Sazuna/UAT_keywords huggingface dataset:
Cosmic-Ray North–South Anisotropy: Rigidity Spectrum and Solar Cycle Variations Observed by Ground-based Muon Detectors. The north–south (NS) anisotropy of galactic cosmic rays (GCRs) is dominated by a diamagnetic drift flow of GCRs in the interplanetary magnetic field (IMF), allowing us to derive key parameters of cosmic-ray propagation, such as the density gradient and diffusion coefficient. We propose a new method to analyze the rigidity spectrum of GCR anisotropy and reveal a solar cycle variation of the NS anisotropy's spectrum using ground-based muon detectors in Nagoya, Japan, and Hobart, Australia. The physics-based correction method for the atmospheric temperature effect on muons is used to combine the different-site detectors free from local atmospheric effects. NS channel pairs in the multidirectional muon detectors are formed to enhance sensitivity to the NS anisotropy, and in this process, general graph matching in graph theory is introduced to survey optimized pairs. Moreover, Bayesian estimation with the Gaussian process allows us to unfold the rigidity spectrum without supposing any analytical function for the spectral shape. Thanks to these novel approaches, it has been discovered that the rigidity spectrum of the NS anisotropy is dynamically varying with solar activity every year. It is attributed to a rigidity-dependent variation of the radial density gradient of GCRs based on the nature of the diamagnetic drift in the IMF. The diffusion coefficient and mean free path length of GCRs as functions of the rigidity are also derived from the diffusion–convection flow balance. This analysis expands the estimation limit of the mean free path length into the ≤200 GV rigidity region from the &lt;10 GV region achieved by solar energetic particle observations.

Keywords: Galactic cosmic rays, Secondary cosmic rays, Interplanetary medium, Heliosphere
Kinematic Analysis of z = 4.3 Galaxies in the SPT2349–56 Protocluster Core. SPT2349‑56 is a protocluster discovered in the 2500 deg2 South Pole Telescope (SPT) survey. In this paper, we study the kinematics of the galaxies found in the core of SPT2349‑56 using high-resolution (1.55 kpc spatial resolution at z = 4.303) redshifted [C II] 158 μm data. Using the publicly available code  3D  BAROLO, we analyze the seven far-infrared brightest galaxies within the protocluster core. Based on conventional definitions for the detection of rotating disks, we classify six sources to be rotating disks in an actively star-forming protocluster environment, with weighted mean V rot/σ disp = 4.5 ± 1.3. The weighted mean rotation velocity (V ro t) and velocity dispersion (σ disp) for the sample are 357.1 ± 114.7 km s‑1 and 43.5 ± 23.5 km s‑1, respectively. We also assess the disk stability of the galaxies and find a mean Toomre parameter of Q T = 0.9 ± 0.3. The galaxies show a mild positive correlation between disk stability and dynamical support. Using the position–velocity maps, we find that five sources further classify as disturbed disks, and one classifies as a strictly rotating disk. Our sample joins several observations at similar redshift with high V/σ values, with the exception that they are morphologically disturbed, kinematically rotating, and interacting galaxies in an extreme protocluster environment.

Keywords: Protoclusters, Galaxy kinematics, High-redshift galaxies, Galaxies
CSS 161010: A Luminous Fast Blue Optical Transient with Broad Blueshifted Hydrogen Lines. We present ultraviolet, optical, and near-infrared photometric and optical spectroscopic observations of the luminous fast blue optical transient (LFBOT) CSS 161010:045834–081803 (CSS 161010). The transient was found in a low-redshift (z = 0.033) dwarf galaxy. The light curves of CSS 161010 are characterized by an extremely fast evolution and blue colors. The V-band light curve shows that CSS 161010 reaches an absolute peak of   mag in 3.8 days from the start of the outburst. After maximum, CSS 161010 follows a power-law decline ∝t ‑2.8±0.1 in all optical bands. These photometric properties are comparable to those of well-observed LFBOTs such as AT 2018cow, AT 2020mrf, and AT 2020xnd. However, unlike these objects, the spectra of CSS 161010 show a remarkable transformation from a blue and featureless continuum to spectra dominated by very broad, entirely blueshifted hydrogen emission lines with velocities of up to 10% of the speed of light. The persistent blueshifted emission and the lack of any emission at the rest wavelength of CSS 161010 are unique features not seen in any transient before CSS 161010. The combined observational properties of CSS 161010 and its M * ∼ 108 M ⊙ dwarf galaxy host favor the tidal disruption of a star by an intermediate-mass black hole as its origin.

