Sazuna/UAT_keywords huggingface dataset:
Spatial Distribution of O VI Covering Fractions in the Simulated Circumgalactic Medium. We use adaptive mesh refinement cosmological simulations to study the spatial distribution and covering fraction of ${\rm{O}}\,{\rm\small{VI}}$ absorption in the circumgalactic medium (CGM) as a function of projected virial radius and azimuthal angle. We compare these simulations to an observed sample of 53 galaxies from the Multiphase Galaxy Halos Survey. Using MOCKSPEC, an absorption-line analysis pipeline, we generate synthetic quasar absorption-line observations of the simulated CGM. To best emulate observations, we studied the averaged properties of 15,000 "mock samples," each of 53 sight lines having a distribution of $D/{R}_{\mathrm{vir}}$ and sight-line orientation statistically consistent with the observations. We find that the ${\rm{O}}\,{\rm\small{VI}}$ covering fraction obtained for the simulated galaxies agrees well with the observed value for the inner halo ( $D/{R}_{\mathrm{vir}}\leqslant 0.375$ ) and is within 1.1σ in the outer halo ( $D/{R}_{\mathrm{vir}}\gt 0.75$ ), but is underproduced within $0.375\lt D/{R}_{\mathrm{vir}}\leqslant 0.75$ . The observed bimodal distribution of the ${\rm{O}}\,{\rm\small{VI}}$ covering fraction with azimuthal angle, showing a higher frequency of absorption along the projected major and minor axes of galaxies, is not reproduced in the simulations. Further analysis reveals the spatial-kinematic distribution of ${\rm{O}}\,{\rm\small{VI}}$ -absorbing gas is dominated by outflows in the inner halo mixed with an inflowing gas that originates from farther out in the halo. Though the CGM of the individual simulated galaxies exhibits spatial structure, the flat azimuthal distribution occurs because the individual simulated galaxies do not develop a CGM structure that is universal from galaxy to galaxy.

Keywords: Extragalactic astronomy, Quasar absorption line spectroscopy, Circumgalactic medium
The Evolution of Magellanic-like Galaxy Pairs and the Production of Magellanic Stream Analogs in Simulations with Tides, Ram Pressure, and Stellar Feedback. We present a series of chemodynamical simulations of Magellanic-like systems consisting of two interacting, equal-mass dwarf galaxies orbiting a massive host galaxy, including feedback and star formation, tides, and ram pressure. We study the star formation and chemical enrichment history of the dwarfs and the production of a Magellanic Stream analog. The dwarfs interact with each other through tidal forces, distorting their morphologies and triggering star formation. A stream is naturally produced as outflows, induced by feedback, and interactions are stretched by tidal forces. Counter to some recent simulations, we find that the leading arm persists even in the presence of ram pressure from the host galaxy. Interactions between the dwarfs and the host galaxies produce multiple kinematic components in the stream, as observed. A combination of ongoing star formation and entrained low-metallicity gas causes the stream to have a complex chemical structure, with an average metallicity that is generally lower than that of the dwarfs.

Keywords: Hydrodynamical simulations, Stellar feedback, Ram pressure stripped tails, Galaxy interactions, Galaxy tides, Dwarf galaxies, Magellanic Stream, Circumgalactic medium, Magellanic Clouds
Dynamically Tagged Groups of Very Metal-poor Halo Stars from the HK and Hamburg/ESO Surveys. We analyze the dynamical properties of ∼1500 very metal-poor (VMP; [Fe/H] ≲ -2.0) halo stars, based primarily on medium-resolution spectroscopic data from the HK and Hamburg/ESO surveys. These data, collected over the past 30 yr, are supplemented by a number of calibration stars and other small samples, along with astrometric information from Gaia DR2. We apply a clustering algorithm to the 4D energy-action space of the sample, and identify a set of 38 dynamically tagged groups (DTGs), containing between 5 and 30 member stars. Many of these DTGs can be associated with previously known prominent substructures such as Gaia-Sausage/Enceladus (GSE), Sequoia, Helmi Stream (HStr), and Thamnos. Others are associated with previously identified smaller dynamical groups of stars and streams. We identify 10 new DTGs as well, many of which have strongly retrograde orbits. We also investigate possible connections between our DTGs and ∼300 individual r-process-enhanced (RPE) stars from a recent literature compilation. We find that several of these objects have similar dynamical properties to GSE (5), the HStr (4), Sequoia (1), and Rg5 (1), indicating that their progenitors might have been important sources of RPE stars in the Galaxy. Additionally, a number of our newly identified DTGs are shown to be associated with at least two RPE stars each (DTG-2: 3, DTG-7: 2; DTG-27: 2). Taken as a whole, these results are consistent with ultra-faint and/or dwarf spheroidal galaxies as birth environments in which r-process nucleosynthesis took place, and then were disrupted by the Milky Way.

