Sazuna/UAT_keywords huggingface dataset:
The Role of Adaptive Ray Tracing in Analyzing Black Hole Structure. The recent advent of the Event Horizon Telescope (EHT) has made direct imaging of supermassive black holes a reality. Simulated images of black holes produced via general relativistic ray tracing and radiative transfer provide a key counterpart to these observational efforts. Black hole images have a wide range of physically interesting image structures, ranging from extremely fine scales in their lensed "photon rings" to the very large scales in their relativistic jets. The multiscale nature of the black hole system is therefore suitable for a multiscale approach to generate simulated images that capture all key elements of the system. Here, we present a prescription for adaptive ray tracing, which enables efficient computation of extremely high-resolution images of black holes. Using the polarized ray-tracing code IPOLE, we image a combination of semianalytic and general relativistic magnetohydrodynamic (GRMHD) models, and we show that images can be reproduced with a mean squared error of less than 0.1% even after tracing 12× fewer rays. We then use adaptive ray tracing to explore the properties of the photon ring. We illustrate the behavior of individual subrings in GRMHD simulations, and we explore their signatures in interferometric visibilities.

Keywords: Radiative transfer simulations, Radio interferometry, Gravitational lensing, Black holes
The Observability of Plasmoid-powered γ-Ray Flares with the Fermi Large Area Telescope. The exact mechanism for the production of fast γ-ray variability in blazars remains debated. Magnetic reconnection, in which plasmoids filled with relativistic particles and magnetic fields are formed, is a viable candidate to explain the broadband electromagnetic spectrum and variability of these objects. Using state-of-the-art magnetic reconnection simulations, we generate realistic γ-ray light curves that would be observed with the Fermi Large Area Telescope. A comparison with observed γ-ray flares from flat spectrum radio quasars (FSRQs) reveals that magnetic reconnection events lead to comparable flux levels and variability patterns, in particular, when the reconnection layer is slightly misaligned with the line of sight. Emission from fast plasmoids moving close to the line of sight could explain the fast variability on the timescales of minutes for which evidence has been found in observations of FSRQs. Our results motivate improvements in existing radiative transfer simulations as well as dedicated searches for fast variability as evidence for magnetic reconnection events.

Keywords: Blazars, Relativistic jets, Non-thermal radiation sources, Time domain astronomy, Gamma-ray astronomy
The Intrinsic Scatter of Galaxy Scaling Relations. We present a compendium of disk galaxy scaling relations and a detailed characterization of their intrinsic scatter. Observed scaling relations are typically characterized by their slope, intercept, and scatter; however, these parameters are a mixture of observational errors and astrophysical processes. We introduce a novel Bayesian framework for computing the intrinsic scatter of scaling relations that accounts for nonlinear error propagation and covariant uncertainties. Bayesian intrinsic scatters are ∼25% more accurate than those obtained with a first-order classical method, which systematically underestimates the true intrinsic scatter. Structural galaxy scaling relations based on velocity (V23.5), size (R23.5), luminosity (L23.5), color (g - z), central stellar surface density (Σ1), stellar mass (M*), dynamical mass (Mdyn), stellar angular momentum (j*), and dynamical angular momentum (jdyn) are examined to demonstrate the power and importance of the Bayesian formalism. Our analysis is based on a diverse selection of over 1000 late-type galaxies from the Photometry and Rotation Curve Observations from Extragalactic Surveys compilation with deep optical photometry and extended rotation curves. We determine the tightest relation for each parameter by intrinsic orthogonal scatter, finding M* - V23.5, R23.5 - j*, and L23.5 - jdyn to be especially tight. The scatter of the R23.5 - L23.5, V23.5 - (g - z), and R23.5 - jdyn relations is mostly intrinsic, making them ideal for galaxy formation and evolutionary studies. Our code to compute the Bayesian intrinsic scatter of any scaling relation is also presented. We quantify the correlated nature of many uncertainties in galaxy scaling relations and scrutinize the uncertain nature of disk inclination corrections and their effect on scatter estimates.

