Sazuna/UAT_keywords huggingface dataset:
A Lower Bound on the Mass of Compact Objects from Dissipative Dark Matter. We study the fragmentation scale of dark gas formed in dissipative dark-matter halos and show that the simple atomic-dark-matter model consistent with all current observations can create low-mass fragments that can evolve into compact objects forbidden by stellar astrophysics. We model the collapse of the dark halo's dense core by tracing the thermochemical evolution of a uniform-density volume element under two extreme assumptions for density evolution: hydrostatic equilibrium and pressure-free collapse. We then compute the opacity-limited minimum fragment mass from the minimum temperature achieved in these calculations. The results indicate that much of the parameter space is highly unstable to small-scale fragmentation.

Keywords: Gravitational collapse, Dark matter, Compact objects
Probing the Structure and Evolution of BASS Active Galactic Nuclei through Eddington Ratios. We constrain the intrinsic Eddington ratio (λ Edd) distribution function for local active galactic nuclei (AGN) in bins of low and high obscuration $[\mathrm{log}({N}_{{\rm{H}}}/{\mathrm{cm}}^{-2})\leqslant 22$ and $22\lt \mathrm{log}({N}_{{\rm{H}}}/{\mathrm{cm}}^{-2})\lt 25$ ], using the Swift Burst Alert Telescope 70 month/BASS DR2 survey. We interpret the fraction of obscured AGN in terms of circumnuclear geometry and temporal evolution. Specifically, at low Eddington ratios ( $\mathrm{log}\,{\lambda }_{\mathrm{Edd}}\,\lt \,$ -2), obscured AGN outnumber unobscured ones by a factor of ~4, reflecting the covering factor of the circumnuclear material (0.8, or a torus opening angle of ~34°). At high Eddington ratios ( $\mathrm{log}\,{\lambda }_{\mathrm{Edd}}\,\gt \,$ -1), the trend is reversed, with &lt;30% of AGN having $\mathrm{log}({N}_{{\rm{H}}}/{\mathrm{cm}}^{-2})\gt 22$ , which we suggest is mainly due to the small fraction of time spent in a highly obscured state. Considering the Eddington ratio distribution function of narrow-line and broad-line AGN from our prior work, we see a qualitatively similar picture. To disentangle temporal and geometric effects at high λ Edd, we explore plausible clearing scenarios such that the time-weighted covering factors agree with the observed population ratio. We find that the low fraction of obscured AGN at high λ Edd is primarily due to the fact that the covering factor drops very rapidly, with more than half the time spent with &lt;10% covering factor. We also find that nearly all obscured AGN at high-λ Edd exhibit some broad lines. We suggest that this is because the height of the depleted torus falls below the height of the broad-line region, making the latter visible from all lines of sight.

Keywords: Luminosity function, Supermassive black holes, Astronomical models, Astronomy data modeling, Accretion, Active galactic nuclei, X-ray surveys, X-ray active galactic nuclei
Search for Coincident Gravitational Waves and Long Gamma-Ray Bursts from 4-OGC and the Fermi-GBM/Swift-BAT Catalog. The recent discovery of a kilonova associated with an apparent long-duration gamma-ray burst has challenged the typical classification that long gamma-ray bursts originate from the core collapse of massive stars and short gamma-ray bursts are from compact binary coalescence. The kilonova indicates a neutron star merger origin and suggests the viability of gravitational-wave and long gamma-ray burst multimessenger astronomy. Gravitational waves play a crucial role by providing independent information for the source properties. This work revisits the archival 2015-2020 LIGO/Virgo gravitational-wave candidates from the 4-OGC catalog that are consistent with a binary neutron star or neutron star-black hole merger and the long-duration gamma-ray bursts from the Fermi-GBM and Swift-BAT catalogs. We search for spatial and temporal coincidence with up to a 10 s time lag between gravitational-wave candidates and the onset of long-duration gamma-ray bursts. The most significant candidate association has only a false-alarm rate of once every 2 yr; given the LIGO/Virgo observational period, this is consistent with a null result. We report an exclusion distance for each search candidate for a fiducial gravitational-wave signal with conservative viewing angle assumptions.

