Sazuna/UAT_keywords huggingface dataset:
The Supersonic Project: To Cool or Not to Cool Supersonically Induced Gas Objects (SIGOs)?. Supersonically induced gas objects (SIGOs) primarily form in the early universe, outside of dark matter halos due to the presence of a relative stream velocity between baryons and dark matter. These structures may be the progenitors of globular clusters. Since SIGOs are made out of pristine gas, we investigate the effect of atomic cooling on their properties. We run a suite of simulations by using the moving-mesh code AREPO, with and without baryon dark matter relative velocity and with and without the effects of atomic cooling. We show that SIGO's density, temperature, and prolateness are determined by gravitational interactions rather than cooling. The cold gas fraction in SIGOs is much higher than that of dark matter halos. Specifically, we show that SIGO's characteristically low temperature and extremely high gas density forges a nurturing ground for the earliest star formation sites.

Keywords: Cosmology, Computational methods, Galaxies
Impact of Microlensing on Observational Strategies for Gravitational Time-delay Measurements. Microlensing not only allows for extra magnification lightcurves on top of the intrinsic ones but also shifts them in time domain, causing the actual time delays between images of strongly lensed active galactic nucleus to change on the ∼day(s) light-crossing timescale of the emission region. The microlensing-induced time delays would bias strong lens time-delay cosmography if unaccounted for. However, due to the uncertainties of the disk size and the disk model, the impact is hard to accurately estimate. In this work, we study how to reduce the bias with a designed observation strategy based on a standard disk model. We find that long time monitoring of the images could alleviate the impact since it averages the microlensing time-lag maps due to the peculiar motion of the source relative to the lens galaxy. In addition, images in bluer bands correspond to smaller disk sizes and therefore benefit time-delay measurements as well. We conduct a simulation based on a PG 1115+080-like lensed quasar. The results show that the time-delay dispersions caused by microlensing can be reduced by ∼40% with 20 yr lightcurves, while u band relative to r band reduces ∼75% of the dispersions. Nevertheless, such an effect cannot be totally eliminated in any cases. Further studies are still needed to appropriately incorporate this effect into inferences of an accurate Hubble constant.

Keywords: Gravitational microlensing, Strong gravitational lensing, Quasar microlensing
Bi-lognormal Distribution of Sunspot Group Areas. We use daily observations from the Royal Greenwich Observatory and Kislovodsk Mountain Astronomical Station of Pulkovo Observatory to study the distribution properties of sunspot areas. To mitigate the poor statistics in the distribution of small areas, we introduce a "precision randomization" approach based on the assumption that all measured areas have a random component within the measurement uncertainty of 1 millionth of the solar hemisphere (M.S.H.). We confirm the presence of two distinct components in the distribution of sunspots previously reported by several authors, and show that the area distribution is described by the sum of two lognormal distributions responsible for small and large groups (sunspots), respectively. We also demonstrate that the area of the main spots in the groups correlates well with the total area of the group, and, thus, the findings derived for the total group areas are equally applicable to the main spots of groups.

Keywords: Sunspots
The Iron Line Profile from Warped Black Hole Accretion Disks. The profile of the fluorescent iron line from black hole accretion disks is a powerful diagnostic of black hole properties, such as spin and inclination. The state of the art, however, considers an accretion disk whose angular momentum is aligned with that of the black hole; this is a very constraining assumption that is unlikely to apply to many astrophysical systems. Here, we present the first simulation of the reflection spectrum from warped accretion disks using a realistic model of the reflected emission based on the XILLVER code. We present the effects that the radial location of the warp and the tilt angle have on the line profile, showing that the affect becomes significant at relatively low angles, between 5° and 15°. We highlight that the results are highly dependent on the azimuth position of the observer relative to the tilt angle. We fit these profiles in XSPEC with the standard relxill lamppost model to quantify the effect that neglecting the disk warps has on the inferred black hole spins and inclinations, finding that the spin parameter can be off by as much as 0.2. We show that fits with two-component relxill can be used to derive more accurate parameter estimates and can recover the radial location of the warp.

