Sazuna/UAT_keywords huggingface dataset:
A Chandra X-Ray Survey of Optically Selected AGN Pairs. We present a Chandra archival study of optically selected active galactic nucleus (AGN) pairs at a median redshift $\bar{z}\sim 0.1$ . Out of 1286 AGN pairs (with projected separations rp &lt; 100 kpc and velocity offsets Δv &lt; 600 km s-1) optically identified from the Sloan Digital Sky Survey Seventh Data Release, we find 67 systems with archival Chandra observations, which represents the largest sample of optically selected AGN pairs studied in the X-ray. Among the 67 AGN pairs, 21 systems have both nuclei detected in the X-ray, 36 have one nucleus detected in the X-ray, and 10 have no X-ray detection. The X-ray detection rate, 78/134 = 58% (±7% 1σ Poisson errors), is significantly higher than that (23/134 = 17% ± 4%) of a comparison sample of star-forming galaxy pairs, lending support to the optical AGN classification. In the conservative case where X-ray contamination from star formation is removed, the X-ray detection rate becomes 27% ± 4%, consistent with predictions from the latest galaxy merger simulations. The 2-10 keV X-ray luminosity L2-10 keV increases with decreasing projected separation in AGN pairs for rp ≳ 15 kpc, suggesting an enhancement of black hole accretion even in early-stage mergers. On the other hand, L2-10 keV appears to decrease with decreasing projected separation at rp ≲15 kpc, which is contradictory to predictions from merger simulations. The apparent decrease in L2-10 keV of AGN pairs at rp ≲ 15 kpc may be caused by (i) enhanced absorbing columns from merger-induced gas inflows, (ii) feedback effects from early-stage mergers, and/or (iii) small number statistics. Future X-ray studies with larger samples are needed to put our results on firmer statistical ground.

Keywords: Black hole physics, X-ray active galactic nuclei, Galaxy pairs, Galaxy nuclei
Inferring Parameters of GW170502: The Loudest Intermediate-mass Black Hole Trigger in LIGO's O1/O2 data. Gravitational wave (GW) measurements provide the most robust constraints of the mass of astrophysical black holes. Using state-of-the-art GW signal models and a unique parameter estimation technique, we infer the source parameters of the loudest marginal trigger, GW170502, found by LIGO from 2015 to 2017. If this trigger is assumed to be a binary black hole merger, we find it corresponds to a total mass in the source frame of ${157}_{-41}^{+55}\,{\text{}}{M}_{\odot }$ at redshift $z={1.37}_{-0.64}^{+0.93}$ . The primary and secondary black hole masses are constrained to ${94}_{-28}^{+44}\,{\text{}}{M}_{\odot }$ and ${62}_{-25}^{+30}\,{\text{}}{M}_{\odot }$ , respectively, with 90% confidence. Across all signal models, we find ≳70% probability for the effective spin parameter χeff &gt; 0.1. Furthermore, we find that the inclusion of higher-order modes in the analysis narrows the confidence region for the primary black hole mass by 10%; however, the evidence for these modes in the data remains negligible. The techniques outlined in this study could lead to robust inference of the physical parameters for all intermediate-mass black hole binary candidates (≳100 M⊙) in the current GW network.

Keywords: Intermediate-mass black holes, Gravitational wave sources
Solving Grain Size Inconsistency between ALMA Polarization and VLA Continuum in the Ophiuchus IRS 48 Protoplanetary Disk. The protoplanetary disk around Ophiuchus IRS 48 shows an azimuthally asymmetric dust distribution in (sub)millimeter observations, which is interpreted as a vortex, where millimeter/centimeter-sized particles are trapped at the location of the continuum peak. In this paper, we present 860 μm ALMA observations of polarized dust emission from this disk. The polarized emission was detected toward a part of the disk. The polarization vectors are parallel to the disk minor axis, and the polarization fraction was derived to be 1%-2%. These characteristics are consistent with models of self-scattering of submillimeter-wave emission, which indicate a maximum grain size of ∼100 μm. However, this is inconsistent with the previous interpretation of millimeter/centimeter dust particles being trapped by a vortex. To explain both ALMA polarization and previous ALMA and Very Large Array observations, we suggest that the thermal emission at 860 μm wavelength is optically thick (τabs ∼ 7.3) at the dust trap with a maximum observable grain size of ∼100 μm rather than an optically thin case with centimeter-sized dust grains. We note that we cannot rule out that larger dust grains are accumulated near the midplane if the 860 μm thermal emission is optically thick.

