adsabs/SciX_UAT_keywords huggingface dataset:
Effects of Coronal Magnetic Field Configuration on Particle Acceleration and Release during the Ground Level Enhancement Events in Solar Cycle 24

Ground level enhancements (GLEs) are extreme solar energetic particle (SEP) events that are of particular importance in space weather. In solar cycle 24, two GLEs were recorded on 2012 May 17 (GLE 71) and 2017 September 10 (GLE 72), respectively, using a range of advanced modern instruments. Here we conduct a comparative analysis of the two events by focusing on the effects of large-scale magnetic field configuration near active regions on particle acceleration and release. Although the active regions are both located near the western limb, temporal variations of SEP intensities and energy spectra measured in situ display different behaviors at early stages. By combining a potential field model, we find the coronal mass ejection (CME) in GLE 71 originated below the streamer belt, while in GLE 72 it originated near the edge of the streamer belt. We reconstruct the CME shock fronts with an ellipsoid model based on nearly simultaneous coronagraph images from multiple viewpoints and further derive the 3D shock geometry at the GLE onset. The highest-energy particles are primarily accelerated in the shock-streamer interaction regions, i.e., likely at the nose of the shock in GLE 71 and the eastern flank in GLE 72, due to quasi-perpendicular shock geometry and confinement of closed fields. Subsequently, they are released to the field lines connecting to near-Earth spacecraft when the shocks move through the streamer cusp region. This suggests that magnetic structures in the corona, especially shock-streamer interactions, may have played an important role in the acceleration and release of the highest-energy particles in the two events.

Keywords: solar energetic particles; solar coronal mass ejection shocks; solar particle emission; solar coronal mass ejections; solar coronal streamers; solar corona; solar active region magnetic fields
A Priori Validation of Subgrid-scale Models for Astrophysical Turbulence

We perform a priori validation tests of subgrid-scale (SGS) models for the turbulent transport of momentum, energy, and passive scalars. To this end, we conduct two sets of high-resolution hydrodynamical simulations with a Lagrangian code: an isothermal turbulent box with rms Mach numbers of 0.3, 2, and 8, and the classical wind tunnel where a cold cloud traveling through a hot medium gradually dissolves due to fluid instabilities. Two SGS models are examined: the eddy diffusivity (ED) model widely adopted in astrophysical simulations and the "gradient model" due to Clark et al. We find that both models predict the magnitude of the SGS terms equally well (correlation coefficient >0.8). However, the gradient model provides excellent predictions for the orientation and shape of the SGS terms while the ED model predicts both poorly, indicating that isotropic diffusion is a poor approximation to the instantaneous turbulent transport. The best-fit coefficient of the gradient model is in the range of [0.16, 0.21] for the momentum transport, and the turbulent Schmidt number and Prandtl number are both close to unity, in the range of [0.92, 1.15].

Keywords: computational methods; hydrodynamical simulations; hydrodynamics
All Known SN Ia Models Fail to Reproduce the Observed t0-MN I56 Correlation

SNe Ia are likely the thermonuclear explosions of carbon-oxygen white-dwarf stars, but their progenitor systems remain elusive. A few theoretical scenarios for the progenitor systems have been suggested, which have been shown to agree with some observational properties of SNe Ia. However, several computational challenges prohibit a robust comparison to the observations. We focus on the observed ${t}_{0}\mbox{--}{M}_{{\rm{N}}{\rm{\small{I}}}56}$ relation, where t0 (the γ-rays' escape time from the ejecta) is positively correlated with ${M}_{{\rm{N}}{\rm{\small{I}}}56}$ (the synthesized 56Ni mass). Comparing to the ${t}_{0}\mbox{--}{M}_{{\rm{N}}{\rm{\small{I}}}56}$ relation bypasses the need for radiation transfer calculations, as the value of t0 can be directly inferred from the ejecta. We show that all known SNe Ia models fail to reproduce the observed ${t}_{0}\mbox{--}{M}_{{\rm{N}}{\rm{\small{I}}}56}$ correlation.

