Sazuna/UAT_keywords huggingface dataset:
A Study of Gas Entropy Profiles of 47 Galaxy Clusters and Groups out to the Virial Radius. Some observations, such as those presented in Walker et al., show that the observed entropy profiles of the intracluster medium (ICM) deviate from the power-law prediction of adiabatic simulations. This implies that nongravitational processes, which are absent in the simulations, may be important in the evolution of the ICM, and by quantifying the deviation, we may be able to estimate the feedback energy in the ICM and use it as a probe of the nongravitational processes. To address this issue, we calculate the ICM entropy profiles in a sample of 47 galaxy clusters and groups, which have been observed out to at least ∼r500 with Chandra, XMM-Newton, and/or Suzaku, by constructing a physical model to incorporate the effects of both gravity and nongravitational processes to fit the observed gas temperature and surface brightness profiles via Bayesian statistics. After carefully evaluating the effects of systematic errors, we find that the gas entropy profiles derived with best-fit results of our model are consistent with the simulation-predicted power-law profile near the virial radius, while the flattened profiles reported previously can be explained by introducing the gas clumping effect, the existence of which is confirmed in 19 luminous targets in our sample. We calculate the total feedback energy per particle and find that it decreases from ∼10 keV at the center to about zero at ∼0.35r200 and is consistent with zero outside ∼0.35r200, implying an upper limit of the feedback efficiency of ∼0.02 for the supermassive black holes hosted in the brightest cluster galaxies.

Keywords: Galaxy clusters, Intracluster medium, X-ray sources
Eridanus II: A Fossil from Reionization with an Off-center Star Cluster. We present deep Hubble Space Telescope (HST) photometry of the ultra-faint dwarf galaxy Eridanus II (Eri II). Eri II, which has an absolute magnitude of MV = -7.1, is located at a distance of 339 kpc, just beyond the virial radius of the Milky Way. We determine the star formation history of Eri II and measure the structure of the galaxy and its star cluster. We find that a star formation history consisting of two bursts, constrained to match the spectroscopic metallicity distribution of the galaxy, accurately describes the Eri II stellar population. The best-fit model implies a rapid truncation of star formation at early times, with &gt;80% of the stellar mass in place before z ∼ 6. A small fraction of the stars could be as young as 8 Gyr, but this population is not statistically significant; Monte Carlo simulations recover a component younger than 9 Gyr only 15% of the time, where they represent an average of 7 ± 4% of the population. These results are consistent with theoretical expectations for quenching by reionization. The HST depth and angular resolution enable us to show that Eri II's cluster is offset from the center of the galaxy by a projected distance of 23 ± 3 pc. This offset could be an indication of a small (∼50-75 pc) dark matter core in Eri II. Moreover, we demonstrate that the cluster has a high ellipticity of ${0.31}_{-0.06}^{+0.05}$ and is aligned with the orientation of Eri II within 3° ± 6°, likely due to tides. The stellar population of the cluster is indistinguishable from that of Eri II itself.

Keywords: Local Group, Globular star clusters, Stellar populations, Dwarf galaxies, Galaxy structure, Galaxy ages, Dark matter
Black Hole Mass Measurements of Radio Galaxies NGC 315 and NGC 4261 Using ALMA CO Observations. We present Atacama Large Millimeter/submillimeter Array (ALMA) Cycle 5 and Cycle 6 observations of CO (2-1) and CO (3-2) emission at 0"2-0"3 resolution in two radio-bright, brightest group/cluster early-type galaxies, NGC 315 and NGC 4261. The data resolve CO emission that extends within their black hole (BH) spheres of influence (rg), tracing regular Keplerian rotation down to just tens of parsecs from the BHs. The projected molecular gas speeds in the highly inclined (i ≳ 60°) disks rise at least to 500 km s-1 near their galaxy centers. We fit dynamical models of thin-disk rotation directly to the ALMA data cubes and account for the extended stellar mass distributions by constructing galaxy surface brightness profiles corrected for a range of plausible dust extinction values. The best-fit models yield $({M}_{\mathrm{BH}}/{10}^{9}\,{M}_{\odot })=2.08\pm 0.01(\mathrm{stat}{)}_{-0.14}^{+0.32}(\mathrm{sys})$ for NGC 315 and $({M}_{\mathrm{BH}}/{10}^{9}\,{M}_{\odot })=1.67\pm 0.10(\mathrm{stat}{)}_{-0.24}^{+0.39}(\mathrm{sys})$ for NGC 4261, the latter of which is larger than previous estimates by a factor of ∼3. The BH masses are broadly consistent with the relations between BH masses and host galaxy properties. These are among the first ALMA observations to map dynamically cold gas kinematics well within the BH-dominated regions of radio galaxies, resolving the respective rg by factors of ∼5-10. The observations demonstrate ALMA's ability to precisely measure BH masses in active galaxies, which will enable more confident probes of accretion physics for the most massive galaxies. * Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with programs #5124, 6673, 14219, and 15909.

