Sazuna/UAT_keywords huggingface dataset:
Conditions for Bar Formation in Bulgeless Disk Galaxies. While bars are commonly observed in disk galaxies, the precise conditions governing their formation remain incompletely understood. To investigate these conditions, we perform a suite of N-body simulations of bulgeless disk galaxies with stellar masses in the range 109 ≤ Md ≤ 1011 M⊙. Our galaxy models are constructed based on the observed properties of nearby barred galaxies from the S4G survey, and we systematically vary the halo scale radius to isolate its dynamical influence. Bars in our simulations form via repeated swing amplifications of disk perturbations, sustained by feedback loops. The amplification factor Γ depends on both the Toomre stability parameter QT and the dimensionless wavelength X. Based on our simulation results, we propose a two-parameter bar formation criterion, QT + 0.4(X − 1.4)2 ≤ 1.8, corresponding to Γ = 10, which better captures the onset of bar formation than traditional one-parameter conditions. Bars in low-mass galaxies tend to be shorter and weaker, and are more susceptible to disruption by outer spiral arms. In contrast, bars in high-mass galaxies are longer, stronger, and more resilient to spiral interference. Bars in low-mass galaxies undergo only slight vertical thickening over time, whereas those in high-mass galaxies thicken rapidly via buckling instability.

Keywords: Galaxy dark matter halos, Galaxy bars, Disk galaxies, Galaxy disks, Barred spiral galaxies
Mapping Atmospheric Features of the Planetary-mass Brown Dwarf SIMP 0136 with JWST NIRISS. In this paper, we analyze James Webb Space Telescope Near-Infrared Imager and Slitless Spectrograph time-series spectroscopy data to characterize the atmosphere of the planetary-mass brown dwarf SIMP J01365662+093347. Principal component analysis reveals that 81% of spectral variations can be described by two components, implying that variability within a single rotational phase is induced by at least three distinct spectral regions. By comparing our data to a grid of Sonora Diamondback atmospheric models, we confirm that the time-averaged spectrum cannot be explained by a single model but requires a linear combination of at least three regions. Projecting these models onto the principal component plane shows that the overall variability is highly correlated with changes in temperature, cloud coverage, and possibly effective metallicity. We also extract brightness maps from the lightcurve and establish north─south asymmetry in the atmosphere. A combined multidimensional analysis of spectrophotometric variability links the three spectral regions to three atmospheric layers. Forsterite cloud and water abundance at each level form unique harmonics of atmospheric variability observed in different spectral bands. Atmospheric retrievals on the time-averaged spectrum are consistent with an optically thick iron cloud deck beneath a patchy forsterite cloud layer and with the overall adiabatic curve. We also demonstrate two new analysis methods: a regionally resolved spectra retrieval that relies on multiwavelength spherical harmonics maps, and a method to constrain brightness maps using Doppler information present in the spectra. Future observations of variable brown dwarfs of higher spectral resolution or those spanning multiple rotations should help break the mapping degeneracy.

Keywords: Brown dwarfs, Exoplanet atmospheric variability, Exoplanet atmospheric structure, Extrasolar gaseous giant planets, Exoplanet atmospheres, T dwarfs
Early Stellar Flybys are Unlikely: Improved Constraints from Sednoids and Large-q Trans-Neptunian Objects. Sedna-like objects (a.k.a. sednoids) are trans-Neptunian objects (TNOs) characterized by large semimajor axes and exceptionally high perihelia. Their high-q orbits are detached from the influence of the four giant planets and need extra perturbation to form. One hypothesis posits that close stellar flybys could have perturbed objects from the primordial scattering disk, generating the sednoid population. In this study, we run N-body simulations with different stellar encounter configurations to explore whether such a close stellar flyby can satisfy new constraints identified from sednoid (and detached extreme TNO) observation, including the low-inclination (i &lt; 30°) profile and primordial orbital alignment. Our results suggest that flybys with field stars are unable to generate a sufficient population, whereas flybys within the birth cluster fail to produce the primordial orbital alignment. To meet the inclination constraint of detached extreme TNOs, flybys have to be either coplanar (i⋆ ∼ 0°) or symmetric about the ecliptic plane (ω⋆ ∼ 0°, i⋆ ∼ 90°). After taking into account their occurrence rate at the early stage of the solar system, we conclude that close-in stellar flybys (q⋆ ≤ 1000 au) that satisfy all constraints are unlikely to happen (≲5%). Future discoveries of additional sednoids with precise orbital determinations are crucial to confirm the existence of the low-inclination tendency and the primordial alignment, and to further constrain the early dynamical evolution of the solar system.

