Sazuna/UAT_keywords huggingface dataset:
Study Turbulence and Probe Magnetic Fields Using the Gradient Technique: Application to H I-to-H<SUB>2</SUB> Transition Regions. The atomic-to-molecular (H I-to-H2) transition in photodissociation regions (PDRs) has been investigated over the past several decades through analytic and numerical modeling. However, classical PDR models typically assume a uniform-density gas, ignoring the turbulent nature of the interstellar medium. Recently, Bialy et al. have presented a theoretical framework for studying the H I-to-H2 transition in a realistic turbulent medium with a nonhomogeneous density structure. Here we extend these turbulent-chemical models to explore the possibility of tracing the magnetic field direction in turbulent PDRs using the gradient technique. We utilize both subsonic and supersonic magnetohydrodynamic numerical simulations for chemical H I/H2 balance calculations. We confirm that the density fluctuations induced by turbulence can disperse the distribution of the H2 and H I fractions. We find that the energy spectrum of moment maps gets shallower when the sonic Mach number MS increases. We explore the ability in magnetic field tracing of gradients of higher-order velocity centroids and compare their performance with that of traditional velocity centroid gradients (VCGs) and with intensity gradients (IGs). We find that the velocity gradients of the second-order centroids (VC2Gs) are more accurate than VCGs and IGs in probing the magnetic field orientation.

Keywords: Interstellar magnetic fields, Interstellar dynamics, Interstellar medium
Synchrotron Intensity and Polarization Gradients: Tools to Obtain the Magnetization Level in a Turbulent Medium. Synchrotron intensity and polarization gradients (SIG and SPG), proposed by Lazarian et al. and Lazarian &amp; Yuen, present a new way to recover the mean magnetic field direction in the plane of the sky. To measure the magnetization level, Lazarian et al. suggested that the methods used in the context of the "Velocity Gradient Technique" could also be used on the SIG and SPG contexts. In this work we test the two proposed methods, named "top-base" and the circular standard deviation, "S," to obtain the level of magnetization from synchrotron emission. In order to test the methods, we generate synthetic observations from magnetohydrodynamic computer simulations, with Alfvénic Mach numbers, MA ∈ [0.2,1.7]. Using a Bayesian analysis we find that the circular standard deviations for the SIG and SPG methods are able to recover the magnetization for cases with signal-to-noise ratio ≳5. We found that for weak Faraday depolarization and different angles between the magnetic field direction and the line of sight the magnetization level can still be estimated.

Keywords: Interstellar medium, Magnetohydrodynamics, Interstellar synchrotron emission, Interstellar plasma
JWST Transit Spectra. I. Exploring Potential Biases and Opportunities in Retrievals of Tidally Locked Hot Jupiters with Clouds and Hazes. The atmospheres on tidally locked planets likely exhibit large differences between their day- and night-sides. In this paper, we illustrate how the combined effects of aerosols and day-night temperature gradients shape transit spectra of tidally locked exoplanets and evaluate the implications for retrievals of atmospheric properties. We have developed a new code, Multi-dimensional Exoplanet TransIt Spectra (METIS), which can compute transit spectra for arbitrary longitude-latitude-altitude grids of temperature and pressure. Using METIS, we pair flexible treatments of clouds and hazes with simple parameterized day-night temperature gradients to compute transit spectra and perform retrieval experiments across a wide array of possible exoplanet atmospheric properties. Our key findings are that: (1) the presence of aerosols can increase the effects of day-night temperature gradients on transit spectra; (2) ignoring day-night temperature gradients when attempting to perform Bayesian parameter estimation will return biased results, even when aerosols are present; (3) when a day-night temperature gradient is accounted for in the retrieval, some spectra contain sufficient information to constrain temperatures and the width of the transition from day to night. The presence of clouds and hazes can actually tighten such constraints, but also weaken constraints on metallicity and reference pressure. These last findings are predicated on the assumptions made in parameterizing the day-night atmospheric structure and the assumption of thermochemical equilibrium. Our results imply that this may be a promising avenue to pursue and represent a step toward the larger goal of developing models and theory of adequate complexity to match the superior-quality data that will soon be available.