Keywords: Gravitational wave astronomy, Gamma-ray bursts
Searching for the Signal of a Primordial Black Hole from CMB Lensing and γ-Ray Emissions. In this letter, we search for the signal of primordial black holes (PBHs) by correlating the γ-ray emissions in the MeV energy band produced by the Hawking evaporation and the lensing effect of the cosmic microwave background (CMB). We use the conservative case of the astrophysical model as much as possible in the calculations, since the potential astrophysical origins dominate the observed emission in the MeV energy band. By carefully discussing the appropriate energy bands corresponding to different PBH masses, it is worth expecting a tight constraint on the fraction of the Schwarzschild PBHs in the mass range of 1016-5 × 1017 g by simulations of the sensitivity of the future CMB-S4 project and the γ-ray telescope e-ASTROGAM. Furthermore, we also consider the PBH model with spins and find that the constraining ability of the PBH fraction from the correlation between CMB lensing and γ-ray emissions can be improved by another order of magnitude, which could importantly fill the gaps with PBH fraction limits in the mass range of 5 × 1017-2 × 1018 g.

Keywords: Gamma-ray sources, Cosmic microwave background radiation, Primordial black holes
A Transient "Changing-look" Active Galactic Nucleus Resolved on Month Timescales from First-year Sloan Digital Sky Survey V Data. We report the discovery of a new "changing-look" active galactic nucleus (CLAGN) event, in the quasar SDSS J162829.17+432948.5 at z = 0.2603, identified through repeat spectroscopy from the fifth Sloan Digital Sky Survey (SDSS-V). Optical photometry taken during 2020-2021 shows a dramatic dimming of Δg ≈ 1 mag, followed by a rapid recovery on a timescale of several months, with the ≲2 month period of rebrightening captured in new SDSS-V and Las Cumbres Observatory spectroscopy. This is one of the fastest CLAGN transitions observed to date. Archival observations suggest that the object experienced a much more gradual dimming over the period of 2011-2013. Our spectroscopy shows that the photometric changes were accompanied by dramatic variations in the quasar-like continuum and broad-line emission. The excellent agreement between the pre- and postdip photometric and spectroscopic appearances of the source, as well as the fact that the dimmest spectra can be reproduced by applying a single extinction law to the brighter spectral states, favor a variable line-of-sight obscuration as the driver of the observed transitions. Such an interpretation faces several theoretical challenges, and thus an alternative accretion-driven scenario cannot be excluded. The recent events observed in this quasar highlight the importance of spectroscopic monitoring of large active galactic nucleus samples on weeks-to-months timescales, which the SDSS-V is designed to achieve.

Keywords: Supermassive black holes, Active galactic nuclei, Transient sources, Quasars
Disks of Stars in the Galactic Center Triggered by Tidal Disruption Events. In addition to a supermassive black hole (SMBH), the central parsec of the Milky Way hosts over 100 massive, high-velocity young stars whose existence, and organization of a subset of them in one, or possibly two, misaligned disks, is puzzling. Due to a combination of low medium density and strong tidal forces in the vicinity of Sgr A*, stars are not expected to form. Here we propose a novel scenario for their in situ formation: a jetted tidal disruption event (TDE) from an older wandering star triggers an episode of positive feedback of star formation in the plane perpendicular to the jet, as demonstrated via numerical simulations in the context of jet-induced feedback in galactic outflows. An overpressured cocoon surrounding the jet shock-compresses clumps to densities high enough to resist the SMBH tidal field. The TDE rate of 10-5-10-4 yr-1 per galaxy, out of which a few percent of events are jetted, implies a jetted TDE event per galaxy to occur every few million years. This timescale is interestingly of the same order of the age of the disk stars. The mass function predicted by our mechanism is top heavy. Additionally, since TDEs are isotropic, our model predicts a random orientation for the disk of stars with respect to the plane of the galaxy and, due to the relatively high TDE rate, can account for multiple disks of stars with uncorrelated orientations.

Keywords: Supermassive black holes, Tidal disruption, Star formation
Cross-loop Propagation of a Quasiperiodic Extreme-ultraviolet Wave Train Triggered by Successive Stretching of Magnetic Field Structures during a Solar Eruption. Solar extreme-ultraviolet (EUV) waves generally refer to large-scale disturbances propagating outward from sites of solar eruptions in EUV imaging observations. Using the recent observations from the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory, we report a quasiperiodic wave train propagating outward at an average speed of ~308 km s-1. At least five wave fronts can be clearly identified with the period being ~120 s. These wave fronts originate from the coronal loop expansion, which propagates with an apparent speed of ~95 km s-1, about 3 times slower than the wave train. In the absence of a strong lateral expansion, these observational results might be explained by the theoretical model of Chen et al., which predicted that EUV waves may have two components: a faster component that is a fast-mode magnetoacoustic wave or shock wave and a slower apparent front formed as a result of successive stretching of closed magnetic field lines. In this scenario, the wave train and the successive loop expansion we observed likely correspond to the fast and slow components in the model, respectively.

