Sazuna/UAT_keywords huggingface dataset:
Linear and Nonlinear Kelvin-Helmholtz Instability and Magnetohydrodynamic Wave Emission in Sheared Astrophysical Plasma Flows. The evolution of the Kelvin-Helmholtz instability (KHI) and magnetohydrodynamic (MHD) wave emission is investigated at shear-flow boundaries of magnetized plasmas. While MHD wave emission has been suggested to be only possible during the nonlinear stages, we find that there is also significant wave emission during the KHI's linear stages. These emitted MHD waves may have stronger impacts than KHI surface waves since they can act to transport energy away from the local region of the shear flow. The removal of energy from the shear-flow region, instead of just the local redistribution considered in previous studies, and its propagation away from the interface could have major implications for the evolution of astrophysical objects characterized by fast plasma flow shears.

Keywords: Galaxy clusters, Space plasmas, Magnetohydrodynamics, Heliopause, Stellar-interstellar interactions, Galaxy collisions, Galaxy accretion disks, Plasma astrophysics, Comet dynamics, Interstellar plasma, Stellar accretion disks, Interacting galaxies
The Role of Strong Magnetic Fields in Stabilizing Highly Luminous Thin Disks. We present and analyze a set of three-dimensional, global, general relativistic radiation magnetohydrodynamic simulations of thin, radiation-pressure-dominated accretion disks surrounding a nonrotating, stellar-mass black hole. The simulations are initialized using the Shakura-Sunyaev model with a mass accretion rate of $\dot{M}=3{L}_{\mathrm{Edd}}/{c}^{2}$ (corresponding to L = 0.17L Edd). Our previous work demonstrated that such disks are thermally unstable when accretion is driven by an α-viscosity. In the present work, we test the hypothesis that strong magnetic fields can both drive accretion through magnetorotational instability and restore stability to such disks. We test four initial magnetic field configurations: (1) a zero-net-flux case with a single, radially extended set of magnetic field loops (dipole), (2) a zero-net-flux case with two radially extended sets of magnetic field loops of opposite polarity stacked vertically (quadrupole), (3) a zero-net-flux case with multiple radially concentric rings of alternating polarity (multiloop), and (4) a net-flux, vertical magnetic field configuration (vertical). In all cases, the fields are initially weak, with a gas-to-magnetic pressure ratio ≳100. Based on the results of these simulations, we find that the dipole and multiloop configurations remain thermally unstable like their α-viscosity counterpart, in our case collapsing vertically on the local thermal timescale and never fully recovering. The vertical case, on the other hand, stabilizes and remains so for the duration of our tests (many thermal timescales). The quadrupole case is intermediate, showing signs of both stability and instability. The key stabilizing factor is the ability of specific field configurations to build up and sustain strong, P mag ≳ 0.5P tot, toroidal fields near the midplane of the disk. We discuss the reasons why certain configurations are able to do this effectively and others are not. We then compare our stable simulations to the standard Shakura-Sunyaev disk.

Keywords: Black hole physics, General relativity, Compact radiation sources, Magnetohydrodynamical simulations
Variability in Protoplanetary Nebulae. IX. Evidence for Evolution in a Decade. We have carried out a new photometric V,R  C  study of 12 protoplanetary nebulae, objects in the short-lived transition between the asymptotic giant branch and planetary nebula phases of stellar evolution. These had been the subjects of an earlier study, using data from 1994-2007, that found that all 12 varied periodically, with pulsation periods in the range of ~38 to ~150 days. They are all carbon-rich, with F-G spectral types. We combined our new (2008-2018) data with publicly available All-Sky Automated Survey for Supernovae data and determined new periods for their variability. The older and newer period values were compared to investigate evidence of period change, for which there is theoretical support that it might be detectable in a decade or two in some cases. Such a detection is challenging since the light curves are complicated, with multiple periods, changing amplitudes, and evidence of shocks. Nevertheless, we found one, and possibly two, such cases, which are associated with the higher-temperature stars in the sample (7250 and 8000 K). These results are most consistent with the evolution of stars at the lower end of the mass range of carbon stars, ~1.5-2 M ☉. Several of the stars show longer-term trends of increasing (six cases) or decreasing (one case) brightness, which we think is most likely due to changes in the circumstellar dust opacity. There is one case of a possible ~1.8 yr period in addition to the shorter pulsation. This is interpreted as possible evidence of an orbiting companion.

