adsabs/SciX_UAT_keywords huggingface dataset:
Observations of Magnetic Reconnection and Particle Acceleration Locations in Solar Coronal Jets

We present a multiwavelength analysis of two flare-related jets on 2014 November 13, using data from the Solar Dynamics Observatory/Atmospheric Imaging Assembly (SDO/AIA), the Reuven High Energy Solar Spectroscopic Imager (RHESSI), the Hinode/X-ray Telescope (XRT), and the Interface Region Imaging Spectrograph (IRIS). Unlike most coronal jets, where hard X-ray (HXR) emissions are usually observed near the jet base, in these events HXR emissions are found at several locations, including in the corona. We carry out the first differential emission measure analysis that combines both AIA (and XRT, when available) bandpass filter data and RHESSI HXR measurements for coronal jets, and obtain self-consistent results across a wide temperature range and into nonthermal energies. In both events, hot plasma first appears at the jet base, but as the base plasma gradually cools, hot plasma also appears near the jet top. Moreover, nonthermal electrons, while only mildly energetic, are found in multiple HXR locations and contain large amounts of total energy. In particular, the energetic electrons that produce the HXR sources at the jet top are accelerated near the top location, rather than traveling from a reconnection site at the jet base. This means that there is more than one particle acceleration site in each event. Jet velocities are consistent with previous studies, including the upward and downward velocities around ~200 km s-1 and ~100 km s-1, respectively, and fast outflows of 400-700 km s-1. We also examine the energy partition in the later event, and find that the nonthermal energy in the accelerated electrons is most significant compared to the other energy forms considered. We discuss the interpretations and provide constraints on the mechanisms for coronal jet formation.

Keywords: the sun; solar x-ray flares; solar energetic particles; jets
Pulsar Timing Response to Gravitational Waves with Spherical Wave Fronts from a Massive Compact Source in the Quadrupole Approximation

Pulsar timing arrays (PTAs) are searching for nanohertz-frequency gravitational waves (GWs) through cross-correlation of pulse arrival times from a set of radio pulsars. PTAs have relied on a frequency-shift formula of the pulse, where planar GWs are usually assumed. Phase corrections due to the wave front curvature have been recently discussed. In this paper, frequency-shift and timing-residual formulae are derived for GWs with fully spherical wave fronts from a compact source such as a binary of supermassive black holes, where the differences in the GW amplitude and direction between Earth and the pulsar are examined in the quadrupole approximation. By using the new formulae, effects beyond the plane-wave approximation are discussed, and a galactic center PTA and nearby GW source candidates are also mentioned.

Keywords: pulsar timing method; gravitational wave astronomy; gravitational waves; millisecond pulsars; supermassive black holes
Impact Experiment on Asteroid (162173) Ryugu: Structure beneath the Impact Point Revealed by In Situ Observations of the Ejecta Curtain

An impact experiment was performed on the surface of the C-type asteroid (162173) Ryugu using an instrument called the Small Carry-on Impactor (SCI) carried by the Japan Aerospace Exploration Agency spacecraft Hayabusa2. Using a small camera separated from the spacecraft, we observed the development of the ejecta curtain formed by the SCI impact in situ. Based on the patterns appearing in the ejecta curtain, we evaluated the physical properties of large boulders and regolith grains on Ryugu. We found that the large boulders on the surface near the SCI impact point had a compressive strength consistent with the previous estimation of a tensile strength based on low thermal inertia observed for boulders on Ryugu. Furthermore, the ejecta curtain consisted of the boulders with a maximum size of several decimeters. Moreover, the filament structure was formed in the SCI ejecta curtain, strongly suggesting that the SCI impact ejecta curtain particles had a size range greater than one order of magnitude; a characteristic size of the regolith grains in the curtain was estimated to be several centimeters. These regolith grains primarily originated from the subsurface layer. We propose three different hypotheses for the geological process that formed the subsurface structure at the SCI impact point consistent with the above observations. Because these hypotheses have different predictions for materials in SCI ejecta, the samples obtained from the second touchdown will be able to constrain which hypothesis is the most likely.

