Sazuna/UAT_keywords huggingface dataset:
Effects of Hydrogen versus Helium on Electromagnetic Black Hole Observables. The centers of our Galaxy and the nearby Messier 87 are known to contain supermassive black holes, which support accretion flows that radiate across the electromagnetic spectrum. Although the composition of the accreting gas is unknown, it is likely a mix of ionized hydrogen and helium. We use a simple analytic model and a suite of numerical general relativistic magnetohydrodynamic accretion simulations to study how polarimetric images and spectral energy distributions of the source are influenced by the hydrogen/helium content of the accreting matter. We aim to identify general trends rather than make quantitatively precise predictions, since it is not possible to fully explore the parameter space of accretion models. If the ion-to-electron temperature ratio is fixed, then increasing the helium fraction increases the gas temperature; to match the observational flux density constraints, the number density of electrons and magnetic field strengths must therefore decrease. In our numerical simulations, emission shifts from regions of low to high plasma β-both altering the morphology of the image and decreasing the variability of the light curve-especially in strongly magnetized models with emission close to the midplane. In polarized images, we find that the model gas composition influences the degree to which linear polarization is (de)scrambled and therefore affects estimates for the resolved linear polarization fraction. We also find that the spectra of helium-composition flows peak at higher frequencies and exhibit higher luminosities. We conclude that gas composition may play an important role in predictive models for black hole accretion.

Keywords: Accretion, Magnetohydrodynamics, Plasma astrophysics, Radiative transfer
Potential Signature of Population III Pair-instability Supernova Ejecta in the BLR Gas of the Most Distant Quasar at z = 7.54. The search for Population III stars has fascinated and eluded astrophysicists for decades. One promising place for capturing evidence of their presence must be high-redshift objects; signatures should be recorded in their characteristic chemical abundances. We deduce the Fe and Mg abundances of the broadline region (BLR) from the intensities of ultraviolet Mg II and Fe II emission lines in the near-infrared spectrum of UKIDSS Large Area Survey (ULAS) J1342+0928 at z = 7.54, by advancing our novel flux-to-abundance conversion method developed for quasars up to z ~ 3. We find that the BLR of this quasar is extremely enriched, by a factor of 20 relative to the solar Fe abundance, together with a very low Mg/Fe abundance ratio: [Fe/H] = +1.36 ± 0.19 and [Mg/Fe] =-1.11 ± 0.12, only 700 million years after the Big Bang. We conclude that such an unusual abundance feature cannot be explained by the standard view of chemical evolution that considers only the contributions from canonical supernovae. While there remains uncertainty in the high-mass end of the Population III initial mass function, here we propose that the larger amount of iron in ULAS J1342+0928 was supplied by a pair-instability supernova (PISN) caused by the explosion of a massive Population III star in the high-mass end of the possible range of 150-300 M ☉ . Chemical evolution models based on initial PISN enrichment well explain the trend in [Mg/Fe]-z all the way from z &lt; 3 to z = 7.54. We predict that stars with very low [Mg/Fe] at all metallicities are hidden in the galaxy, and they will be efficiently discovered by ongoing new-generation photometric surveys. *At the time of writing this paper, the highest redshift record has been updated to z = 7.642, ULAS J0313-1806, as reported by Wang et al. ().

Keywords: Population III stars, Chemical abundances, Nucleosynthesis, Quasars
Lorentz Invariance Violation Test from Time Delays Measured with Gravitationally Lensed GRB Candidates 950830 and 200716C. The spectral lag features in gamma-ray bursts (GRBs) have been widely used to investigate possible Lorentz invariance violation (LIV). However, these constraints could depend on the unknown source-intrinsic time delays in different energy bands. Biesiada &amp; Piórkowska theoretically proposed that gravitational lensing time delays in a strongly lensed GRB can become a tool for testing LIV free from the intrinsic time lag problem. Recently GRB 950830 and GRB 200716C have been proposed to be lensed by an intermediate-mass black hole. They should still be considered as candidates of strongly lensed bursts, since no angular offset (i.e., the evidence for multiple images) was detected, but only a double peak structure in the light curve. The redshift of the burst z  s  and of the lens z  l  have not been measured in either case; hence we assumed a reasonable guess of z  l  = 1.0, z  s  = 2.0 for GRB 950830 and z  l  = 0.174, z  s  = 0.348 for GRB 200716C. Bearing all this in mind, we attempted to constrain LIV theories in a prospective way based on the two GRBs by considering time delays between two pulses in different energy channels. By directly fitting the time delay data of GRBs 950830 and 200716C we obtained the following limits on LIV energy scale: E QG,1 ≥ 3.2 × 109 GeV and E QG,1 ≥ 6.3 × 109 GeV, respectively. Sensitivity analysis regarding the (unknown) redshifts leads to the most conservative estimate, E QG,1 ≥ 1.5 × 108 GeV for GRB 950830 and E QG,1 ≥ 4.8 × 108 GeV for GRB 200716C, when they would be located at z  s  ~ 5.

