Sazuna/UAT_keywords huggingface dataset:
A Method for Habitability Analysis of Planets with True Polar Wander. Finding unambiguous signs of extraterrestrial life is a central challenge in astrophysics and astrobiology. Habitability assessments typically focus on conditions such as the presence of liquid water. However, True Polar Wander (TPW)—the motion of the planet's rotation axis relative to its surface—can produce large latitudinally dependent climate perturbations that are not captured by typical energy balance models. Here, we present a theoretical framework that incorporates TPW into a planet's global energy balance model. The framework couples the radiative balance with the geometric and temporal effects of pole reorientation and identifies the planetary structural and atmospheric prerequisites for significant climate forcing induced by TPW: an atmosphere that allows for surface, grounded ice formation and ablation, and an interior that supports viscous mantle flow (sufficient mantle viscosity and convective vigor) so that TPW can occur on geologically relevant timescales. Using analytic arguments, we show that both the amplitude and the direction of TPW modify latitudinal insolation and surface albedo in ways that can drive abrupt, global redistribution of ice and surface temperatures. Above certain thresholds of TPW, these changes can produce rapid climate transitions with major implications for biospheric stability, as has been reported for the case of the planet Earth. Although the link between TPW and specific extinction events on Earth remains debated, TPW is a plausible mechanism for large, rapid environmental change on habitable worlds. Our methodology is broadly applicable to planets that undergo TPW and yields testable predictions that might help prioritize observational targets in the search for life.

Keywords: Planetary atmospheres, Celestial mechanics, Astrobiology, Planetary climates, Habitable planets
The Major Solar Energetic Particle Event on 2024 May 20: Multispacecraft Observations of a Long-lasting Energetic Particle Reservoir. The fleet of spacecraft distributed across the inner heliosphere during 2024 May─June provided a unique opportunity to analyze, over a broad range of heliolongitudes, the effects produced by the complex sunspot group associated with Active Region 13664. The intense solar activity from 2024 May 8 to 2024 June 21 produced unusually elevated solar energetic particle (SEP) intensities observed at heliocentric distances ≲1 au by Solar Orbiter, Parker Solar Probe, STEREO-A, and near-Earth spacecraft. This activity resulted in a &gt;40 day period of enhanced ≲10 MeV proton intensities spanning at least ∼170° in longitude. Among these events, the 2024 May 20 SEP event was remarkable for its high intensity and wide spatial extent. It was associated with a fast (≳1500 km s−1) halo coronal mass ejection (CME) and an X16.5 solar flare located ∼171° in longitude from Earth. Near Earth, the event produced a long-lasting ∼100 MeV proton intensity enhancement with energy spectra flattening between 30 and 80 MeV. It also led to the formation of an energetic particle reservoir that persisted for ∼2 weeks and extended across at least ∼170° in longitude. Several mechanisms contributed to the broad longitudinal spread of SEPs and formation of the energetic particle reservoir, including acceleration at an extended CME-driven shock, particle drifts along the heliospheric current sheet, particle reflection and redistribution caused by the merging of preceding CMEs beyond 1 au, and predominantly cross-field particle transport processes.

Keywords: Solar energetic particles, Solar coronal mass ejection shocks, Solar physics, Interplanetary physics
Kinematics of Circumgalactic O VI Gas and Disk Rotation of z ≍ 0.2 Star-forming Galaxies. Quasar sightline observations reveal that low ionization state gas corotates with the galaxy disk and often at subcentrifugal velocities, suggesting that the gas is spiraling toward the galaxy disk. However, while observations ubiquitously detect O VI absorption around low-redshift, ∼L* star-forming galaxies, the relationship between O VI and the galaxy disk, especially the kinematics, is not well established. This work focuses on the O VI kinematics and its comparison with that of the low ions and galactic disk rotation. We present observations of 18 pairs of quasars and z ≍ 0.2 star-forming galaxies. All quasar sightlines intersect the circumgalactic medium (CGM) within 45° from the galaxy major axes. We show that while individual O VI velocity components do not correlate with disk rotation, the bulk of the O VI gas in individual sightlines rarely counterrotates. We then match O VI velocity components with those of low ions by minimizing the difference of their velocity centroids. The O VI velocity components with successful low-ion matches are typically found at small sightline impact parameters and are more likely to corotate with the disk. We suggest that the low-ion-matched O VI velocity components trace the gas cospatial with the low ions near the extended disk plane in the inner CGM, whereas those without low-ion matches represent the gas at large 3D radii. While the gas at large radii is theoretically expected to kinematically correlate with the disk angular momentum, this correlation is expected to be weaker due to the higher turbulent to mean rotation velocity ratio at large radii, consistent with our results.

