Sazuna/UAT_keywords huggingface dataset:
Differential Accretion of Ionized Low-velocity Gas at the Milky Way's Disk─Halo Interface. We measure line-of-sight velocities of metal absorption and H I emission along 132 QSO sight lines in order to study gas accretion and outflow at the disk─halo interface of the Milky Way. While previous studies have focused on high- and intermediate-velocity clouds and complexes, we examine material at predominantly low velocities relative to the local standard of rest (i.e., all absorbers at ∣vLSR∣ &lt; 90 km s−1, and absorbers at 90 &lt; ∣vLSR∣ &lt; 150 km s−1 not associated with any well-defined cloud complexes). We find that gas accretion velocities in the northern Galactic hemisphere are correlated with the ionization potential energy of the multiphase metal ions we include in our analysis; more highly ionized material traced by C IV , Si IV , and N V is moving toward the disk 10−15 km s−1 faster than low ionization state material traced by S II , C II* , and Ni II . We interpret this dependence as potential evidence of warm accreting gas cooling as it reaches the disk─halo interface, causing a pileup of slower-moving cool gas. We find that with the number of available sight lines, kinematic modeling cannot rule out exponential density distributions or layers of gas that sandwich the Galactic disk. Our results paint a picture of a complex, dynamic disk─halo interface in which low-velocity material likely plays an important role in fueling star formation in the Milky Way.

Keywords: Milky Way dynamics, Galactic and extragalactic astronomy, Warm ionized medium, Galaxy accretion, Circumgalactic medium, Milky Way Galaxy fountains, Milky Way evolution, Galaxy processes
Isolated Binary Black Hole Formation and Merger Rates from Galaxy Evolution. The LIGO─Virgo─KAGRA collaboration has detected over 150 confirmed gravitational-wave events through Observing Run 4a. Binary black hole (BBH) systems represent the overwhelming majority of these observations. We construct a model for the population of BBHs based on the distribution of metallicities in galaxies and state-of-the-art stellar evolution models implemented through the Stellar Evolution N-body code. We calculate the redshift evolution of the total merger rate of BBHs and the differential rates with respect to primary mass, secondary mass, and the mass ratio. We explore variations in the delay-time distribution's power-law index and show that it affects the total merger rate's spectral shape, but primarily acts as an amplitude shift on the differential rates. When comparing to the primary mass distribution, our results indicate that either the average initial mass function in dwarf galaxies must be top heavy, or most of the 30─40 M⊙ BHs must be formed through a dynamical capture mechanism. For masses greater than about 50 M⊙, the predicted number of BBH systems plummets to zero, revealing the well-known mass gap due to the pair instability mechanism and mass loss in binary systems.

Keywords: Black holes, Stellar mass black holes, Gravitational wave sources, Gravitational wave astronomy, Gravitational waves, Compact objects, Astrophysical black holes
Analysis of Solar Surface Oscillations and Energy Transport with Bispectral Electronic Thermostatistics. The ubiquitous 5 minute solar p-mode oscillations, excited at the photosphere, play a crucial role in driving various coronal instabilities and mediating upward energy transport. These modes are strongly influenced by nonthermal electron populations. To investigate this, we employ a double-spectral electronic thermostatistical framework—the generalized (r, q)-distribution—to analyze the oscillation dynamics, growth behavior, and mechanical energy transport properties of longitudinal helioseismic modes at the photosphere. A local linear perturbative analysis, applied to inhomogeneous, viscous, turbulent, and nonthermal solar plasmas, yields a cubic eigenmode equation (dispersion relation) capturing diverse signatures of collective global modes. We examine the influence of nonthermality indices, electron temperature, and ion dynamic viscosity on dispersion and mode stability. Numerical analysis of the coupled dynamics of low-energy (thermal) and high-energy (suprathermal) electrons reveals their significant impact on solar surface oscillations. Notably, the nonthermality spectral indices r and q play mode-accelerating roles, counteracting damping from temperature and viscosity. Our results suggest that the high-frequency (short-period) p-modes can carry energy fluxes exceeding 106 W m−2 near the lower photosphere—energizing the chromosphere and quiet corona—thereby potentially influencing the excitation of spicules, microspicules, and coronal loop oscillations. In contrast, the low-frequency (long-period) g-modes have no such active influences on coronal heating. A hybrid power-law decay formalism is developed to model the attenuation of p-mode energy flux with height and is quantitatively fitted to Solar Dynamics Observatory/Helioseismic and Magnetic Imager Doppler velocity observations. Complementary 2D simulations further elucidate the spatiotemporal evolution of vertical energy flux, shaped by the nonthermal electron distribution.