Keywords: Gamma-ray bursts
Fast Fourier Transformation Based Evaluation of Microlensing Magnification with Extended Source. The extended source effect on microlensing magnification is nonnegligible and must be taken into account for an analysis of microlensing. However, the evaluation of the extended source magnification is numerically expensive because it includes the two-dimensional integral over the source profile. Various studies have developed methods to reduce this integral down to the one-dimensional-integral- or integral-free form, which adopt some approximations or depend on the exact form of the source profile, e.g., a disk or linear/quadratic limb-darkening profile. In this paper, we develop a new method to evaluate the extended source magnification based on fast Fourier transformation (FFT), which does not adopt any approximations and is applicable to any source profiles. Our implementation of the FFT based method enables the fast evaluation of the extended source magnification as fast as ~1 ms (CPU time on a laptop) and guarantees an accuracy better than 0.3%. The FFT based method can be used for the template fitting to a huge data set of light curves from the existing and upcoming surveys.

Keywords: Gravitational microlensing, Publicly available software
The Galactic Nova Rate: Estimates from the ASAS-SN and Gaia Surveys. We present the first estimate of the Galactic nova rate based on optical transient surveys covering the entire sky. Using data from the All-Sky Automated Survey for Supernovae (ASAS-SN) and Gaia-the only two all-sky surveys to report classical nova candidates-we find 39 confirmed Galactic novae and 7 additional unconfirmed candidates discovered from 2019 to 2021, yielding a nova discovery rate of ≈14 yr-1. Using accurate Galactic stellar mass models and three-dimensional dust maps and incorporating realistic nova light curves, we have built a sophisticated Galactic nova model to estimate the fraction of Galactic novae discovered by these surveys over this time period. The observing capabilities of each survey are distinct: the high cadence of ASAS-SN makes it sensitive to fast novae, while the broad observing filter and high spatial resolution of Gaia make it more sensitive to highly reddened novae across the entire Galactic plane and bulge. Despite these differences, we find that ASAS-SN and Gaia give consistent Galactic nova rates, with a final joint nova rate of 26 ± 5 yr-1. This inferred nova rate is substantially lower than found by many other recent studies. Critically assessing the systematic uncertainties in the Galactic nova rate, we argue that the role of faint, fast-fading novae has likely been overestimated, but that subtle details in the operation of transient alert pipelines can have large, sometimes unappreciated effects on transient recovery efficiency. Our predicted nova rate can be directly tested with forthcoming red/near-infrared transient surveys in the southern hemisphere.

Keywords: White dwarf stars, Cataclysmic variable stars, Novae, Classical novae
Spectropolarimetric Measurements of Hidden Broad Lines in Nearby Megamaser Galaxies: A Lack of Clear Evidence for a Correlation between Black Hole Masses and Virial Products. High-accuracy black hole (BH) masses require excellent spatial resolution that is only achievable for galaxies within ~100 Mpc using present-day technology. At larger distances, BH masses are often estimated with single-epoch scaling relations for active galactic nuclei. This method requires only luminosity and the velocity dispersion of the broad-line region (BLR) to calculate a virial product, and an additional virial factor, f, to determine the BH mass. The accuracy of these single-epoch masses, however, is unknown, and there are few empirical constraints on the variance of f between objects. We attempt to calibrate single-epoch BH masses using spectropolarimetric measurements of nine megamaser galaxies from which we measure the velocity distribution of the BLR. We do not find strong evidence for a correlation between the virial products used for single-epoch masses and dynamical mass, either for the megamaser sample alone or when it is combined with dynamical masses from reverberation mapping modeling. Furthermore, we find evidence that the virial parameter f varies between objects, but we do not find strong evidence for a correlation with other observable parameters such as luminosity or broad-line width. Although we cannot definitively rule out the existence of any correlation between dynamical mass and virial product, we find tension between the allowed f-values for masers and those widely used in the literature. We conclude that the single-epoch method requires further investigation if it is to be used successfully to infer BH masses. * Based on observations made with the Southern African Large Telescope.