Keywords: Galaxy formation, Bayesian statistics, Disk galaxies, Galaxy properties, Galaxy structure, Galaxy physics, Astrostatistics, Scaling relations, Galaxy photometry, Galaxy rotation curves, Galaxies
A Hard Look at Relativistic Reverberation in MCG-5-23-16 and SWIFT J2127.4+5654: Testing the Lamppost Model. X-ray reverberation mapping has emerged as a new tool to probe accretion in active galactic nuclei (AGN), providing a potentially powerful probe of accretion at the black hole scale. The lags, along with relativistic spectral signatures are often interpreted in light of the lamppost model. Focusing specifically on testing the prediction of the relativistic reverberation model, we have targeted several of the brightest Seyfert Galaxies in X-rays with different observing programs. Here, we report the results from two large campaigns with NuSTAR targeting MCG-5-23-16 and SWIFT J2127.4+5654 to test the model predictions in the 3-50 keV band. These are two of three sources that showed indications of a delayed Compton hump in early data. With triple the previously analyzed exposures, we find no evidence for relativistic reverberation in MCG-5-23-16, and the energy-dependent lags are consistent with a log-linear continuum. In SWIFT J2127.4+5654, although a continuum-only model explains the data, the relativistic reverberation model provides a significant improvement to the energy and frequency-dependent lags, but with parameters that are not consistent with the time-averaged spectrum. This adds to mounting evidence showing that the lag data is not consistent with a static lamppost model.

Keywords: X-ray active galactic nuclei, Active galactic nuclei, High energy astrophysics, Astrophysical black holes
A Self-consistent, Time-dependent Treatment of Dynamical Friction: New Insights Regarding Core Stalling and Dynamical Buoyancy. Dynamical friction is typically regarded as a secular process, in which the subject ("perturber") evolves very slowly (secular approximation) and has been introduced to the host over a long time (adiabatic approximation). These assumptions imply that dynamical friction arises from the LBK torque with nonzero contribution only from purely resonant orbits. However, dynamical friction is only of astrophysical interest if its timescale is shorter than the age of the universe. In this paper we therefore relax the adiabatic and secular approximations. We first derive a generalized LBK torque, which reduces to the LBK torque in the adiabatic limit, and show that it gives rise to transient oscillations due to nonresonant orbits that slowly damp out, giving way to the LBK torque. This is analogous to how a forced, damped oscillator undergoes transients before settling to a steady state, except that here the damping is due to phase mixing rather than dissipation. Next, we present a self-consistent treatment that properly accounts for time dependence of the perturber potential and circular frequency (memory effect), which we use to examine orbital decay in a cored galaxy. We find that the memory effect results in a phase of accelerated, super-Chandrasekhar friction before the perturber stalls at a critical radius, Rcrit, in the core (core stalling). Inside Rcrit the torque flips sign, giving rise to dynamical buoyancy, which counteracts friction and causes the perturber to stall. This phenomenology is consistent with N-body simulations, but has thus far eluded proper explanation.

Keywords: Galaxy dark matter halos, Orbital resonances, Stellar dynamics, Galaxy nuclei, Gravitational interaction, Dynamical friction
The Color and Brightness of the F-corona Inferred from the 2019 July 2 Total Solar Eclipse. Total solar eclipses (TSEs) provide a unique opportunity to quantify the properties of the K-corona (electrons), F-corona (dust), and E-corona (ions) continuously from the solar surface out to a few solar radii. We apply a novel inversion method to separate emission from the K- and F-corona continua using unpolarized total brightness (tB) observations from five 0.5 nm bandpasses acquired during the 2019 July 2 TSE between 529.5 and 788.4 nm. The wavelength dependence relative to the photosphere (i.e., color) of the F-corona itself is used to infer the tB of the K- and F-corona for each line of sight. We compare our K-corona emission results with the Mauna Loa Solar Observatory (MLSO) K-Cor polarized brightness (pB) observations from the day of the eclipse, and the forward modeled K-corona intensity from the Predictive Science Inc. (PSI) magnetohydrodynamic (MHD) model prediction. Our results are generally consistent with previous work and match both the MLSO data and PSI-MHD predictions quite well, supporting the validity of our approach and of the PSI-MHD model. However, we find that the tB of the F-corona is higher than expected in the low corona, perhaps indicating that the F-corona is slightly polarized—challenging the common assumption that the F-corona is entirely unpolarized.