Keywords: Supermassive black holes, Molecular gas, Astronomy data modeling, Millimeter astronomy, Galaxy kinematics, Fanaroff-Riley radio galaxies, Submillimeter astronomy
On the Use of Field RR Lyrae as Galactic Probes. II. A New ∆S Calibration to Estimate Their Metallicity. We performed the largest and most homogeneous spectroscopic survey of field RR Lyraes (RRLs). We secured ≍6300 high-resolution (HR, R ∼ 35,000) spectra for 143 RRLs (111 fundamental, RRab; 32 first-overtone, RRc). The atmospheric parameters were estimated by using the traditional approach and the iron abundances were measured by using an LTE line analysis. The resulting iron distribution shows a well-defined metal-rich tail approaching solar iron abundance. This suggests that field RRLs experienced a complex chemical enrichment in the early halo formation. We used these data to develop a new calibration of the ∆S method. This diagnostic, based on the equivalent widths of Ca II K and three Balmer (Hδ,γ,β) lines, traces the metallicity of RRLs. For the first time, the new empirical calibration: (i) includes spectra collected over the entire pulsation cycle; (ii) includes RRc variables; (iii) relies on spectroscopic calibrators covering more than three dex in iron abundance; and (iv) provides independent calibrations based on one/two/three Balmer lines. The new calibrations were applied to a data set of both SEGUE-SDSS and degraded HR spectra totalling 6451 low-resolution (R ∼ 2000) spectra for 5001 RRLs (3439 RRab, 1562 RRc). This resulted in an iron distribution with a median η = -1.55 ± 0.01 and σ = 0.51 dex, in good agreement with literature values. We also found that RRc are 0.10 dex more metal-poor than RRab variables, and have a distribution with a smoother metal-poor tail. This finding supports theoretical prescriptions suggesting a steady decrease in the RRc number when moving from metal-poor to metal-rich stellar environments. * Based on observations obtained with the du Pont telescope at Las Campanas Observatory, operated by Carnegie Institution for Science. Based in part on data collected at Subaru Telescope, which is operated by the National Astronomical Observatory of Japan. Based partly on data obtained with the STELLA robotic telescopes in Tenerife, an AIP facility jointly operated by AIP and IAC. Some of the observations reported in this paper were obtained with the Southern African Large Telescope (SALT). Based on observations made with the Italian Telescopio Nazionale Galileo (TNG) operated on the island of La Palma by the Fundación Galileo Galilei of the INAF (Istituto Nazionale di Astrofisica) at the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias. Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere.

Keywords: High resolution spectroscopy, RR Lyrae variable stars, Milky Way stellar halo, Metallicity
Understanding the Velocity Distribution of the Galactic Bulge with APOGEE and Gaia. We revisit the stellar velocity distribution in the Galactic bulge/bar region with Apache Point Observatory Galactic Evolution Experiment DR16 and Gaia DR2, focusing in particular on the possible high-velocity (HV) peaks and their physical origin. We fit the velocity distributions with two different models, namely with Gauss-Hermite polynomials and Gaussian mixture models (GMMs). The result of the fit using Gauss-Hermite polynomials reveals a positive correlation between the mean velocity ( $\,\overline{V}$ ) and the "skewness" (h3) of the velocity distribution, possibly caused by the Galactic bar. The n = 2 GMM fitting reveals a symmetric longitudinal trend of ∣μ2∣ and σ2 (the mean velocity and the standard deviation of the secondary component), which is inconsistent with the x2 orbital family predictions. Cold secondary peaks could be seen at ∣l∣ ∼ 6°. However, with the additional tangential information from Gaia, we find that the HV stars in the bulge show similar patterns in the radial-tangential velocity distribution (VR-VT), regardless of the existence of a distinct cold HV peak. The observed VR-VT (or VGSR-μl) distributions are consistent with the predictions of a simple Milky Way bar model. The chemical abundances and ages inferred from ASPCAP and CANNON suggest that the HV stars in the bulge/bar are generally as old as, if not older than, the other stars in the bulge/bar region.