Keywords: Extragalactic astronomy, Quasar absorption line spectroscopy, Circumgalactic medium
Bayesian Inference of Hybrid Star Properties from Future High-precision Measurements of Their Radii. Future high-precision X-ray and gravitational-wave observations of neutron stars (NSs) are expected to constrain NS radii with uncertainties as small as σ ≃ 0.1 km. Such unprecedented precision offers a unique opportunity to extract new information about the nature and equation of state (EOS) of supradense matter in NS cores. Using mock radius data with uncertainties ranging from σ = 1.0 to 0.1 km, together with a flexible meta-model NS EOS that allows for a first-order hadron─quark phase transition, we perform a Bayesian statistical analysis to assess the impact of radius measurements on EOS constraints. We find that high-precision radius measurements, particularly for massive NSs, significantly tighten constraints on the hadron─quark transition density ρt, the quark matter mass fraction in NS cores, and several parameters characterizing the EOS of supranuclear hadronic matter, although the degree of improvement depends on the assumed prior range of ρt. In contrast, even with the highest precision considered, NS radii—including those of massive stars—remain largely insensitive to the stiffness of quark matter, independent of the measurement accuracy or the prior range adopted for ρt.

Keywords: Neutron stars, Nuclear astrophysics
A Unified Photometric Redshift Calibration for Weak Lensing Surveys Using the Dark Energy Spectroscopic Instrument. The effective redshift distribution n(z) of galaxies is a critical component in the study of weak gravitational lensing. Here, we introduce a new method for determining n(z) for weak lensing surveys based on high-quality redshifts and neural-network-based importance weights. Additionally, we present the first unified photometric redshift calibration of the three leading stage-III weak lensing surveys, the Dark Energy Survey (DES), the Hyper Suprime-Cam (HSC) survey, and the Kilo-Degree Survey (KiDS), with state-of-the-art spectroscopic data from the Dark Energy Spectroscopic Instrument (DESI). We verify our method using a new, data-driven approach and obtain n(z) constraints with statistical uncertainties of the order of  σz̄∼0.01  and smaller. Our analysis is largely independent of previous photometric redshift calibrations and, thus, provides an important cross-check in light of recent cosmological tensions. Overall, we find excellent agreement with previously published results on the DES Y3 and HSC Y1 data sets, while there are some differences on the mean redshift with respect to the previously published KiDS-1000 results. We attribute the latter to mismatches in photometric noise properties in the COSMOS field compared to the wider KiDS self-organizing map-gold catalog. At the same time, the new n(z) estimates for KiDS do not significantly change estimates of cosmic structure growth from cosmic shear. Finally, we discuss how our method can be applied to future weak lensing calibrations with DESI data.

Keywords: Weak gravitational lensing, Redshift surveys, Astrostatistics
Joint Constraint on the Propagation Origin of the Cosmic-Ray Spectral Knee from Energy Spectrum and Anisotropy Observations. The origin mechanism of the cosmic-ray knee region remains an unresolved mystery, with acceleration, interaction, and propagation models drawing significant attention. The latest experimental observations of the PeV total spectrum, composition energy spectrum, and anisotropy—particularly the precise measurements of the proton spectrum by the LHAASO experiment—have provided crucial breakthroughs in uncovering its origin. Based on the latest LHAASO measurements of the proton energy spectrum, combined with cosmic-ray spectral and anisotropy data, this study proposes that the spectral index variation in the knee region arises from changes in the propagation coefficient. By introducing a knee position  Rknee  and an index variation δknee, we construct a rigidity-dependent double-power-law diffusion model to reproduce the knee-region spectral structure. Through modifications to the diffusion coefficient, we successfully replicate the observed knee-region spectral structure in the LHAASO proton spectrum and calculate the corresponding anisotropy. Under current data and model dependencies, a joint analysis of the energy spectrum and anisotropy does not support the propagation-origin model of the cosmic-ray knee at a 95% confidence level. We hope that future LHAASO experiments will provide precise measurements of the energy spectra and anisotropies of various nuclei in the knee region, thereby offering a definitive test of the propagation model as the origin mechanism of the knee-region spectral structure.