Keywords: Megamasers, Reverberation mapping, Active galactic nuclei
Deconfusing Detections in Directly Imaged Multiplanet Systems. High-contrast images from future space-based telescopes may contain several planets from multiplanet systems and potentially a few planet-like speckles. When taken several months apart, the short-period planets and speckles will appear to move significantly, to the point that it might not be clear which point source (detection) in the image belongs to which object. In this work, we develop a tool, the deconfuser, to test quickly all the plausible partitions of detections by planets based on orbital mechanics. We then apply the deconfuser to a large set of simulated observations to estimate "confusion" rates, i.e., how often there are multiple distinct orbit combinations that describe the data well. We find that in the absence of missed and false detections, four observations are sufficient to avoid confusion, except for systems with high inclinations (above 75°). In future work, the deconfuser will be integrated into mission simulation tools, such as EXOSIMS, to assess the risk of confusion in missions such as the IR/O/UV large telescope recommended by the Astro2020 decadal survey. * Submitted on April, 1st, 2022

Keywords: Regression, Coronagraphic imaging, Astrometric exoplanet detection, Orbit determination
Statistical Mechanics of Collisionless Orbits. V. The Approach to Equilibrium for Idealized Self-gravitating Systems. Self-gravitating Newtonian systems consisting of a very large number of particles have generally defied attempts to describe them using statistical mechanics. This is paradoxical since many astronomical systems, or simulations thereof, appear to have universal, equilibrium structures for which no physical basis exists. A decade ago we showed that extremizing the number of microstates with a given energy per unit mass, under the constraints of conserved total energy and mass, leads to the maximum entropy state, $n(E)\propto \exp (-\beta (E-{{\rm{\Phi }}}_{0}))-1$ , known as DARKexp. This differential energy distribution, and the resulting density structures, closely approximate those of dark matter halos with central cusps, ρ ~ r -1, and outer parts, ρ ~ r -4. Here we define a nonequilibrium functional, S  D , which is maximized for DARKexp and increases monotonically during the evolution toward equilibrium of idealized collisionless systems of the extended spherical infall model. Systems that undergo more mixing more closely approach DARKexp.

Keywords: Galaxy dark matter halos, Gravitation, Galaxy structure, Galaxy physics, Newtonian gravitation, Navarro-Frenk-White profile, Dark matter
Catastrophic Cooling in Superwinds. III. Nonequilibrium Photoionization. Observations of some starburst-driven galactic superwinds suggest that strong radiative cooling could play a key role in the nature of feedback and the formation of stars and molecular gas in star-forming galaxies. These catastrophically cooling superwinds are not adequately described by adiabatic fluid models, but they can be reproduced by incorporating nonequilibrium radiative cooling functions into the fluid model. In this work, we have employed the atomic and cooling module MAIHEM implemented in the framework of the FLASH hydrodynamics code to simulate the formation of radiatively cooling superwinds as well as their corresponding nonequilibrium ionization (NEI) states for various outflow parameters, gas metallicities, and ambient densities. We employ the photoionization program CLOUDY to predict radiation- and density-bounded photoionization for these radiatively cooling superwinds, and we predict UV and optical line emission. Our nonequilibrium photoionization models built with the NEI states demonstrate the enhancement of C IV, especially in metal-rich, catastrophically cooling outflows, and O VI in metal-poor ones.