Keywords: Post-asymptotic giant branch stars, Evolved stars, Stellar pulsations, Protoplanetary nebulae, Pulsating variable stars, Late stellar evolution, Multi-periodic variable stars, Stellar evolution
Anisotropic Magnetic Turbulence in the Inner Heliosphere-Radial Evolution of Distributions Observed by Parker Solar Probe. Observations from Parker Solar Probe's first five orbits are used to investigate the helioradial evolution of probability density functions (pdfs) of fluctuations of magnetic-field components between ~28 and 200 R ⊙. Transformation of the magnetic-field vector to a local mean-field coordinate system permits examination of anisotropy relative to the mean magnetic-field direction. Attention is given to effects of averaging-interval size. It is found that pdfs of the perpendicular fluctuations are well approximated by a Gaussian function, with the parallel fluctuations less so: kurtoses of the latter are generally larger than 10, and their pdfs indicate increasing skewness with decreasing distance r from the Sun, with the latter observation possibly explained by the increasing Alfvénicity of the fluctuations. The ratio of perpendicular to parallel variances is greater than unity; this variance anisotropy becomes stronger with decreasing r. The ratio of the total rms fluctuation strength to the mean-field magnitude decreases with decreasing r, with a value ~0.8 near 1 au and ~0.5 at 0.14 au; the ratio is well approximated by an r 1/4 power law. These findings improve our understanding of the radial evolution of turbulence in the solar wind, and have implications for related phenomena such as energetic-particle transport in the inner heliosphere.

Keywords: Interplanetary turbulence, Solar wind, Interplanetary magnetic fields
DarkMix: Mixture Models for the Detection and Characterization of Dark Matter Halos. Dark matter simulations require statistical techniques to properly identify and classify their halos and structures. Nonparametric solutions provide catalogs of these structures but lack the additional learning of a model-based algorithm and might misclassify particles in merging situations. With mixture models, we can simultaneously fit multiple density profiles to the halos that are found in a dark matter simulation. In this work, we use the Einasto profile to model the halos found in a sample of the Bolshoi simulation, and we obtain their location, size, shape, and mass. Our code is implemented in the R statistical software environment and can be accessed on https://github.com/LluisHGil/darkmix.

Keywords: Mixture model, Galaxy dark matter halos, Dark matter distribution, Spatial point processes
Improved Measurements of Galaxy Star Formation Stochasticity from the Intrinsic Scatter of Burst Indicators. Measurements of short-timescale star formation variations (i.e., "burstiness" or star formation stochasticity) are integral to our understanding of star formation feedback mechanisms and the assembly of stellar populations in galaxies. We expand upon the work of Broussard et al. by introducing a new analysis of galaxy star formation burstiness that accounts for variations in the ${Q}_{{sg}}=E{\left(B-V\right)}_{\mathrm{stars}}/E{\left(B-V\right)}_{\mathrm{gas}}$ distribution, a major confounding factor. We use Balmer decrements from the MOSFIRE Deep Evolution Field (MOSDEF) survey to measure Q  sg , which we use to construct mock catalogs from the Santa Cruz Semi-Analytic Models and MUFASA cosmological hydrodynamical simulation based on 3D-HST, Fiber Multi-Object Spectrograph (FMOS)-COSMOS, and MOSDEF galaxies with Hα detections. The results of the mock catalogs are compared against observations using the burst indicator $\eta ={\mathrm{log}}_{10}({\mathrm{SFR}}_{{\rm{H}}\alpha }/{\mathrm{SFR}}_{\mathrm{NUV}})$ , with the standard deviation of the η distribution indicating burstiness. We find decent agreement between mock and observed η distribution shapes; however, the FMOS-COSMOS and MOSDEF mocks show a systematically low median and scatter in η in comparison to the observations. This work also presents the novel approach of analytically deriving the relationship between the intrinsic scatter in η, scatter added by measurement uncertainties, and observed scatter, resulting in an intrinsic burstiness measurement of 0.06-0.16 dex.