Keywords: Supernovae, Transient sources
Investigation of the Nonthermal X-Ray Emission from the Supernova Remnant CTB 37B Hosting the Magnetar CXOU J171405.7-381031. We present a detailed X-ray investigation of a region (S1) exhibiting nonthermal X-ray emission within the supernova remnant (SNR) CTB 37B hosting the magnetar CXOU J171405.7−381031. Previous analyses modeled this emission with a power law (PL), inferring various values for the photon index (Γ) and absorbing column density (N H). Based on these, S1 was suggested to be an SNR shell, a background pulsar wind nebula, or an interaction region between the SNR and a molecular cloud. Our analysis of a larger data set favors a steepening (broken or curved PL) spectrum over a straight PL, with the best-fit broken power-law (BPL) parameters of Γ = 1.23 ± 0.23 and 2.24 ± 0.16 below and above a break at 5.57 ± 0.52 keV, respectively. However, a simple PL or srcut model cannot be definitively ruled out. For the BPL model, the inferred N H = (4.08 ± 0.72) × 1022 cm−2 towards S1 is consistent with that of the SNR, suggesting a physical association. The BPL-inferred spectral break ∆Γ ≍ 1 and hard Γ can be naturally explained by a nonthermal bremsstrahlung (NTB) model. We present an evolutionary NTB model that reproduces the observed spectrum, which indicates the presence of subrelativistic electrons within S1. However, alternate explanations for S1, an unrelated PWN or the SNR shock with unusually efficient acceleration, cannot be ruled out. We discuss these explanations and their implications for gamma-ray emission from CTB 37B and describe future observations that could settle the origin of S1.

Keywords: High energy astrophysics, Gamma-ray sources, Supernova remnants, Non-thermal radiation sources, X-ray sources, Magnetars
A Dust Attenuation Model Inspired by the NIHAO-SKIRT-Catalog. We use simulated attenuation curves from the NIHAO-SKIRT-Catalog to test the flexibility of commonly used dust attenuation models in the face of the variations expected from realistic star–dust geometries. Motivated by lack of flexibility in these existing models, we propose a novel dust attenuation model with three free parameters that can accurately recover the simulated attenuation curves as well as the best-fitting curves from the commonly used models. This new model is fully analytic and treats all starlight equally, in contrast to two-component dust attenuation models. We use the parameterization to investigate the relationship between the overall attenuation law shape and the strength of the 2175 Å bump. Our results indicate variation in star–dust geometry leads these features to correlate tightly, with grayer attenuation curves having weaker bumps.

Keywords: Interstellar dust, Hydrodynamics, Stellar populations, Interstellar dust extinction, Radiative transfer, Galaxy evolution
Size Growth on Short Timescales of Star-forming Galaxies: Insights from Size Variation with Rest-frame Wavelength with JADES. We investigate size variation with rest-frame wavelength for star-forming galaxies based on the second James Webb Space Telescope Advanced Deep Extragalactic Survey data release. Star-forming galaxies are typically smaller at longer wavelengths from the UV to the near-IR at z &lt; 3.5, especially for more massive galaxies, indicating the inside-out assembly with in situ star formation if ignoring dust attenuation. The size variation with wavelength shows a strong dependence on stellar mass and shows little or no dependence on redshift, specific star formation rate, and galaxy environment. This suggests that the size growth of star-forming galaxies is a self-regulated process primarily governed by stellar mass. We model size as a function of both mass and redshift simultaneously, obtaining   at a wavelength of 0.45 μm, and   at 1.0 μm. Based on this size evolution and the star formation main sequence from the literature, we obtain the locus of typical size growth for individual galaxies of different masses on the mass–size plane. The moving trend of galaxies on the mass–size plane, which indicates the slopes of their locus, strongly correlates with the size ratio between 0.45 μm and 1.0 μm, supporting the idea that the size variation with wavelength provides important information on the size growth of galaxies on short timescales.