Keywords: Galactic winds, Starburst galaxies, Cooling flows, Star forming regions, Emission line galaxies, Lyman-alpha galaxies, Lyman-break galaxies, H II regions, Superbubbles
MHD Simulations of Dense Core Collision. We investigated the effect of magnetic fields on the collision process between dense molecular cores. We performed three-dimensional magnetohydrodynamic simulations of collisions between two self-gravitating cores using the Enzo adaptive mesh refinement code. The core was modeled as a stable isothermal Bonnor-Ebert (BE) sphere immersed in uniform magnetic fields. Collisions were characterized by the offset parameter b, Mach number of the initial core ${ \mathcal M }$ , magnetic field strength B 0, and angle θ between the initial magnetic field and collision axis. For head-on (b = 0) collisions, one protostar was formed in the compressed layer. The higher the magnetic field strength, the lower the accretion rate. For models with b = 0 and θ = 90°, the accretion rate was more dependent on the initial magnetic field strength compared with b = 0 and θ = 0° models. For off-center (b = 1) collisions, the higher specific angular momentum increased; therefore, the gas motion was complicated. In models with b = 1 and ${ \mathcal M }=1$ , the number of protostars and gas motion highly depended on B 0 and θ. For models with b = 1 and ${ \mathcal M }=3$ , no significant shock-compressed layer was formed and star formation was not triggered.

Keywords: Molecular gas, Star formation, Magnetic fields, Magnetohydrodynamical simulations
Higher-order Turbulence Statistics in the Sub-Alfvénic Solar Wind Observed by Parker Solar Probe. Parker Solar Probe has been the first spacecraft to enter the deep corona below the Alfvén critical point. Here we examine the higher-order statistical properties of magnetic-field fluctuations in the sub-Alfvénic solar wind and compare the results with the neighboring super-Alfvénic region. The intermittency and multifractal properties are analyzed by inspecting the probability density functions, the scale-dependent kurtosis, and fractal spectrum of magnetic-field fluctuations. It is found that the magnetic-field fluctuations present distinct intermittency and multifractal properties in the inertial range and the B  R  component reveals much higher intermittency and more asymmetrical multifractal spectrum than the other components. The non-Gaussian self-similarity of fluctuations of B  R  at larger scales has also been observed. Further comparative analysis shows that all the solar wind periods share nearly the same intermittency and multifractal features, and the only difference lies in that the fluctuations of the B  T  and B  N  components have slight variations.

Keywords: Interplanetary turbulence, Solar wind
Contribution of Spicules to Solar Coronal Emission. Recent high-resolution imaging and spectroscopic observations have generated renewed interest in spicules' role in explaining the hot corona. Some studies suggest that some spicules, often classified as type II, may provide significant mass and energy to the corona. Here we use numerical simulations to investigate whether such spicules can produce the observed coronal emission without any additional coronal heating agent. Model spicules consisting of a cold body and hot tip are injected into the base of a warm (0.5 MK) equilibrium loop with different tip temperatures and injection velocities. Both piston- and pressure-driven shocks are produced. We find that the hot tip cools rapidly and disappears from coronal emission lines such as Fe XII 195 and Fe XIV 274. Prolonged hot emission is produced by preexisting loop material heated by the shock and by thermal conduction from the shock. However, the shapes and Doppler shifts of synthetic line profiles show significant discrepancies with observations. Furthermore, spatially and temporally averaged intensities are extremely low, suggesting that if the observed intensities from the quiet Sun and active regions were solely due to type II spicules, one to several orders of magnitude more spicules would be required than have been reported in the literature. This conclusion applies strictly to the ejected spicular material. We make no claims about emissions connected with waves or coronal currents that may be generated during the ejection process and heat the surrounding area.

Keywords: Solar extreme ultraviolet emission, Solar coronal loops, Solar coronal heating, Solar spicules, Solar corona, Shocks, Solar chromosphere, Magnetohydrodynamical simulations
Survival of Terrestrial N<SUB>2</SUB>-O<SUB>2</SUB> Atmospheres in Violent XUV Environments through Efficient Atomic Line Radiative Cooling. Atmospheres play a crucial role in planetary habitability. Around M dwarfs and young Sun-like stars, planets receiving the same insolation as the present-day Earth are exposed to intense stellar X-rays and extreme-ultraviolet (XUV) radiation. This study explores the fundamental question of whether the atmosphere of present-day Earth could survive in such harsh XUV environments. Previous theoretical studies suggest that stellar XUV irradiation is sufficiently intense to remove such atmospheres completely on short timescales. In this study, we develop a new upper-atmospheric model and re-examine the thermal and hydrodynamic responses of the thermospheric structure of an Earth-like N2-O2 atmosphere, on an Earth-mass planet, to an increase in the XUV irradiation. Our model includes the effects of radiative cooling via electronic transitions of atoms and ions, known as atomic line cooling, in addition to the processes accounted for by previous models. We demonstrate that atomic line cooling dominates over the hydrodynamic effect at XUV irradiation levels greater than several times the present level of the Earth. Consequentially, the atmosphere's structure is kept almost hydrostatic, and its escape remains sluggish even at XUV irradiation levels up to a thousand times that of the Earth at present. Our estimates for the Jeans escape rates of N2-O2 atmospheres suggest that these 1 bar atmospheres survive in early active phases of Sun-like stars. Even around active late M dwarfs, N2-O2 atmospheres could escape significant thermal loss on timescales of gigayears. These results give new insights into the habitability of terrestrial exoplanets and the Earth's climate history.