Keywords: Starburst galaxies, Star formation, Galaxy evolution
Turbulent Regimes in Collisions of 3D Alfvén-wave Packets. Using three-dimensional gyrofluid simulations, we revisit the problem of Alfvén-wave (AW) collisions as building blocks of the Alfvénic turbulent cascade and their interplay with magnetic reconnection at magnetohydrodynamic (MHD) scales. Depending on the large-scale value of the nonlinearity parameter χ 0 (the ratio between the AW linear propagation time and nonlinear turnover time), different regimes are observed. For strong nonlinearities (χ 0 ~ 1), turbulence is consistent with a dynamically aligned, critically balanced cascade-fluctuations exhibit a scale-dependent alignment $\sin {\theta }_{{k}_{\perp }}\propto {k}_{\perp }^{-1/4}$ , resulting in a ${k}_{\perp }^{-3/2}$ spectrum and ${k}_{\parallel }\propto {k}_{\perp }^{1/2}$ spectral anisotropy. At weaker nonlinearities (small χ 0), a spectral break marking the transition between a large-scale weak regime and a small-scale ${k}_{\perp }^{-11/5}$ tearing-mediated range emerges, implying that dynamic alignment occurs also for weak nonlinearities. At χ 0 &lt; 1 the alignment angle ${\theta }_{{k}_{\perp }}$ shows a stronger scale dependence than in the χ 0 ~ 1 regime, namely $\sin {\theta }_{{k}_{\perp }}\propto {k}_{\perp }^{-1/2}$ at χ 0 ~ 0.5, and $\sin {\theta }_{{k}_{\perp }}\propto {k}_{\perp }^{-1}$ at χ 0 ~ 0.1. Dynamic alignment in the weak regime also modifies the large-scale spectrum, scaling approximately as ${k}_{\perp }^{-3/2}$ for χ 0 ~ 0.5 and as ${k}_{\perp }^{-1}$ for χ 0 ~ 0.1. A phenomenological theory of dynamically aligned turbulence at weak nonlinearities that can explain these spectra and the transition to the tearing-mediated regime is provided; at small χ 0, the strong scale dependence of the alignment angle combines with the increased lifetime of turbulent eddies to allow tearing to onset and mediate the cascade at scales that can be larger than those predicted for a critically balanced cascade by several orders of magnitude. Such a transition to tearing-mediated turbulence may even supplant the usual weak-to-strong transition.

Keywords: Space plasmas, Magnetohydrodynamics, CCD photometry, Interplanetary turbulence, Plasma astrophysics, Alfven waves, Magnetohydrodynamical simulations
Revisiting the Hubble Constant, Spatial Curvature, and Cosmography with Strongly Lensed Quasar and Hubble Parameter Observations. It is well known that time delays due to strong lensing offer the opportunity of a one-step measurement of the Hubble constant H 0 that is independent of the cosmic distance ladder. In this paper, we go further and propose a cosmological model-independent approach to simultaneously determine the Hubble constant and cosmic curvature with measurements of the time delay due to strong lensing, without any prior assumptions regarding the content of the universe. The data we use comprise the recent compilation of six well studied strongly lensed quasars, while the cosmic chronometer data are utilized to reconstruct distances via cosmographic parameters. In the framework of third-order Taylor expansion and (2, 1) order Padé approximation for cosmographic analysis, our results provide model-independent estimations of the Hubble constant ${H}_{0}={72.24}_{-2.52}^{+2.73}\,\mathrm{km}\,{{\rm{s}}}^{-1}\,{\mathrm{Mpc}}^{-1}$ and ${H}_{0}={72.45}_{-2.02}^{+1.95}\,\mathrm{km}\,{{\rm{s}}}^{-1}\,{\mathrm{Mpc}}^{-1}$ , which are well consistent with that derived from the local distance ladder by the SH0ES collaboration. The measured cosmic curvature ${{\rm{\Omega }}}_{k}={0.062}_{-0.078}^{+0.117}$ and ${{\rm{\Omega }}}_{k}={0.069}_{-0.103}^{+0.116}$ shows that zero spatial curvature is supported by the current observations of time delays due to strong lensing and cosmic chronometers. Imposing the prior of spatial flatness leads to more precise (at 1.6% level) determinations of the Hubble constant ${H}_{0}={70.47}_{-1.15}^{+1.14}\,\mathrm{km}\,{{\rm{s}}}^{-1}\,{\mathrm{Mpc}}^{-1}$ and ${H}_{0}={71.66}_{-1.57}^{+1.15}\,\mathrm{km}\,{{\rm{s}}}^{-1}\,{\mathrm{Mpc}}^{-1}$ , values located between the results from Planck and the SH0ES collaboration. If a prior of local (SH0ES) H 0 measurement is adopted, the constraint on curvature parameter can be further improved to ${{\rm{\Omega }}}_{k}={0.123}_{-0.046}^{+0.060}$ and ${{\rm{\Omega }}}_{k}={0.101}_{-0.072}^{+0.090}$ , supporting no significant deviation from a flat universe. Finally, we also discuss the effectiveness of the Padé approximation in reconstructing the cosmic expansion history for redshifts up to z ~ 2.3, considering its better performance in the Bayes information criterion.

