads to remarkably different predictions for reverse shock emission. In particular, we find that the reverse shock emission in the thin shell case is significantly overestimated in analytic models. We also explore the off-axis reverse shock emission from structured jets, where the cores belong to thick shell cases and the wings belong to thin shell cases. We have confirmed the prediction that off-axis observers may see a thin-to-thick transition, but we find that the light curve morphology is hard to distinguish from pure thin or thick shell cases. A radial profile also introduces hydrodynamic energy injection. As such, our code can naturally apply to refreshed shock cases, where the modeling of kilonova afterglows is demonstrated as an example. To validate our method, we fit the optical flash of GRB 990123, showing good agreement with the data. The upgraded jetsimpy provides unprecedented flexibility in modeling the afterglow emission of jets with various profiles, including those derived from general relativistic magnetohydrodynamic simulations.

Keywords: Hydrodynamical simulations, Shocks, Gamma-ray bursts, Jets
The Interstellar Medium in I Zw 18 Seen with JWST/MIRI. III. Spatially Resolved Three Ionization State Oxygen Abundance. We present observations of the nearby extremely metal-poor galaxy I Zw 18 using the Keck Cosmic Web Imager (KCWI) and the JWST Mid-InfraRed Instrument (MIRI) Integral Field Spectrographs. From optical and mid-IR oxygen emission lines, we measured direct-method abundances for three ionic states of oxygen, including O3+/H+. In contrast to previous studies of I Zw 18 the high spatial resolution afforded by KCWI and MIRI/MRS revealed chemical inhomogeneities on 60 pc scales in the form of metal-poor pockets and metal-enriched gas. These are located outside I Zw 18's star-forming complexes having possibly been dispersed beyond these regions via stellar feedback effects. We found that metallicities derived using a single low-ionization density tracer, and Te([O II]) derived from a temperature relationship commonly used in high-z galaxy studies, exhibited the largest scatter and underestimated the metallicity compared to those derived using multi-ion densities and estimated Te([N II]). Finally, we compared O3+/H+ abundances from a theoretical ionization correction factor (ICF) against observed values and found that the oxygen ICF underestimates the O3+/H+ abundance by a factor of 2, indicating that either additional ionizing sources are needed or standard stellar population models are unable to produce the requisite ionizing flux.

Keywords: Blue compact dwarf galaxies, Metallicity, Interstellar medium
Massive Interacting Binaries Enhance Feedback in Star-forming Regions. We present a new framework to incorporate feedback from massive interacting binaries in simulations of star cluster formation. Our new feedback model adds binary stellar evolution to the cluster formation code TORCH, and couples it in AMUSE to the preexisting modules for collisional stellar dynamics, magnetohydrodynamics, and mechanical and radiative feedback. Our model accounts for the effects of mass transfer on the stars' mass-loss rates, their radiation spectra, and the timing of core-collapse supernovae. It also injects mass lost through nonconservative mass transfer and CE ejection into the interstellar medium (ISM). We demonstrate the use of our feedback model through simulations of isolated binaries in a gaseous medium, and of embedded clusters of massive binaries. Feedback from interacting binaries efficiently couples with the surrounding ISM. It increases the size of H II regions, increases the kinetic and thermal energy of the gas, and increases the pressure within H II regions compared to models that use single star stellar evolution. Those differences arise from the ionizing radiation, which increases by 3 orders of magnitude, resulting in H II regions that expand due to thermal pressure rather than radiation pressure. The effects of stellar dynamics and the gravitational potential of the background gas cause the evolution of individual binaries to deviate from the predictions made by secular evolution, impacting the subsequent feedback from the binary. We conclude that massive interacting binaries are an important source of feedback in cluster-forming regions, and must be considered when studying the emerging timescales of young star clusters.

