Sazuna/UAT_keywords huggingface dataset:
The H I Reservoir in Central Spiral Galaxies and the Implied Star Formation Process. The cold interstellar medium (ISM) as the raw material for star formation is critical to understanding galaxy evolution. It is generally understood that galaxies stop making stars when, in one way or another, they run out of gas. However, here we provide evidence that central spiral galaxies remain rich in atomic gas even if their star formation rate (SFR) and molecular gas fraction have dropped significantly compared to "normal" star-forming galaxies of the same mass. Since H I is sensitive to external processes, here we investigate central spiral galaxies using a combined sample from the Sloan Digital Sky Survey, Arecibo Legacy Fast ALFA survey, and the extended GALEX Arecibo SDSS Survey. After proper incompleteness corrections, we find that the key H I scaling relations for central spirals show significant but regular systematic dependence on stellar mass. At any given stellar mass, the H I gas mass fraction is about constant with changing specific star formation rate (sSFR), which suggests that H I reservoir is ubiquitous in central spirals with any star formation status down to M * ∼ 109 M ⊙. Together with the tight correlation between the molecular gas mass fraction and sSFR for galaxies across a wide range of different properties, it suggests that the decline of SFR of all central spirals in the local Universe is due to the halt of H2 supply, though there is plenty of H I gas around. These hence provide critical observations of the dramatically different behavior of the cold multiphase ISM, and a key to understand the star formation process and quenching mechanism. ∗ This is the fourth paper in the "From Halos to Galaxies" series.

Keywords: Galaxy quenching, Galaxy evolution, Interstellar medium, Interstellar atomic gas
Cautionary Tales on Heating-rate Prescriptions in Kilonovae. A major ingredient for kilonova lightcurves is the radioactive heating rate and its dependence on the electron fraction and velocity of the ejecta and, in principle, on the nuclear mass formula. Heating-rate formulae commonly used as the basis for kilonova models previously employed in the literature produce substantially different outputs for high electron fractions (Y  e  ≳ 0.3) and at late times (t ≳ 1 day) compared to newer prescriptions. Here, we employ standard semianalytical models for kilonovae with better heating rate prescriptions valid for the full parameter space of kilonova velocities and electron fractions to explore the impact of the heating rate on kilonova lightcurves. We show the dangers of using inappropriate heating rate estimates by simulating realistic observations and inferring the kilonova parameters via a misspecified heating-rate prescription. While providing great fits to the photometry, an incorrect heating-rate prescription fails to recover the input ejecta masses with a bias significantly larger than the typical statistical uncertainty. This bias from an incorrect prescription has significant consequences for interpreting kilonovae, their use as additional components in gamma-ray burst afterglows, and understanding their role in cosmic chemical evolution or for multimessenger constraints on the nuclear equation of state. We showcase a framework and tool to better determine the impact of different modeling assumptions and uncertainties on inferences into kilonova properties.

Keywords: Neutron stars, R-process, Gravitational wave astronomy
XRISM Spectroscopy of the Fe Kα Emission Line in the Seyfert Active Galactic Nucleus NGC 4151 Reveals the Disk, Broad-line Region, and Torus. We present an analysis of the first two XRISM/Resolve spectra of the well-known Seyfert-1.5 active galactic nucleus (AGN) in NGC 4151, obtained in 2023 December. Our work focuses on the nature of the narrow Fe K α  emission line at 6.4 keV, the strongest and most common X-ray line observed in AGN. The total line is found to consist of three components. Even the narrowest component of the line is resolved with evident Fe K α,1 (6.404 keV) and K α,2 (6.391 keV) contributions in a 2:1 flux ratio, fully consistent with neutral gas with negligible bulk velocity. Subject to the limitations of our models, the narrowest and intermediate-width components are consistent with emission from optically thin gas, suggesting that they arise in a disk atmosphere and/or wind. Modeling the three line components in terms of Keplerian broadening, they are readily associated with (1) the inner wall of the "torus," (2) the innermost optical "broad-line region" (or "X-ray BLR"), and (3) a region with a radius of r ≃ 100 GM/c 2 that may signal a warp in the accretion disk. Viable alternative explanations of the broadest component include a fast-wind component and/or scattering; however, we find evidence of variability in the narrow Fe K α  line complex on timescales consistent with small radii. The best-fit models are statistically superior to simple Voigt functions, but when fit with Voigt profiles the time-averaged lines are consistent with a projected velocity broadening of FWHM =1600−200+400kms−1 . Overall, the resolution and sensitivity of XRISM show that the narrow Fe K line in AGN is an effective probe of all key parts of the accretion flow, as it is currently understood. We discuss the implications of these findings for our understanding of AGN accretion, future studies with XRISM, and X-ray-based black hole mass measurements.