Keywords: Strong gravitational lensing, Cosmological parameters
Faint Stars in a Faint Galaxy. II. The Low-mass Stellar Initial Mass Function of the Boötes I Ultrafaint Dwarf Spheroidal Galaxy. This paper presents improved constraints on the low-mass stellar initial mass function (IMF) of the Boötes I (Boo I) ultrafaint dwarf galaxy, based on our analysis of recent deep imaging from the Hubble Space Telescope. The identification of candidate stellar members of Boo I in the photometric catalog produced from these data was achieved using a Bayesian approach, informed by complementary archival imaging data for the Hubble Ultra Deep Field. Additionally, the existence of earlier-epoch data for the fields in Boo I allowed us to derive proper motions for a subset of the sources and thus identify and remove likely Milky Way stars. We were also able to determine the absolute proper motion of Boo I, and our result is in agreement with, but completely independent of, the measurement(s) by Gaia. The best-fitting parameter values of three different forms of the low-mass IMF were then obtained through forward modeling of the color-magnitude data for likely Boo I member stars within an approximate Bayesian computation Markov Chain Monte Carlo algorithm. The best-fitting single power-law IMF slope is $\alpha =-{1.95}_{-0.28}^{+0.32}$ , while the best-fitting broken power-law slopes are ${\alpha }_{1}=-{1.67}_{-0.57}^{+0.48}$ and ${\alpha }_{2}=-{2.57}_{-1.04}^{+0.93}$ . The best-fitting lognormal characteristic mass and width parameters are ${M}_{c}={0.17}_{-0.11}^{+0.05}{{ \mathcal M }}_{\odot }$ and $\sigma ={0.49}_{-0.20}^{+0.13}$ . These broken power-law and lognormal IMF parameters for Boo I are consistent with published results for the stars within the Milky Way, and thus it is plausible that Boötes I and the Milky Way are populated by the same stellar IMF.

Keywords: Initial mass function, Low mass stars, Space astrometry, Dwarf spheroidal galaxies, Proper motions
GRB 110213A: A Study of Afterglow Electromagnetic Cascade Radiation. We obtained well-sampled optical photometry of GRB 110213A, including Swift/UVOT and XRT. Combining our data from those of other ground-based telescopes, we present 15 optical multicolor light curves showing similar shapes with two peaks. In contrast, in the X-ray band, only a single peak is observed between the two optical peaks. Temporal and spectral analysis of GRB 110213A shows that the X-rays differ from the optical for Phases I-III (before the second peak of the optical band at ~5.6 ks). Moreover, they have the same spectral behavior at late times (Phases IV-VI). These data indicate that the optical and X-ray emission are dominated by different components. The synchrotron-supported pair cascade emission is included in the standard external forward-shock model, which is dominated by synchrotron radiation and synchrotron self-Compton (SSC). We find that the optical bands of GRB 110213A are dominated by the cascade emission from synchrotron radiation + SSC at the early stage, while the primary synchrotron + SSC radiation dominates the X-ray band. At late stages, both the X-ray and optical bands are dominated by emission from primary synchrotron + SSC radiation. The cascade component can reasonably explain the first optical peak. In contrast, the primary synchrotron + SSC emission mainly contributes to the second peak.

Keywords: Gamma-ray bursts
Exploring Stellar and Ionized Gas Noncircular Motions in Barred Galaxies with MUSE. We present Multi Unit Spectroscopic Explorer (MUSE) integral-field stellar and ionized velocity maps for a sample of 14 barred galaxies. Most of these objects exhibit "S"-shape isovelocities in the bar region indicative of the presence of streaming motions in the velocity fields. By applying circular rotation models we observe that bars leave symmetric structures in the residual maps of the stellar velocity. We built noncircular rotation models using the XookSuut tool to characterize the observed velocity fields; in particular we adopt bisymmetric models and a harmonic decomposition for a bar potential for describing the nonaxisymmetric velocities. We find that both models are able to reproduce the oval distortion observed in the velocity maps. Furthermore, the position angle of the oval distortion estimated from the bisymmetric model correlates with the photometric bar position angle (ρ pearson = 0.95), which suggests that noncircular velocities are caused by the bar. Because of the weak detection of Hα in our objects we are not able to compare gas to stellar noncircular motions in our sample, although we show that when galaxies are gas-rich, oval distortion is also observed but with larger amplitudes. Finally, we do not find evidence that the amplitude of the noncircular motions is dependent on the bar size, stellar mass, or global star formation rate.