Keywords: type ia supernovae; supernovae
The Effects of Early Collisional Evolution on Amorphous Water Ice Bodies

Conditions in the outer protoplanetary disk during solar system formation were thought to be favorable for the formation of amorphous water ice (AWI), a glassy phase of water ice. However, subsequent collisional processing could have shock-crystallized any AWI present. Here we use the iSALE shock physics hydrocode to simulate impacts between large icy bodies at impact velocities relevant to these collisional environments, and then we feed these results into a custom-built AWI crystallization script, to compute how much AWI crystallizes/survives these impact events. We find that impact speeds between icy bodies after planet migration (i.e., between trans-Neptunian objects) are too slow to crystallize any meaningful fraction of AWI. During planet migration, however, the amount of AWI that crystallizes is highly stochastic: relatively little AWI crystallizes at lower impact velocities (less than ~2 km s-1), yet most AWI present in the bodies (if equally sized) or impactor and impact site (if different sizes) crystallizes at higher impact velocities (greater than ~4 km s-1). Given that suspected impact speeds during planet migration were ~2-4 km s-1, this suggests that primordial AWI's ability to survive planet migration is highly stochastic. However, if proto-Edgeworth-Kuiper Belt (proto-EKB) objects and their fragments experienced multiple impact events, nearly all primordial AWI could have crystallized; such a highly collisional proto-EKB during planet migration is consistent with the lack of any unambiguous direct detection of AWI on any icy body. Ultimately, primordial AWI's survival to the present day depends sensitively on the proto-EKB's size-frequency distribution, which is currently poorly understood.

Keywords: comet volatiles; solar system formation; impact phenomena; kuiper belt
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 medium; interstellar clouds; computational methods; interstellar molecules; reaction rates; astrochemistry
A Catalog of Host Galaxies for WISE-selected AGN: Connecting Host Properties with Nuclear Activity and Identifying Contaminants

We present a catalog of physical properties for galaxies hosting active galactic nuclei (AGN) detected by the Wide-field Infrared Survey Explorer (WISE). By fitting broadband spectral energy distributions of sources in the WISE AGN Catalog with empirical galaxy and AGN templates, we derive photometric redshifts, AGN bolometric luminosities, measures of AGN obscuration, host galaxy stellar masses, and host galaxy star formation rates (SFRs) for 695,273 WISE AGN. The wide-area nature of this catalog significantly augments the known number of obscured AGN out to redshifts z ~ 3 and will be useful for studies focused on AGN or their host galaxy physical properties. We first show that the most likely non-AGN contaminants are galaxies at redshifts z = 0.2-0.3, with relatively blue W1-W2 colors, and with high specific SFRs for which the dust continuum emission is elevated in the W2 filter. Toward increasingly lower redshifts, WISE AGN host galaxies have systematically lower specific SFRs relative to those of normal star-forming galaxies, likely due to decreased cold gas fractions and the time delay between global star formation and AGN triggering. Finally, WISE AGN obscuration is not strongly correlated with AGN bolometric luminosity but shows a significant negative correlation with the Eddington ratio. This result is consistent with a version of the receding torus model in which the obscuring material is located within the supermassive black hole gravitational sphere of influence and the dust inner radius increases due to radiation pressure.

Keywords: agn host galaxies; active galactic nuclei; high-redshift galaxies; galaxy masses; galaxy stellar content; dust continuum emission; catalogs; spectral energy distribution; infrared galaxies
VTSCat: The VERITAS Catalog of Gamma-Ray Observations

The ground-based gamma-ray observatory Very Energetic Radiation Imaging Telescope Array System (VERITAS, https://veritas.sao.arizona.edu/) is sensitive to photons of astrophysical origin with energies in the range between ≈85 GeV and ≈30 TeV. The instrument consists of four 12 m diameter imaging Cherenkov telescopes operating at the Fred Lawrence Whipple Observatory in southern Arizona. VERITAS started four-telescope operations in 2007 and collects about 1100 hr of good-weather data per year. The VERITAS collaboration has published over 100 journal articles since 2008 reporting on gamma-ray observations of a large variety of objects: Galactic sources like supernova remnants, pulsar wind nebulae, and binary systems; extragalactic sources like star-forming galaxies, dwarf-spheroidal galaxies, and highly variable active galactic nuclei. This note presents VTSCat: the catalog of high-level data products from all VERITAS publications.