Keywords: Accretion, High-luminosity active galactic nuclei, High energy astrophysics, Astrophysical black holes
Solar Wind Structures from the Gaussianity of Magnetic Magnitude. The heliosphere is permeated with highly structured solar wind originating from the Sun. One of the primary science objectives of Parker Solar Probe (PSP) is to determine the structures and dynamics of the plasma and magnetic fields at the sources of the solar wind. However, establishing the connection between in situ measurements and structures and dynamics in the solar atmosphere is challenging: most of the magnetic footpoint mapping techniques have significant uncertainties in the source localization of a plasma parcel observed in situ, and the PSP plasma measurements suffer from a limited field of view. Therefore, it lacks a universal tool to self-contextualize the in situ measurements. Here we develop a novel time series visualization method named Gaussianity Scalogram. Utilizing this method, by analyzing the magnetic magnitude data from both PSP and Ulysses, we successfully identify in situ structures that are possible remnants of solar atmospheric and magnetic structures spanning more than 7 orders of magnitude, from years to seconds, including polar and midlatitude coronal holes, as well as structures compatible with supergranulation, "jetlets" and "picoflares." Furthermore, computer simulations of Alfvénic turbulence successfully reproduce the Gaussianization of magnetic magnitude, supporting the observed distribution. Building upon these discoveries, the Gaussianity Scalogram can help future studies to reveal the fractal-like fine structures in the solar wind time series from both PSP and a decades-old data archive.

Keywords: Interplanetary turbulence, Solar wind, Solar physics, Solar magnetic fields, Solar corona
The Formation of Milky Way "Bones": Ubiquitous HI Narrow Self-absorption Associated with CO Emission. Long and skinny molecular filaments running along Galactic spiral arms are known as "bones," since they make up the skeleton of the Milky Way. However, their origin is still an open question. Here, we compare spectral images of HI taken by the Five-hundred-meter Aperture Spherical radio Telescope (FAST) with archival CO and Herschel dust emission to investigate the conversion from HI to H2 in two typical Galactic bones, CFG028.68-0.28 and CFG047.06+0.26. Sensitive FAST HI images and an improved methodology enabled us to extract HI narrow self-absorption (HINSA) features associated with CO line emission on and off the filaments, revealing the ubiquity of HINSA toward distant clouds for the first time. The derived cold HI abundances, [HI]/[H2], of the two bones range from ∼(0.5 to 44.7) × 10‑3, which reveal different degrees of HI–H2 conversion, and are similar to those of nearby, low-mass star-forming clouds, Planck Galactic cold clumps, and a nearby active high-mass star-forming region G176.51+00.20. The HI–H2 conversion has been ongoing for 2.2–13.2 Myr in the bones, a timescale comparable to that of massive star formation therein. Therefore, we are witnessing young giant molecular clouds (GMCs) with rapid massive star formation. Our study paves the way of using HINSA to study cloud formation in Galactic bones and, more generally, in distant GMCs in the FAST era.