Keywords: Helioseismology
Correlation between Hα Emitters and Their Cosmic Web Environment at z ∼ 1. Future near-infrared spectroscopic galaxy surveys will target high-redshift emission-line galaxies (ELGs) to test cosmological models. Deriving optimal constraints from ELG clustering hinges on a robust understanding of their environmental dependence. Using the TNG300-1 simulation, we explore the correlation between properties of Hα emitters and their environment anisotropy rather than traditional density-based measures. Our galactic Hα emission model includes contributions from the warm interstellar medium. The environment anisotropy and type are assigned using a halo-mass-dependent smoothing scale. We find that most luminous Hα emitters (LHα &gt; 1042 erg s−1) reside in filaments and knots. More generally, Hα emitters are more biased in strongly anisotropic environments. While correlations with galactic properties are found to be weak, they are statistically significant for host halo masses M ≲ 1012 M⊙ h−1. Our analysis motivates further investigation into how environmental anisotropy influences galaxy evolution, and highlights the potential for leveraging these effects in the analyses of upcoming cosmological surveys.

Keywords: Emission line galaxies
The Uncertainty in Water Mass Fraction of Wet Planets. Planets with masses between Earth and Neptune often have radii that imply the presence of volatiles, suggesting that water may be abundant in their interiors. However, directly observing the precise water mass fraction and water distribution remains unfeasible. In our study, we employ an internal structure code, MAGRATHEA, to model planets with high water content and explore potential interior distributions. Departing from traditional assumptions of a layered structure, we determine water and rock distribution based on water─rock miscibility criteria. We model wet planets with an iron core and a homogeneous mixture of rock and water above it. At the outer regions of the planet, the pressure and temperature are below the rock─water miscibility point (the second critical point), causing the segregation of water and rock. Consequently, a shell of water is formed in the outermost layers. By considering the water-rock miscibility and the vapor state of water, our approach highlights the uncertainty in estimating the water mass fraction of detected exoplanets.

Keywords: Ocean planets, Exoplanet structure, Planetary interior, Planetary structure, Exoplanet atmospheric structure
Pressure and Star Formation in LITTLE THINGS Dwarf Irregular Galaxies. The surface densities of star formation, ΣSFR, in 24 dwarf irregular (dIrr) galaxies from the LITTLE THINGS survey are combined with gas surface densities and midplane pressures to examine the correlations found previously for spiral galaxies. The pressure is the weight of the disk inside the gas layer, including gas, stars, and dark matter, which usually dominates disk gravity in dIrrs. We compare the results to the outer part of M33, which has similar local properties but a slightly higher metallicity, enabling the detection of CO. All the data are convolved to the H I beam, but to study the effects of resolution, the galaxies are examined first with average radial profiles, and then with maps having 1 .″ 5 pixels and 244 pc pixels. The correlations are found to be independent of resolution from 24 to 424 pc. The average ratio of molecular to atomic surface density is estimated to be 0.23 ± 0.1, from the H2 surface density in M33 compared to the H I surface density at the same ΣSFR in the dIrrs. With this ratio, the average star formation rate per molecule is about the same for all the dIrrs, and a factor of 2 less than the rate in M33. The pressure in dIrrs is so low that CO is essentially a dense gas tracer, with the same surface density threshold at the low metallicities of dIrrs as HCN has in spiral galaxies. As a result, CO regions in dIrrs should be strongly self-gravitating.