Keywords: High energy astrophysics, Atomic spectroscopy, Black holes, Relativistic disks
Decihertz Gravitational Waves from Double White Dwarf Merger Remnants. Close binaries of double white dwarfs (DWDs) inspiral and merge by emitting gravitational waves (GWs). Orbital motion of some of these binaries is expected to be observed at a low-frequency band by space-borne laser interferometric detectors of GWs. The merger remnant may suffer thermonuclear runaway and explode as SNe Ia if they are massive enough. As GW sources, the remnants have so far been scarcely studied. Here we propose a new mechanism of GW emission from DWD merger remnants that may be observed by planned GW detectors in a decihertz frequency band. A remnant is temporarily expected to have a high degree of differential rotation as a consequence of the merger process. It is then unstable to oscillation modes whose azimuthal pattern speed coincides with the stellar rotation. We solve the eigenvalue problem of differentially rotating remnants and identify unstable eigenmodes, which may be categorized to inertial modes. The estimate of characteristic strain of GWs shows that they may be detectable within the distance of the Virgo cluster by planned gravitational wave observatories targeting the decihertz band.

Keywords: Close binary stars, White dwarf stars, Gravitational wave sources
Origin of the UV to X-Ray Emission of Radio Galaxy NGC 1275 Explored by Analyzing Its Variability. We analyze the ultraviolet (UV) and X-ray data of NGC 1275 obtained with Swift/UV/Optical Telescope (UVOT), X-ray Telescope (XRT), Burst Alert Telescope (BAT) and Fermi Large Area Telescope over about 10 yr to investigate the origin of the nuclear emission from NGC 1275. We confirm that the UV and soft/hard X-ray fluxes gradually increased along with the GeV gamma rays. At times, short-term variations in the UV or soft X-ray spectral regions showed rapid variations correlated with the GeV gamma rays. However there was no significant correlation between the UV and soft X-rays. The UV spectrum had a narrow spectral shape that could be represented by single-temperature blackbody radiation. These results could possibly indicate that the long-term variability of UV and X-ray emissions is caused by the jet, while the emissions from the accretion disk contribute to the UV and X-ray bands to some extent.

Keywords: Seyfert galaxies, Galaxy jets
Line Identification and Excitation of Autoionizing States in a Late-type, Low-mass Wolf-Rayet Star. Identifications of a large fraction of previously unidentified lines in the complex spectrum of the low mass, late-type LMC [WC11] star J060819.93-715737.4 have been made utilizing electronic databases. There are an exceptionally large number of C II emission lines originating from autoionizing (AI) levels. Resonance fluorescence between the C II ground state and excited AI levels is shown to be an important photoabsorption process that is competitive with dielectronic recombination in exciting AI emission lines in stellar winds, and has broad application to many types of emission-line stars. In addition, numerous C II quartet multiplets appear in emission that are not excited directly by recombination or resonance fluorescence, signifying high wind densities in the emission region that enhance collisional transfer between doublet and quartet states.

Keywords: WC stars, Stellar spectral lines
Strong Mg II and Fe II Absorbers at 2.2 &lt; z &lt; 6.0. We present a study of strong intervening absorption systems in the near-IR spectra of 31 luminous quasars at z &gt; 5.7. The quasar spectra were obtained with Gemini GNIRS that provide continuous wavelength coverage from ∼0.9 to ∼2.5 μm. We detect 32 strong Mg II doublet absorbers with rest-frame equivalent width Wr(λ2796) &gt; 1.0 Å at 2.2 &lt; z &lt; 6.0. Each Mg II absorber is confirmed by at least two associated Fe II absorption lines in the rest-frame wavelength range of ∼1600-2600 Å. We find that the comoving line density (dN/dX) of the strong Fe II-bearing Mg II absorbers decreases toward higher redshift at z &gt; 3, consistent with previous studies. Compared with strong Mg II absorbers detected in damped Lyα systems at 2 &lt; z &lt; 4, our absorbers are potentially less saturated and show much larger rest-frame velocity widths. This suggests that the gas traced by our absorbers are potentially affected by galactic superwinds. We analyze the Hubble Space Telescope near-IR images of the quasars and identify possible associated galaxies for our strong absorbers. There are a maximum of two galaxy candidates found within 5″ radius of each absorber. The median F105W-band magnitude of these galaxy candidates is 24.8 mag, which is fainter than the L* galaxy luminosity at z ∼ 4. By using our observed dN/dX of strong Mg II absorbers and galaxy candidates median luminosity, we suggest that at high redshift, strong Mg II absorbers tend to have a more disturbed environment but smaller halo size than that at z &lt; 1.