Keywords: Star formation, Interstellar filaments, Interstellar atomic gas, Molecular clouds
Cavitating Bubbles in Condensing Gas as a Means of Forming Clumps, Chondrites, and Planetesimals. Vaporized metal, silicates, and ices on the verge of recondensing into solid or liquid particles appear in many contexts: behind shocks, in impact ejecta, and within the atmospheres and outflows of stars, disks, planets, and minor bodies. We speculate that a condensing gas might fragment, forming overdensities within relative voids, from a radiation–condensation instability. Seeded with small thermal fluctuations, a condensible gas will exhibit spatial variations in the density of particle condensates. Regions of higher particle density may radiate more, cooling faster. Faster cooling leads to still more condensation, lowering the local pressure. Regions undergoing runaway condensation may collapse under the pressure of their less condensed surroundings. Particle condensates will compactify with collapsing regions, potentially into macroscopic bodies (planetesimals). As a first step toward realizing this hypothetical instability, we calculate the evolution of a small volume of condensing silicate vapor—a spherical test "bubble" embedded in a background medium whose pressure and radiation field are assumed fixed for simplicity. Such a bubble condenses and collapses upon radiating its latent heat to the background, assuming that its energy loss is not stopped by background irradiation. Collapse speeds can range up to sonic, similar to cavitation in terrestrial settings. Adding a noncondensible gas like hydrogen to the bubble stalls the collapse. We discuss whether cavitation can provide a way for millimeter-sized chondrules and refractory solids to assemble into meteorite parent bodies, focusing on CB/CH chondrites whose constituent particles likely condensed from silicate/metal vapor released from the most energetic asteroid collisions.

Keywords: Impact phenomena, Chondrites, Asteroids, Protoplanetary disks, Planetesimals, Meteorites, Debris disks, Planet formation, Collapsing clouds
On the Kinematic Nature of Apparent Disks at High Redshifts: Local Counterparts are Not Dominated by Ordered Rotation but by Tangentially Anisotropic Random Motion. It is not straightforward to physically interpret the apparent morphology of galaxies. Recent observations by the James Webb Space Telescope (JWST) revealed a dominant galaxy population at high redshifts (z &gt; 2) that were visually classified as disks for their flattened shapes and/or exponential light profiles. The extensively accepted interpretation is that they are dynamically cold disks supported by bulk rotation. However, it is long known that flattened shapes and exponential profiles are not exclusive for rotating disk structure. To break degeneracy and assess the rotational support of typical high-z galaxies in the JWST samples, those with active star formation and stellar masses  lg(M⋆/M⊙)∼9 , we study the kinematics of their equal-mass counterparts at z = 0. While these local star-forming low-mass galaxies are photometrically similar to real dynamically cold disks, they are not supported by ordered rotation but primarily by random motion, and their flattened shapes result largely from tangential orbital anisotropy. Given the empirical and theoretical evidence that young galaxies are dynamically hotter at higher redshifts, our results suggest that the high-z JWST galaxies may not be cold disks but are dynamically warm/hot galaxies with flattened shapes driven by anisotropy. While both have low rotational support, local low-mass galaxies possess oblate shapes, contrasting the prolate shapes (i.e., cigar like) of low-mass systems at high redshifts. Such shape transition (prolate ⇒ oblate) indicates an associated change in orbital anisotropy (radial ⇒ tangential), with roots likely in the assembly of their host dark matter halos.

Keywords: Extragalactic astronomy
TESS Investigation—Demographics of Young Exoplanets (TI-DYE). II. A Second Giant Planet in the 17 Myr System HIP 67522. The youngest (&lt;50 Myr) planets are vital to understand planet formation and early evolution. The 17 Myr system HIP 67522 is already known to host a giant (≃10R ⊕) planet on a tight orbit. In their discovery paper, Rizzuto et al. reported a tentative single-transit detection of an additional planet in the system using TESS. Here, we report the discovery of HIP 67522c, a 7.9 R ⊕ planet that matches with that single-transit event. We confirm the signal with ground-based multiwavelength photometry from Sinistro and MuSCAT4. At a period of 14.33 days, planet c is close to a 2:1 mean-motion resonance with b (6.96 days or 2.06:1). The light curve shows distortions during many of the transits, which are consistent with spot-crossing events and/or flares. Fewer stellar activity events are seen in the transits of planet b, suggesting that planet c is crossing a more active latitude. Such distortions, combined with systematics in the TESS light-curve extraction, likely explain why planet c was previously missed.