Keywords: Polarimetry, Protoplanetary disks, Planet formation
The Origin of Massive Stars: The Inertial-inflow Model. We address the problem of the origin of massive stars, namely the origin, path, and timescale of the mass flows that create them. Based on extensive numerical simulations, we propose a scenario where massive stars are assembled by large-scale, converging, inertial flows that naturally occur in supersonic turbulence. We refer to this scenario of massive-star formation as the inertial-inflow model. This model stems directly from the idea that the mass distribution of stars is primarily the result of turbulent fragmentation. Under this hypothesis, the statistical properties of turbulence determine the formation timescale and mass of prestellar cores, posing definite constraints on the formation mechanism of massive stars. We quantify such constraints by analyzing a simulation of supernova-driven turbulence in a 250 pc region of the interstellar medium, describing the formation of hundreds of massive stars over a time of approximately 30 Myr. Due to the large size of our statistical sample, we can say with full confidence that massive stars in general do not form from the collapse of massive cores nor from competitive accretion, as both models are incompatible with the numerical results. We also compute synthetic continuum observables in the Herschel and ALMA bands. We find that, depending on the distance of the observed regions, estimates of core mass based on commonly used methods may exceed the actual core masses by up to two orders of magnitude and that there is essentially no correlation between estimated and real core masses.

Keywords: Magnetohydrodynamics, Interstellar dynamics, Star formation, Interstellar medium, Protostars
Exploring the Energy Sources Powering the Light Curve of the Type Ibn Supernova PS15dpn and the Mass-loss History of the SN Progenitor. PS15dpn is a luminous rapidly rising Type Ibn supernova (SN) discovered by Pan-STARRS1. Previous study has showed that its bolometric light curve (LC) cannot be explained by the 56Ni model. In this paper, we used the 56Ni model, the magnetar model, the circumstellar interaction (CSI) model, and the CSI plus 56Ni model to fit the bolometric LC of PS15dpn. We found that the 56Ni model can fit the bolometric LC but the parameters are unrealistic, and that the magnetar model, the CSI model, and the CSI plus 56Ni model can match the data with reasonable parameters. Considering the fact that the emission lines indicative of the interaction between the ejecta and the circumstellar medium (CSM) have been confirmed, and that the SNe produced by the explosions of massive stars can synthesize moderate amounts of 56Ni, we suggest that the CSI plus 56Ni model is the most promising model. Assuming that the CSM is a shell (wind), the masses of the ejecta, the CSM, and the 56Ni are ${15.79}_{-4.77}^{+5.44}$ ${{\rm{M}}}_{\odot }$ ( ${14.18}_{-1.64}^{+1.81}$ M⊙), ${0.84}_{-0.10}^{+0.13}$ M⊙ ( ${0.88}_{-0.12}^{+0.11}$ M⊙), and ${0.32}_{-0.11}^{+0.11}$ M⊙ ( ${0.16}_{-0.08}^{+0.13}$ M⊙), respectively. The inferred ejecta masses are consistent with the scenario that the progenitors of SNe Ibn are massive Wolf-Rayet stars. Adopting the shell CSM scenario, the shell might be expelled by an eruption of the progenitor just ∼17-167 days prior to the SN explosion; for the wind scenario, the inferred mass-loss rate of the wind is ∼8.0 M⊙ yr-1, indicating that the wind is a "super-wind" having an extremely high mass-loss rate.