Keywords: Solar K corona, Solar eclipses, Solar optical telescopes, Solar F corona, Solar corona
Accurate Identification of Galaxy Mergers with Stellar Kinematics. To determine the importance of merging galaxies to galaxy evolution, it is necessary to design classification tools that can identify the different types and stages of merging galaxies. Previously, using GADGET-3/SUNRISE simulations of merging galaxies and linear discriminant analysis (LDA), we created an accurate merging galaxy classifier based on imaging predictors. Here, we develop a complementary tool, based on stellar kinematic predictors, derived from the same simulation suite. We design mock stellar velocity and velocity dispersion maps to mimic the specifications of the Mapping Nearby Galaxies at Apache Point (MaNGA) integral field spectroscopy (IFS) survey, and utilize an LDA to create a classification, based on a linear combination of 11 kinematic predictors. The classification varies significantly with mass ratio; the major (minor) merger classifications have a mean statistical accuracy of 80% (70%), a precision of 90% (85%), and a recall of 75% (60%). The major mergers are best identified by predictors that trace global kinematic features, while the minor mergers rely on local features that trace a secondary stellar component. While the kinematic classification is less accurate than the imaging classification, the kinematic predictors are better at identifying post-coalescence mergers. A combined imaging + kinematic classification has the potential to reveal more complete merger samples from imaging and IFS surveys such as MaNGA. We note that since the suite of simulations used to train the classifier covers a limited range of galaxy properties (i.e., the galaxies are of intermediate mass, and disk-dominated), the results may not be applicable to all MaNGA galaxies.

Keywords: Stellar kinematics, Galaxy interactions, Galaxy kinematics, Galaxy mergers, Galaxy evolution
A Large Fraction of Hydrogen-rich Supernova Progenitors Experience Elevated Mass Loss Shortly Prior to Explosion. Spectroscopic detection of narrow emission lines traces the presence of circumstellar mass distributions around massive stars exploding as core-collapse supernovae. Transient emission lines disappearing shortly after the supernova explosion suggest that the material spatial extent is compact and implies an increased mass loss shortly prior to explosion. Here, we present a systematic survey for such transient emission lines (Flash Spectroscopy) among Type II supernovae detected in the first year of the Zwicky Transient Facility survey. We find that at least six out of ten events for which a spectrum was obtained within two days of the estimated explosion time show evidence for such transient flash lines. Our measured flash event fraction (&gt;30% at 95% confidence level) indicates that elevated mass loss is a common process occurring in massive stars that are about to explode as supernovae.

Keywords: Observational astronomy, Type II supernovae, Massive stars, Transient sources, Stellar mass loss, Flash spectra
The Interstellar Medium toward the Galactic Center Source 2MASS J17470898-2829561. We describe and discuss remarkable infrared spectra, covering key portions of the 2-5 μm wavelength interval, of the probable OH/IR supergiant 2MASS J17470898-2829561 (2M1747), located in direction of the Sgr B molecular cloud complex within the Central Molecular Zone (CMZ) of the Galaxy. This star was originally singled out for examination based on its suitability for spectroscopy of lines of ${{\rm{H}}}_{3}^{+}$ in the CMZ. Analysis of the spectra shows that 2M1747 is deeply embedded within Sgr B1, with AV ≳ 100 mag, making it the only star within Sgr B for which infrared spectra have been obtained at present, and thereby a unique infrared probe of the dense interstellar medium within the CMZ. Despite the high extinction, spectra of 2M1747 reveal a veiled photosphere in the K band and circumstellar gas in the M band, giving clues as to its nature. Its 3.5-4.0 μm spectrum contains the strongest absorption lines of ${{\rm{H}}}_{3}^{+}$ observed toward any object to date. The 4.5-4.8 μm spectrum has impressively deep and wide absorption lines of interstellar CO, most of which arise in dense gas within Sgr B1. The 3-5 μm spectrum also contains several solid-state absorption features, which are characteristic of both dense and diffuse clouds, and which raise questions about the identifications of some of these features. We discuss the nature of the star, the extinction to it, the extinction law for dust in the CMZ, and the identifications of the various solid-state features and where they are produced along this complex line of sight.