Keywords: Milky Way dynamics, Galactic bulge
Detection of GeV Gamma-ray Emission of Kepler's SNR With Fermi-LAT. A likely detection of γ-ray emission from the region of Kepler's Supernova Remnant (SNR) is reported by analyzing ∼12 yr of Pass 8 data of the Fermi Large Area Telescope. Its photon flux is (4.85 ± 0.60) × 10-10 ph cm-2 s-1 with ∼4σ significance in 0.2-500 GeV. Moreover, our results show that there is no significant variability in the light curve of ∼12 yr, and its position can well overlap with the observation result of Chandra in hard X-ray band with a good spatial resolution of 0"5, so the source is likely to be the GeV γ-ray counterpart of Kepler's SNR. The spectral energy distribution of γ-rays from Kepler's SNR favors a hadronic origin in GeV band. Through analyzing multi-band data from radio to γ-ray and surveying the distribution from the surrounding CO molecules cloud, we found that if this γ-ray emission is from Kepler's SNR, then it may originate from interactions between the relativistic protons escaping from the shock of Kepler's SNR and surrounding CO gas molecules. However, more observation data are necessary to firmly confirm the association between the γ-ray source and Kepler's SNR in the future.

Keywords: Cosmic ray astronomy, Molecular clouds, Astronomical radiation sources, Supernova remnants, Non-thermal radiation sources, Gamma-rays, Cosmic rays
Wave-driven Shocks in Stellar Outbursts: Dynamics, Envelope Heating, and Nascent Blast Waves. We address the shocks from acoustic pulses and wave trains in general one-dimensional flows, with an emphasis on the application to super-Eddington outbursts in massive stars. Using approximate adiabatic invariants, we generalize the classical equal-area technique in its integral and differential forms. We predict shock evolution for the case of an initially sinusoidal but finite wave train, with separate solutions for internal shocks and head or tail shocks, and demonstrate detailed agreement with numerical simulations. Our internal shock solution motivates improved expressions for the shock-heating rate. Our solution for head and tail shocks demonstrates that these preserve dramatically more wave energy to large radii and have a greater potential for the direct ejection of matter. This difference highlights the importance of the waveform for shock dynamics. Our weak-shock analysis predicts when shocks will become strong and provides a basis from which this transition can be addressed. We use it to estimate the mass ejected by sudden sound pulses and weak central explosions.

Keywords: Stellar oscillations, Astrophysical fluid dynamics, Supernova dynamics
Measuring Distances to Low-luminosity Galaxies Using Surface Brightness Fluctuations. We present an in-depth study of surface brightness fluctuations (SBFs) in low-luminosity stellar systems. Using the MIST models, we compute theoretical predictions for absolute SBF magnitudes in the LSST, HST ACS/WFC, and proposed Roman Space Telescope filter systems. We compare our calculations to observed SBF-color relations of systems that span a wide range of age and metallicity. Consistent with previous studies, we find that single-age population models show excellent agreement with observations of low-mass galaxies with 0.5 ≲ g - i ≲ 0.9. For bluer galaxies, the observed relation is better fit by models with composite stellar populations. To study SBF recovery from low-luminosity systems, we perform detailed image simulations in which we inject fully populated model galaxies into deep ground-based images from real observations. Our simulations show that LSST will provide data of sufficient quality and depth to measure SBF magnitudes with precisions of ∼0.2-0.5 mag in ultra-faint $\left({10}^{4}\leqslant {M}_{\star }/{M}_{\odot }\leqslant {10}^{5}\right)$ and low-mass classical (M⋆ ≤ 107 M⊙) dwarf galaxies out to ∼4 Mpc and ∼25 Mpc, respectively, within the first few years of its deep-wide-fast survey. Many significant practical challenges and systematic uncertainties remain, including an irreducible "sampling scatter" in the SBFs of ultra-faint dwarfs due to their undersampled stellar mass functions. We nonetheless conclude that SBFs in the new generation of wide-field imaging surveys have the potential to play a critical role in the efficient confirmation and characterization of dwarf galaxies in the nearby universe.

