Sazuna/UAT_keywords huggingface dataset:
Analysis of the Spatially Resolved V-3.6 μm Colors and Dust Extinction in 257 Nearby NGC and IC Galaxies. We present and analyze spatially resolved maps for the observed V- and g-band to 3.6 μm flux ratios and the inferred dust-extinction values, A  V , for a sample of 257 nearby NGC and IC galaxies. Flux ratio maps are constructed using point-spread function-matched mosaics of Sloan Digital Sky Survey g- and r-band images and Spitzer/InfraRed Array Camera 3.6 μm mosaics, with all pixels contaminated by foreground stars or background objects masked out. By applying the β  V  method, which was recently calibrated as a function of redshift and morphological type by Kim et al., dust-extinction maps were created for each galaxy. The typical 1σ scatter in β  V  around the average, both within a galaxy and in each morphological type bin, is ∼20%. Combined, these result in a ∼0.4 mag scatter in A  V . β  V  becomes insensitive to small-scale variations in stellar populations once resolution elements subtend an angle larger than that of a typical giant molecular cloud (∼200 pc). We find noticeably redder V-3.6 μm colors in the center of star-forming galaxies and galaxies with a weak active galactic nucleus. The derived intrinsic V-3.6 μm colors for each Hubble type are generally consistent with the model predictions of Kim et al. Finally, we discuss the applicability of the β  V  dust-correction method to more distant galaxies, for which well-matched Hubble Space Telescope rest-frame visible and James Webb Space Telescope rest-frame ∼3.5 μm images will become available in the near-future.

Keywords: Stellar populations, Surveys, Extinction, Photometry, Extragalactic astronomy
Solar Active Region Heating Diagnostics from High-temperature Emission Using the MaGIXS. The relative amount of high-temperature plasma has been found to be a useful diagnostic to determine the frequency of coronal heating on sub-resolution structures. When the loops are infrequently heated, a broad emission measure (EM) over a wider range of temperatures is expected. A narrower EM is expected for high-frequency heating where the loops are closer to equilibrium. The soft X-ray spectrum contains many spectral lines that provide high-temperature diagnostics, including lines from Fe XVII-XIX. This region of the solar spectrum will be observed by the Marshall Grazing Incidence Spectrometer (MaGIXS) in 2020. In this paper, we derive the expected spectral line intensity in MaGIXS to varying amounts of high-temperature plasma to demonstrate that a simple line ratio provides a powerful diagnostic to determine the heating frequency. Similarly, we examine ratios of AIA channel intensities, filter ratios from a XRT, and energy bands from the FOXSI sounding rocket to determine their sensitivity to this parameter. We find that both FOXSI and MaGIXS provide good diagnostic capabilities for high-temperature plasma. We then compare the predicted line ratios to the output of a numerical model and confirm that the MaGIXS ratios provide an excellent diagnostic for heating frequency.

Keywords: High resolution spectroscopy, Solar coronal heating, Solar coronal lines, Solar active regions, Solar corona, Solar electromagnetic emission
Revisiting the Spectral and Timing Properties of NGC 4151. NGC 4151 is the brightest Seyfert 1 nucleus in X-rays. It was the first object to show short time delays in the Fe K band, which were attributed to relativistic reverberation, providing a new tool for probing regions at the black hole scale. Here we report the results of a large XMM-Newton campaign in 2015 to study these short delays further. Analyzing high-quality data that span timescales between hours and decades, we find that neutral and ionized absorption contributes significantly to the spectral shape. Accounting for their effects, we find no evidence for a relativistic reflection component, contrary to early work. Energy-dependent lags are significantly measured in the new data, but with an energy profile that does not resemble a broad iron line, in contrast to the old data. The complex lag-energy spectra, along with the lack of strong evidence for a relativistic spectral component, suggest that the energy-dependent lags are produced by absorption effects. The long-term spectral variations provide new details on the variability of the narrow Fe Kα line. We find that its variations are correlated with, and delayed with respect to, the primary X-ray continuum. We measure a delay of τ ={3.3}-0.7+1.8 days, implying an origin in the inner broad-line region (BLR). The delay is half the Hβ line delay, suggesting a geometry that differs slightly from the optical BLR.