Keywords: Hot Jupiters, Exoplanet atmospheres, Transmission spectroscopy
SCORCH. III. Analytical Models of Reionization with Varying Clumping Factors. In the Simulations and Constructions of the Reionization of Cosmic Hydrogen (SCORCH) project, we compare analytical models of the hydrogen ionization fraction with radiation-hydrodynamic simulations. We derive analytical models of the mass-weighted hydrogen ionization fraction from the local ionization balance equations as a more accurate alternative to the widely adopted model based on the volume filling factor. In particular, our model has a recombination term quadratic in the ionization fraction, which is consistent with the two-body interaction nature of recombination. Then, we use the radiation-hydrodynamic simulations to study the clumping factors needed to solve the analytical equations and provide accurate fitting functions. We find that the ionized hydrogen clumping factors from our radiative transfer simulations are significantly different than those from other simulations that use a uniform photoionization background. In addition to redshift dependence, we also see the dependence of the ionized hydrogen clumping factor on ionization fraction, and we incorporate this into our fits. We calculate the reionization histories using our analytical models and clumping factors and compare with widely adopted models, and all of our models achieve &lt;7% difference from simulation results, while the other models have &gt;20% deviations. The Thomson optical depths from reionization calculated from our analytical models result in &lt;5% deviation from simulations, while the previous analytical models have a &gt;20% difference and could result in biased conclusions of the intergalactic medium reionization.

Keywords: Radiative transfer simulations, Reionization, Large-scale structure of the universe
Characterizing the Circumgalactic Medium of the Lowest-mass Galaxies: A Case Study of IC 1613. Using 10 sight lines observed with the Hubble Space Telescope/Cosmic Origins Spectrograph, we study the circumgalactic medium (CGM) and outflows of IC 1613, which is a low-mass (M* ∼ 108 M⊙), dwarf irregular galaxy on the outskirts of the Local Group. Among the sight lines, four are pointed toward UV-bright stars in IC 1613, and the other six sight lines are background QSOs at impact parameters from 6 kpc (&lt;0.1R200) to 61 kpc (0.6R200). We detect a number of Si II, Si III, Si IV, C II, and C IV absorbers, most of which have velocities less than the escape velocity of IC 1613 and thus are gravitationally bound. The line strengths of these ion absorbers are consistent with the CGM absorbers detected in dwarf galaxies at low redshifts. Assuming that Si II, Si III, and Si IV comprise nearly 100% of the total silicon, we find 3% (∼8 × 103 M⊙), 2% (∼7 × 103 M⊙), and 32%-42% [∼(1.0-1.3) × 105 M⊙] of the silicon mass in the stars, interstellar medium, and within 0.6R200 of the CGM of IC 1613. We also estimate the metal outflow rate to be ${\dot{{\rm{M}}}}_{\mathrm{out},{\rm{Z}}}\geqslant 1.1\times {10}^{-5}\,{{\rm{M}}}_{\odot }\,{\mathrm{yr}}^{-1}$ and the instantaneous metal mass loading factor to be ηZ ≥ 0.004, which are in broad agreement with available observation and simulation values. This work is the first time a dwarf galaxy of such low mass is probed by a number of both QSO and stellar sight lines, and it shows that the CGM of low-mass, gas-rich galaxies can be a large reservoir enriched with metals from past and ongoing outflows.

Keywords: Local Group, Dwarf irregular galaxies, Magellanic Stream, Circumgalactic medium, Metallicity
Noninteracting Black Hole Binaries with Gaia and LAMOST. Until recently, black holes (BHs) could be discovered only through accretion from other stars in X-ray binaries, or in merging double compact objects. Improvements in astrometric and spectroscopic measurements have made it possible to detect BHs also in noninteracting BH binaries (nBHBs) through a precise analysis of the companion's motion. In this study, using an updated version of the StarTrack binary-star population modeling code and a detailed model of the Milky Way (MW) galaxy, we calculate the expected number of detections for Gaia and LAMOST surveys. We develop a formalism to convolve the binary population synthesis output with a realistic stellar density distribution, star formation history (SFH), and chemical evolution for the MW, which produces a probability distribution function of the predicted compact-binary population over the MW. This avoids the additional statistical uncertainty that is introduced by methods that Monte Carlo sample from binary population synthesis output to produce one potential specific realization of the MW compact-binary distribution, and our method is also comparatively fast to such Monte Carlo realizations. Specifically, we predict ∼41-340 nBHBs to be observed by Gaia, although the numbers may drop to ∼10-70 if the recent (≲100 Myr) star formation is low (∼1 M⊙ yr-1). For LAMOST we predict ≲14 detectable nBHBs, which is lower partially because its field of view covers just ∼6% of the Galaxy.