Keywords: Dwarf galaxies, Star formation, Dense interstellar clouds
In the Quest for Pulsation in Main-sequence M Dwarf Stars from TESS Observations. We report the results of an extensive survey in the quest for pulsation signatures in main-sequence M dwarf stars, based on observations acquired by the TESS space mission. Using TESS 2 minutes cadence light curves from a sample of 56,217 targets, observed in Sectors 1─89 of the mission, we identify low-amplitude modulation for 15 targets, with period values ranging from 0.0421 days (∼1.01 hr) to 0.1148 days (∼2.75 hr). These periodicities fall within the predicted range for pulsations in low-mass main-sequence M-type stars. For instance, for low-mass stars, pulsation is a fundamental observable for solving persistent discrepancies between observed and predicted parameters (e.g., radii, masses). Nevertheless, the detection of a pulsating M dwarf has not yet been achieved despite solid theoretical predictions. Among the 15 targets referred to, only one star, the dwarf MGC 2543, appears to be a good candidate for a pulsator, despite a mean modulation amplitude of 1647 μmag, which is higher than the predicted values.

Keywords: M dwarf stars, Stellar photometry, Stellar pulsations, Space observatories, Low mass stars, Variable stars
A Self-consistent Scenario for the External-shock Emission in Density Jump Environments. The standard external-shock model, assuming a homogeneous turbulent downstream, has been widely used to decipher the afterglows of gamma-ray bursts. However, such assumption is invalid when the shock encounters a density jump. In this paper, we propose a self-consistent scenario to model the external forward shock emission, involving the advection and decaying behaviors of the shock-generated magnetic fields (sgMFs) in the downstream as found in particle-in-cell simulations. In an interstellar medium, our model is almost returned to the standard model but with  ϵB∝(1+tdyn/tB)αt . Here, ϵB describes the sgMFs' fraction of shock energy in the standard model, tdyn is the shock dynamic time, and tB together with αt depicts the sgMFs' decaying behavior in our model. The situation is the same for the wind medium but with weak deviation in the early phase. When the shock encounters the density rise/dip, a shallower/deeper decay appears in the light curve. These behaviors are obvious for high-frequency emission or at the phase after the jet break. The GeV emission in the afterglow can serve to probe the circumburst density jump. We apply our model to decipher the later afterglows of the giant flare from SGR 1806-20. It is shown that a fireball propagating into a magnetar bow shock environment can well reproduce the observed peculiar steep decay in the radio light curve at ∼10 days from the burst.

Keywords: Gamma-ray bursts
Seeking Spectroscopic Binaries with Data-driven Models. Data-driven stellar classification has a long and important history in astronomy, dating as far back as Annie Jump Cannon's "by-eye" classifications of stars into spectral types, still used today. In recent years, data-driven spectroscopy has proven to be an effective means of deriving stellar properties for large samples of stars, sidestepping issues with computational efficiency, incomplete line lists, and radiative transfer calculations associated with physical stellar models. A logical application of these algorithms is the detection of unresolved stellar binaries, which requires accurate spectroscopic models to resolve flux contributions from a fainter secondary star in the spectrum. Here, we use The Cannon to train a data-driven model on spectra from the Keck High Resolution Echelle Spectrometer. We show that our model is competitive with existing data-driven models in its ability to predict stellar properties Teff, R⋆, [Fe/H], and  vsini , as well as the instrumental point-spread function, particularly when we apply a novel wavelet-based processing step to spectra before training. We find that even with accurate estimates of star properties, our model's ability to detect unresolved binaries is limited by its ∼3% accuracy in per-pixel flux predictions, illuminating possible limitations of data-driven model applications.