Keywords: Stellar populations, Low surface brightness galaxies, Dwarf galaxies, Distance indicators
The Host Galaxy of the Dwarf Seyfert UGC 06728. We present multi-color high-resolution imaging of the host galaxy of the dwarf Seyfert UGC 06728. As the lowest-mass black hole to be described with both a direct mass constraint and a spin constraint, UGC 06728 is an important source for comparison with black hole evolutionary models, yet little is known about the host galaxy. Using Hubble Space Telescope imaging in the optical and near-infrared, we find that UGC 06728 is a barred lenticular (SB0) galaxy with prominent ansae at the ends of the bar. We cleanly separated the active galactic nucleus (AGN) from the resolved galaxy with two-dimensional image decompositions, thus allowing accurate surface brightness profiles to be derived in all filters from the outer edge of the galaxy all the way into the nucleus. Based on a sample of 51 globular cluster candidates identified in the images, the globular cluster luminosity function predicts a distance to UCG 06728 of 32.5 ± 3.5 Mpc. Combining the galaxy photometry with the distance estimate, we derive a starlight-corrected AGN luminosity, the absolute magnitude of the galaxy, and a constraint on the galaxy stellar mass of $\mathrm{log}{M}_{\star }/{M}_{\odot }=9.9\pm 0.2$ .

Keywords: Lenticular galaxies, Supermassive black holes, AGN host galaxies, Galaxy distances, Seyfert galaxies, Galaxy photometry
Whistlers in the Solar Vicinity That Are Spiky in Time and Frequency. Spiky whistlers are short duration chirps of electric field that have fine structures in both frequency and time. They are observed on the Parker Solar Probe for the first time. From the limited available data, they appear to be accompanied by low-frequency ion waves and to occur relatively frequently. The origin of these wave pairs and their correlations are not understood.

Keywords: Solar physics, Solar wind, Solar electromagnetic emission
A Tidally Induced Global Corrugation Pattern in an External Disk Galaxy Similar to the Milky Way. We study the two-dimensional (2D) line-of-sight velocity (Vlos) field of the low-inclination, late-type galaxy VV304a. The resulting 2D kinematic map reveals a global, coherent, and extended perturbation that is likely associated with a recent interaction with the massive companion VV304b. We use multiband imaging and a suite of test-particle simulations to quantify the plausible strength of in-plane flows due to nonaxisymmetric perturbations and show that the observed velocity flows are much too large to be driven either by a spiral structure or by a bar. We use fully cosmological hydrodynamical simulations to characterize the contribution from in- and off-plane velocity flows to the Vlos field of recently interacting galaxy pairs like the VV304 system. We show that, for recently perturbed low-inclination galactic disks, the structure of the residual velocity field, after subtraction of an axisymmetric rotation model, can be dominated by vertical flows. Our results indicate that the Vlos perturbations in VV304a are consistent with a corrugation pattern. Its Vlos map suggests the presence of a structure similar to the Monoceros ring seen in the Milky Way. Our study highlights the possibility of addressing important questions regarding the nature and origin of vertical perturbations by measuring the line-of-sight velocities in low-inclination nearby galaxies.