Keywords: Extragalactic astronomy, Quasar absorption line spectroscopy, Circumgalactic medium
The Maximum Energy of Shock-accelerated Electrons in a Microturbulent Magnetic Field. Relativistic shocks propagating into a medium with low magnetization are generated and sustained by small-scale but very strong magnetic field turbulence. This so-called "microturbulence" modifies the typical shock acceleration process, and in particular that of electrons. In this work we perform Monte Carlo (MC) simulations of electrons encountering shocks with microturbulent fields. The simulations cover a three-dimensional parameter space in shock speed, acceleration efficiency, and peak magnetic field strength. From these, a Markov Chain Monte Carlo (MCMC) method was employed to estimate the maximum electron momentum from the MC-simulated electron spectra. Having estimated this quantity at many points well-distributed over an astrophysically relevant parameter space, an MCMC method was again used to estimate the parameters of an empirical formula that computes the maximum momentum of a Fermi-accelerated electron population anywhere in this parameter space. The maximum energy is well-approximated as a broken power law in shock speed, with the break occurring when the shock decelerates to the point where electrons can begin to escape upstream from the shock.

Keywords: Gamma-ray bursts, Markov chain Monte Carlo, Shocks, Magnetic fields, Cosmic rays
Generally Applicable Formalism for Modeling the Observable Signatures of Inflows, Outflows, and Moving Coronal Plasma Close to Kerr Black Holes. We present a generally applicable formalism for modeling the emission, absorption, reflection, and reprocessing of radiation by moving plasma streams close to a Kerr black hole. The formalism can be used to investigate the observational signatures of a wide range of phenomena, including (i) the reflection of coronal X-ray radiation off plasma plunging from the inner edge of a black hole accretion disk toward the black hole, (ii) the reflection of coronal X-ray emission off the upper layers of a geometrically thick accretion flow, (iii) the illumination of the accretion disk by a corona moving with relativistic velocities toward or away from the accretion disk, and (iv) the emission from a jet forming close to the black hole. After introducing the general relativistic treatment, we show the results for a fast wind forming close to a Kerr black hole. The approach presented here can be used to model X-ray spectral, timing, reverberation, and polarization data.

Keywords: Black hole physics, Kerr black holes, Quasars
The Diagnostic Potential of JWST in Characterizing Elusive AGNs. It is now clear that a significant population of accreting black holes are undetected by commonly employed optical, mid-infrared color, X-ray, and radio selection methods as a result of obscuration or contamination of the emission from the nuclear region caused by star formation in the host galaxy. These elusive active galactic nuclei (AGNs) are an important component of the AGN population. They are often found in mergers, where significant black hole growth likely takes place, and in the lowest-mass galaxies or galaxies that lack classical bulges, a demographic that places important constraints on models of supermassive black hole seed formation and merger-free models of AGN fueling. In this work, we demonstrate the power of the James Webb Space Telescope (JWST) in uncovering and characterizing these elusive AGNs. We present an integrated modeling approach in which both the line and emergent continuum are predicted from gas exposed to the ionizing radiation from a young starburst and an AGN, focusing specifically on the spectral diagnostics available through JWST, and provide predictions on the detectability of key diagnostic lines by the near- and mid-infrared spectrometers, assuming typical conditions for the gas. We demonstrate the crucial need for JWST in uncovering low-level accretion activity even in nearby galaxies and out to redshifts of ≈1-3, depending on the ionization parameter, and gas phase metallicity. We present a redshift-dependent selection strategy that can be used to identify promising elusive AGN candidates for future follow-up study. The full suite of simulations is available online, where users can select specific parameters and retrieve the predicted continuum and infrared line luminosities from our models.