Keywords: high energy astrophysics
The Pantheon+ Analysis: The Full Data Set and Light-curve Release

Here we present 1701 light curves of 1550 unique, spectroscopically confirmed Type Ia supernovae (SNe Ia) that will be used to infer cosmological parameters as part of the Pantheon+ SN analysis and the Supernovae and H 0 for the Equation of State of dark energy distance-ladder analysis. This effort is one part of a series of works that perform an extensive review of redshifts, peculiar velocities, photometric calibration, and intrinsic-scatter models of SNe Ia. The total number of light curves, which are compiled across 18 different surveys, is a significant increase from the first Pantheon analysis (1048 SNe), particularly at low redshift (z). Furthermore, unlike in the Pantheon analysis, we include light curves for SNe with z < 0.01 such that SN systematic covariance can be included in a joint measurement of the Hubble constant (H 0) and the dark energy equation-of-state parameter (w). We use the large sample to compare properties of 151 SNe Ia observed by multiple surveys and 12 pairs/triplets of "SN siblings"-SNe found in the same host galaxy. Distance measurements, application of bias corrections, and inference of cosmological parameters are discussed in the companion paper by Brout et al., and the determination of H 0 is discussed by Riess et al. These analyses will measure w with ~3% precision and H 0 with ~1 km s-1 Mpc-1 precision.

Keywords: distance measure; dark energy
Mapping Discrete Galaxies at Cosmic Dawn with 21 cm Observations

At cosmic dawn, the 21 cm signal from intergalactic hydrogen was driven by Ly-α photons from some of the earliest stars, producing a spatial pattern that reflected the distribution of galaxies at that time. Due to the large foreground, it is thought that at around redshift 20 it is only observationally feasible to detect 21 cm fluctuations statistically, yielding a limited indirect probe of early galaxies. Here, we show that 21 cm images at cosmic dawn should actually be dominated by large (tens of comoving megaparsecs) high-contrast bubbles surrounding individual galaxies. We demonstrate this using a substantially upgraded seminumerical simulation code that realistically captures the formation and 21 cm effects of the small galaxies expected during this era. Small number statistics associated with the rarity of early galaxies, combined with the multiple scattering of photons in the blue wing of the Ly-α line, create the large bubbles, and also enhance the 21 cm power spectrum by a factor of 2-7 and add to it a feature that measures the typical brightness of galaxies. These various signatures of discrete early galaxies are potentially detectable with planned experiments, such as the Square Kilometer Array and the Hydrogen Epoch of Reionization Array, even if the early stars prove to be formed in dark matter halos with masses as low as 108 M ⊙, 10,000 times smaller than the Milky Way halo.

Keywords: cosmology; h i line emission
Ice Sublimation in Planetesimals Formed at the Outward Migrating Snowline

Isotopic studies of meteorites suggest that planetesimals were formed as two distinct populations: noncarbonaceous (NC) and carbonaceous (CC) reservoirs. A recent model explains this dichotomy by considering planetesimal formation at the snowline during its migration in the protoplanetary disk, suggesting that NC planetesimals were formed during the outward migration and CC planetesimals were formed during the inward migration. This model has been suggested to contradict meteorite observations because planetesimals formed at the snowline are expected to be rich in H2O and, therefore, develop more oxidizing environments than those inferred from NC iron meteorites. However, if the accreted ice sublimates into vapor without transitioning into a liquid state, the planetesimals may lose most water without being oxidized because reactions between vapor and solids are negligibly slow at temperatures relevant to direct ice sublimation. Here, we investigate the transport of vapor inside a planetesimal and suggest that the pore pressure would have been sufficiently low for direct ice sublimation if (1) the planetesimals were formed during the outward snowline migration (such that they lay inside the snowline after formation and had surfaces permeable to water vapor), (2) these planetesimals were formed by dust-aggregate boulders through "streaming instabilities" instead of being formed directly by submicrometer dust grains, and (3) the boulders were between a few centimeters to ~10 m in size. With these results, the snowline model for NC/CC planetesimal formation may be reconciled with the observations of iron meteorite oxidation states.