Keywords: Cosmic anisotropy, Particle astrophysics, Cosmic rays
Thermal Effects of Acoustic-gravity Waves in Titan's Upper Atmosphere and Their Implications for Atmospheric Jeans Escape. Early observations from the Cassini spacecraft revealed the presence of acoustic-gravity waves in Titan's upper atmosphere. However, the impacts of wave modes with different temporal and spatial scales on the thermal structure and atmospheric escape have not been fully investigated. In this study, we use a linearized full-wave model to examine the wave heating/cooling effects and the resulting Jeans escape flux of molecular hydrogen in Titan's atmosphere. The results show that wave-induced heating/cooling is primarily governed by the sensible heat flux and viscous heating rate. Acoustic waves consistently heat the upper atmosphere, with maximum heating rates of up to 80 K day−1 and exobase temperature increases of up to 22 K, leading to enhancements of the Jeans escape flux by 3%─24%. Gravity waves with high phase speeds (&gt;69 m s−1) also contribute to thermospheric heating, producing heating rates of up to 30 K day−1, increasing the exobase temperature by 4─5 K and elevating the escape flux by 2%─6%. In contrast, gravity waves with lower phase speeds predominantly cool the upper atmosphere, with peak cooling rates reaching 10 K day−1, reducing the exobase temperature by up to 3.5 K and decreasing the escape flux by up to 4%. These findings highlight the important role of acoustic-gravity waves in governing Titan's upper atmospheric thermal structure and regulating atmospheric escape and provide broader insights into the contribution of these waves to the thermal structure of upper atmospheres of different planets and moons.

Keywords: Internal waves, Titan, Upper atmosphere
Radio Emission from Broad Absorption Line Quasars. Broad Absorption Line Quasars (BALQs) generally exhibit significant outflows that may interact with the surrounding medium, resulting in radio emission. We selected a sample of 13 powerful radio-quiet (RQ) BALQs, where the UV outflow kinetic power is measurable, and detected nine of them with the Very Large Array A configuration at 5.5 and 9.0 GHz. The radio emission is mostly unresolved and is generally constrained within a scale of &lt;1─4 kpc. In the nine detected objects, the radio spectral slope α5.5−9.0 is steep (&lt;−0.5) in five objects and is flat or inverted (&gt;−0.5) in four objects. We discuss how the steep-slope emission can be associated with the UV outflows, and how the flat-slope emission can be intrinsically steep but flattened by free─free absorption from the UV outflowing gas. However, we find no correlation between the radio luminosity and the estimated outflow kinetic power, which suggests that the outflows are likely not a major source of the observed radio emission. In addition, the radio-loudness of these RQ BALQs is comparable to that of typical RQ quasars, implying that the UV outflows likely do not produce stronger radio emission compared to non-BALQs. Follow-up radio observations can test the free─free absorption interpretation and can be used as a new probe for outflows in AGN.

Keywords: Radio continuum emission, Radio quiet quasars, Active galactic nuclei, Broad-absorption line quasar
Environment and Gas Fraction in Type 2 AGN versus Non-AGN Galaxies. We investigate the environmental parameters and gas fraction (fgas ) properties of type 2 active galactic nuclei (AGN) and non-AGN galaxies, utilizing a large sample of galaxies from the Sloan Digital Sky Survey DR7 with z ≤ 0.3. We find that the environment affects type 2 AGN and non-AGN galaxies in similar ways and does not impact the strength of AGN-driven outflows. The fgas of type 2 AGN and non-AGN host galaxies show no variation between group and isolated environments, suggesting that host galaxy gas content is largely independent of large-scale environment. We find that type 2 AGN host galaxies possess systematically lower fgas than their non-AGN counterparts when matched in stellar mass and star formation rate (SFR). This suggests that AGN activity plays a significant role in regulating the molecular gas reservoir and, consequently, the star formation processes within galaxies. We find that type 2 AGNs exhibiting strong outflows are associated with higher gas fractions, higher SFRs, and younger stellar populations than those with weak or no outflows. This may indicate either concurrent star formation in gas-rich systems hosting powerful outflows, or a time delay between AGN activity and its effect on star formation consistent with a delayed AGN feedback scenario.