Keywords: Star formation, High-redshift galaxies, Galaxy evolution
Revisiting Radio Variability of the Blazar 3C 454.3. We examine lengthy radio light curves of the flat spectrum radio galaxy 3C 454.3 for possible quasiperiodic oscillations (QPOs). The data used in this work were collected at five radio frequencies, 4.8, 8.0, 14.5, 22.0, and 37.0 GHz between 1979 and 2013 as observed at the University of Michigan Radio Astronomical Observatory, Crimean Astrophysical Observatory, and Aalto University Metsähovi Radio Observatory. We employ generalized Lomb–Scargle periodogram and weighted wavelet transform analyses to search for periodicities in these light curves. We confirm a QPO period of ∼2000 days to be at least 4σ significant using both methods at all five radio frequencies between 1979 and 2007, after which a strong flare changed the character of the light curve. We also find a ∼600 day period, which is at least 4σ significant, but only in the 22.0 and 37.0 GHz light curves. We briefly discuss physical mechanisms capable of producing such variations.

Keywords: Blazars, Radio astronomy, Active galactic nuclei, Quasars
On the Origins, Remnant, and Multimessenger Prospects of the Compact Binary Merger GW230529. This study investigates the origins of GW230529, delving into its formation from massive stars within isolated binary systems. Utilizing population-synthesis models, we present compelling evidence that the neutron star component forms second. However, the event's low signal-to-noise ratio introduces complexities in identifying the underlying physical mechanisms driving its formation. Augmenting our analysis with insights from numerical relativity, we estimate the final black hole mass and spin to be approximately 5.3 M ⊙ and 0.53, respectively. Furthermore, we employ the obtained posterior samples to calculate the ejecta mass and kilonova light curves resulting from r-process nucleosynthesis. We find the ejecta mass to be within 0–0.06 M ⊙, contingent on the neutron star equation of state. The peak brightness of the kilonova light curves indicates that targeted follow-up observations with a Rubin-like observatory may have detected this emission.

Keywords: Gravitational wave astronomy, Neutron stars
Artificial Polytropic Behavior of Plasmas Determined from the Application of Chi-squared Minimization Analysis to Data with Significant Statistical Uncertainty. The effective polytropic index of plasmas is typically determined from the analysis of the plasma temperature (or pressure) and density, which are plasma bulk parameters determined from analyses of in situ plasma observations. Here, we show that the use of the typical chi-squared minimization method in plasma observation analyses results in artificial correlations between the plasma density and temperature, which will introduce errors in the determination of the plasma polytropic relationship. We quantify this potential error by analyzing simulated plasma observations. We specifically show that even in cases of nonvarying plasma, a significant statistical uncertainty in the observations leads to the determination of plasma parameters, which seemingly follow a nearly adiabatic model. Moreover, we consider isobaric plasma variations and discuss the error in the determined polytropic relationship as a function of the actual plasma variations and the statistical uncertainties of the determined parameters. We finally show that the use of an alternative analysis method improves the accuracy of the results.

Keywords: Space plasmas
Large Dark Matter Content and Steep Metallicity Profile Predicted for Ultradiffuse Galaxies Formed in High-spin Halos. We study the stellar properties of a sample of simulated ultradiffuse galaxies (UDGs) with stellar mass M ⋆ = 107.5–109 M ⊙, selected from the TNG50 simulation, where UDGs form mainly in high-spin dwarf-mass halos. We divide our sample into star-forming and quenched UDGs, finding good agreement with the stellar assembly history measured in observations. Star-forming UDGs and quenched UDGs with M ⋆ ≥ 108 M ⊙ in our sample are particularly inefficient at forming stars, having 2–10 times less stellar mass than non-UDGs for the same virial mass halo. These results are consistent with recent mass inferences in UDG samples and suggest that the most inefficient UDGs arise from a late assembly of the dark matter mass followed by a stellar growth that is comparatively slower (for star-forming UDGs) or that was interrupted due to environmental removal of the gas (for quenched UDGs). Regardless of efficiency, UDGs are 60% poorer in [Fe/H] than the population of non-UDGs at a fixed stellar mass, with the most extreme objects having metal content consistent with the simulated mass–metallicity relation at z ∼ 2. Quenched UDGs stop their star formation in shorter timescales than non-UDGs of similar mass and are, as a consequence, alpha enhanced with respect to non-UDGs. We identify metallicity profiles in UDGs as a potential avenue to distinguish between different formation paths for these galaxies, where gentle formation as a result of high-spin halos would present well-defined declining metallicity radial profiles while powerful-outflows or tidal stripping formation models would lead to flatter or constant metallicity as a function of radius due to the inherent mixing of stellar orbits.