Keywords: asteroids; impact phenomena; planetary science
Obtaining the Strength of the Magnetic Field from E- and B-Modes of Dust Polarization

We perform numerical simulations of supersonic magnetohydrodynamic (MHD) turbulence and calculate Fourier power spectra of E- and B-modes arising from dust polarization. We pay close attention to the ratio of E-mode to B-mode spectra (a.k.a. E/B power asymmetry) on small spatial scales. We find that the ratio depends on the strength of the mean magnetic field: the stronger the mean magnetic field, the smaller the ratio. More precisely speaking, the ratio scales with the Alfvén Mach number M A , the rms velocity divided by the Alfvén speed of the mean magnetic field, when it lies in the range 1 ≲ M A ≲ 30. This result implies that we can use the E/B power asymmetry to constrain the strength of the mean magnetic field in supersonic and super-Alfvénic MHD turbulence.

Keywords: interstellar dust; interstellar magnetic fields; interplanetary turbulence; polarimetry
RESOLVE and ECO: Finding Low-metallicity z 0 Dwarf AGN Candidates Using Optimized Emission-line Diagnostics

Existing star-forming vs. active galactic nucleus (AGN) classification schemes using optical emission-line diagnostics mostly fail for low-metallicity and/or highly star-forming galaxies, missing AGN in typical z ~ 0 dwarfs. To recover AGN in dwarfs with strong emission lines (SELs), we present a classification scheme optimizing the use of existing optical diagnostics. We use Sloan Digital Sky Survey emission-line catalogs overlapping the volume- and mass-limited REsolved Spectroscopy Of a Local VolumE (RESOLVE) and Environmental COntex (ECO) surveys to determine the AGN percentage in SEL dwarfs. Our photoionization grids show that the [O III]/Hβ versus [S II]/Hα diagram (S II plot) and [O III]/Hβ versus [O I]/Hα diagram (O I plot) are less metallicity sensitive and more successful in identifying dwarf AGN than the popular [O III]/Hβ versus [N II]/Hα diagnostic (N II plot or "BPT diagram"). We identify a new category of "star-forming AGN" (SF-AGN) classified as star-forming by the N II plot but as AGN by the S II and/or O I plots. Including SF-AGN, we find the z ~ 0 AGN percentage in dwarfs with SELs to be ~3%-16%, far exceeding most previous optical estimates (~1%). The large range in our dwarf AGN percentage reflects differences in spectral fitting methodologies between catalogs. The highly complete nature of RESOLVE and ECO allows us to normalize strong emission-line galaxy statistics to the full galaxy population, reducing the dwarf AGN percentage to ~0.6%-3.0%. The newly identified SF-AGN are mostly gas-rich dwarfs with halo mass <1011.5 M ⊙, where highly efficient cosmic gas accretion is expected. Almost all SF-AGN also have low metallicities (Z ≲ 0.4 Z ⊙), demonstrating the advantage of our method.

Keywords: galaxies; agn host galaxies; dwarf galaxies; surveys; galaxy spectroscopy
On the Nature of the T Tauri Triple System

We present a multiwavelength analysis to reveal the nature of the enigmatic T Tauri triple star system. New optical and infrared measurements are coupled with archival X-ray, UV, and millimeter data sets to show the morphologies of disk material and outflow kinematics. A dark lane of obscuring material is seen in silhouette in several emission lines and in model-subtracted ALMA millimeter continuum dust residuals near the position of T Tau Sa+Sb, revealing the attenuating circumbinary ring around T Tau S. The flux variability of T Tau S is linked in part to the binary orbit; T Tau Sb brightens near orbital apastron as it emerges from behind circumbinary material. Outflow diagnostics confirm that T Tau N powers the blueshifted western outflow, and the T Tau S binary drives the northwest-southeastern flow. Analysis of the southern outflow shows periodic arcs ejected from the T Tau system. Correlation of these arc locations and tangential kinematics with the orbit timing suggests that launch of the last four southern outflow ejections is contemporaneous with, and perhaps triggered by, the T Tau Sa+Sb binary periastron passage. We present a geometry of the T Tau triple that has the southern components foreground to T Tau N, obscured by a circumbinary ring, with misaligned disks and interacting outflows. Particularly, a wind from T Tauri Sa that is perpendicular to its circumstellar disk might interact with the circumbinary material, which may explain conflicting high-contrast measurements of the system outflows in the literature. T Tauri is an important laboratory for understanding early dynamical processes in young multiple systems. We discuss the historical and future characteristics of the system in this context.