Keywords: Celestial mechanics, Kuiper belt, Trans-Neptunian objects
The Periodicity of Three-dimensional Oscillatory Reconnection. Oscillatory reconnection is a dynamic, magnetic relaxation mechanism in which a perturbed null point reverts to equilibrium via time-dependent reconnection. In this paper, we investigate the long-term periodic signal generated by a 3D magnetic null point when it is perturbed by a nonperiodic driver for a variety of driving amplitudes. We solve the 3D nonlinear magnetohydrodynamic equations using a bespoke numerical boundary condition (a sponge region) that damps wave reflections and thus allows the long-term periodic signal at the 3D null point to be investigated. We observe multiple cycles of the 3D oscillatory reconnection mechanism for the first time. We find that the periodicity is both constant and independent of the choice of driving amplitude. Furthermore, the resultant time-dependent current density at the null point, normalized by the driving amplitude, is invariant. We extract a single period for oscillatory reconnection at a 3D null point, opening the future possibility of using this characteristic period as a diagnostic tool to reveal indirectly the fundamental plasma properties of 3D null points.

Keywords: Solar coronal transients, Magnetohydrodynamics, Solar magnetic reconnection, Solar coronal heating, Solar physics
pop-cosmos: Insights from Generative Modeling of a Deep, Infrared-selected Galaxy Population. We present an extension of the pop-cosmos model for the evolving galaxy population up to redshift z ∼ 6. The model is trained on distributions of observed colors and magnitudes, from 26-band photometry of ∼420,000 galaxies in the COSMOS2020 catalog with Spitzer IRAC Channel 1 &lt; 26 mag. The generative model includes a flexible distribution over 16 stellar population synthesis (SPS) parameters, and a depth-dependent photometric uncertainty model, both represented using score-based diffusion models. We use the trained model to predict scaling relationships for the galaxy population, such as the stellar mass function, star-forming main sequence, and gas phase and stellar metallicity versus mass relations, demonstrating reasonable to excellent agreement with previously published results. We explore the connection between mid-infrared emission from active galactic nuclei (AGN) and star formation rate, finding high AGN activity for galaxies above the star-forming main sequence at 1 ≲ z ≲ 2. Using the trained population model as a prior distribution, we perform inference of the redshifts and SPS parameters for 429,669 COSMOS2020 galaxies, including 39,588 with publicly available spectroscopic redshifts. The resulting redshift estimates exhibit minimal bias (median[∆z] = −8 × 10−4), scatter (σMAD = 0.0132), and outlier fraction (6.19%) for the full 0 &lt; z &lt; 6 spectroscopic compilation. These results establish that pop-cosmos can achieve the accuracy and realism needed to forward model modern wide, deep surveys for Stage IV cosmology. We publicly release pop-cosmos software, mock galaxy catalogs, and COSMOS2020 redshift and SPS parameter posteriors.

Keywords: Astronomy data modeling, Astrostatistics, Galaxy photometry, Galaxy evolution, Spectral energy distribution, Redshift surveys
Chemical Abundances of M and G Dwarfs in the Hyades and Coma Berenices Open Clusters from APOGEE Spectra. Open clusters are one of the best astrophysical laboratories we have available for stellar astrophysics studies. This work presents metallicities and individual abundances for 14 M dwarfs and six G dwarfs from two well-known open clusters: Hyades and Coma Berenices. Our analysis is based on near-infrared (1.51─1.69 μm), high-resolution (R ∼ 22,500) spectra obtained from the Sloan Digital Sky Survey (SDSS) IV/APOGEE Survey. Using one-dimensional, plane-parallel MARCS model atmospheres, the APOGEE line list, and the Turbospectrum radiative transfer code in local thermodynamic equilibrium, we derived spectroscopic stellar parameters for the M dwarfs, along with abundances of 13 elements (C, O, Na, Mg, Al, Si, K, Ca, Ti, V, Cr, Mn, and Fe) for both M and G dwarfs. We find a high degree of chemical homogeneity within each cluster when comparing abundances derived from M and G dwarfs: δ[M/H] (M dwarfs─G dwarfs) of 0.01 ± 0.04, and 0.02 ± 0.03 for the Hyades and Coma Berenices, respectively. The overall cluster metallicities derived from M dwarfs (Hyades: 0.16 ± 0.03 and Coma Berenices: 0.02 ± 0.06) are consistent with previous literature determinations. Finally, we demonstrate the value of M dwarfs as key tracers in Galactic archeology, emphasizing their potential for studying Galactic metallicity gradients and chemical evolution.