Keywords: Solar oscillations, Solar coronal waves, Solar flares, Solar coronal mass ejections
The Exoplanet Radius Valley from Gas-driven Planet Migration and Breaking of Resonant Chains. The size frequency distribution of exoplanet radii between 1 and 4R ⊕ is bimodal with peaks at ~1.4 R ⊕ and ~2.4 R ⊕, and a valley at ~1.8 R ⊕. This radius valley separates two classes of planets-usually referred to as "super-Earths" and "mini-Neptunes"-and its origin remains debated. One model proposes that super-Earths are the outcome of photoevaporation or core-powered mass loss stripping the primordial atmospheres of the mini-Neptunes. A contrasting model interprets the radius valley as a dichotomy in the bulk compositions, where super-Earths are rocky planets and mini-Neptunes are water-ice-rich worlds. In this work, we test whether the migration model is consistent with the radius valley and how it distinguishes these views. In the migration model, planets migrate toward the disk's inner edge, forming a chain of planets locked in resonant configurations. After the gas disk dispersal, orbital instabilities "break the chains" and promote late collisions. This model broadly matches the period-ratio and planet-multiplicity distributions of Kepler planets and accounts for resonant chains such as TRAPPIST-1, Kepler-223, and TOI-178. Here, by combining the outcome of planet formation simulations with compositional mass-radius relationships and assuming the complete loss of primordial H-rich atmospheres in late giant impacts, we show that the migration model accounts for the exoplanet radius valley and the intrasystem uniformity ("peas in a pod") of Kepler planets. Our results suggest that planets with sizes of ~1.4 R ⊕ are mostly rocky, whereas those with sizes of ~2.4 R ⊕ are mostly water-ice-rich worlds. Our results do not support an exclusively rocky composition for the cores of mini-Neptunes.

Keywords: Exoplanets, Planet formation
Globular Cluster UVIT Legacy Survey (GlobULeS). III. Omega Centauri in Far-ultraviolet. We present the first comprehensive study of the most massive globular cluster, Omega Centauri, in the far-ultraviolet (FUV), extending from the center to ~28% of the tidal radius using the Ultraviolet Imaging Telescope on board AstroSat. A comparison of the FUV-optical color-magnitude diagrams with available canonical models reveals that horizontal branch (HB) stars bluer than the knee (hHBs) and the white dwarfs (WDs) are fainter in the FUV by ~0.5 mag than model predictions. They are also fainter than their counterparts in M13, another massive cluster. We simulated HB with at least five subpopulations, including three He-rich populations with a substantial He enrichment of Y up to 0.43 dex, to reproduce the observed FUV distribution. We find the He-rich younger subpopulations to be radially more segregated than the He-normal older ones, suggesting an in situ enrichment from older generations. The ω Cen hHBs span the same T eff range as their M13 counterparts, but some have smaller radii and lower luminosities. This may suggest that a fraction of ω Cen hHBs are less massive than those of M13, similar to the result derived from earlier spectroscopic studies of outer extreme HB stars. The WDs in ω Cen and M13 have similar luminosity-radius-T eff parameters, and 0.44-0.46 M ⊙ He-core WD model tracks evolving from progenitors with Y = 0.4 dex are found to fit the majority of these. This study provides constraints on the formation models of ω Cen based on the estimated range in age, [Fe/H], and Y (in particular) for the HB stars.