Keywords: classical t tauri stars; circumstellar disks; stellar jets
High-resolution Transmission Spectra of Earth Through Geological Time

The next generation of ground- and space-based telescopes will be able to observe rocky Earth-like planets in the near future, transiting their host star. We explore how the transmission spectrum of Earth changed through its geological history. These transmission spectra provide a template for how to characterize an Earth-like exoplanet—from a young prebiotic world to a modern Earth. They also allow us to explore at what point in its evolution a distant observer could identify life on our Pale Blue Dots and other worlds like it. We chose atmosphere models representative of five geological epochs of Earth's history, corresponding to a prebiotic high CO2-world 3.9 billion years ago (Ga), an anoxic world around 3.5 Ga, and 3 epochs through the rise of oxygen from 0.2% to present atmospheric levels of 21%. Our transmission spectra show atmospheric spectral features, which would show a remote observer that Earth had a biosphere since about 2 billion years ago. The high-resolution transmission spectral database of Earth through geological time from the VIS to the IR is available online and can be used as a tool to optimize our observation strategy, train retrieval methods, and interpret upcoming observations with the James Webb Space Telescope, the Extremely Large Telescopes, and future mission concepts like Origins, HabEx, and LUOVIR.

Keywords: exoplanet atmospheres; exoplanet astronomy; exoplanets; high resolution spectroscopy; molecular spectroscopy; spectroscopy
Colliding in the Shadows of Giants: Planetesimal Collisions during the Growth and Migration of Gas Giants

Giant planet migration is an important phenomenon in the evolution of planetary systems. Recent works have shown that giant planet growth and migration can shape the asteroid belt, but these works have not considered interactions between planetesimals. We have calculated the evolution of planetesimal disks, including planetesimal-planetesimal collisions, during gas giant growth and migration. The numbers, locations, and impact velocities of these collisions depend on the specific growth and migration path. We find that giant planet growth alone has little effect on impact velocities, and most of the planetesimals scattered by growing giants do not undergo collisions. In contrast, we find that giant planet migration induces large numbers of high-velocity collisions between planetesimals. These impacts have sufficient velocities to cause shock-induced vaporization for both water ice and silicate components of planetesimals and to cause disruption of the bodies. New bodies may form from impact debris. Collisional evolution reduces the efficiency of planetesimal implantation into the asteroid belt. A small fraction of the largest planetesimals implanted into the asteroid belt would have been processed via collisions. We identify important consequences of planetesimal collisions that have not been considered in planet accretion models. The prevalence of high-velocity collisions during giant planet migration, and their potential links to the properties of meteorites and the formation of chondrules, makes impact vaporization a critically important phenomenon. The consequences of vaporizing planetesimal constituents require further detailed study. New collision outcome models for impacts within the nebula, and models for new planetesimal formation are needed.

Keywords: planetesimals; planet formation; protoplanetary disks; impact phenomena; planetary science; solar system formation; small solar system bodies; asteroid belt; solar system planets; chondrules; meteorites; chondrites
Electromagnetic Precursors to Gravitational-wave Events: Numerical Simulations of Flaring in Pre-merger Binary Neutron Star Magnetospheres

The detection of gravitational waves from neutron star merger events has opened up a new field of multimessenger astronomy linking gravitational-wave events to short gamma-ray bursts and kilonova afterglows. A further - yet to be discovered - electromagnetic counterpart is a precursor emission produced by the nontrivial interaction of the magnetospheres of the two neutron stars prior to merger. By performing special-relativistic force-free simulations of orbiting neutron stars we discuss the effect of different magnetic field orientations and show how the emission can be significantly enhanced by differential motion present in the binary, either due to stellar spins or misaligned stellar magnetospheres. We find that the buildup of twist in the magnetic flux tube connecting the two stars can lead to the repeated emission of powerful flares for a variety of orbital configurations. We also discuss potential coherent radio emission mechanisms in the flaring process.