Keywords: X-ray active galactic nuclei, Compact objects
Neutrino-driven Instability of Ion Acoustic Waves in an Ultrarelativistic Degenerate Plasma. The coupling between ion acoustic waves (IAWs) and a neutrino beam undergoing flavor oscillations in a dense, relativistically degenerate plasma is analyzed. The neutrino-driven streaming instability of the IAWs is investigated with relevance to plasma conditions at the last stage of stellar evolution in a massive supernova progenitor. The influence of neutrino beam parameters such as the energy of the incident neutrino beam and eigenfrequency of the neutrino flavor oscillations on the instability growth rate is obtained numerically. It is observed that the neutrino flavor oscillations significantly affect the neutrino-driven instability of the IAWs. Our results also indicate that the time period for the onset of the streaming neutrino-driven instability is shorter than the typical time period of a core-collapse supernova explosion. The findings of this investigation may shed new light on the understanding of the underlying physical mechanism responsible for the core-collapse supernova.

Keywords: Supernova neutrinos, Degenerate matter, Core-collapse supernovae, Plasma physics, Neutrino oscillations, Relativistic fluid dynamics
Using X-Ray Morphological Parameters to Strengthen Galaxy Cluster Mass Estimates via Machine Learning. We present a machine-learning approach for estimating galaxy cluster masses, trained using both Chandra and eROSITA mock X-ray observations of 2041 clusters from the Magneticum simulations. We train a random forest (RF) regressor, an ensemble learning method based on decision tree regression, to predict cluster masses using an input feature set. The feature set uses core-excised X-ray luminosity and a variety of morphological parameters, including surface brightness concentration, smoothness, asymmetry, power ratios, and ellipticity. The regressor is cross-validated and calibrated on a training sample of 1615 clusters (80% of sample), and then results are reported as applied to a test sample of 426 clusters (20% of sample). This procedure is performed for two different mock observation series in an effort to bracket the potential enhancement in mass predictions that can be made possible by including dynamical state information. The first series is computed from idealized Chandra-like mock cluster observations, with high spatial resolution, long exposure time (1 Ms), and the absence of background. The second series is computed from realistic-condition eROSITA mocks with lower spatial resolution, short exposures (2 ks), instrument effects, and background photons modeled. We report a 20% reduction in the mass estimation scatter when either series is used in our RF model compared to a standard regression model that only employs core-excised luminosity. The morphological parameters that hold the highest feature importance are smoothness, asymmetry, and surface brightness concentration. Hence these parameters, which encode the dynamical state of the cluster, can be used to make more accurate predictions of cluster masses in upcoming surveys, offering a crucial step forward for cosmological analyses.

Keywords: Galaxy clusters, Astrostatistics, Cosmological constant
Supermassive Black Hole Binary Candidates from the Pan-STARRS1 Medium Deep Survey. We present a systematic search for periodically varying quasar and supermassive black hole binary (SMBHB) candidates in the Pan-STARRS1 Medium Deep Survey (MDS). From ∼9000 color-selected quasars in an ∼50 °2 sky area, we initially identify 26 candidates with more than 1.5 cycles of variation. We extend the baseline of observations via our imaging campaign with the Discovery Channel Telescope and the Las Cumbres Observatory network and reevaluate the candidates using a more rigorous, maximum likelihood method. Using a range of statistical criteria and assuming the damped random walk model for normal quasar variability, we identify one statistically significant periodic candidate. We also investigate the capabilities of detecting SMBHBs with the Large Synoptic Survey Telescope using our study with MDS as a benchmark and explore any complementary multiwavelength evidence for SMBHBs in our sample.