Keywords: Exoplanets, Stellar activity, Exoplanet evolution, Young stellar objects, Transit photometry
Analyzing the Sequence of Phases Leading to the Formation of the Active Region 13664, with Potential Carrington-like Characteristics. Several recurrent X-class flares from Active Region (AR) 13664 triggered a severe G5-class geomagnetic storm between 2024 May 10 and 11. The morphology and compactness of this AR closely resemble the AR responsible for the famous Carrington Event of 1859. Although the induced geomagnetic currents produced a value of the Dst index, probably 1 order of magnitude weaker than that of the Carrington Event, the characteristics of AR 13664 warrant special attention. Understanding the mechanisms of magnetic field emergence and transformation in the solar atmosphere that lead to the formation of such an extensive, compact, and complex AR is crucial. Our analysis of the emerging flux and horizontal motions of the magnetic structures observed in the photosphere reveals the fundamental role of a sequence of emerging bipoles at the same latitude and longitude, followed by converging and shear motions. This temporal order of processes frequently invoked in magnetohydrodynamic models—emergence, converging motions, and shear motions—is critical for the storage of magnetic energy preceding strong solar eruptions that, under the right timing, location, and direction conditions, can trigger severe space weather events on Earth.

Keywords: Sunspot groups
Reconciling M/L Ratios Across Cosmic Time: a Concordance IMF for Massive Galaxies. The stellar initial mass function (IMF) is thought to be bottom heavy in the cores of the most massive galaxies, with an excess of low-mass stars compared to the Milky Way. However, studies of the kinematics of quiescent galaxies at 2 &lt; z &lt; 5 find M/L ratios that indicate lighter IMFs. Light IMFs have also been proposed for the unexpected populations of luminous galaxies that JWST has uncovered at z &gt; 7 to reduce tensions with galaxy formation models. Here we explore "ski slope" IMFs that are simultaneously bottom heavy, with a steep slope at low stellar masses, and top heavy, with a shallow slope at high masses. We derive a form of the IMF for massive galaxies that is consistent with measurements in the local universe and yet produces relatively low M/L ratios at high redshift. This concordance IMF has slopes γ 1 = 2.40 ± 0.09, γ 2 = 2.00 ± 0.14, and γ 3 = 1.85 ± 0.11 in the regimes 0.08 M ⊙ – 0.5 M ⊙, 0.5 M⊙ – 1 M ⊙, and &gt;1 M ⊙, respectively. The IMF parameter α, the mass excess compared to a Milky Way IMF, ranges from  log(α)≈+0.3  for present-day galaxies to  log(α)≈‑0.1  for their star-forming progenitors. The concordance IMF applies only to the central regions of the most massive galaxies, with velocity dispersions σ ∼ 300 km s‑1, and their progenitors. However, it can be generalized using a previously measured relation between α and σ. We arrive at the following modification to the Kroupa (2001) IMF for galaxies with σ ≳ 160 km s‑1:  γ1≈1.3+4.3logσ160 ,  γ2≈2.3‑1.2logσ160 , and  γ3≈2.3‑1.7logσ160 , with σ 160 = σ/160 km s‑1. If galaxies grow primarily inside out, so that velocity dispersions are relatively stable, these relations should also hold at high redshift.

Keywords: Galaxy formation, Initial mass function, Star formation, Galaxy evolution, Early-type galaxies
Repeated Partial Disruptions in a White Dwarf–Neutron Star or White Dwarf–Black Hole Merger Modulate the Prompt Emission of Long-duration Merger-type GRBs. The progenitors of gamma-ray bursts (GRBs) have long been an unresolved issue. GRB 230307A stands out as an exceptionally bright event, belonging to the long-duration GRBs but also exhibiting a late-emission component reminiscent of a kilonova. Together with the similar events GRBs 060614 and 211211A, they make up a new subgroup of GRBs with intriguing progenitors. If such long-duration merger-type GRBs originated from the coalescence of a white dwarf (WD) with a neutron star (NS) or a black hole (BH), as proposed in the recent literature, then the larger tidal disruption radius of the WD, together with a nonnegligible residual orbital eccentricity, would make repeated partial tidal disruptions inevitable. This may modulate the mass accretion and jet launching process at the NS or BH, resulting in a quasiperiodic modulation (QPM) in the light curve of the GRB, with a period equal to the orbital period. The detection of potential QPMs during the early episode of prompt emission of these three GRBs supports this scenario, and the relatively slow QPM (&gt; 1 s) suggests that the lighter object cannot be an NS. We propose that the progenitor system of GRBs 230307A, 060614, and 211211A consist of a WD of mass 1.3 M ⊙, 0.9 M ⊙, and 1.4 M ⊙, respectively, and an NS (or BH). After several cycles of modulations, the WD is completely destroyed, and the accretion of the remaining debris dominates the extended emission episode.