Keywords: planetesimals; planet formation; protoplanetary disks; iron meteorites; planetary interior
Completeness of the NASA/IPAC Extragalactic Database (NED) Local Volume Sample

We introduce the NASA/IPAC Extragalactic Database (NED) Local Volume Sample (NED-LVS), a subset of ~1.9 million objects with distances out to 1000 Mpc. We use UV and IR fluxes available in NED from all-sky surveys to derive physical properties, and estimate the completeness relative to the expected local luminosity density. The completeness relative to near-IR luminosities (which traces a galaxy's stellar mass) is roughly 100% at D < 30 Mpc and remains moderate (70%) out to 300 Mpc. For brighter galaxies (≳L *), NED-LVS is ~100% complete out to ~400 Mpc. When compared to other local Universe samples (GLADE and HECATE), all three are ~100% complete below 30 Mpc. At distances beyond ~80 Mpc, NED-LVS is more complete than both GLADE and HECATE by ~10%-20%. NED-LVS is the underlying sample for the NED gravitational-wave follow-up service (NED-GWF), which provides prioritized lists of host candidates for GW events within minutes of alerts issued by the LIGO-Virgo-KAGRA collaboration. We test the prioritization of galaxies in the volume of GW170817 by three physical properties, where we find that both stellar mass and inverse specific star formation rate place the correct host galaxy in the top 10. In addition, NED-LVS can be used for a wide variety of other astrophysical studies: galaxy evolution, star formation, large-scale structure, galaxy environments, and more. The data in NED are updated regularly, and NED-LVS will be updated concurrently. Consequently, NED-LVS will continue to provide an increasingly complete sample of galaxies for a multitude of astrophysical research areas for years to come.

Keywords: galaxies; astronomy databases; surveys; catalogs
Estimation of the Galaxy Quenching Rate in the Illustris Simulation

Quenching is a key topic in exploring the formation and evolution of galaxies. In this work, we study the quenching rate, i.e., the variation in the fraction of quenched galaxies per unit time, of the Illustris-1 simulation. By building the quenched fraction function f(m, ρ, t) of each snapshot in the simulation, we derive an accurate form of quenching rate as ${{\mathfrak{R}}}_{q}={df}(m,\rho ,t)/{dt}$ . According to the analytic expression of the quenching rate ${{\mathfrak{R}}}_{q}$ , we split it into four components: mass quenching, environmental quenching, intrinsic mass quenching, and intrinsic environmental quenching. The precise value and evolutions can be given via the formula of ${{\mathfrak{R}}}_{q}$ . With this method, we analyze the Illustris-1 simulation. We find that quenched galaxies concentrate around M* ≃ 1011 h-1 M⊙ and δ + 1 ≃ 103.5 at earlier times and that the quenching galaxy population slowly shifts to lower stellar mass and lower overdensity regions with time. We also find that mass quenching dominates the quenching process in this simulation, in agreement with some previous analytical models. Intrinsic quenching is the second most important component. Environmental quenching is very weak, because it is possible that the pre- or post-processing of environments disguises environmental quenching as intrinsic quenching. We find that our method roughly predicts the actual quenching rate. It could well predict the actual number of galaxies quenched by intrinsic quenching. However, it overestimates the amount of mass quenching galaxies and underestimates the amount of environmental quenching. We suggest that the reason is the nonlinearity of the environmental overdensity change and mass growth of the galaxy.