Keywords: R-process, Milky Way dynamics, Milky Way stellar halo, Population II stars, Milky Way evolution
Blind H I and OH Absorption Line Search: First Results with MALS and uGMRT Processed Using ARTIP. We present details of the Automated Radio Telescope Imaging Pipeline (ARTIP) and the results of a sensitive blind search for H I and OH absorbers at z &lt; 0.4 and z &lt; 0.7, respectively. ARTIP is written in Python 3.6, extensively uses the Common Astronomy Software Application tools and tasks, and is designed to enable the geographically distributed MeerKAT Absorption Line Survey (MALS) team to collaboratively process large volumes of radio interferometric data. We apply it to the first MALS data set obtained using the 64-dish MeerKAT radio telescope and 32 K channel mode of the correlator. With merely 40 minutes on target, we present the most sensitive spectrum of PKS 1830-211 ever obtained and characterize the known H I (z = 0.19) and OH (z = 0.89) absorbers. We further demonstrate ARTIP's capabilities to handle realistic observing scenarios by applying it to a sample of 72 bright radio sources observed with the upgraded Giant Metrewave Radio Telescope (uGMRT) to blindly search for H I and OH absorbers. We estimate the numbers of H I and OH absorbers per unit redshift to be n21(z ∼ 0.18) &lt; 0.14 and nOH(z ∼ 0.40) &lt; 0.12, respectively, and constrain the cold gas covering factor of galaxies at large impact parameters (50 kpc &lt; ρ &lt; 150 kpc) to be less than 0.022. Due to the small redshift path, Δz ∼ 13 for H I with column density &gt;5.4 × 1019 cm-2, the survey has probed only the outskirts of star-forming galaxies at ρ &gt; 30 kpc. MALS with the expected Δz ∼ 103-4 will overcome this limitation and provide stringent constraints on the cold gas fraction of galaxies in diverse environments over 0 &lt; z &lt; 1.5.

Keywords: Radio loud quasars, Quasar absorption line spectroscopy
Improved Fe II Emission-line Models for AGNs Using New Atomic Data Sets. Understanding the Fe II emission from active galactic nuclei (AGNs) has been a grand challenge for many decades. The rewards from understanding the AGN spectra would be immense, involving both quasar classification schemes such as "Eigenvector 1" and tracing the chemical evolution of the cosmos. Recently, three large Fe II atomic data sets with radiative and electron collisional rates have become available. We have incorporated these into the spectral synthesis code CLOUDY and examined predictions using a new generation of AGN spectral energy distribution (SED), which indicates that the ultraviolet (UV) emission can be quite different depending on the data set utilized. The Smyth et al. data set better reproduces the observed Fe II template of the I ZW 1 Seyfert galaxy in the UV and optical regions, and we adopt these data. We consider both thermal and microturbulent clouds and show that a microturbulence of ≈100 km s-1 reproduces the observed shape and strength of the so-called Fe II "UV bump." Comparing our predictions to the observed Fe II template, we derive a typical cloud density of 1011 cm-3 and photon flux of 1020 cm-2 s-1, and show that these largely reproduce the observed Fe II emission in the UV and optical. We calculate the I(Fe II)/I(Mg II) emission-line intensity ratio using our best-fitting model and obtain log(I(Fe II)/I(Mg II)) ∼ 0.7, suggesting many AGNs have a roughly solar Fe/Mg abundance ratio. Finally, we vary the Eddington ratio and SED shape as a step in understanding the Eigenvector 1 correlation.