Keywords: Core-collapse supernovae, Type Ib supernovae, Circumstellar matter, Magnetars, Supernovae
High-resolution Observations of Small-scale Flux Emergence by GST. Recent observations demonstrated that emerging flux regions, which constitute the early stage of solar active regions, consist of emergence of numerous small-scale magnetic elements. They in turn interact, merge, and form mature sunspots. However, observations of fine magnetic structures on photosphere with subarcsecond resolution are very rare due to limitations of observing facilities. In this work, taking advantage of the high resolution of the 1.6 m Goode Solar Telescope, we jointly analyze vector magnetic fields, continuum images, and Hα observations of NOAA AR 12665 on 2017 July 13, with the goal of understanding the signatures of small-scale flux emergence, as well as their atmospheric responses as they emerge through multiple heights in the photosphere and chromosphere. Under such a high resolution of 0"1-0"2, our results confirm two kinds of small-scale flux emergence: magnetic flux sheet emergence associated with the newly forming granules, and the traditional magnetic flux loop emergence. With direct imaging in the broadband TiO, we observe that both types of flux emergence are associated with darkening of granular boundaries, while only flux sheets elongate granules along the direction of emerging magnetic fields and expand laterally. With a life span of 10 ∼ 15 minutes, the total emerged vertical flux is on the order of 1018 Mx for both types of emergence. The magnitudes of the vertical and horizontal fields are comparable in the flux sheets, while the former is stronger in flux loops. Hα observations reveal transient brightenings in the wings in the events of magnetic loop emergence, which are most probably the signatures of Ellerman bombs.

Keywords: Solar activity, Solar magnetic fields, Solar magnetic flux emergence, Solar photosphere
The Quest for a Plausible Formation Route of Formyl Cyanide in the Interstellar Medium: a State-of-the-art Quantum-chemical and Kinetic Approach. Interstellar complex organic molecules are assumed to be mainly formed on dust-grain surfaces. However, neutral gas-phase reactions in the interstellar medium can play an important role. In this paper, by investigating the reaction between aldehydes and the cyano radical, we show that both formaldehyde (CH2O) and acetaldehyde (CH3CHO) can lead to the formation of formyl cyanide (HCOCN). Owing to accurate quantum-chemical computations followed by rate constant evaluations, we have been able to suggest and validate an effective mechanism for the formation of HCOCN, one of the molecules observed in the ISM. Quite interestingly, the mechanism starting from CH2O is very effective at a low temperature, while that involving CH3CHO becomes more efficient at temperatures above 200 K.

Keywords: Interstellar molecules, Reaction rates, Astrochemistry, Computational methods, Interstellar clouds, Interstellar medium
Identifying Magnetic Reconnection in 2D Hybrid Vlasov Maxwell Simulations with Convolutional Neural Networks. Magnetic reconnection is a fundamental process that quickly releases magnetic energy stored in a plasma. Identifying from simulation outputs where reconnection is taking place is nontrivial and, in general, has to be performed by human experts. Hence, it would be valuable if such an identification process could be automated. Here, we demonstrate that a machine-learning algorithm can help to identify reconnection in 2D simulations of collisionless plasma turbulence. Using a Hybrid Vlasov Maxwell model, a data set containing over 2000 potential reconnection events was generated and subsequently labeled by human experts. We test and compare two machine-learning approaches with different configurations on this data set. The best results are obtained with a convolutional neural network combined with an "image cropping" step that zooms in on potential reconnection sites. With this method, more than 70% of reconnection events can be identified correctly. The importance of different physical variables is evaluated by studying how they affect the accuracy of predictions. Finally, we also discuss various possible causes for wrong predictions from the proposed model.

Keywords: Convolutional neural networks, Solar magnetic reconnection
Solar Wind Turbulence from 1 to 45 au. I. Evidence for Dissipation of Magnetic Fluctuations Using Voyager and ACE Observations. As part of a published effort to study low-frequency magnetic waves excited by newborn interstellar pickup ions seen by the Voyager spacecraft, we developed a set of control intervals that represent the background turbulence when the observations are not dominated by wave excitation. This paper begins an effort to better understand solar wind turbulence from 1 to 45 au while spanning greater than one solar cycle. We first focus on the diagnostics marking the onset of dissipation. This includes an expected break in the power spectrum at frequencies greater than the proton cyclotron frequency and a resultant steepening of the spectrum at higher frequencies. Contrary to what is established at 1 au, we only see the spectral break in rare instances. The expected scaling of the spectral index with the turbulence rate is seen, but it is not as clearly established as it was at 1 au. We also find that both Voyager data from 1 to 45 au and Advanced Composition Explorer data from 1 au show significant bias of the magnetic helicity at dissipation scales when the dissipation-range power-law spectral index steepens. We conclude that dissipation dynamics are similar throughout the heliosphere in so far as we have examined to date.