Keywords: Molecular gas, Galaxy environments, Active galaxies, Galaxy interactions, Star formation, Galaxy groups
Joint Analysis of Small-scale Galaxy Clustering and Galaxy─Galaxy Lensing from BOSS Galaxies. We present a joint analysis of galaxy clustering and galaxy─galaxy lensing measurements from BOSS galaxies using a simulation-based emulation method combined with a halo occupation distribution model. Our emulators are constructed with the Aemulus ν simulations, a suite of wνCDM N-body simulations with massive neutrinos as independent particle species. We combine small-scale analysis of clustering from 0.1 to 60.2 h−1 Mpc and lensing from 1.7 to 60.2 h−1 Mpc to perform cosmological constraints. We split the BOSS galaxies into three redshift bins to measure their clustering and employ galaxies from Dark Energy Camera Legacy Survey and Hyper Suprime-Cam as source galaxies to measure lensing separately. We find that the addition of lensing significantly improves the constraining power on  S8=σ8(Ωm/0.3)0.5 , with a weak improvement for fσ8. Our results of fσ8 indicate tensions of around 1σ−4σ below the results of the cosmic microwave background observations of Planck. For S8, our results are also lower than Planck, and the tension can be mitigated when considering possible systematics in lensing measurement. As a by-product, our analysis prefers a nonzero neutrino mass but without strong significance, with the constraining power dominated by the clustering. Given the accuracy and precision of our model and the observational data, it is anticipated that larger and higher-quality spectroscopic data sets will improve the constraints on this fundamental property in the near future.

Keywords: Cosmology, Observational cosmology, Large-scale structure of the universe
Prediction of Multiwavelength Afterglows Associated with FRB 20200120E and FRB 20201124A. Fast radio bursts (FRBs) are mysterious radio transients with uncertain origins and environments. Recent studies suggest that some active FRBs may originate from compact objects in binary systems. In this work, we develop a unified theoretical framework to model the multiwavelength afterglows of FRBs residing in binary systems and apply it to two representative repeaters, FRB 20200120E and FRB 20201124A. By solving the dynamics and radiation processes of FRB ejecta interacting with the surrounding medium, we compute afterglow light curves in the radio, optical, and X-ray bands. Our results show that radio afterglows offer the best prospects for detection, with their brightness highly sensitive to ejecta kinetic energy and ambient density. Future high-sensitivity radio telescopes, such as the Square Kilometre Array, could detect these signals. Optical afterglows, though short-lived and challenging to observe, may be significantly enhanced in dense environments, potentially making them detectable with facilities like the Large Synoptic Survey Telescope. In contrast, X-ray afterglows are predicted to be too faint for detection with current instruments. Our study highlights the potential of multiwavelength afterglows as probes of FRB progenitors and their surrounding environments, offering crucial insights into the nature of these mysterious transients.

Keywords: Radio transient sources
An Improved Fit to the Density Fluctuations in Supersonic Isothermal Turbulence. The density distribution of supersonic isothermal turbulence plays a critical role in many astrophysical systems. It is commonly approximated by a log-normal distribution with a variance of  σs,V2≍ln(1+b2MV2) , where  s≡lnρ/ρ0, MV is the rms volume-weighted Mach number, and b is a parameter that depends on the driving mechanism, which can be solenoidal (divergence-free), compressive (curl-free), or a mix of both. However, this fit neglects the driving correlation time, τa, which plays a key role when compressive driving is significant. Here, we conduct turbulence simulations spanning a wide range of Mach numbers, driving mechanisms, and τa values. In the compressive case,  σs,V2  is not well fit by the standard expression. Instead, it scales approximately linearly with MV, and its dependence on τa is  σs,V2≍MV[1+23(1+λa)Θ(1+λa)] , where  λa≡ln(τa/τe) , τe is the eddy turnover time, and Θ is the Heaviside step function. Mixed driven turbulence shows a weak dependence on τa, and for solenoidally driven turbulence,  σs,V2≍13MV , which is consistent with the standard expression when MV ≲ 8. The volume-weighted mean and skewness also show systematic trends with MV and τa, deviating from log-normal expectations. The mass-weighted density distribution displays significant broadening and skewness in compressively driven cases, especially at large τa/τe. These results provide a refined framework for modeling astrophysical turbulence.