Keywords: Galaxy stellar disks, Galaxy dynamics, Galaxy kinematics, Disk galaxies
Coronal Heating and Solar Wind Formation in Quiet Sun and Coronal Holes: A Unified Scenario. Coronal holes (CHs) are darker than the quiet Sun (QS) when observed in coronal channels. This study aims to understand the similarities and differences between CHs and QS in the transition region using the Si IV 1394 Å line, recorded by the Interface Region Imaging Spectrograph, by considering the distribution of magnetic field measured by the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory. We find that Si IV intensities obtained in CHs are lower than those obtained in QS for regions with identical magnetic flux densities. Moreover, the difference in intensities between CHs and QS increases with increasing magnetic flux. For the regions with equal magnetic flux density, QS line profiles are more redshifted than those measured in CHs. Moreover, the blueshifts measured in CHs show an increase with increasing magnetic flux density unlike in the QS. The non-thermal velocities in QS, as well as in CHs, show an increase with increasing magnetic flux. However, no significant difference was observed in QS and CHs, albeit a small deviation at small flux densities. Using these results, we propose a unified model for the heating of the corona in the QS and in CHs and the formation of solar wind.

Keywords: Slow solar wind, Fast solar wind, Quiet sun, Solar coronal heating, Solar wind, Solar magnetic fields, Solar transition region, Solar coronal holes
NuSTAR Observation of Energy Release in 11 Solar Microflares. Solar flares are explosive releases of magnetic energy. Hard X-ray (HXR) flare emission originates from both hot (millions of Kelvin) plasma and nonthermal accelerated particles, giving insight into flare energy release. The Nuclear Spectroscopic Telescope ARray (NuSTAR) utilizes direct-focusing optics to attain much higher sensitivity in the HXR range than that of previous indirect imagers. This paper presents 11 NuSTAR microflares from two active regions (AR 12671 on 2017 August 21 and AR 12712 on 2018 May 29). The temporal, spatial, and energetic properties of each are discussed in context with previously published HXR brightenings. They are seen to display several "large flare" properties, such as impulsive time profiles and earlier peak times in higher-energy HXRs. For two events where the active region background could be removed, microflare emission did not display spatial complexity; differing NuSTAR energy ranges had equivalent emission centroids. Finally, spectral fitting showed a high-energy excess over a single thermal model in all events. This excess was consistent with additional higher-temperature plasma volumes in 10/11 microflares and only with an accelerated particle distribution in the last. Previous NuSTAR studies focused on one or a few microflares at a time, making this the first to collectively examine a sizable number of events. Additionally, this paper introduces an observed variation in the NuSTAR gain unique to the extremely low livetime (&lt;1%) regime and establishes a correction method to be used in future NuSTAR solar spectral analysis.

Keywords: Solar flares, The Sun, Solar flare spectra, Solar physics, Non-thermal radiation sources, Solar x-ray flares
Radiation Hydrodynamics of Turbulent H II Regions in Molecular Clouds: A Physical Origin of LyC Leakage and the Associated Lyα Spectra. We examine Lyman continuum (LyC) leakage through H II regions regulated by turbulence and radiative feedback in a giant molecular cloud in the context of fully coupled radiation hydrodynamics (RHD). The physical relations of the LyC escape with H I covering fraction, kinematics, ionizing photon production efficiency, and emergent Lyα line profiles are studied using a series of RHD turbulence simulations performed with RAMSES-RT. The turbulence-regulated mechanism allows ionizing photons to leak out at early times before the onset of supernova feedback. The LyC photons escape through turbulence-generated low column density channels that are evacuated efficiently by radiative feedback via photoheating-induced shocks across the D-type ionization fronts. The Lyα photons funnel through the photoionized channels along the paths of LyC escape, resulting in a diverse Lyα spectral morphology including narrow double-peaked profiles. The Lyα peak separation is controlled by the residual H I column density of the channels, and the line asymmetry correlates with the porosity and multiphase structure of the H II region. This mechanism through the turbulent H II regions can naturally reproduce the observed Lyα spectral characteristics of some of the LyC-leaking galaxies. This RHD turbulence origin provides an appealing hypothesis to explain high LyC leakage from very young (∼3 Myr) star-forming galaxies found in the local universe without need of extreme galactic outflows or supernova feedback. We discuss the implications of the turbulent H II regions on other nebular emission lines and a possible observational test with the Magellanic System and local blue compact dwarf galaxies as analogs of reionization-era systems.

Keywords: Reionization, H II regions, Radiative transfer, Hydrodynamics