Keywords: Computational astronomy, Binary stars, Astronomy databases, Stellar mass black holes, Gravitational wave sources, Astrostatistics, Spectroscopic binary stars, Astrometric binary stars, Markov chain Monte Carlo
The Global Stability of M33 in MOND. The dynamical stability of disk galaxies is sensitive to whether their anomalous rotation curves are caused by dark matter halos or Milgromian dynamics (MOND). We investigate this by setting up a MOND model of M33. We first simulate it in isolation for 6 Gyr, starting from an initial good match to the rotation curve (RC). Too large a bar and bulge form when the gas is too hot, but this is avoided by reducing the gas temperature. A strong bar still forms in 1 Gyr, but rapidly weakens and becomes consistent with the observed weak bar. Previous work showed this to be challenging in Newtonian models with a live dark matter halo, which developed strong bars. The bar pattern speed implies a realistic corotation radius of 3 kpc. However, the RC still rises too steeply, and the central line-of-sight velocity dispersion (LOSVD) is too high. We then add a constant external acceleration field of 8.4 × 10-12 m s-2 at 30° to the disk as a first-order estimate for the gravity exerted by M31. This suppresses buildup of material at the center, causing the RC to rise more slowly and reducing the central LOSVD. Overall, this simulation bears good resemblance to several global properties of M33, and highlights the importance of including even a weak external field on the stability and evolution of disk galaxies. Further simulations with a time-varying external field, modeling the full orbit of M33, will be needed to confirm its resemblance to observations.

Keywords: Hydrodynamical simulations, Stellar dynamics, Triangulum Galaxy, Galaxy evolution, Barred spiral galaxies, Modified Newtonian dynamics
Hot Jupiter and Ultra-cold Saturn Formation in Dense Star Clusters. The discovery of high incidence of hot Jupiters in dense clusters challenges the field-based hot Jupiter formation theory. In dense clusters, interactions between planetary systems and flyby stars are relatively common. This has a significant impact on planetary systems, dominating hot Jupiter formation. In this paper, we perform high precision, few-body simulations of stellar flybys and subsequent planet migration in clusters. A large parameter space exploration demonstrates that close flybys that change the architecture of the planetary system can activate high eccentricity migration mechanisms: LK and planet-planet scattering, leading to high hot Jupiter formation rate in dense clusters. Our simulations predict that many of the hot Jupiters are accompanied by "ultra-cold Saturns," expelled to apastra of thousands of astronomical units. This increase is particularly remarkable for planetary systems originally hosting two giant planets with semimajor axis ratios of ∼4 and the flyby star approaching nearly perpendicular to the planetary orbital plane. The estimated lower limit to the hot Jupiter formation rate of a virialized cluster is $\sim 1.6\times {10}^{-4}{(\sigma /1\mathrm{km}{{\rm{s}}}^{-1})}^{5}{({a}_{{\rm{p}}}/20\mathrm{au})({M}_{{\rm{c}}}/1000{M}_{\odot })}^{-2}$ Gyr-1 per star, where σ is the cluster velocity dispersion, ap is the size of the planetary system, and Mc is the mass of the cluster. Our simulations yield a hot Jupiter abundance that is ∼50 times smaller than that observed in the old open cluster M67. We expect that interactions involving binary stars, as well as a third or more giant planets, will close the discrepancy.