Keywords: Stellar kinematics, Barred spiral galaxies
Magellan/IMACS Spectroscopy of Grus I: A Low Metallicity Ultra-faint Dwarf Galaxy. We present a chemodynamical study of the Grus I ultra-faint dwarf galaxy (UFD) from medium-resolution (R ~ 11,000) Magellan/IMACS spectra of its individual member stars. We identify eight confirmed members of Grus I, based on their low metallicities and coherent radial velocities, and four candidate members for which only velocities are derived. In contrast to previous work, we find that Grus I has a very low mean metallicity of &lt;[Fe/H]&gt; = -2.62 ± 0.11 dex, making it one of the most metal-poor UFDs. Grus I has a systemic radial velocity of -143.5 ± 1.2 km s-1 and a velocity dispersion of ${\sigma }_{\mathrm{rv}}={2.5}_{-0.8}^{+1.3}$ km s-1, which results in a dynamical mass of ${M}_{1/2}({r}_{h})={8}_{-4}^{+12}\times {10}^{5}$ M ⊙ and a mass-to-light ratio of M/L  V  = ${440}_{-250}^{+650}$ M ⊙/L ⊙. Under the assumption of dynamical equilibrium, our analysis confirms that Grus I is a dark-matter-dominated UFD (M/L &gt; 80 M ⊙/L ⊙). However, we do not resolve a metallicity dispersion (σ [Fe/H] &lt; 0.44 dex). Our results indicate that Grus I is a fairly typical UFD with parameters that agree with mass-metallicity and metallicity-luminosity trends for faint galaxies. This agreement suggests that Grus I has not lost an especially significant amount of mass from tidal encounters with the Milky Way, in line with its orbital parameters. Intriguingly, Grus I has among the lowest central densities ( ${\rho }_{1/2}\sim {3.5}_{-2.1}^{+5.7}\times {10}^{7}$ M ⊙ kpc-3) of the UFDs that are not known to be tidally disrupting. Models of the formation and evolution of UFDs will need to explain the diversity of these central densities, in addition to any diversity in the outer regions of these relic galaxies. *This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile.

Keywords: Population II stars, Dwarf galaxies
Axisymmetric Pulsar Magnetosphere Revisited. We present a global kinetic plasma simulation of an axisymmetric pulsar magnetosphere with self-consistent e ± pair production. We use the particle-in-cell method and log-spherical coordinates with a grid size 4096 × 4096. This allows us to achieve a high voltage induced by the pulsar rotation and investigate pair creation in a young pulsar far from the death line. We find the following: (1) The energy release and e ± creation are strongly concentrated in the thin, Y-shaped current sheet, with a peak localized in a small volume at the Y-point. (2) The Y-point is shifted inward from the light cylinder by ~15% and "breathes" with a small amplitude. (3) The dense e ± cloud at the Y-point is in ultrarelativistic rotation, which we call superrotation, because it exceeds corotation with the star. The cloud receives angular momentum flowing from the star along the poloidal magnetic field lines. (4) Gamma-ray emission peaks at the Y-point and is collimated in the azimuthal direction, tangent to the Y-point circle. (5) The separatrix current sheet between the closed magnetosphere and the open magnetic field lines is sustained by the electron backflow from the Y-point cloud. Its thickness is self-regulated to marginal charge starvation. (6) Only a small fraction of dissipation occurs in the separatrix inward of the Y-point. A much higher power is released in the equatorial plane, including the Y-point where the created dense e ± plasma is spun up and intermittently ejected through the nozzle between the two open magnetic fluxes.

Keywords: Magnetic fields, Plasma astrophysics, Rotation powered pulsars
Solving the Multimessenger Puzzle of the AGN-starburst Composite Galaxy NGC 1068. Multiwavelength observations indicate that some starburst galaxies show a dominant nonthermal contribution from their central region. These active galactic nuclei (AGN)-starburst composites are of special interest, as both phenomena on their own are potential sources of highly energetic cosmic rays and associated γ-ray and neutrino emission. In this work, a homogeneous, steady-state two-zone multimessenger model of the nonthermal emission from the AGN corona as well as the circumnuclear starburst region is developed and subsequently applied to the case of NGC 1068, which has recently shown some first indications of high-energy neutrino emission. Here, we show that the entire spectrum of multimessenger data-from radio to γ-rays including the neutrino constraint-can be described very well if both, starburst and AGN corona, are taken into account. Using only a single emission region is not sufficient.

Keywords: Starburst galaxies, High-energy cosmic radiation, Neutrino astronomy, Infrared astronomy, Seyfert galaxies, Gamma-ray astronomy, Radio astronomy