Keywords: Interplanetary turbulence, Interstellar medium
How Beaming Shapes the Demographics of Ultraluminous X-Ray Sources. Ultraluminous X-ray sources (ULXs) are off-nuclear compact objects with apparent luminosities above 1039 erg s−1, often exceeding the Eddington limit for stellar-mass black holes. Beaming is a commonly invoked mechanism to explain their extreme brightness, and the dependence of the beaming factor on accretion rate is a critical parameter. In this work, we investigate how different beaming prescriptions affect the predicted properties of ULX populations. Using binary population synthesis, we construct synthetic X-ray luminosity functions (XLFs) for both classical and log-modified beaming models at solar and subsolar metallicities. The classical model predicts a larger intrinsic number of bright ULXs, but strong beaming reduces their observable fraction, resulting in fewer visible ULXs compared to the log-modified model. The log-modified prescription yields a shallower slope at high luminosity, aligning better with observed XLFs, and increases the fraction of observable neutron star ULXs above 1039 erg s−1. These results underscore the significant role of the beaming law in shaping ULX statistical distributions and assessing neutron star contributions to the population.

Keywords: Accretion, Neutron stars, Binary stars, Black holes
Characterizing Compact-object Binaries in the Lower Mass Gap with Gravitational Waves. The source binary of the gravitational-wave (GW) event GW230529, detected at the beginning of the fourth LIGO-Virgo-KAGRA observing run, was inferred to consist of a neutron star (NS) and a compact object in the lower mass gap, a purported gap between the most massive NSs (∼3 M⊙) and least massive black holes (BHs; ∼5 M⊙) based on compact-object observations in the Milky Way. While the nature of the mass-gap object could not be determined from the GW data alone for this event, definitively distinguishing whether this object is a NS or BH would have profound implications for the NS equation of state, supernova physics, and multimessenger astronomy. In this work, we perform parameter estimation on a suite of simulated GW systems with parameters similar to those of the GW230529 source binary to investigate whether the ambiguity in the physical nature of the source is a generic result for such systems. We vary the intrinsic properties of the simulated systems, the detector noise properties, the signal-to-noise ratios (SNRs), and the waveform model used in recovery. We find that the low SNR of GW230529 is the key reason for the ambiguity in determining whether the mass of the primary object in the binary is consistent with a low-mass BH or a high-mass NS, and thus the priors used for the masses and spins have a significant impact on the posterior distribution, which is a generic result for low-SNR events. The inclusion of tidal effects in the waveform model also contributes to the observed degeneracies in the posteriors, since the statistical uncertainties in analyses of GW events like GW230529 are larger for waveform models including tidal effects. We show that the future observation of such a system with a higher SNR (∼30) would increase the precision of the mass measurements sufficiently to allow us to determine the nature of the mass-gap object.

Keywords: Neutron stars, LIGO, Black holes, Gravitational wave sources
Danger Zone: Establishing Buffers for Enhanced Classification in BPT Diagrams. This study utilizes unsupervised machine learning, specifically the uniform manifold approximation and projection (UMAP) algorithm, to classify optical spectra originating from star-forming regions, Seyferts, and low-ionization (nuclear) emission-line regions (LI[N]ERs) based on their line ratios. Typically the ionization source of a region is determined from the intensity ratio of different combinations of pairs of spectral lines. However, using current boundary definitions, ∼10% of spectra change classes between diagnostic diagrams. We apply the machine learning technique to ∼1.3 million optical spectra from 6439 galaxies observed in the MaNGA survey. By training UMAP on consistently classified data, we can classify these "ambiguous" spectra and delineate boundary zones where such ambiguities arise. Furthermore, we identify physically interesting subsets within the ambiguous spectra. Future work will incorporate additional parameters, such as alternative emission line ratios and velocity dispersions, to enhance classification accuracy.

Keywords: Star forming regions, Emission line galaxies, LINER galaxies, Seyfert galaxies, Active galactic nuclei