Keywords: Interstellar molecules, High resolution spectroscopy, Galactic center, Interstellar line absorption, Interstellar dust extinction, Dense interstellar clouds, Infrared astronomy, Interstellar clouds, OH/IR stars, Diffuse interstellar clouds
Secondary Energization in Compressing Plasmoids during Magnetic Reconnection. Plasmoids—magnetized quasi-circular structures formed self-consistently in reconnecting current sheets—were previously considered to be the graveyards of energetic particles. In this paper, we demonstrate the important role of plasmoids in shaping the particle energy spectrum in relativistic reconnection (i.e., with upstream magnetization σup ≫ 1). Using 2D particle-in-cell simulations in pair plasmas with σup = 10 and 100, we study a secondary particle energization process that takes place inside compressing plasmoids. We demonstrate that plasmoids grow in time, while their interiors compress, amplifying the internal magnetic field. The magnetic field felt by particles injected in an isolated plasmoid increases linearly with time, which leads to particle energization as a result of magnetic moment conservation. For particles injected with a power-law distribution function, this energization process acts in such a way that the shape of the injected power law is conserved, while producing an additional nonthermal tail f(E) ∝ E-3 at higher energies, followed by an exponential cutoff. The cutoff energy, which increases with time as ${E}_{\mathrm{cut}}\propto \sqrt{t}$ , can greatly exceed σupmec2. We analytically predict the secondary acceleration timescale and the shape of the emerging particle energy spectrum, which can be of major importance in certain astrophysical systems, such as blazar jets.

Keywords: Accretion, X-ray binary stars, High energy astrophysics, Blazars, Plasma astrophysics, Pulsars, Stellar accretion disks
Investigating Clumpy Galaxies in the Sloan Digital Sky Survey Stripe 82 Using the Galaxy Zoo. Giant, star-forming clumps are a common feature prevalent among high-redshift star-forming galaxies and play a critical role in shaping their chaotic morphologies and yet, their nature and role in galaxy evolution remains to be fully understood. A majority of the effort to study clumps has been focused at high redshifts, and local clump studies have often suffered from small sample sizes. In this work, we present an analysis of clump properties in the local universe, and for the first time, performed with a statistically significant sample. With the help of the citizen science-powered Galaxy Zoo: Hubble project, we select a sample of 92 z &lt; 0.06 clumpy galaxies in Sloan Digital Sky Survey Stripe 82 galaxies. Within this sample, we identify 543 clumps using a contrast-based image analysis algorithm and perform photometry as well as estimate their stellar population properties. The overall properties of our z &lt; 0.06 clump sample are comparable to the high-redshift clumps. However, contrary to the high-redshift studies, we find no evidence of a gradient in clump ages or masses as a function of their galactocentric distances. Our results challenge the inward migration scenario for clump evolution for the local universe, potentially suggesting a larger contribution of ex situ clumps and/or longer clump migration timescales.