Keywords: Tidal disruption, Gamma-ray bursts
Observation of the Galactic Center PeVatron beyond 100 TeV with HAWC. We report an observation of ultrahigh-energy (UHE) gamma rays from the Galactic center (GC) region, using 7 yr of data collected by the High-Altitude Water Cherenkov (HAWC) Observatory. The HAWC data are best described as a point-like source (HAWC J1746-2856) with a power-law spectrum ( dN/dE=ϕE/26TeVγ ), where γ = ‑2.88 ± 0.15stat ‑ 0.1sys and ϕ = 1.5 × 10‑15 (TeV cm2 s)‑1  ±0.3stat‑0.13sys+0.08sys  extending from 6 to 114 TeV. We find no evidence of a spectral cutoff up to 100 TeV using HAWC data. Two known point-like gamma-ray sources are spatially coincident with the HAWC gamma-ray excess: Sgr A* (HESS J1745-290) and the Arc (HESS J1746-285). We subtract the known flux contribution of these point sources from the measured flux of HAWC J1746-2856 to exclude their contamination and show that the excess observed by HAWC remains significant (&gt;5σ), with the spectrum extending to &gt;100 TeV. Our result supports that these detected UHE gamma rays can originate via hadronic interaction of PeV cosmic-ray protons with the dense ambient gas and confirms the presence of a proton PeVatron at the GC.

Keywords: Galactic center, Gamma-rays, Ultra-high-energy cosmic radiation
Alpha–Proton Differential Flow of a Coronal Mass Ejection at 15 Solar Radii. Alpha–proton differential flow (V  α p ) of coronal mass ejections (CMEs) and solar wind from the Sun to 1 au and beyond could influence the instantaneous correspondence of absolute abundances of alpha particles (He2+/H+) between the solar corona and interplanetary space as the abundance of a coronal source can vary with time. Previous studies based on Ulysses and Helios showed that V  α p  is negligible within CMEs from 5 to 0.3 au, similar to slow solar wind (&lt;400 km s‑1). However, recent new observations using Parker Solar Probe (PSP) revealed that the V  α p  of slow wind increases to ∼60 km s‑1 inside 0.1 au. It is important to answer whether the V  α p  of CMEs exhibits similar behavior near the Sun. In this Letter, we report the V  α p  of a CME measured by PSP at ∼15 R ⊙ for the first time, which demonstrates that the V  α p  of CMEs is obvious and complex inside 0.1 au while keeping lower than the local Alfvén speed. A very interesting point is that the same one CME duration can be divided into A and B intervals clearly with Coulomb number below and beyond 0.5, respectively. The means of V  α p  and alpha-to-proton temperature ratios of interval A (B) is 96.52 (21.96) km s‑1 and 7.65 (2.23), respectively. This directly illustrates that Coulomb collisions play an important role in reducing the nonequilibrium features of CMEs. Our study indicates that the absolute elemental abundances of CMEs also might vary during their propagation.

Keywords: Solar abundances, Solar wind, Solar coronal mass ejections
Nonlinear Alfvén-wave Dynamics and Premerger Emission from Crustal Oscillations in Neutron Star Mergers. Neutron stars have solid crusts threaded by strong magnetic fields. Perturbations in the crust can excite nonradial oscillations, which can in turn launch Alfvén waves into the magnetosphere. In the case of a compact binary close to merger involving at least one neutron star, this can happen through tidal interactions causing resonant excitations that shatter the neutron star crust. We present the first numerical study that elucidates the dynamics of Alfvén waves launched in a compact binary magnetosphere. We seed a magnetic field perturbation on the neutron star crust, which we then evolve in fully general-relativistic force-free electrodynamics using a GPU-based implementation. We show that Alfvén waves steepen nonlinearly before reaching the orbital light cylinder, form flares, and dissipate energy in a transient current sheet. Our results predict radio and X-ray precursor emission from this process.

Keywords: Neutron stars, Magnetospheric radio emissions, Plasma astrophysics, Gravitational wave sources, X-ray transient sources, General relativity, Astronomical simulations, Radio transient sources