Keywords: M dwarf stars, Open star clusters, Interstellar abundances, Near infrared astronomy
Empirical Optimization of the Source-surface Height in the Potential Field Source Surface Extrapolation. The potential field source surface (PFSS) method is a widely used magnetic field extrapolation technique in the space weather community. The only free parameter in the PFSS method is the source-surface height (RSS), beyond which all field lines are open. Although RSS is known to vary with solar activity, there is no consensus on how to determine it for a given surface magnetic field distribution. In this study, we investigate the nature of RSS using a long-period (2006─2023) dataset, covering two solar minima and one maximum. We adopt ADAPT-GONG magnetograms and determine RSS by matching the open flux estimated from observations at 1 au with that calculated using the PFSS method. Our analysis reveals that RSS increases slightly after the solar minima and around the solar maximum, and that it can be characterized by both the mean unsigned photospheric magnetic field strength and the dipolarity parameter fdip, defined as  fdip=Bdip2/(Bdip2+Bquad2+Boct2) , with Bdip, Bquad, and Boct denoting the magnitudes of dipolar, quadrupolar, and octupolar components of photospheric radial magnetic field, respectively. Our results suggest that RSS does not exhibit a simple monotonic dependence on the solar activity and must be determined by properly considering both surface magnetic field strength and global field structure.

Keywords: Space weather, Solar wind, Solar magnetic fields, Heliosphere
A Gigaparsec-scale Hydrodynamic Volume Reconstructed with Deep Learning. The next generation of spectroscopic surveys will map the large-scale structure of the Universe at high redshifts (2 ≤ z ≤ 5) using millions of quasar spectra, enabling major advances in constraining both the standard cosmological model and its extensions. Robust cosmological analyses of these data sets require numerical simulations that both cover gigaparsec volumes and resolve features on ∼10 kpc scales and smaller. However, running such large-volume, high-resolution hydrodynamic simulations is computationally prohibitive. We present a generative deep learning model that enhances a low-resolution, gigaparsec-scale (960 h−1 Mpc) hydrodynamic simulation using a smaller (80 h−1 Mpc) high-resolution input hydrodynamic simulation as training data. The resulting enhanced simulation reproduces the line-of-sight power spectrum to within ∼10% and the three-dimensional power spectrum at the ∼20% level at intermediate to small scales (k ≲ 2 h Mpc−1). Our method shows strong promise for producing realistic simulations for cosmological analyses with current surveys such as the Dark Energy Spectroscopic Instrument and upcoming next-generation experiments, but further improvements are needed to accurately recover the large-scale modes. We publicly release the enhanced hydrodynamic simulation, along with a halo catalog from a companion N-body dark matter simulation to support the calibration of data analysis pipelines for these large-scale surveys.

Keywords: Cosmology, Lyman alpha forest, Large-scale structure of the universe, Convolutional neural networks, Intergalactic medium
Tidal Disruption Events in Active Galactic Nuclei: on Orbital Inclination and Schwarzschild Apsidal Precession. Tidal disruption events (TDEs) in active galactic nuclei (AGNs) mark a regime where traditional vacuum models fail to capture the full dynamics, especially due to interaction between stellar debris and preexisting accretion disks. We perform meshless hydrodynamic simulations incorporating both general relativistic (GR) effects and radiative cooling to study TDEs in AGNs with different orbital inclinations (θinc) of the disrupted star, ranging from projected prograde to retrograde orbits. We postprocess the simulations to derive multiwavelength light curves and identify several distinct features in the light curves, including a precursor flare from early debris-disk collision and a major flare driven by fallback. The dynamics of the stellar debris and accretion disk, and subsequently the light-curve features, are strongly affected by θinc and GR effects. Retrograde orbits (θinc = 135°) yield a more luminous, shorter major flare and a more prominent precursor than prograde ones (θinc = 22 .° 5). During fallback, prograde cases (θinc = 22 .° 5, 45°) develop a central cavity with spirals in the inner region of the AGN disk, leading to transient UV/X-ray suppression accompanied by oscillations, while higher inclinations (θinc = 90°, 135°) form a gradually tilting inner disk, potentially causing UV/X-ray dips via geometric effects at certain viewing angles. Relativistic apsidal precession alters stream collisions, producing structural differences in the inner disk, outer disk, and debris compared to Newtonian cases, and drives quasi-periodic signals in prograde configurations. These results provide predictive diagnostics for identifying AGN TDEs and interpreting observed light-curve diversity.