Keywords: Observational astronomy, Starburst galaxies, Galaxy formation, Star forming regions, Star formation, Galaxy evolution, Catalogs
Magnetohydrodynamic Wave Modes of Solar Magnetic Flux Tubes with an Elliptical Cross Section. The purpose of this paper is to study the behavior of magnetohydrodynamic (MHD) wave modes that propagate in compressible magnetic flux tubes with an elliptical cross section embedded in a magnetic environment. The dispersion relation that describes the behavior of MHD wave modes permitted in an elliptical magnetic flux tube is solved numerically. Distortion of the spatial structure of the purely real eigenmodes from the well-known circular flux tube model has been considered. It has been studied under both photospheric and coronal conditions. It has been shown that (i) solutions in the form of even Mathieu functions are more sensitive to the value of eccentricity than solutions with the form of odd Mathieu functions; (ii) if the ellipticity of the cross section of the magnetic flux tube increases, a sausage mode (m = 0) cannot be easily identified; (iii) even solutions that correspond to the fluting mode (m = 3) can be misinterpreted as a kink mode (m = 1) due to their similarities. In contrast to the fluting modes that are polarized along the major axis and strongly depend on the ellipticity of the magnetic flux tube, the kink and sausage surface modes are practically unaffected by ellipticity. Several examples of the spatial structure of the eigenmodes permitted in the pores and sunspots have been visualized. The solutions obtained in the approximation of cylindrical symmetry are in agreement with previous studies.

Keywords: Solar corona, Magnetohydrodynamics, Solar photosphere
Elemental Abundances of Prominence Material inside ICMEs. A small number of interplanetary coronal mass ejections (ICMEs) have been identified that contain measurable contributions from prominence plasma. In situ measurements from during these events are marked by the presence of unusually low-charge states of C, O, and Fe, representing ionization equilibrium formation temperatures of ∼104-105 K, consistent with prominence material observed at the Sun. We present a thorough analysis of the elemental abundances of a wide variety of heavy ions, measured by Advanced Composition Explorer/SWICS, in prominence material observed in the solar wind. We find that prominence material observed in situ tends to be more enriched in heavy ions than the surrounding ICME plasma and the fast and slow solar wind. We also find that the material is on average moderately enhanced in low first ionization potential elements compared to photospheric abundances, with values that lie between fast and slow solar wind. In rare instances, where in situ prominence material is observed to have clear, persistent, low-charge states over longer periods of time, it exhibits elemental abundances that are photospheric in nature. However, in most prominence events we see indications that the associated material contains a mixture of prominence and adjacent ICME plasma. The anomalous behavior of the elemental and ionic composition in ICMEs with and without prominence material can be used to study physical processes that occur during CME initiation and release.

Keywords: Solar prominences, Heliosphere, Solar wind, Solar filaments, Solar coronal mass ejections
R-process-rich Stellar Streams in the Milky Way. We present high-resolution Magellan/MIKE spectra of 22 bright (9 &lt; V &lt; 13.5) metal-poor stars (-3.18 &lt; [Fe/H] &lt; -1.37) in three different stellar streams, the Helmi debris stream, the Helmi trail stream, and the ω Centauri progenitor stream. We augment our Helmi debris sample with results for 10 stars by Roederer et al. for a total of 32 stars. Detailed chemical abundances of light elements as well as heavy neutron-capture elements have been determined for our 22 stars. All three streams contain carbon-enhanced stars. For 13 stars, neutron-capture element lines were detectable, and they all show signatures in agreement with the scaled solar r-process pattern, albeit with a large spread of -0.5 &lt; [Eu/Fe] &lt; +1.3. Eight of these stars show an additional small s-process contribution superposed onto their r-process pattern. This could be discerned because of the relatively high signal-to-noise ratio of the spectra given that the stars are close by in the halo. Our results suggest that the progenitors of these streams experienced one or more r-process events early on, such as a neutron star merger or another prolific r-process source. This widely enriched these host systems before their accretion by the Milky Way. The small s-process contribution suggests the presence of asymptotic giant branch stars and associated local (inhomogeneous) enrichment as part of the ongoing chemical evolution by low-mass stars. Stars in stellar streams may thus be a promising avenue for studying the detailed history of large dwarf galaxies and their role in halo assembly with easily accessible targets for high-quality spectra of many stars. * This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile.

Keywords: Population II stars, Milky Way stellar halo, Dwarf galaxies, Halo stars