Keywords: Photoionization, Quasars, Atomic physics, Seyfert galaxies, Active galactic nuclei, Ionization
Transition Region from Turbulent to Dead Zone in Protoplanetary Disks: Local Shearing Box Simulations. The dynamical evolution of protoplanetary disks is of key interest for building a comprehensive theory of planet formation and to explain the observational properties of these objects. Using the magnetohydrodynamics code Athena++, with an isothermal shearing box setup, we study the boundary between the active and dead zone, where the accretion rate changes and mass can accumulate. We quantify how the turbulence level is affected by the presence of a non-uniform Ohmic resistivity in the radial x direction that leads to a region of inhibited turbulence (or dead zone). Comparing the turbulent activity to that of ideal simulations, the turbulence-inhibited area shows density fluctuations and magnetic activity at its boundaries, driven by energy injection from the active (ideal) zone boundaries. We find magnetic dissipation to be significantly stronger in the ideal regions, and the turbulence penetration through the boundary of the dead zone is determined by the value of the resistivity itself, through the Ohmic dissipation process, though the thickness of the transition does not play a significant role in changing the dissipation. We investigate the 1D spectra along the shearing direction: magnetic spectra appear flat at large scales both in ideal as well as resistive simulations, though a Kolmogorov scaling over more than one decade persists in the dead zone, suggesting the turbulent cascade is determined by the hydrodynamics of the system: magnetorotational instability dynamo action is inhibited where sufficiently high resistivity is present.

Keywords: Stellar accretion disks, Star formation, Planet formation
An X-Ray- and SZ-bright Diffuse Source toward M31: A Local Hot Bridge. We report a large-scale ( $r\approx 20^\circ $ ) X-ray-bright and Sunyaev-Zeldovich (SZ)-bright diffuse enhancement toward M31, which might be a Local Hot Bridge connecting the Milky Way (MW) with M31. We subtract the Galactic emission from the all-sky O VII and O VIII emission-line measurement survey, and find that the emission of these two ions is enhanced within $r\approx 20^\circ $ projected around M31. The mean emission enhancements are 5.6 ± 1.3 L.U., and 2.8 ± 0.6 L.U. for O VII and O VIII, respectively ( $\gt 4\sigma $ for both ions). We also extract the SZ signal around M31, which suggests a surface brightness y of $2-4\times {10}^{-7}$ , an enhancement $\gt 2.5\sigma $ (and a best fit of $5.9\sigma $ ). These three measurements trace the hot gas with a temperature $\mathrm{log}\,T({\rm{K}})\gt 6$ , showing similar plateau shapes (flat within $\approx 15^\circ $ , and zero beyond ≍30°). A single-phase assumption leads to a temperature of $\mathrm{log}\,T({\rm{K}})=6.34\pm 0.03$ , which is determined by the O VII/O VIII line ratio. Combining X-ray and SZ measurements, we suggest that this feature is unlikely to be the hot halo around M31 (too massive) or in the MW (too high pressure and X-ray bright). The plateau shape may be explained by a cylinder connecting the MW and M31 (the Local Hot Bridge). We constrain its length to be about 400 kpc, with a radius of 120 kpc, a density of $\approx 2\times {10}^{-4}\mbox{--}{10}^{-3}\,{\mathrm{cm}}^{-3}$ , and a metallicity of $0.02\mbox{--}0.1\,{Z}_{\odot }$ . The baryon mass is $\gtrsim {10}^{11}\,{M}_{\odot }$ , and the oxygen mass is about $\gtrsim {10}^{8}\,{M}_{\odot }$ , which contribute to the baryon or metal budget of the Local Group.

Keywords: Local Group, Diffuse x-ray background, Sunyaev-Zeldovich effect, Circumgalactic medium
Elemental Abundances of Major Elements in the Solar Wind as Measured in Genesis Targets and Implications on Solar Wind Fractionation. We present elemental abundance data of C, N, O, Na, Mg, Al, Ca, and Cr in Genesis silicon targets. For Na, Mg, Al, and Ca, data from three different solar wind (SW) regimes are also presented. Data were obtained by backside depth profiling using secondary ion mass spectrometry. The accuracy of these measurements exceeds those obtained by in situ observations; therefore, the Genesis data provide new insights into elemental fractionation between Sun and SW, including differences between SW regimes. We integrate previously published noble gas and hydrogen elemental abundances from Genesis targets, as well as preliminary values for K and Fe. The abundances of the SW elements measured display the well-known fractionation pattern that correlates with each element's first-ionization potential (FIP). When normalized either to spectroscopic photospheric solar abundances or to those derived from CI-chondritic meteorites, the fractionation factors of low-FIP elements (K, Na, Al, Ca, Cr, Mg, Fe) are essentially identical within uncertainties, but the data are equally consistent with increasing fractionation with decreasing FIP. The elements with higher FIPs between ∼11 and ∼16 eV (C, N, O, H, Ar, Kr, Xe) display a relatively well-defined trend of increasing fractionation with decreasing FIP, if normalized to modern 3D photospheric model abundances. Among the three Genesis regimes, the fast SW displays the least elemental fractionation for almost all elements (including the noble gases) but differences are modest: for low-FIP elements, the precisely measured fast-slow SW variations are less than 3%.