Keywords: Hot Jupiters, Stellar dynamics, Planetary system formation, Planetary science, N-body simulations
Estimation of Turbulent Heating of Solar Wind Protons at 1 au. The paper presents a new method for deriving turbulent heating of the solar wind using plasma moments and magnetic field data. We develop the method and then apply it to compute the turbulent heating of the solar wind proton plasma at 1 au. The method employs two physical properties of the expanding solar wind plasma, the wave-particle thermodynamic equilibrium, and the transport of entropic rate. We analyze plasma moments and field data taken from Wind S/C, in order to compute (i) the fluctuating magnetic energy, (ii) the corresponding correlation length, and (iii) the turbulent heating rate. We identify their relationships with the solar wind speed, as well as the variation of these relationships relative to solar wind and interplanetary coronal mass ejection plasma.

Keywords: Space plasmas, Solar wind, Plasma astrophysics, Heliosphere
A Herschel Mapping of [{C}{II}],[{O}{I}], and [{O}{III}] Lines from the Circumnuclear Region of M31. The circumnuclear region of M31, consisting of multiphase interstellar media, provides a close-up view of the interaction of the central supermassive black hole and surrounding materials. Far-infrared (FIR) fine-structure lines and their flux ratios can be used as diagnostics of physical properties of the neutral gas in this region. Here we present the first FIR spectroscopic mapping of the circumnuclear region of M31 in [C II] 158 μm, [O I] 63 μm, and [O III] 88 μm lines with the Herschel Space Observatory, covering an ∼500 × 500 pc (2' × 2') field. Significant emissions of all three lines are detected along the so-called nuclear spiral across the central kiloparsec of M31. The velocity field under a spatial resolution of ∼50 pc of the three lines are broadly consistent and also consistent with previous CO(3-2) line observations in the central region. Combined with existing [C II] and CO(3-2) observations of five other fields targeting the disk, we derived the radial distribution of [C II]/CO(3-2) flux ratio, and found that this ratio is higher in the center than in the disk, indicating a low gas density and strong radiation field in the central region. We also found that the [C II]/FIR ratio in the central region is 5.4 (±0.8) × 10-3, which exhibits an increasing trend with the galactocentric radius, suggesting an increasing contribution from the old stellar population to dust heating toward the center.

Keywords: Andromeda Galaxy, Interstellar atomic gas, Interstellar medium, Galaxy nuclei
A Model for Coronal Inflows and In/Out Pairs. This report presents a three-dimensional (3D) numerical magnetohydrodynamics (MHD) model of the white-light coronagraph observational phenomena known as coronal inflows and in/out pairs. Coronal inflows in the Large Angle and Spectrometric Coronagraph/C2 field of view (approximately $2\mbox{--}6\,{R}_{\odot }$ ) were thought to arise from the dynamic and intermittent release of solar wind plasma associated with the helmet streamer belt as the counterpart to outward-propagating streamer blobs, formed by magnetic reconnection. This interpretation was essentially confirmed with the subsequent identification of in/out pairs and the multispacecraft observations of their 3D structure. The MHD simulation results show relatively narrow lanes of density depletion form high in the corona and propagate inward with sinuous motion that has been characterized as "tadpole-like" in coronagraph imagery. The height-time evolution and velocity profiles of the simulation inflows and in/out pairs are compared to their corresponding observations and a detailed analysis of the underlying magnetic field structure associated with the synthetic white-light and mass density evolution is presented. Understanding the physical origin of this structured component of the slow solar wind's intrinsic variability could make a significant contribution to solar wind modeling and the interpretation of remote and in situ observations from Parker Solar Probe and Solar Orbiter.

Keywords: Solar coronal transients, Magnetohydrodynamics, Solar magnetic reconnection, Solar magnetic fields, Active solar corona, Solar coronal streamers
Repeating Fast Radio Bursts from Pulsar-Asteroid Belt Collisions: Frequency Drifting and Polarization. Fast radio bursts (FRBs) are a new kind of extragalactic radio transients. Some of them show repeating behaviors. Recent observations indicate that a few repeating FRBs (e.g., FRB 121102) present time-frequency downward drifting patterns and nearly 100% linear polarization. Following the model of Dai et al. who proposed that repeating FRBs may originate from a slowly rotating, old-aged pulsar colliding with an asteroid belt around a stellar-mass object, we focus on the prediction of time-frequency drifting and polarization. In this scenario, the frequency drifting is mainly caused by the geometric structure of a pulsar magnetosphere, and the drifting rate-frequency index is found to be 25/17. On the other hand, by considering the typical differential mass distribution of incident asteroids, we find that an asteroid with mass m ≳ 1017 g colliding with the pulsar would contribute abundant gravitational energy, which powers an FRB. A broad frequency band of the FRBs would be expected, due to the mass difference of the incident asteroids. In addition, we simulate the linear polarization distribution for the repeating FRBs, and constrain the linear polarization with ≳30% for the FRBs with flux of an order of magnitude lower than the maximum flux.