Keywords: Galaxy dark matter halos, Dwarf galaxies, Star formation, Galaxy evolution
Classification of Wolf–Rayet Stars Using Ensemble-based Machine Learning Algorithms. We develop a robust machine learning classifier model utilizing the eXtreme-Gradient Boosting (XGB) algorithm for improved classification of Galactic Wolf–Rayet (WR) stars based on IR colors and positional attributes. For our study, we choose an extensive data set of 6555 stellar objects (from 2MASS and AllWISE data releases) lying in the Milky Way (MW) with available photometric magnitudes of different types, including WR stars. Our XGB classifier model can accurately (with an 86% detection rate) identify a sufficient number of WR stars against a large sample of non-WR sources. The XGB model outperforms other ensemble classifier models, such as Random Forest. Also, using the XGB algorithm, we develop a WR subtype classifier model that can differentiate the WR subtypes from the non-WR sources with a high model accuracy (&gt;60%). Further, we apply both XGB-based models to a selection of 6457 stellar objects with unknown object types, detecting 58 new WR star candidates and predicting subtypes for 10 of them. The identified WR sources are mainly located in the local spiral arm of the MW and mostly lie in the solar neighborhood.

Keywords: Massive stars, Two-color diagrams, Stellar classification, Wolf-Rayet stars, Random Forests, Infrared photometry
Low-latitude Auroras: Insights from 2023 April 23 Solar Storm. In 2023 April, a low-latitude aurora observed by the all-sky camera at Hanle, Ladakh, India (33°14'N geographic latitude), generated significant interest. This was the first such aurora recorded from the Indian region in the space era and occurred during a moderate solar storm. This study explores this low-latitude auroral sighting, which happened during the sheath-region passage of an interplanetary coronal mass ejection. We analyze in situ multispacecraft particle measurements and geomagnetic field observations from both ground-based and satellite-based magnetometers. The auroral observations at Hanle coincided with intense substorm activity. Our findings indicate that the aurora did not actually reach India; the equatorward boundary was beyond 50°N geographic latitude. Enhanced electron fluxes with energies below 100 eV were detected at 54°N geographic latitude at about 830 km altitude in the predawn sector (4–5 hr local time). In the midnight sector, the equatorward boundary is estimated to be around 52°N geographic latitude, based on Hanle observations and considering emission altitudes of 600–650 km due to low-energy electrons. Thus, the low-latitude red aurora observed from India resulted from the emissions at higher altitudes due to low-energy electron precipitation in the auroral oval and a slight equatorward expansion of the auroral oval. The low-energy electrons likely originated from the plasma sheet and were precipitated due to enhanced wave–particle interactions from strong magnetosphere compression during high solar wind pressure. This study is crucial in understanding low-latitude auroras in the modern space era.

Keywords: Solar storm, Solar particle emission, Solar coronal mass ejections, Aurorae
SCExAO/CHARIS Near-infrared Scattered-light Imaging and Integral Field Spectropolarimetry of the AB Aurigae Protoplanetary System. We analyze near-infrared integral field spectropolarimetry of the AB Aurigae protoplanetary disk and protoplanet (AB Aur b), obtained with SCExAO/CHARIS in 22 wavelength channels covering the J, H, and K passbands (λ 0 = 1.1–2.4 μm) over angular separations of ρ ≈ 0.″13 to 1.″1 (∼20–175 au). Our images resolve spiral structures in the disk in each CHARIS channel. At the longest wavelengths, the data may reveal an extension of the western spiral seen in previous polarimetric data at ρ &lt; 0.″3 out to larger distances clockwise from the protoplanet AB Aur b, coincident with the Atacama Large Millimeter/submillimeter Array–detected CO gas spiral. While AB Aur b is detectable in complementary total intensity data, it is a nondetection in polarized light at λ &gt; 1.3 μm. While the observed disk color is extremely red across JHK, the disk has a blue intrinsic scattering color consistent with small dust grains. The disk's polarization spectrum is redder than AB Aur b's total intensity spectrum. The polarization fraction peaks at ∼0.6 along the major disk axis. Radiative transfer modeling of the CHARIS data shows that small, porous dust grains with a porosity of p = 0.6–0.8 better reproduce the scattered-light appearance of the disk than more compact spheres (p = 0.3), especially the polarization fraction. This work demonstrates the utility of integral field spectropolarimetry to characterize structures in protoplanetary disks and elucidate the properties of the disks' dust.