Keywords: AGN host galaxies, Intermediate-mass black holes, Photoionization, Infrared astronomy, Low-luminosity active galactic nuclei, Active galactic nuclei, Galaxy mergers, Interstellar medium, Astrophysical black holes
Linking Soft Excess in Ultraluminous X-Ray Sources with Optically Thick Wind Driven by Supercritical Accretion. Supercritical accretion onto compact objects may drive massive winds that are nearly spherical, optically thick, and Eddington limited. Blackbody emission from the photosphere is the direct observational signature of the wind. Here we investigate whether or not it can explain the soft emission component seen in the energy spectra of ultraluminous X-ray sources (ULXs). Based on high-quality XMM-Newton spectra of 15 ULXs, we find that the soft component can be modeled as blackbody emission with a nearly constant luminosity, and the five known pulsating ULXs (PULXs) in the sample display a blackbody luminosity among the lowest. These are consistent with the scenario that the soft emission originates from the photosphere of the optically thick wind. However, the derived blackbody luminosity for PULXs is significantly above the Eddington limit for neutron stars. A possible explanation is that a considerable fraction of the optically thick wind roots in the inner accretion flow, where the radiative flux could exceed the Eddington limit due to a reduced scattering cross-section or enhanced radiation transfer with magnetic buoyancy. Based on a wind model, the inferred mass accretion rate in these standard ULXs overlaps but is on average lower than that in luminous and very soft X-ray sources, which are also candidates with supercritical accretion. Alternatively, it cannot be ruled out that the soft emission component is a result of the hard component, e.g., via down-scattering in a cool medium, as a weak correlation may exist between them.

Keywords: Stellar accretion, X-ray binary stars, X-ray sources, Compact objects
The Impact of Kinetic Neutrals on the Heliotail. The shape of the heliosphere is thought to resemble a long, comet tail, however, recently it has been suggested that the heliosphere is tailless with a two-lobe structure. The latter study was done with a three-dimensional (3D) magnetohydrodynamic code, which treats the ionized and neutral hydrogen atoms as fluids. Previous studies that described the neutrals kinetically claim that this removes the two-lobe structure of the heliosphere. In this work, we use the newly developed Solar-wind with Hydrogen Ion Exchange and Large-scale Dynamics (SHIELD) model. SHIELD is a self-consistent kinetic-MHD model of the outer heliosphere that couples the MHD solution for a single plasma fluid from the BATS-R-US MHD code to the kinetic solution for neutral hydrogen atoms solved by the Adaptive Mesh Particle Simulator, a 3D, direct simulation Monte Carlo model that solves the Boltzmann equation. We use the same boundary conditions as our previous simulations using multi-fluid neutrals to test whether the two-lobe structure of the heliotail is removed with a kinetic treatment of the neutrals. Our results show that despite the large difference in the neutral hydrogen solutions, the two-lobe structure remains. These results are contrary to previous kinetic-MHD models. One such model maintains a perfectly ideal heliopause and does not allow for communication between the solar wind and interstellar medium. This indicates that magnetic reconnection or instabilities downtail play a role for the formation of the two-lobe structure.

Keywords: Heliopause, Magnetohydrodynamics, Stellar wind bubbles, Heliosphere, Termination shock, Solar wind termination, Heliosheath, Magnetohydrodynamical simulations
Black Hole Accretion Correlates with Star Formation Rate and Star Formation Efficiency in Nearby Luminous Type 1 Active Galaxies. We investigate the relationship between black hole accretion and star formation in a sample of 453 z ≈ 0.3 type 1 active galactic nuclei (AGNs). We use available CO observations to demonstrate that the combination of nebular dust extinction and metallicity provides reliable estimates of the molecular gas mass even for the host galaxies of type 1 AGNs. Consistent with other similar but significantly smaller samples, we reaffirm the notion that powerful AGNs have comparable gas content as nearby star-forming galaxies and that AGN feedback does not deplete the host of cold gas instantaneously. We demonstrate that while the strong correlation between star formation rate and black hole accretion rate is in part driven by the mutual dependence of these parameters on molecular gas mass, the star formation rate and black hole accretion rate are still weakly correlated after removing the dependence of star formation rate on molecular gas mass. This, together with a positive correlation between star formation efficiency and black hole accretion rate, may be interpreted as evidence for positive AGN feedback.