Keywords: Neutron stars, Asteroids, Radio bursts, Radio transient sources
Stellar Tidal Disruption Events with Abundances and Realistic Structures (STARS): Library of Fallback Rates. We present the STARS library, a grid of tidal disruption event (TDE) simulations interpolated to provide the mass fallback rate (dM/dt) to the black hole for a main-sequence star of any stellar mass, stellar age, and impact parameter. We use a one-dimensional stellar evolution code to construct stars with accurate stellar structures and chemical abundances, then perform tidal disruption simulations in a three-dimensional adaptive-mesh hydrodynamics code with a Helmholtz equation of state, in unprecedented resolution: from 131 to 524 cells across the diameter of the star. The interpolated library of fallback rates is available on GitHub (github.com/jamielaw-smith/STARS_library) and version 1.0.0 is archived on Zenodo; one can query the library for any stellar mass, stellar age, and impact parameter. We provide new fitting formulae for important disruption quantities ( ${\beta }_{\mathrm{crit}},{\rm{\Delta }}M,{\dot{M}}_{\mathrm{peak}},{t}_{\mathrm{peak}},{n}_{\infty }$ ) as a function of stellar mass, stellar age, and impact parameter. Each of these quantities varies significantly with stellar mass and stellar age, but we are able to reduce all of our simulations to a single relationship that depends only on stellar structure, characterized by a single parameter ${\rho }_{c}/\bar{\rho }$, and impact parameter β. We also find that, in general, more centrally concentrated stars have steeper dM/dt rise slopes and shallower decay slopes. For the same ΔM, the dM/dt shape varies significantly with stellar mass, promising the potential determination of stellar properties from the TDE light curve alone. The dM/dt shape depends strongly on stellar structure and to a certain extent stellar mass, meaning that fitting TDEs using this library offers a better opportunity to determine the nature of the disrupted star and the black hole.

Keywords: Black hole physics, Hydrodynamics, Gravitation, Tidal disruption, Active galaxies, Galaxy nuclei, Main sequence stars
Coherent Events at Ion Scales in the Inner Heliosphere: Parker Solar Probe Observations during the First Encounter. The Parker Solar Probe mission has shown the ubiquitous presence of strong magnetic field deflections, namely switchbacks, during its first perihelion where it was embedded in a highly Alfvénic slow stream. Here, we study the turbulent magnetic fluctuations around ion scales in three intervals characterized by a different switchback activity, identified by the behavior of the magnetic field radial component, Br. Quiet (Br does not show significant fluctuations), weakly disturbed (Br has strong fluctuations but no reversals), and highly disturbed (Br has full reversals) periods also show different behavior for ion quantities. However, the spectral analysis shows that each stream is characterized by the typical Kolmogorov/Kraichnan power law in the inertial range, followed by a break around the characteristic ion scales. This frequency range is characterized by strong intermittent activity, with the presence of noncompressive coherent events, such as current sheets, vortex-like structures, and wave packets identified as ion cyclotron modes. Although all these events have been detected in the three periods, they have different influences in each of them. Current sheets are dominant in the highly disturbed period, wave packets are the most common in the quiet interval; while, in the weakly disturbed period, a mixture of vortices and wave packets is observed. This work provides an insight into the heating problem in collisionless plasmas, fitting in the context of the new solar missions, and, especially for Solar Orbiter, which will allow an accurate magnetic connectivity analysis to link the presence of different intermittent events to the source region.

Keywords: Interplanetary turbulence, Space plasmas, Solar wind