Keywords: neutron stars; pulsars; magnetars; plasma astrophysics; magnetohydrodynamics; high energy astrophysics; compact binary stars
The Redshift Evolution of the Binary Black Hole Merger Rate: A Weighty Matter

Gravitational-wave detectors are starting to reveal the redshift evolution of the binary black hole (BBH) merger rate, R BBH(z). We make predictions for R BBH(z) as a function of black hole mass for systems originating from isolated binaries. To this end, we investigate correlations between the delay time and black hole mass by means of the suite of binary population synthesis simulations, COMPAS. We distinguish two channels: the common envelope (CE), and the stable Roche-lobe overflow (RLOF) channel, characterized by whether the system has experienced a common envelope or not. We find that the CE channel preferentially produces BHs with masses below about 30 M ⊙ and short delay times (t delay ≲ 1 Gyr), while the stable RLOF channel primarily forms systems with BH masses above 30 M ⊙ and long delay times (t delay ≳ 1 Gyr). We provide a new fit for the metallicity-dependent specific star formation rate density based on the Illustris TNG simulations, and use this to convert the delay time distributions into a prediction of R BBH(z). This leads to a distinct redshift evolution of R BBH(z) for high and low primary BH masses. We furthermore find that, at high redshift, R BBH(z) is dominated by the CE channel, while at low redshift, it contains a large contribution (~40%) from the stable RLOF channel. Our results predict that, for increasing redshifts, BBHs with component masses above 30 M ⊙ will become increasingly scarce relative to less massive BBH systems. Evidence of this distinct evolution of R BBH(z) for different BH masses can be tested with future detectors.

Keywords: stellar mass black holes; gravitational wave sources; close binary stars; stellar evolution; astrophysical black holes
The Search for Topographic Correlations within the Reiner Gamma Swirl

Lunar swirls have been traditionally considered to be unaffected by topographic changes. Yet, correlations between areas of high albedo and lower elevations are observed in regions of the Mare Ingenii swirl. Here, we apply similar techniques used at Mare Ingenii to determine if correlations between swirl units and topography also exist within Reiner Gamma. We generate topography using the techniques of stereophotoclinometry to Lunar Reconnaissance Orbiter Camera Narrow Angle Camera images to derive meter- to submeter-scale topography. We choose a 50 km2 study region with a 2.6 m ground sample distance (GSD), and within this region there is a 1 km2 subregion with a 0.8 m GSD. We use surface reflectance data at multiple viewing geometries to classify these regions into different swirl units using machine learning techniques. Statistical analyses of the data show mean height variations between on- and off-swirl of ~4 m, with on-swirl at a lower elevation. It is not clear how this scale of elevation difference influences the formation of swirl units, but it supports postulations of dust migration and magnetic sorting contributing to their formation.

Keywords: lunar surface; the moon; lunar features; albedo; planetary science; lunar regolith; surface processes; solar system planets; solar system terrestrial planets
Properties of Nuclear Star Clusters in Low Surface Brightness Galaxies

Using the Systematically Measuring Ultra-Diffuse Galaxies and Sloan Digital Sky Survey catalogs and our own reprocessing of the Legacy Survey imaging, we investigate the properties of nuclear star clusters (NSCs) in galaxies having central surface brightnesses as low as 27 mag arcsec‑2. We identify 273 (123 with known redshift) and 32 NSC-bearing galaxies in the two samples, respectively, where we require candidate NSCs to have a separation of less than 0.10r e from the galaxy center. We find that galaxies with low central surface brightness (μ 0,g > 24 mag arcsec‑2) are more likely to contain an NSC if they (1) have a higher stellar mass, (2) have a higher stellar-to-total mass ratio, (3) have a brighter central surface brightness, (4) have a larger axis ratio, or (5) lie in a denser environment. Because of the correlations among these various quantities, it is likely that only one or two are true physical drivers. We also find scaling relations for the NSC mass with stellar mass (M NSC/ ) and halo mass (M NSC/ ), although it is the scaling with halo mass that is consistent with a direct proportionality. In galaxies with an NSC, M NSC ≈ 10‑4 M h,gal. This proportionality echoes the finding of a direct proportionality between the mass (or number) of globular clusters (GCs) in galaxies and the galaxy's total mass. These findings favor a related origin for GCs and NSCs.