Keywords: galaxy formation; hydrodynamical simulations; galaxy quenching
Morphology and Mach Number Dependence of Subsonic Bondi–Hoyle Accretion

We carry out three-dimensional computations of the accretion rate onto an object (of size R sink and mass m) as it moves through a uniform medium at a subsonic speed v ∞. The object is treated as a fully absorbing boundary (e.g., a black hole). In contrast to early conjectures, we show that for an accretor with ${R}_{\mathrm{sink}}\ll {R}_{A}=2{Gm}/{v}_{\infty }^{2}$ in a gaseous medium with adiabatic index γ = 5/3, the accretion rate is independent of Mach number and is determined only by m and the gas entropy. Our numerical simulations are conducted using two different numerical schemes via the Athena++ and Arepo hydrodynamics solvers, which reach nearly identical steady-state solutions. We find that pressure gradients generated by the isentropic compression of the flow near the accretor are sufficient to suspend much of the surrounding gas in a near-hydrostatic equilibrium, just as predicted from the spherical Bondi–Hoyle calculation. Indeed, the accretion rates for steady flow match the Bondi–Hoyle rate, and are indicative of isentropic flow for subsonic motion where no shocks occur. We also find that the accretion drag may be predicted using the Safronov number, Θ = R A /R sink, and is much less than the dynamical friction for sufficiently small accretors (R sink ≪ R A ).

Keywords: bondi accretion; hydrodynamics; astrophysical black holes; galaxy accretion; exoplanet formation; stellar accretion
A Catalog of Solar Flare Events Observed by the SOHO/EIT

We have compiled a catalog of solar flares (SFs) as observed by the Extreme ultraviolet Imaging Telescope (EIT) on board the Solar and Heliospheric Observatory (SOHO) spacecraft and the Geostationary Operational Environmental Satellites (GOES) spacecraft over a span from 1997 to 2010. During mid-1998, the cadence of EIT images was revised from two images per day to 12 minutes. However, the low temporal resolution causes significant data gaps in capturing much of the flaring phenomenon. Therefore, we monitor possible errors in flare detection by flare parameters such as temporal overlap, observational wavelength, and considering full field-of-view images. We consider the GOES flare catalog as the primary source. We describe the technique used to enhance the GOES detected flares using the extreme ultraviolet image captured by the EIT telescope. In order to detect brightenings, we subtract the images with a maximum cadence of 25 minutes. We have downloaded and analyzed the EIT data via the Virtual Solar Observatory. This flare data set from the SOHO/EIT period proves indispensable to the process of the SF predictions as the instrument has covered most of Solar Cycle 23.

Keywords: solar flares; catalogs; solar physics
Thermodynamics of Dipolarization Fronts of Magnetic Reconnection in Anisotropic Plasma: MMS Observations and Resistive Double-polytropic MHD Simulations

Dipolarization fronts (DFs) of magnetic reconnection are a transient field structure accompanied with a sharp increase of magnetic field component normal to plasma sheet and a high-speed plasma flow. The thermodynamics of DFs in the anisotropic plasma, which have not been studied so far, are investigated in this paper using two-dimensional, resistive magnetohydrodynamic simulations with double-polytropic energy laws in which two polytropic exponents, γ∥ and ${\gamma }_{\perp }$ , are used as parameters to describe various thermodynamic conditions. The subscripts ∥ and $\perp $ denote, respectively, directions parallel and perpendicular to the local magnetic field. Four different types of DFs observed by the Magnetospheric Multiscale Mission (MMS) in the plasma sheet of the Earth's magnetotail are presented—namely, (1) both temperatures T∥ and ${T}_{\perp }$ decrease; (2) both T∥ and ${T}_{\perp }$ increase; (3) T∥ decreases while ${T}_{\perp }$ increases; (4) T∥ increases while ${T}_{\perp }$ decreases. By using four different pairs of γ∥ and ${\gamma }_{\perp }$ , these four types of DFs can be reproduced, where the thermodynamics of Type-4 DF may correspond to the double-adiabatic Chew-Goldberger-Low conditions. It is concluded that the thermodynamic condition is seen to resemble most closely an adiabatic process for Type-1, -2, and -4 DFs, but to an isothermal process for Type-3 DF.

Keywords: magnetohydrodynamics; magnetohydrodynamical simulations