Keywords: Hydrodynamical simulations, Tidal disruption, Active galactic nuclei, High energy astrophysics
The Accretion Disk Size Problem in AGN Disk Reverberation Mapping Is an Obscuration Effect: A Uniform AGN Sample Study with Swift. In the past decade, Swift has performed several active galactic nucleus (AGN) high-cadence reverberation mapping campaigns, and it has generally found that the UV/optical interband lags are ∼3 times longer than predicted for a standard thin disk, thus coined "the accretion disk size problem." Here we present a systematic sample of Swift-monitored AGN. In this analysis, we confirm the accretion disk size problem but find that the lag excess occurs only in the subset of obscured AGN, which show a significantly elevated mean normalization of 5.21 ± 0.47 (p = 0.008), whereas the unobscured AGN exhibit a mean excess consistent with standard disk predictions (1.00 ± 0.31). Correlation and regression analyses similarly reveal X-ray column density as the strongest predictor of lag excess, explaining over 80% of its variance. We interpret these results as line-of-sight obscuration being linked to the too-long lags via additional reprocessed emission from the absorbing material itself. The consistency of lags in the unobscured subgroup with standard disk predictions suggests that the accretion disk size problem is not the result of shortcomings of standard accretion disk theory or contamination by the broad-line region. X-ray to UV lag amplitudes and correlations show more complex and variable behavior in obscured AGN, suggesting that obscuration may disrupt or complicate the connection between high- and low-energy emission potentially through reprocessing, scattering, and/or ionization changes.

Keywords: Accretion, Supermassive black holes, Reverberation mapping, Active galactic nuclei, Time series analysis
Experimental Absorption Cross Sections for ZrO. Absorption cross sections for ZrO are provided and can be used as a template to interpret spectra of S-type stars. The ZrO spectrum was measured in emission from a carbon furnace at 2700 K and calibrated using synthetic spectra of 90Zr16O. A set of nearly isolated molecular lines has been used for the calibration. We also thoroughly review the literature on the spectroscopy of ZrO. Comparison of the experimental spectrum with currently available line lists revealed issues in ZrO spectral simulation. (a) Within band systems, the relative intensities are not always well reproduced. (b) We identify yet unreported band systems, the strongest ones being E1Φ−a3∆ and b3Π−X1Σ+; this is to our knowledge the first observation of the theoretically predicted E1Φ state of ZrO. (c) Three significant band heads in the red are unassigned to this day. We determine spectroscopic constants for E1Φ (v = 0) and F1∆ (v = 0, 1) and line lists for associated transitions with Einstein As and oscillator strengths. The C1Σ+−X1Σ+ ab initio transition dipole moment is updated and the line list of this transition is recalculated.

Keywords: Molecular data, Rotational spectroscopy, Laboratory astrophysics, Molecular spectroscopy, Stellar atmospheric opacity
The X-Ray Emission of NGC 5005: An Unobscured Low-luminosity Active Galactic Nucleus with a Weakly Accreting Broad-line Region. We present deep Chandra X-ray observations of NGC 5005, a LINER-dominated galaxy previously reported to host a broad Hα emission line. The diffuse soft X-ray emission (&lt;3 keV) extends out to ∼800 pc, while harder emission (&gt;3 keV) is confined to the central ∼400 pc. Spatially resolved spectroscopy of the nuclear (r &lt; 150 pc) and extended (150 &lt; r &lt; 500 pc) regions reveals that these are best described by models including both photoionized and thermal plasma components, consistent with excitation by a low-luminosity active galactic nucleus (AGN) and shock-heated gas. Narrowband imaging and excitation maps from the Hubble Space Telescope (HST) support this interpretation, closely matching the X-ray morphology and ionization structure. The detection of a faint hard X-ray nuclear source with Chandra, combined with stringent upper limits from NuSTAR and Swift, and consistency with the X-ray luminosity predicted from the HST [O III]λ5007 emission, indicates that NGC 5005 hosts an intrinsically low-luminosity (Lbol ∼ 1041 erg s−1), unobscured AGN. Despite the extremely low Eddington ratio inferred from our measurements (λEdd ∼ 5 × 10−6), the presence of a broad Hα line in the optical spectrum suggests the persistence of a thin accretion disk, challenging standard paradigms of accretion flow configurations at such low accretion rates.