Keywords: Globular star clusters, Horizontal branch stars, Late stellar evolution, Helium-rich stars, White dwarf stars, Ultraviolet photometry, Extreme horizontal branch stars, Hertzsprung Russell diagram
Populations of Magnetized Filaments in the Intracluster Medium and the Galactic Center. Magnetized radio filaments are found in abundance in the inner few hundred parsecs of our galaxy. Progress in understanding this population of filaments has been slow over the last few decades, in part due to a lack of detection elsewhere in the galaxy or in external galaxies. Recent highly sensitive radio continuum observations of radio galaxies in galaxy clusters have revealed remarkable isolated filamentary structures in the intracluster medium (ICM) that are linked to radio jets, tails, and lobes. The origin of this class of filaments is not understood either. Here, we argue that the underlying physical mechanisms responsible for the creation of the two populations are the same because of their similarities in morphology, spacing between the filaments, aspect ratio, and magnetic energy densities to the thermal pressure of the medium and that both populations have undergone synchrotron aging. These similarities provide an opportunity to investigate the physical processes in the interstellar medium (ISM) and ICM for the first time. We consider that the origin of the filaments in both the Galactic center and ICM is a result of the interaction of a large-scale wind with clouds, or the filaments arise through the stretching and collection of field lines by turbulence in a weakly magnetized medium. We examine these ideas in four radio galaxy filaments associated with four radio galaxies-IC 40B, IC 4496, J1333-3141, ESO 137-006-and argue that much can be understood in the future by comparing these two populations of filaments.

Keywords: Galaxy clusters, Galactic center, Interstellar magnetic fields, Fanaroff-Riley radio galaxies, Intracluster medium, Cosmic rays
The Challenge of Ruling Out Inflation via the Primordial Graviton Background. Recent debates around the testability of the inflationary paradigm raise the question of how to model-independently discriminate it from competing scenarios. We argue that a detection of the cosmic graviton background (CGB), the relic radiation from gravitons decoupling around Planck time, would rule out the inflationary paradigm, as realistic inflationary models would dilute the CGB to an unobservable level. The CGB contribution to the effective number of relativistic species, ΔN eff,g  ≈ 0.054, is well within the reach of next-generation cosmological probes. We argue that detecting the high-frequency stochastic gravitational wave background associated to the CGB will be challenging but potentially feasible. We briefly discuss expectations within alternatives to inflation, focusing on bouncing cosmologies and emergent scenarios.

Keywords: Cosmology, Observational cosmology, Cosmic inflation, Alternatives to cosmic inflation, Gravitational waves
Prograde and Retrograde Gas Flow around Disk-embedded Companions: Dependence on Eccentricity, Mass, and Disk Properties. We apply 3D hydrodynamical simulations to study the rotational aspect of gas flow patterns around eccentric companions embedded in an accretion disk. We sample a wide range of companion mass ratios q and disk aspect ratios h 0, and confirm a generic transition from prograde (steady tidal interaction dominated) to retrograde (background Keplerian shear dominated) circumcompanion flow when orbital eccentricity exceeds a critical value e  t . We find e  t  ~ h 0 for subthermal companions while ${e}_{t}\sim {(q/{h}_{0}^{3})}^{1/3}$ for superthermal companions, and propose an empirical formula to unify the two scenarios. Our results also suggest that e  t  is insensitive to modest levels of turbulence, modeled in the form of a kinematic viscosity term. In the context of stellar-mass black holes (sBHs) embedded in active galactic nucleus (AGN) accretion disks, the bifurcation of their circumstellar disk rotation suggests the formation of a population of nearly antialigned sBHs, whose relevance to low spin gravitational wave events can be probed in more detail with future population models of sBH evolution in AGN disks, making use of our quantitative scaling for e  t ; in the context of circumplanetary disks (CPDs), our results suggest the possibility of forming retrograde satellites in situ in retrograde CPDs around eccentric planets.

Keywords: Galaxy accretion disks, Eccentricity, Protoplanetary disks, Astrophysical black holes
Connection between Emission and Absorption Outflows through the Study of Quasars with Extremely High Velocity Outflows. A recently discovered class of outflows, extremely high velocity outflows (EHVOs), may be key to understanding feedback processes, as it is likely the most powerful in terms of mass energy. These EHVOs have been observed at redshifts 1.052 &lt; z em &lt; 7.641, but the potential connection with outflows in emission has not been studied. We find that EHVOs, albeit their small numbers at the moment, appear to show distinct C IV and He II properties. In particular, EHVOs are more predominant in quasars with large blueshifts of the C IV emission line, suggesting a connection between emission and absorption outflowing signatures for these extreme outflows. We also find incipient trends with the maximum velocity of the outflows, which is similar to what has been previously found in BALQSOs but now extending previous studies to speeds up to ~0.2c. We find that the bolometric luminosities, Eddington ratios, and black hole masses of our sample are overall very similar to the general quasar population upon considering their C IV emission properties. This is close to the case for He II EW, as we observe a tentative upper limit to the He II strength for a quasar to host an EHVO. This study shows that extreme outflows such as EHVOs appear in quasars that are clearly a distinct class from the overall BALQSO population and solidify the relation between outflows observed in emission and absorption.