Keywords: Upper atmosphere, Exoplanets, Earth atmosphere, Habitable planets, Exoplanet atmospheres
Inferring the Neutron Star Maximum Mass and Lower Mass Gap in Neutron Star-Black Hole Systems with Spin. Gravitational-wave (GW) detections of merging neutron star-black hole (NSBH) systems probe astrophysical neutron star (NS) and black hole (BH) mass distributions, especially at the transition between NS and BH masses. Of particular interest are the maximum NS mass, minimum BH mass, and potential mass gap between them. While previous GW population analyses assumed all NSs obey the same maximum mass, if rapidly spinning NSs exist, they can extend to larger maximum masses than nonspinning NSs. In fact, several authors have proposed that the ~2.6 M ⊙ object in the event GW190814-either the most massive NS or least massive BH observed to date-is a rapidly spinning NS. We therefore infer the NSBH mass distribution jointly with the NS spin distribution, modeling the NS maximum mass as a function of spin. Using four LIGO-Virgo NSBH events including GW190814, if we assume that the NS spin distribution is uniformly distributed up to the maximum (breakup) spin, we infer the maximum nonspinning NS mass is ${2.7}_{-0.4}^{+0.5}\,{M}_{\odot }$ (90% credibility), while assuming only nonspinning NSs, the NS maximum mass must be &gt;2.53 M ⊙ (90% credibility). The data support the mass gap's existence, with a minimum BH mass at ${5.4}_{-1.0}^{+0.7}{M}_{\odot }$ . With future observations, under simplified assumptions, 150 NSBH events may constrain the maximum nonspinning NS mass to ±0.02 M ⊙, and we may even measure the relation between the NS spin and maximum mass entirely from GW data. If rapidly rotating NSs exist, their spins and masses must be modeled simultaneously to avoid biasing the NS maximum mass.

Keywords: Neutron stars, Gravitational waves, Black holes
The Physical Properties of Low-redshift FeLoBAL Quasars. I. Spectral-synthesis Analysis of the Broad Absorption-line (BAL) Outflows Using SimBAL. We present the first systematic study of 50 low-redshift (0.66 &lt; z &lt; 1.63) iron low-ionization broad absorption-line quasars (FeLoBALQs) using SimBAL, which represents a more than five-fold increase in the number of FeLoBALQs with detailed absorption line spectral analyses. We found the outflows have a wide range of ionization parameters, $-4\lesssim \mathrm{log}U\lesssim 1.2$ and densities, $2.8\lesssim \mathrm{log}n\lesssim 8\ [{\mathrm{cm}}^{-3}]$ . The objects in our sample showed FeLoBAL gas located at a wide range of distances $0\lesssim \mathrm{log}R\lesssim 4.4$ [pc], although we do not find any evidence for disk winds (with R ≪ 0.01 pc) in our sample. The outflow strength primarily depends on the outflow velocity with faster outflows found in quasars that are luminous or that have flat or redder spectral energy distributions. We found that ~18% of the FeLoBALQs in the sample have the significantly powerful outflows needed for quasar feedback. Eight objects showed overlapping troughs in the spectra, and we identified eleven loitering outflow objects, a new class of FeLoBALQs that are characterized by low outflow velocities and high column density winds located $\mathrm{log}R\lesssim 1$ [pc] from the central engine. The FeLoBALs in loitering outflows objects do not show properties expected for radiatively driven winds, and these objects may represent a distinct population among FeLoBALQs. We discuss how the potential acceleration mechanisms and the origins of the FeLoBAL winds may differ for outflows at different locations in quasars.

Keywords: High-luminosity active galactic nuclei, Broad-absorption line quasar, Quasars, Active galactic nuclei, Spectroscopy, Galaxies