Keywords: LINER galaxies
X-Ray Polarimetry of Accreting White Dwarfs: A Case Study of EX Hydrae. We present the first first X-ray polarization measurements of a white dwarf (WD), the intermediate polar EX Hya. We measured significant polarization only in the 2─3 keV energy band with a polarization degree of 8% at a 3σ significance. No significant polarization was detected above 3 keV, which we attribute to the higher energy bands having lower signal to noise. We found that the scattering surface detected by the Imaging X-ray Polarimetry Explorer appears to be nearly perpendicular to the optical scattering plane, showing that the X-ray scattering surface is the WD and close to the base of the accretion column. Finally, we show how the polarization can be used to estimate the height of the accretion shock above the WD's surface.

Keywords: X-ray astronomy, DQ Herculis stars, Cataclysmic variable stars, Spectropolarimetry
The Dark Matter Content of Milky Way Dwarf Spheroidal Galaxies: Draco, Sextans, and Ursa Minor. The Milky Way Survey of the Dark Energy Spectroscopic Instrument (DESI) has so far observed three classical dwarf spheroidal galaxies (dSphs): Draco, Sextans, and Ursa Minor. Based on the observed line-of-sight velocities and metallicities of their member stars, we apply the axisymmetric Jeans Anisotropic Multi-Gaussian Expansion modeling (JAM) approach to recover their inner dark matter distributions. In particular, both the traditional single-population Jeans model and the multiple population chemodynamical model are adopted. With the chemodynamical model, we divide member stars of each dSph into metal-rich and metal-poor populations. The metal-rich populations are more centrally concentrated and dynamically colder, featuring lower velocity dispersion profiles than the metal-poor populations. We find a diversity of the inner density slopes γ of dark matter halos, with the best constraints by the single-population or chemodynamical models consistent with each other. The inner density slopes are  0.71−0.35+0.34 ,  0.26−0.12+0.22 , and  0.33−0.16+0.20  for Draco, Sextans, and Ursa Minor, respectively. We also present the measured astrophysical J and D factors of the three dSphs. Our results indicate that the study of the dark matter content of dSphs through stellar kinematics is still subject to uncertainties behind both the methodology and the observed data, through comparisons with previous measurements and datasets.

Keywords: Galaxy dynamics, Dark matter, Dwarf spheroidal galaxies
Simulating Propagation of a Coronal Mass Ejection from Solar Corona to 1 au with the Alfvén Wave Solar Atmosphere Model and Fitting of Gibson─Low. Fitting of Gibson─Low (FGL) is a newly developed time-dependent self-similar forward-reconstruction method of coronal mass ejections (CMEs) based on the analytic Gibson─Low model. This method is able to reconstruct the plasma velocity, density, pressure, and magnetic field of CMEs using data from coronagraphs and magnetographs. In this paper, the reconstructed CME on 2011 March 7 is inserted into the CR2107 background solar wind generated by steady-state mode of Alfvén Wave Solar atmosphere Model (AWSoM), which heats and drives the solar wind based on the propagation, dissipation, and reflection of the Alfvén wave turbulence. Then the time-accurate mode of AWSoM simulates the CME propagation from solar corona to inner heliosphere. We compare the simulation results and observations to evaluate the performance of AWSoM+FGL through two quantitative criteria, Pearson correlation coefficient and mean absolute percentage error. At last, the parameters of FGL are changed to different values to show how such adjustment may influence the simulation results. The simulation results indicate that AWSoM+FGL successfully captures characters of both background solar wind and CME propagation.

Keywords: Solar activity, Solar storm, Solar coronal mass ejections