Keywords: Quasar absorption line spectroscopy, Active galactic nuclei, Broad-absorption line quasar, Quasars
Tidally-induced Magnetar Super Flare at the Eve of Coalescence with Its Compact Companion. In the late inspiral phase of a double neutron star (NS) or NS-black hole system in which one NS is a magnetar, the tidal force on the magnetar arisen from its companion will increase dramatically as the binary approaches. The tidal-induced deformation may surpass the maximum that the magnetar's crust can sustain just seconds or subseconds before the coalescence. A catastrophic global crust destruction may thus occur, and the magnetic energy stored in the magnetar's interior will have the opportunity to be released, which would be observed as a superflare with energy 100s of times larger than giant flares of magnetars. Such a mechanism can naturally explain the recently observed precursor of GRB 211211A, including its quasiperiodic oscillation. We predict that in the coming gravitational wave O4/O5 period, there could be a fraction of detected double NS mergers associated with such super flares. If observed, copious information on the structure and magnetic field in an NS interior can be obtained, which is hard to study elsewhere.

Keywords: Neutron stars, Gamma-ray bursts, Stellar mergers, Stellar mass black holes, Gravitational wave sources, Compact objects, Magnetars
On the Origin of the Dichotomy of Stellar Activity Cycles. The presence of possible correlations between stellar rotation rate Ω and the frequency of the activity cycle ω cyc is still much debated. We implement a new Bayesian classification algorithm based on a simultaneous regression analysis of multiple scaling laws and we demonstrate the existence of two different scalings in the ${\mathrm{log}}_{10}{\omega }_{\mathrm{cyc}}$ - ${\mathrm{log}}_{10}{\rm{\Omega }}$ plane for an extended Mt. Wilson sample of 67 stars. Thanks to metallicity measurements obtained from both ESA Gaia and high-resolution spectroscopy, we argue that the origin of this dichotomy is likely related to the chemical composition: stars whose magnetic cycle frequency increases with rotation rate are less metallic than stars whose magnetic cycle frequency decreases with stellar rotation rates. On the contrary, no clear difference in chromospheric magnetic activity indicators characterizes the two branches.

Keywords: Stellar rotation, Stellar magnetic fields, Stellar activity
Dust Temperature Uncertainties Hamper the Inference of Dust and Molecular Gas Masses from the Dust Continuum Emission of Quiescent High-redshift Galaxies. Single flux density measurements at observed-frame submillimeter and millimeter wavelengths are commonly used to probe dust and gas masses in galaxies. In this Letter, we explore the robustness of this method to infer dust mass, focusing on quiescent galaxies, using a series of controlled experiments on four massive halos from the Feedback in Realistic Environments project. Our starting point is four star-forming central galaxies at seven redshifts between z = 1.5 and z = 4.5. We generate modified quiescent galaxies that have been quenched for 100 Myr, 500 Myr, or 1 Gyr prior to each of the studied redshifts by reassigning stellar ages. We derive spectral energy distributions for each fiducial and modified galaxy using radiative transfer. We demonstrate that the dust mass inferred is highly dependent on the assumed dust temperature, T dust, which is often unconstrained observationally. Motivated by recent work on quiescent galaxies that assumed T dust ~ 25 K, we show that the ratio between dust mass and 1.3 mm flux density can be higher than inferred by up to an order of magnitude, due to the considerably lower dust temperatures seen in non-star-forming galaxies. This can lead to an underestimation of dust mass (and, when submillimeter flux density is used as a proxy for molecular gas content and gas mass). This underestimation is most severe at higher redshifts, where the observed-frame 1.3 mm flux density probes rest-frame wavelengths far from the Rayleigh-Jeans regime, and hence depends superlinearly on dust temperature. We fit relations between ratios of rest-frame far-infrared flux densities and mass-weighted dust temperature that can be used to constrain dust temperatures from observations and hence derive more reliable dust and molecular gas masses.

Keywords: Submillimeter astronomy, Galaxy quenching, Radiative transfer simulations, Galaxy evolution