Keywords: Slow solar wind, Fast solar wind, Solar wind, Chemical abundances, Solar abundances, Solar coronal mass ejections
Alfvénic Perturbations in a Sunspot Chromosphere Linked to Fractionated Plasma in the Corona. In this study, we investigate the spatial distribution of highly varying plasma composition around one of the largest sunspots of solar cycle 24. Observations of the photosphere, chromosphere, and corona are brought together with magnetic field modeling of the sunspot in order to probe the conditions that regulate the degree of plasma fractionation within loop populations of differing connectivities. We find that, in the coronal magnetic field above the sunspot umbra, the plasma has photospheric composition. Coronal loops rooted in the penumbra contain fractionated plasma, with the highest levels observed in the loops that connect within the active region. Tracing field lines from regions of fractionated plasma in the corona to locations of Alfvénic fluctuations detected in the chromosphere shows that they are magnetically linked. These results indicate a connection between sunspot chromospheric activity and observable changes in coronal plasma composition.

Keywords: Solar active region magnetic fields, Sunspots, Solar corona, Solar chromosphere, Magnetic fields
The Metallicity Dependence of the High-mass X-Ray Binary Luminosity Function. In this work, we present detailed constraints on the metallicity dependence of the high-mass X-ray binary (HMXB) X-ray luminosity function (XLF). We analyze ≈5 Ms of Chandra data for 55 actively star-forming galaxies at D ≲ 30 Mpc, with gas-phase metallicities spanning $12+\mathrm{log}({\rm{O}}/{\rm{H}})$ ≈ 7-9.2. Within the galactic footprints, our sample contains a total of 1311 X-ray point sources, of which ≈49% are expected to be HMXBs, with the remaining sources likely to be low-mass X-ray binaries (LMXBs; ≈22%) and unrelated background sources (≈29%). We construct a model that successfully characterizes the average HMXB XLF over the full metallicity range. We demonstrate that the SFR-normalized HMXB XLF shows clear trends with metallicity, showing steadily increasing numbers of luminous and ultraluminous X-ray sources ( $\mathrm{log}L$ (erg s-1) = 38-40.5) with declining metallicity. However, we find that the low-luminosity ( $\mathrm{log}L$ (erg s-1) = 36-38) HMXB XLF appears to show a nearly constant SFR scaling and slope with metallicity. Our model provides a revised scaling relation of integrated LX/SFR versus $12+\mathrm{log}({\rm{O}}/{\rm{H}})$ , and a new characterization of its SFR-dependent stochastic scatter. The general trend of this relation is broadly consistent with past studies based on integrated galaxy emission; however, our model suggests that this relation is driven primarily by the high-luminosity end of the HMXB XLF. Our results have implications for binary population synthesis models, the nature of super-Eddington accreting objects (e.g., ultraluminous X-ray sources), recent efforts to identify active galactic nucleus candidates in dwarf galaxies, and the X-ray radiation fields in the early universe during the epoch of cosmic heating at z ≳ 10.

Keywords: X-ray astronomy, X-ray binary stars, Spiral galaxies, High mass x-ray binary stars, Star formation, Compact objects, Metallicity
Red Supergiants in M31 and M33. I. The Complete Sample. The aim of this paper is to establish a complete sample of red supergiants (RSGs) in M31 and M33. The member stars of the two galaxies are selected from the near-infrared (NIR) point sources after removing the foreground dwarfs from their obvious branch in the J - H/H - K diagram with the archival photometric data taken by the UKIRT/WFCAM. This separation by NIR colors of dwarfs from giants is confirmed by the optical/infrared color-color diagrams (r - z/z - H and B - V/V - R) and the Gaia measurement of parallax and proper motion. The RSGs are then identified by their outstanding location in the members' J - K/K diagram due to high luminosity and low effective temperature. The resultant sample has 5498 and 3055 RSGs in M31 and M33 respectively, which should be complete because the lower limiting K magnitude of RSGs in both cases is brighter than the complete magnitude of the UKIRT photometry. Analysis of the control fields finds that the pollution rate in the RSG sample is less than 1%. The by-product is the complete sample of oxygen-rich asymptotic giant branch stars (AGBs), carbon-rich AGBs, thermally pulsing AGBs, and extreme AGBs. In addition, the tip-RGB is determined together with its implication on the distance modulus to M31 and M33.