Keywords: Surveys, Supermassive black holes, Quasars
On Kinetic Instabilities Driven By Ion Temperature Anisotropy and Differential Flow in the Solar Wind. The ion temperature anisotropy instability is widely thought of as a constraint on the distribution of the ion perpendicular and parallel temperatures in the solar wind. Besides the ion temperature anisotropy, proton and alpha particle beams are permeating in the solar wind. Therefore, this paper presents a comprehensive investigation on unstable waves resulting from both ion temperature anisotropy and ion beams. It finds that the strongest electromagnetic cyclotron instability triggers the left-hand circularly polarized Alfvén/proton-cyclotron wave propagating along the background magnetic field. The strongest fast-magnetosonic/whistler firehose instability generates the right-hand circularly polarized fast-magnetosonic/whistler wave propagating reversely to the background magnetic field. The mirror instability preferably drives oblique mirror mode waves with two anticorrelated perpendicular magnetic components. The Alfvén firehose instability is prior to generating oblique Alfvén waves with two unbalanced perpendicular magnetic components that are nearly positive-correlated. Due to the effects of streaming proton and alpha particles, both the mirror and Alfvén firehose instabilities produce slowly propagating unstable waves in comparison to nonpropagating waves in motionless plasmas. The differential proton and alpha particle flows result in the ion/ion beam instability, destabilizing obliquely propagating Alfvén/proton-cyclotron waves. The ion/ion beam instability can provide a constraint on electromagnetic fluctuations in the low-beta region. Moreover, this paper clearly explores the dependence of the frequency and electromagnetic polarization on the normal angle for each kind of instability, which could be useful for distinguishing the instability mechanism in the solar wind.

Keywords: Space plasmas, Solar wind, Plasma physics
Cooling+Heating Flows in Galaxy Clusters: Turbulent Heating, Spectral Modeling, and Cooling Efficiency. The discrepancy between expected and observed cooling rates of X-ray emitting gas has led to the cooling-flow problem at the cores of clusters of galaxies. A variety of models have been proposed to model the observed X-ray spectra and resolve the cooling-flow problem, which involves heating the cold gas through different mechanisms. As a result, realistic models of X-ray spectra of galaxy clusters need to involve both heating and cooling mechanisms. In this paper, we argue that the heating timescale is set by the magnetohydrodynamic (MHD) turbulent viscous heating for the Intracluster plasma, parameterized by the Shakura-Sunyaev viscosity parameter, α. Using a cooling+heating flow model, we show that a value of α ≃ 0.05 (with 10% scatter) provides improved fits to the X-ray spectra of cooling flow, while at the same time, predicting reasonable cooling efficiency, {ɛ }cool}={0.33}-0.15+0.63. Our inferred values for α based on X-ray spectra are also in line with direct measurements of turbulent pressure in simulations and observations of galaxy clusters. This simple picture unifies astrophysical accretion, as a balance of MHD turbulent heating and cooling, across more than 16 orders of magnitudes in scale, from neutron stars to galaxy clusters.

Keywords: Abell clusters, Intracluster medium, Active galactic nuclei, Cooling flows
A Survey of Magnetic Field Strengths in the Envelopes of Molecular Clouds via the 18 cm OH Zeeman Effect. We present the results of an extensive Arecibo observational survey of magnetic field strengths in the inter-core regions of molecular clouds to determine their role in the evolution and collapse of molecular clouds as a whole. Sensitive 18 cm OH Zeeman observations of absorption lines from Galactic molecular gas in the direction of extragalactic continuum sources yielded 38 independent measurements of magnetic field strengths. Zeeman detections were achieved at the 3σ level toward nine clouds, while the others revealed sensitive upper limits to the magnetic field strength. Our results suggest that total field strengths in the inter-core regions of giant molecular clouds (GMCs) are about 15 μG.