Keywords: High resolution spectroscopy, Astronomical models, Astronomy data modeling, Stellar properties, Stellar abundances, Astrostatistics techniques, Exoplanet systems, Stellar physics, Spectroscopy
SPHEREx: Aromatics, Aliphatics, and PAH Size across the Iris Nebula. Observations by the Spectro-Photometer for the History of the Universe, Epoch of Reionization, and Ices Explorer (SPHEREx) are combined with counterpart Spitzer spectral map data to study the aromatic, aliphatic, and polycyclic aromatic hydrocarbon (PAH) size evolution across the northwest photodissociation region (PDR) of the Iris Nebula (NGC 7023). The 3.3─3.4 μm complex (I3.3) and 11.2 μm (I11.2) PAH band strength are determined through direct integration. In addition, the former is decomposed into a 3.3 ( I'3.3 ) and 3.4 μm ( I'3.4 ) subfeature by fitting SPHEREx bandpass-integrated photometry using a modeled, highly sampled, multicomponent spectrum. I3.3, I11.2,  I'3.3 , and  I'3.4  all peak at the PDR. The NASA Ames PAH IR Spectroscopic Database is used to obtain the average number of carbon atoms ( NC̄ ) and small PAH fraction (fsmall) by fitting the isolated PAH component of the Spitzer segment:  70≲NC̄≲76  and 0.24 ≲ fsmall ≲ 0.36, respectively.  I'3.4 / I'3.3 , I11.2/I3.3,  NC̄ , and fsmall all show a demarcation that matches the large-scale morphology of the region. For  I'3.3  and  I'3.4  this is reflected by two distinct trends when plotted against each other, one associated with the dense medium and the other with the diffuse medium:  [NH,ali/NH,aro]dense  = 0.42 ± 0.01 and  [NH,ali/NH,aro]diffuse  = 0.10 ± 0.01, respectively.  NC̄  and fsmall are tentatively correlated with I11.2/I3.3 (R = 0.54 ± 0.05 and −0.45 ± 0.05, respectively). A wider variety of large(r) extended interstellar medium objects is required to tighten the correlations, turn them into quantitative calibrators for PAH size, and pin down the discrepancy of correlations with  I'3.3  involved.

Keywords: Interstellar molecules, Polycyclic aromatic hydrocarbons, Laboratory astrophysics, Reflection nebulae, Near infrared astronomy
The Influence of Solar Source Information on Energy-dependent Solar Energetic Particle Flux and Timing Based on Solar Energetic Particle Events Observed over Four Solar Cycles. This study is based on proton flux data from ESA's Solar Energetic Particle Environment Modeling database, analyzing solar energetic particle (SEP) events observed near Earth from 1976 to 2017. We have matched these events with corresponding solar flares and coronal mass ejections (CMEs) to create a comprehensive list of SEP events spanning almost four solar cycles. Using this list, we conduct a statistical analysis of the flare─SEP correlation and SEP timing information. Our findings confirm that SEP events recorded at 1 au are more commonly associated with flares occurring in the western hemisphere of the Sun's surface. Moreover, we develop an empirical model relating the SEP proton peak flux to the characteristics of flares and CMEs, which works particularly effectively for SEP events triggered by eastern flares. We also verify that flares with higher intensity are more likely to produce SEP events up to higher energies, such as those detected above 100 MeV. In this energy range, more than half of the SEP events are triggered by X-class flares. Finally, we introduce an empirical model that uses the flare longitude to predict the timing of the SEP peak flux, especially for intense flare events. These models can aid in mitigating particle radiation risks for space missions.

Keywords: Solar energetic particles, Interplanetary shocks, Solar flares, Solar coronal mass ejections
Near-infrared Variability Detected in the Young Star-forming Dwarf Galaxy SBS 0335-052E. SBS 0335-052E is a young star-forming dwarf galaxy with a total stellar mass of M* ≲ 108M⊙ and an extremely low metallicity (Z ∼ 1/40Z⊙), which has long been considered to be devoid of an active galactic nucleus (AGN). Here, we report the detection of temporal flux variability of SBS 0335-052E in near-infrared (NIR) 3─4 μm bands on timescales of several years, showing dimming and brightening of up to 50% over 14 yr, based on archival data from the Wide-field Infrared Survey Explorer. Our spectral energy distribution (SED) fitting of archival ultraviolet (UV)-NIR photometry, including AGN SED models, indicates that the variable NIR emission arises from an edge-on AGN dust torus. The UV-optical emission from the accretion disk is obscured and does not reach us, leading to the dominance of the host galaxy's young stellar population in the UV-optical wavelengths. This analysis favors the presence of a Compton-thick, heavily obscured AGN in SBS 0335-052E, consistent with its observed X-ray weakness. From the SED fitting, we estimate an AGN bolometric luminosity of Lbol = 1.2 × 1043 erg s−1, which implies a black hole (BH) mass of MBH ≃ 105M⊙ if the AGN is accreting at the Eddington limit. If confirmed, SBS 0335-052E would be the least massive galaxy known to host an AGN, likely harboring an intermediate-mass BH.