Keywords: Exoplanet formation, Protoplanetary disks, Adaptive optics
JWST/MIRI Detection of a Carbon-rich Chemistry in the Disk of a Solar Nebula Analog. It has been proposed, and confirmed by multiple observations, that disks around low-mass stars display a molecule-rich emission and carbon-rich disk chemistry as compared to their hotter, more massive solar counterparts. In this work, we present JWST Disk Infrared Spectral Chemistry Survey MIRI-MRS observations of the solar-mass star DoAr 33, a low-accretion rate T Tauri star showing an exceptional carbon-rich inner disk. We report detections of H2O, OH, and CO2, as well as the more complex hydrocarbons, C2H2 and C4H2. Through the use of thermochemical models, we explore different spatial distributions of carbon and oxygen across the inner disk and compare the column densities and temperatures obtained from LTE slab model retrievals. We find the best match to the observed column densities with models that have carbon enrichment, and the retrieved emitting temperature and area of C2H2 with models that have C/O = 2─4 inside the 500 K carbon-rich dust sublimation line. This suggests that the origin of the carbon-rich chemistry is likely due to the sublimation of carbon-rich grains near the soot line. This would be consistent with the presence of dust processing as indicated by the detection of crystalline silicates. We propose that this long-lived hydrocarbon-rich chemistry observed around a solar-mass star is a consequence of the unusually low M-star-like accretion rate of the central star, which lengthens the radial mixing timescale of the inner disk, allowing the chemistry powered by carbon grain destruction to linger.

Keywords: Protoplanetary disks, Planet formation, Astrochemistry
An Evaluation of Different Numerical Methods to Calculate the Pitch-angle Diffusion Coefficient from Full-orbit Simulations: Disentangling a Rope of Sand. The pitch-angle diffusion coefficient (PADC) quantifies the effect of pitch-angle scattering on charged particles propagating through turbulent magnetic fields and is a key ingredient in understanding the diffusion of these particles along the background magnetic field. Despite its significance, only a limited number of studies have calculated the PADC from test-particle simulations in synthetic magnetic turbulence, employing various, often quite different, techniques for this purpose. In this study, we undertake a comparative analysis of nine different methods for calculating the PADC from full-orbit simulations. Our objective is to find the strengths and limitations of each method and to determine the most reliable approach. Although all nine methods should theoretically yield comparable results, certain methods may be ill-suited for numerical investigations, while others may not be applicable under conditions of strong turbulence. Through this investigation, we aim to provide recommendations for best practices when employing these methods in future numerical studies of pitch-angle scattering.

Keywords: Interplanetary turbulence, Stellar diffusion, Magnetic fields, Interstellar scattering
Semisupervised Learning for Detecting Inverse Compton Emission in Galaxy Clusters. Inverse Compton (IC) emission associated with the nonthermal component of the intracluster medium (ICM) has been a long-sought phenomenon in cluster physics. Traditional spectral fitting often suffers from the degeneracy between the two-temperature thermal (2T) spectrum and the one-temperature plus IC power-law (1T+IC) spectrum. We present a semisupervised deep-learning approach to search for IC emission in galaxy clusters. We employ a conditional autoencoder (CAE), which is based on an autoencoder with latent representations trained to constrain the thermal parameters of the ICM. The algorithm is trained and tested using synthetic NuSTAR X-ray spectra with instrumental and astrophysical backgrounds included. The training data set only contains 2T spectra, which is more common than 1T+IC spectra. Anomaly detection is performed on the validation and test data sets consisting of 2T spectra as the normal set and 1T+IC spectra as anomalies. With a threshold anomaly score, chosen based on cross validation, our algorithm is able to identify spectra that contain an IC component in the test data set, with a balanced accuracy (BAcc) of 0.64, which outperforms traditional spectral fitting (BAcc = 0.55) and ordinary autoencoders (BAcc = 0.55). Traditional spectral fitting is better at identifying IC cases among true IC spectra (a better recall), while IC predictions made by CAE have a higher chance of being true IC cases (a better precision), demonstrating that they mutually complement each other.

Keywords: Galaxy clusters, Intracluster medium, Astronomy data analysis, X-ray astronomy