Keywords: low surface brightness galaxies; galaxy properties; galaxy structure; galaxy nuclei; star clusters
Stream Fanning and Bifurcations: Observable Signatures of Resonances in Stellar Stream Morphology

Recent observations have revealed a trove of unexpected morphological features in many of the Milky Way's stellar streams. Explanations for such features include time-dependent deformations of the Galactic gravitational potential, local disruptions induced by dark matter substructure, and special configurations of the streams' progenitors. In this paper, we study how these morphologies can also arise in certain static, nonspherical gravitational potentials that host a subset of resonantly trapped orbit families. The transitions, or separatrices, between these orbit families mark abrupt discontinuities in the orbital structure of the potential. We develop a novel numerical approach for measuring the libration frequencies of resonant and near-resonant orbits and apply it to study the evolution of stellar streams on these orbits. We reveal two distinct morphological features that arise in streams on near-resonant orbits: fans, which come about due to a large spread in the libration frequencies near a separatrix, and bifurcations, which arise when a separatrix splits the orbital distribution of the stellar stream between two (or more) distinct orbit families. We demonstrate that these effects can arise in some Milky Way streams for certain choices of the dark matter halo potential and discuss how this might be used to probe and constrain the global shape of the Milky Way's gravitational potential.

Keywords: stellar streams; milky way dynamics; milky way dark matter halo; orbital resonances
Can Cytosine, Uracil, and Thymine Be Formed from HC3N and H2NCO+ in Interstellar Space?

Syntheses of cytosine, uracil, and thymine starting from interstellar molecules were examined theoretically. Potential energy surfaces for the formation of protonated cytosine (CyH+), uracil (UrH+), and thymine (ThH+) from cyanoacetylene (HC3N), protonated isocyanic acid (H2NCO+), and one of NH3, H2O, and CH3OH, respectively, were determined by quantum chemical calculation using the CBS-QB3 method. Barrierless pathways were found for all the three reactions. Investigation of the energetics and kinetics of further possible reactions of CyH+, UrH+, and ThH+ led to the conclusion that cytosine, uracil, and thymine could not be formed along the proposed pathways in the interstellar gas phase, whereas their formation might be possible on interstellar icy grain mantles.

Keywords: interstellar medium; interstellar molecules; astrobiology; astrochemistry
ALMA Lensing Cluster Survey: Properties of Millimeter Galaxies Hosting X-Ray-detected Active Galactic Nuclei

We report the multiwavelength properties of millimeter galaxies hosting X-ray detected active galactic nuclei (AGNs) from the ALMA Lensing Cluster Survey (ALCS). ALCS is an extensive survey of well-studied lensing clusters with ALMA, covering an area of 133 arcmin2 over 33 clusters with a 1.2 mm flux-density limit of ~60 μJy (1σ). Utilizing the archival data of Chandra, we identify three AGNs at z = 1.06, 2.09, and 2.84 among the 180 millimeter sources securely detected in the ALCS (of which 155 are inside the coverage of Chandra). The X-ray spectral analysis shows that two AGNs are not significantly absorbed ( $\mathrm{log}{N}_{{\rm{H}}}/{\mathrm{cm}}^{-2}\lt 23$ ), while the other shows signs of moderate absorption ( $\mathrm{log}{N}_{{\rm{H}}}/{\mathrm{cm}}^{-2}\sim 23.5$ ). We also perform spectral energy distribution modeling of X-ray to millimeter photometry. We find that our X-ray AGN sample shows both high mass-accretion rates (intrinsic 0.5-8 keV X-ray luminosities of ~1044-45 erg s-1) and star formation rates (≳100 M ⊙ yr-1). This demonstrates that a wide-area survey with ALMA and Chandra can selectively detect intense growth of both galaxies and supermassive black holes in the high-redshift universe.

Keywords: active galactic nuclei; x-ray active galactic nuclei; quasars; submillimeter astronomy; galaxy evolution; high-redshift galaxies; spectral energy distribution