Keywords: Intermediate-mass black holes
Detection of Stellar Mass Ejections through Extreme Ultraviolet Spectral Lines. Coronal mass ejections (CMEs), since their first observation in 1971, have been widely acknowledged as the most significant eruptive phenomena and the primary cause of catastrophic space weather events within our solar system. Whether similar processes involving stellar mass ejections (SMEs) occur on other stars holds immense potential for advancing our understanding of stellar behavior and providing insights into the search for extraterrestrial life. However, detecting SMEs remains challenging, particularly in establishing reliable approaches and diagnostics. Here, we conduct a proof-of-concept Sun-as-a-star experiment using solar CMEs as proxies, analyzing EUV spectral lines from the Extreme Ultraviolet Variability Experiment on board the Solar Dynamics Observatory. By comparing 26 front-side fast CMEs with 14 confined flares of class M 1.0 and above, we find that the Doppler responses in 18.04, 19.51, and 28.42 nm during CME events provide a promising diagnostic to distinguish Sun-as-a-star CME signals from flare features. We further show that CME characteristics can be reasonably reproduced from the Doppler velocities in these three lines, providing a hopeful diagnostic for inferring otherwise unobservable properties of eruptions on remote stars. These findings advance the exploration and understanding of mass ejections in stars. We therefore advocate the resumption of the EUV observations of extrasolar stars.

Keywords: Solar flares, Solar extreme ultraviolet emission, Solar coronal mass ejections, Stellar coronal mass ejections, Stellar spectral lines, Doppler shift
Simulating the Solar Corona with Multiple Solar Photospheric Magnetic Maps during the 2024 April 8 Total Solar Eclipse. The 2024 April 8 total solar eclipse provides a unique opportunity to study the solar corona. This work presents our simulations of the solar corona at the time of the eclipse based on magnetohydrodynamic modeling performed with the Alfvén Wave Solar atmosphere Model in the Space Weather Modeling Framework, developed at the University of Michigan. We performed multiple simulations based on photospheric magnetic maps from four sources, i.e., ADAPT-GONG, Lockheed Martin ESFAM-HMI, HipFT-HMI, and NSO-NRT-HMI maps. Our study focuses on how differences in the magnetic field maps affect the coronal magnetic field structure and coronal heating properties in the simulation. The synthesized observables show remarkable differences due to the distinct magnetic coronal topologies, which stem from the different local magnetic flux distributions. We analyze the properties of the open magnetic flux regions of the models. We also study the coronal heating rate in the models. The total volume integrated heating rate yields a difference of 20% across the models. The results also show that the differential emission measure in the high-temperature regions is sensitive to the magnetic field maps. Our findings underscore the importance of comprehensive photospheric magnetic field data in improving future solar coronal models.

Keywords: Solar eclipses, Solar corona, Magnetogram
Magnetic Activity of Ultracool Dwarfs in the LAMOST DR11. Ultracool dwarfs consist of lowest-mass stars and brown dwarfs. Their interior is fully convective, in contrast to that of the partly convective Sun-like stars. The magnetic field generation process beneath the surface of ultracool dwarfs is still poorly understood and controversial. To increase samples of active ultracool dwarfs significantly, we have identified 962 ultracool dwarfs in the latest Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) data release, DR11. We also simulate the Chinese Space Station Survey Telescope (CSST) low-resolution slitless spectra by degrading the LAMOST spectra. A semisupervised machine learning approach with an autoencoder model is built to identify ultracool dwarfs with the simulated CSST spectra, which demonstrates the capability of the CSST all-sky slitless spectroscopic survey in the detection of ultracool dwarfs. The magnetic activity of the ultracool dwarfs is investigated by using the Hα line emission as a proxy. The rotational periods of 82 ultracool dwarfs are derived based on the Kepler/K2 light curves. We also derive the activity─rotation relation of the ultracool dwarfs, which is saturated around a Rossby number of 0.12.

Keywords: M dwarf stars, Starspots, Space telescopes, Stellar activity