Keywords: Magnetohydrodynamics, Solar wind, Heliosphere
Solar Wind Turbulence from 1 to 45 au. II. Analysis of Inertial-range Fluctuations Using Voyager and ACE Observations. We examine both Voyager and Advanced Composition Explorer magnetic field measurements at frequencies that characterize the inertial range using traditional polarization techniques that are designed to characterize plasma waves. Although we find good agreement with both the anticipated spectral index of the power spectrum and the scaling of magnetic power with heliocentric distance, we do not find that the polarization analyses yield results that can be readily described by plasma wave theory. The fluctuations are not circularly polarized and there is a markedly reduced coherence between the components of the fluctuation. The degree of polarization is also generally low, although not as low as the coherence, and the minimum variance direction is essentially random. We conclude that traditional plasma wave theory may not offer a good description for inertial-range fluctuations.

Keywords: Magnetohydrodynamics, Solar wind, Heliosphere
Solar Wind Turbulence from 1 to 45 au. III. Anisotropy of Magnetic Fluctuations in the Inertial Range Using Voyager and ACE Observations. We examine both Voyager and Advanced Composition Explorer magnetic field measurements at frequencies that characterize the inertial range and evaluate the anisotropy of the fluctuations as they relate to both the compressive component and underlying wavevector anisotropy of the turbulence. The magnetic fluctuation anisotropy as it relates to the compressive component is directly dependent upon both the plasma beta of the thermal proton component and the ratio of magnetic fluctuation magnitude to the strength of the mean magnetic field. This has been seen before at 1 au. The magnetic fluctuation anisotropy in the plane perpendicular to the mean magnetic field, which is a measure of the anisotropy of the underlying wavevector distribution, should depend on the angle between the mean magnetic field and the radial direction and should be confined to values between one and the index of the power spectrum, which is typically 5/3. Our results show that the average of this anisotropy exceeds the value of the spectral index and is out of bounds with the theory. Although the results are suggestive of past analyses, we find that spherical expansion of the turbulence may offer at least a partial explanation of the apparent amplification of this measured anisotropy.

Keywords: Magnetohydrodynamics, Solar wind, Heliosphere
Solar Wind Turbulence from 1 to 45 au. IV. Turbulent Transport and Heating of the Solar Wind Using Voyager Observations. We adopt the theory for turbulent transport of energy by solar wind fluctuations and apply that theory to observations by the Voyager 1 and 2 spacecraft to obtain rates of thermal proton heating that are controlled by two sources: the large-scale fluctuations in the solar wind that arise from solar sources and the excitation of waves by newborn interstellar ions. In the process, we compute magnetic spectra for 839 data intervals spanning the range from 1 to 35 au when thermal ion data is available and use those spectra to obtain independent estimates for the energy cascade rates at intermediate scales that we assume equals the rate of thermal proton heating by the turbulence. We compare three analyses that describe different aspects of the solar wind heating problem: the rate of energy cascade through the intermediate scales of the magnetic spectrum, the rate at which energy is supplied to that cascade from the large-scale fluctuations as described by magnetohydrodynamic transport theory, and the rate at which energy is injected into the spectrum via wave excitation by newborn interstellar ions. The first two expressions are found to be in good agreement while the latter source dynamics become important beyond 10 au.