Keywords: Interstellar magnetic fields, Star formation, Molecular clouds
The Mass Inflow and Outflow Rates of the Milky Way. We present new calculations of the mass inflow and outflow rates around the Milky Way (MW), derived from a catalog of ultraviolet metal-line high-velocity clouds (HVCs). These calculations are conducted by transforming the HVC velocities into the Galactic standard of rest (GSR) reference frame, identifying inflowing (v GSR &lt; 0 km s-1) and outflowing (v GSR &gt; 0 km s-1) populations, and using observational constraints on the distance, metallicity, dust content, covering fractions, and total silicon column density of each population. After removing HVCs associated with the Magellanic Stream and the Fermi Bubbles, we find inflow and outflow rates in cool (T ∼ 104 K) ionized gas of dM in/dt ≳ (0.53 ± 0.23)(d/12 kpc)(Z/0.2Z ⊙)-1 M ⊙ yr-1 and dM out/dt ≳ (0.16 ± 0.07)(d/12 kpc)(Z/0.5Z ⊙)-1 M ⊙ yr-1. The apparent excess of inflowing over outflowing gas suggests that the MW is currently in an inflow-dominated phase, but the presence of substantial mass flux in both directions supports a Galactic fountain model, in which gas is constantly recycled between the disk and the halo. We also find that the metal flux in both directions (in and out) is indistinguishable. By comparing the outflow rate to the Galactic star formation rate, we present the first estimate of the mass loading factor (η HVC) of the disk-wide MW wind, finding η HVC ≳ (0.10 ± 0.06)(d/12 kpc)(Z/0.5Z ⊙)-1. Including the contributions from low- and intermediate-velocity clouds and from hot gas would increase these inflow and outflow estimates.

Keywords: Galactic winds, High-velocity clouds, Galaxy accretion, Circumgalactic medium, Milky Way Galaxy fountains, Milky Way evolution, Milky Way Galaxy
Intermediate Luminosity Optical Transients (ILOTs) from Merging Giants. We suggest and study the formation of intermediate luminosity optical transients (ILOTs) from the merger of two cool giant stars. For the two stars to merge when both are in their giant phases, they must have close masses at their zero-age main sequence, and the orbital separation must be in the right range. After the two giants merge, the two cores spiral in toward each other within a common envelope. We study the energy sources of radiation in this process, which includes the ejection of mass that powers radiation by both recombination and by collision with previously ejected mass. This process includes no jets, unlike many other types of ILOTs, hence the event will not form a bipolar nebula. Using the stellar evolution numerical code MESA for two binary systems with stellar masses of (15M ⊙, 15.75M ⊙) and (31M ⊙, 31.5M ⊙), we find that the merger of the two cores releases gravitational energy that marginally ejects the entire common envelope. This implies that in many cases the two cores merge, i.e., a fatal common envelope evolution, leading to a somewhat more luminous ILOT. A typical ILOT from the merger of two cool giant stars lasts for several months to several years, and has a typical average luminosity of {L}ILOT} ≈ {10}6({M}CE}/10{M}⊙ ){L}⊙ , where M CE is the ejected common envelope mass. The merger-driven massive outflow forms dust, hence leading to a very red ILOT, possibly even infrared luminous and undetectable in the visible.

Keywords: Red supergiant stars, Close binary stars, Stellar jets, Transient sources, Variable stars
Inductive Acceleration of Ions in Poynting-flux-dominated Outflows. Two-fluid (electron-positron) plasma modeling has shown that inductive acceleration can convert Poynting flux directly into bulk kinetic energy in the relativistic flows driven by rotating magnetized neutron stars and black holes. Here, we generalize this approach by adding an ion fluid. Solutions are presented in which all particles are accelerated as the flow expands, with comparable power channeled into each of the plasma components. In an ion-dominated flow, each species reaches the limiting rigidity, according to Hillas’ criterion, in a distance significantly shorter than in a lepton-dominated flow. These solutions support the hypothesis that newly born magnetars and pulsars are potential sources of ultrahigh energy cosmic rays. The competing process of Poynting flux dissipation by magnetic reconnection is shown to be ineffective in low-density flows in which the conventionally defined electron multiplicity satisfies {κ }{{e}}≲ {10}5{≤ft(4π {L}38/{{Ω }}\right)}1/4/{{Max}}≤ft({η }ion}1/2,1\right), where L 38 × 1038 erg s-1 is the power carried by the flow in a solid angle Ω, and {η }ion} is the ratio of the ion to lepton power at launch.