Keywords: Massive stars, Andromeda Galaxy, Red supergiant stars, Triangulum Galaxy
The Rise and Emergence of Untwisted Toroidal Flux Ropes on the Sun. Magnetic flux ropes (MFRs) rising buoyantly through the Sun's convection zone are thought to be subject to viscous forces preventing them from rising coherently. Numerous studies have suggested that MFRs require a minimum twist in order to remain coherent during their rise. Furthermore, even MFRs that get to the photosphere may be unable to successfully emerge into the corona unless they are at least moderately twisted, since the magnetic pressure gradient needs to overcome the weight of the photospheric plasma. To date, however, no lower limit has been placed on the critical minimum twist required for an MFR to rise coherently through the convection zone or emerge through the photosphere. In this paper, we simulate an untwisted toroidal MFR that is able to rise from the convection zone and emerge through the photosphere as an active region that resembles those observed on the Sun. We show that untwisted MFRs can remain coherent during their rise and then pile up near the photosphere, triggering undular instability, allowing the MFR to emerge through the photosphere. We propose that the toroidal geometry of our MFR is critical for its coherent rise. Upon emergence, a pair of lobes rises into the corona. The two lobes then interact and reconnect, resulting in a localized high speed jet. The resulting photospheric magnetogram displays the characteristic salt-and-pepper structure often seen in observations. Our major result is that MFRs need not be twisted to rise coherently through the convection zone and emerge through the photosphere.

Keywords: Solar active regions, Solar magnetic flux emergence, Solar magnetic fields, Solar physics
UV/Optical Disk Thermal Reverberation in Active Galactic Nuclei: An In-depth Study with an Analytic Prescription for Time-lag Spectra. Several active galactic nuclei show correlated variations in the UV/optical range, with time delays increasing at longer wavelengths. Thermal reprocessing of the X-rays illuminating the accretion disk has been proposed as a viable explanation. In this scenario, the variable X-ray flux irradiating the accretion disk is partially reflected in X-rays and partially absorbed, thermalized, and reemitted with some delay by the accretion disk at longer wavelengths. We investigate this scenario assuming an X-ray pointlike source illuminating a standard Novikov-Thorne accretion disk around a rotating black hole. We consider all special and general relativistic effects to determine the incident X-ray flux on the disk and in propagating light from the source to the disk and to the observer. We also compute the disk reflection flux, taking into consideration the disk ionization. We investigate the dependence of the disk response function and time lags on various physical parameters, such as the black hole mass and spin; X-ray corona height, luminosity, and photon index; accretion rate; inclination; and inner/outer disk radii. We find it is important to consider relativistic effects and the disk ionization in estimating the disk response. We also find a strong nonlinearity between the X-ray luminosity and the disk response. We present an analytic function for the time-lag dependence on wavelength, which can be used to fit observed time-lag spectra. We also estimate the fraction of the reverberation signal with respect to the total flux, and we suggest possible explanations for the lack of X-ray-UV/optical correlated variations in a few sources.

Keywords: Accretion, Active galactic nuclei, Seyfert galaxies, X-ray active galactic nuclei
Fundamental Properties of Sheared/Guide Field MHD Magnetic Reconnection. The properties of the sheared/guide field magnetic reconnection (MRX) are investigated with two-dimensional MHD simulation. We simulate the spontaneous evolution from the isothermal current sheet (CS) equilibrium in which distribution of the thermodynamical quantities is symmetric about the CS. The magnetic shear is characterized by two parameters: the shear parameter and the asymmetry parameter. The asymmetry of the Alfvén speed (VA0x) perpendicular to the X-line along the CS is essential. We focus on the asymptotic self-similarly expanding phase of the evolution. This research is unique for the discussion based on the consistency across the entire MRX system, although the sheared MRX has been studied since the early 1980s. In addition to reconfirmation of the previously reported properties of the sheared MRX, the following new properties are found. (1) The reconnection jet changes to the "core-envelope structure" (a high-density core with a low-density envelope) for the sheared symmetric VA0x case but the "two-layered structure" (the high-speed, low-density layer and the medium-speed, high-density layer) for the asymmetric VA0x case. (2) The parameter dependence of the reconnection rate is clarified. The MRX is fastest for the symmetric case and slows as the asymmetry increases for any fixed shear angle. For the symmetric case, the reconnection rate has a monotonically decreasing dependence on the shear angle. (3) In the asymmetric case, the plasmas from both sides of the CS coexist on the same magnetic field lines in the larger VA0x side plasmoid. This characteristic structure suggests an efficient plasma mixing when the plasmoid breaks.

Keywords: Plasma astrophysics, Solar magnetic reconnection