Keywords: Quasars, Active galaxies, Galaxy nuclei, Seyfert galaxies, Interstellar medium
Disks as Inhomogeneous, Anisotropic Gaussian Random Fields. We model astrophysical disk surface brightness fluctuations as an inhomogeneous, anisotropic, time-dependent Gaussian random field. The field locally obeys the stochastic partial differential equation of a Matérn field, which has a power spectrum that is flat at large scales and falls off as a power law at small scales. We provide a series of pedagogical examples and along the way provide a convenient parameterization for the local covariance. We then consider two applications to disks. In the first we generate an animation of a disk. In the second, by integrating over an animation of a disk, we generate synthetic light curves and show that the high frequency slope of the resulting power spectrum depends on the local covariance model. We finish with a summary and a brief discussion of other possible astrophysical applications.

Keywords: Accretion, Computational methods, Astrostatistics techniques, Black holes
Flare Activity and Magnetic Feature Analysis of the Flare Stars. II. Subgiant Branch. We present an investigation of the magnetic activity and flare characteristics of the subgiant stars mostly from F and G spectral types and compare the results with the main-sequence (MS) stars. The light curve of 352 stars on the subgiant branch (SGB) from the Kepler mission is analyzed in order to infer stability, relative coverage, and contrast of the magnetic structures and also flare properties using three flare indexes. The results show the following. (i) Relative coverage and contrast of the magnetic features along with rate, power, and magnitude of flares increase on the SGB due to the deepening of the convective zone and more vigorous magnetic field production. (ii) Magnetic activity of the F- and G-type stars on the SGB does not show dependency on the rotation rate and does not obey the saturation regime. This is the opposite of what we saw for the MS, in which the G-, K-, and M-type stars show clear dependency on the Rossby number. (iii) The positive relationship between the magnetic features' stability and their relative coverage and contrast remains true on the SGB; though, it has a lower dependency coefficient in comparison with the MS. (iv) Magnetic proxies and flare indexes of the SGB stars increase with increasing relative mass of the convective zone.

Keywords: Starspots, Magnetic stars, Main sequence, K subgiant stars, Stellar activity, Flare stars, F subgiant stars, G subgiant stars
CMB Cold Spot in the Planck Light. The Cold Spot, with an unusually cold region surrounded by a hot ring, is a statistically significant anomaly in the cosmic microwave background (CMB) sky. In this work we assess whether different sets of multiple subvoids based on the 2dF-VST ATLAS Cold Spot galaxy redshift survey or a collapsing cosmic texture could have produced such an anomaly through a simultaneous search for their gravitational redshift and lensing signatures on the Planck CMB temperature anisotropies. We use patches with radii R = 10° and R = 20° to account for the inner cold region as well as the outer hot ring. As the void model, we explore two sets of ΛLTB templates characterized by different values of the model's free parameters, and a top-hat void template. We detect higher than expected gravitational redshift amplitudes for the first two sets, ${{ \mathcal A }}_{\mathrm{rs}}=5.4\pm 1.4$ and ${{ \mathcal A }}_{\mathrm{rs}}=14.4\pm 3.8$ , and lower than expected for the top-hat model, ${{ \mathcal A }}_{\mathrm{rs}}=0.3\pm 0.1$ . The amplitudes for the lensing imprint are consistent with zero for all these subvoid models. The estimated amplitude for the texture imprint from the gravitational redshift measurement implies the energy scale of the texture, parameterized by ɛ, to be ɛ = (7.6 ± 2.0) × 10-5, with no detection of the lensing trace. We note that the deviation of the subvoid amplitudes from unity and the inability of the texture and some of the void profiles to reproduce the hot ring indicate theoretical insufficiencies, either in the construction of the model or in the assumed gravitational and cosmological framework leading to the imprints for the structures.

Keywords: Cosmology, Astronomy data acquisition, Observational cosmology, Cosmic microwave background radiation, Astronomy data analysis