Keywords: Magnetars, Relativistic jets, Rotation powered pulsars
Radio Spectroscopic Imaging of a Solar Flare Termination Shock: Split-band Feature as Evidence for Shock Compression. Solar flare termination shocks have been suggested as one of the promising drivers for particle acceleration in solar flares, yet observational evidence remains rare. By utilizing radio dynamic spectroscopic imaging of decimetric stochastic spike bursts in an eruptive flare, Chen et al. found that the bursts form a dynamic surface-like feature located at the ending points of fast plasma downflows above the looptop, interpreted as a flare termination shock. One piece of observational evidence that strongly supports the termination shock interpretation is the occasional split of the emission band into two finer lanes in frequency, similar to the split-band feature seen in fast-coronal-shock-driven type II radio bursts. Here, we perform spatially, spectrally, and temporally resolved analysis of the split-band feature of the flare termination shock event. We find that the ensemble of the radio centroids from the two split-band lanes each outlines a nearly co-spatial surface. The high-frequency lane is located slightly below its low-frequency counterpart by ∼0.8 Mm, which strongly supports the shock-upstream-downstream interpretation. Under this scenario, the density compression ratio across the shock front can be inferred from the frequency split, which implies a shock with a Mach number of up to 2.0. Further, the spatiotemporal evolution of the density compression along the shock front agrees favorably with results from magnetohydrodynamics simulations. We conclude that the detailed variations of the shock compression ratio may be due to the impact of dynamic plasma structures in the reconnection outflows, which results in distortion of the shock front.

Keywords: Solar flares, Solar magnetic reconnection, Solar radio emission, Shocks, Magnetohydrodynamical simulations
Entropy Rain: Dilution and Compression of Thermals in Stratified Domains. Large-scale convective flows called giant cells were once thought to transport the Sun’s luminosity in the solar convection zone, but recent observations have called their existence into question. In place of large-scale flows, some authors have suggested the solar luminosity may instead be transported by small droplets of rapidly falling, low-entropy fluid. This “entropy rain” could propagate as dense vortex rings, analogous to rising buoyant thermals in the Earth’s atmosphere. In this work, we develop an analytical theory describing the evolution of dense, negatively buoyant thermals. We verify the theory with 2D cylindrical and 3D Cartesian simulations of laminar, axisymmetric thermals in highly stratified atmospheres. Our results show that dense thermals fall in two categories: a stalling regime in which the droplets slow down and expand, and a falling regime in which the droplets accelerate and shrink as they propagate downwards. We estimate that solar downflows are in the falling regime and maintain their entropy perturbation against diffusion until they reach the base of the convection zone. This suggests that entropy rain may be an effective nonlocal mechanism for transporting the solar luminosity.

Keywords: Solar convective zone, Hydrodynamical simulations, Stellar convection envelopes, Solar interior
A Study of Pre-flare Solar Coronal Magnetic Fields: Magnetic Flux Ropes. Magnetic flux ropes (MFRs) are thought to be the central structures of solar eruptions, and their ideal MHD instabilities can trigger the eruption. Here we performed a study of all the MFR configurations that lead to major solar flares, either eruptive or confined, from 2011 to 2017 near the solar disk center. The coronal magnetic field is reconstructed from observed magnetograms, and based on magnetic twist distribution, we identified the MFR, which is defined as a coherent group of magnetic field lines winding an axis with more than one turn. It is found that 90% of the events possess pre-flare MFRs, and their three-dimensional structures are much more complex in details than theoretical MFR models. We further constructed a diagram based on two parameters, the magnetic twist number which controls the kink instability (KI), and the decay index which controls the torus instability (TI). It clearly shows lower limits for TI and KI thresholds, which are n crit = 1.3 and | {T}w{| }crit}=2, respectively, as all the events above n crit and nearly 90% of the events above | {T}w{| }crit} erupted. Furthermore, by such criterion, over 70% of the events can be discriminated between eruptive and confined flares, and KI seems to play a nearly equally important role as TI in discriminating between the two types of flares. More than half of the events with both parameters are below the lower limits, and 29% are eruptive. These events might be triggered by magnetic reconnection rather than MHD instabilities.

Keywords: Solar active region magnetic fields, Magnetohydrodynamics, Solar flares, Solar prominences, Solar coronal mass ejections, Solar magnetic fields, Solar filament eruptions