Keywords: Binary stars, Stellar feedback, Massive stars, Young massive clusters, Interacting binary stars, Stellar dynamics
OWLS. I. The Olin Wilson Legacy Survey. We present initial results from a planned 10 yr survey of Ca II H and K emission, using observations made with the Astrophysical Research Consortium 3.5 m Telescope at Apache Point Observatory. The primary goal of the survey is to investigate activity cycles in low-mass stars. The sample includes stars chosen from the legacy Mount Wilson Observatory (MWO) survey carried out by Olin Wilson more than 50 yr ago, together with newly identified planet-hosting stars and a select sample of early to mid M dwarfs. This paper presents the first 4 yr of data, comprising 1040 observations of 271 stars, with a specific focus on K and M stars. We identify a subsample of 153 stars for continuing observations over the full 10 yr survey. Early results indicate that our data are consistent with the MWO cycle periods over a time span of more than 50 yr; that there is a bifurcation in activity in the late K range with separate populations of low- and high-activity stars at lower masses; and that M dwarf planet hosts tend to be mainly found in the population of low-activity stars, even in the unbiased (by activity) TESS sample, potentially indicating a link between activity and planet formation. We have also found indications of possible cyclic variability in some of the lower-mass stars in the sample. Our ultimate goal is to link the activity cycle and rotation periods in a robust sample of stars spanning the FGKM spectral types and to investigate the implications for the underlying magnetic dynamo.

Keywords: Solar cycle, M dwarf stars, Stellar magnetic fields, Magnetic fields, Stellar activity, Low mass stars, K dwarf stars, Stellar spectral lines
Learning the Universe: Physically Motivated Priors for Dust Attenuation Curves. Understanding the impact of dust on the spectral energy distributions (SEDs) of galaxies is crucial for inferring their physical properties and for studying the nature and evolution of interstellar dust. In this study, we analyze dust attenuation curves of ∼6400 galaxies (M⋆ ∼ 109–1011.5 M⊙) at z = 0.07 from the IllustrisTNG50 &amp; TNG100 simulations. Using radiative transfer post-processing, we generate synthetic attenuation curves and fit them with a versatile parametric model that encompasses both known extinction and attenuation curves (e.g., Calzetti, MW, SMC, and LMC) and more exotic forms. We present the distributions of the best-fitting parameters—UV slope (c1), optical-to-near-IR (NIR) slope (c2), far-UV (FUV) slope (c3), 2175 Å bump strength (c4), and normalization (AV)—accounting for scatter from orientation effects. Key correlations emerge between AV and the star formation rate surface density ΣSFR, as well as the UV slope c1. Furthermore, the UV and FUV slopes (c1, c3) and the visual attenuation and bump strength (AV, c4) exhibit robust internal correlations (anticorrelation in the latter case). The optical-to-NIR slope exhibits minimal variations. Using these insights from simulations, we provide a set of scaling relations that predict a galaxy's median (averaged over line of sight) dust attenuation curve based solely on its ΣSFR and/or AV. These predictions agree well with observed attenuation curves from the GALEX–Sloan Digital Sky Survey–Wide-field Infrared Survey Explorer Legacy Catalog, although there are minor differences in bump strength. This study delivers the most comprehensive library of synthetic attenuation curves for local galaxies, and provides a foundation for physically motivated priors for SED fitting and galaxy inference studies, such as those performed as part of the Learning the Universe Collaboration.

Keywords: Interstellar dust, Hydrodynamical simulations, Interstellar dust extinction, Galaxy evolution, Radiative transfer, Interstellar medium
Statistical Analysis of Ion Properties in the Martian Magnetosheath Based on MAVEN Observations: A Comparison of Core and Total Ion Populations. This study statistically compares ion properties between the thermal core and total ion populations in the Martian magnetosheath, based on observations collected by the Mars Atmosphere and Volatile EvolutioN (or MAVEN) spacecraft from 2015 to 2023. Ion moments for the core population are derived by fitting measured three-dimensional ion velocity distributions with bi-Maxwellian functions, whereas those for the total population are obtained by directly computing weighted sums over the distributions. The core population accounts for a median of approximately 80% of the total number density and dominates the bulk flow of the total population. In contrast, the total population exhibits significantly higher temperature, thermal pressure, and plasma beta, primarily due to the presence of suprathermal ions. Both populations exhibit greater temperature anisotropies downstream of quasi-perpendicular shocks compared to quasi-parallel shocks, consistent with stronger shock compression and a greater contribution from gyrating reflected ions under quasi-perpendicular conditions. Notably, the core population consistently exhibits significantly higher temperature anisotropy than the total population under both shock geometries, suggesting the presence of additional perpendicular heating mechanisms acting on the core population beyond shock compression. One plausible mechanism is stochastic energization by kinetic Alfvén waves. Overall, this systematic comparison of ion parameters between the core and total populations provides new insights into the thermodynamic structure and governing processes of the Martian magnetosheath.

Keywords: Space plasmas, Mars, Solar wind, Planetary dynamics