Keywords: Magnetohydrodynamics, Solar wind, Heliosphere
The Assembly History of M87 through Radial Variations in Chemical Abundances of Its Field Star and Globular Cluster Populations. We present an extensive study of spectroscopically derived chemical abundances for M87 and its globular cluster (GC) system. Using observations from the Mitchell spectrograph at McDonald, LRIS at Keck, and Hectospec on the MMT, we derive new metallicity gradients from ∼2 to 140 kpc. We use a novel hierarchical statistical framework to simultaneously separate the GC system into subpopulations while measuring the metallicity gradients of those subpopulations. We create physically motivated spectral stacks of the GC subpopulations by leveraging the output of this statistical framework to perform the first application of abundance tagging in a massive early-type galaxy to better constrain the origins of the GC subpopulations and thus the assembly history of M87. We find a metal-poor, α-enhanced population of GCs in both the inner and outer halos unanticipated by current cosmological simulations of galaxy evolution. We use the remarkably flat metallicity gradients we find for both the metal-rich and metal-poor GC subpopulations in the inner halo as tentative evidence that some amount of the metal-poor GCs formed directly in the halo of M87 at high redshift.

Keywords: Globular star clusters, Galaxy chemical evolution, Galaxy stellar content, Galaxy stellar halos, Galaxy mergers
Limits on Protoplanet Growth by Accretion of Small Solids. This paper identifies constraints on the growth of a small planetary core (0.3 M⊕) that accretes millimeter-sized pebbles from a gaseous disk. We construct time-dependent spherical envelope models that capture physical processes that are not included in existing global hydrodynamic simulations, including particle size evolution, dust transport, and realistic gas equations of state. We assume a low enough disk density that pebbles are marginally coupled to the gas and are trapped efficiently near the core Bondi radius. Pebbles then drift rapidly enough to experience erosion by sandblasting, mutual collisions, and sublimation of water ice. We find that pebble fragmentation is more efficient than dust resticking. Therefore the high pebble accretion rate ${\dot{M}}_{p}$ needed to build a core of mass &gt;M⊕ leads to a high envelope metallicity and grain opacity. Above ${\dot{M}}_{p}\sim 1\times {10}^{-7}\,{M}_{\oplus }$ yr-1, and without other luminosity sources, convective motions expand near the Bondi radius. The warm, dusty, and turbulent envelope buffers the inward drift of pebble debris: given a turbulent concentration factor fturb ≳ 1 near the lower convective boundary, the core growth rate is limited to 1 × 10-7 fturb M⊕ yr-1 and the e-folding time 3/fturb Myr. The remainder of the solid debris is expelled as highly processed silicates. Pebble ice never reaches the core, and the envelope contains comparable amounts of H2/He and metals. We interpret our results using simpler steady models and semianalytical estimates. Future global simulations incorporating the processes modeled here are needed to understand the influence of rotation and vertical disk structure.

Keywords: Astrophysical dust processes, Planetary atmospheres, Radiative transfer, Planet formation
Mirror-wave Structures in the Solar Wind: Grad-Shafranov Reconstruction, MHD, and Hall MHD Simulations with Double-polytropic Energy Closures. Mirror-mode waves with anticorrelated density and magnetic field are widely observed in the solar wind and planetary magnetospheres. In this study we analyze the characteristics of three mirror-wave events observed by the Magnetospheric Multiscale Mission in the Earth's magnetosheath based on the Grad-Shafranov (GS) reconstruction model with temperature anisotropy. The GS scheme solves steady, two-dimensional MHD equations with field-aligned flow from the plasma and magnetic field measurements taken by a single spacecraft traversing across a coherent field structure. The reconstructed 2D plasma and field maps are obtained in the de Hoffmann-Teller frame and on the plane perpendicular to the invariant axis. The energy closures are a set of empirical energy laws with two polytropic exponents inferred from the observed mirror events which are in the ranges of ${\gamma }_{\perp }=0.6\sim 0.89$ and ${\gamma }_{| | }=0.99\sim 1.35$ . It is shown that the mirror waves are nonpropagating with linear magnetic field polarization and possess anticorrelated density, temperatures, and magnetic field with the widths of 10-40 ion inertial lengths. The double-polytropic MHD and Hall MHD simulations of mirror instability show consistent results with the GS reconstructions in terms of field-line geometry, phase relations and the sizes of mirror waves, etc.

Keywords: Space plasmas, Magnetohydrodynamics, Plasma physics, Solar wind, Alfven waves, Magnetohydrodynamical simulations