adsabs/SciX_UAT_keywords huggingface dataset:
Large-scale Hydrodynamical Shocks as the Smoking-gun Evidence for a Bar in M31

The formation and evolutionary history of M31 are closely related to its dynamical structures, which remain unclear due to its high inclination. Gas kinematics could provide crucial evidence for the existence of a rotating bar in M31. Using the position-velocity diagram of [O III] and H I, we are able to identify clear sharp velocity jump (shock) features with a typical amplitude over 100 km s-1 in the central region of M31 (4.6 kpc × 2.3 kpc, or $20^{\prime} \times 10^{\prime} $ ). We also simulate gas morphology and kinematics in barred M31 potentials and find that the bar-induced shocks can produce velocity jumps similar to those in [O III]. The identified shock features in both [O III] and H I are broadly consistent, and they are found mainly on the leading sides of the bar/bulge, following a hallmark pattern expected from the bar-driven gas inflow. Shock features on the far side of the disk are clearer than those on the near side, possibly due to limited data coverage on the near side, as well as to obscuration by the warped gas and dust layers. Further hydrodynamical simulations with more sophisticated physics are desired to fully understand the observed gas features and to better constrain the parameters of the bar in M31.

Keywords: andromeda galaxy; hydrodynamics; interstellar medium; galaxy formation
Giant Planet Formation Models with a Self-consistent Treatment of the Heavy Elements

We present a new numerical framework to model the formation and evolution of giant planets. The code is based on the further development of the stellar evolution toolkit Modules for Experiments in Stellar Astrophysics. The model includes the dissolution of the accreted planetesimals/pebbles, which are assumed to be made of water ice, in the planetary gaseous envelope, and the effect of envelope enrichment on the planetary growth and internal structure is computed self-consistently. We apply our simulations to Jupiter and investigate the impact of different heavy-element and gas accretion rates on its formation history. We show that the assumed runaway gas accretion rate significantly affects the planetary radius and luminosity. It is confirmed that heavy-element enrichment leads to shorter formation timescales due to more efficient gas accretion. We find that with heavy-element enrichment Jupiter's formation timescale is compatible with typical disks' lifetimes even when assuming a low heavy-element accretion rate (oligarchic regime). Finally, we provide an approximation for the heavy-element profile in the innermost part of the planet, providing a link between the internal structure and the planetary growth history.

Keywords: extrasolar gaseous giant planets; planet formation; exoplanet formation
Generalized Fluid Models of the Braginskii Type

Several generalizations of the well-known fluid model of Braginskii (1965) are considered. We use the Landau collisional operator and the moment method of Grad. We focus on the 21-moment model that is analogous to the Braginskii model, and we also consider a 22-moment model. Both models are formulated for general multispecies plasmas with arbitrary masses and temperatures, where all of the fluid moments are described by their evolution equations. The 21-moment model contains two "heat flux vectors" (third- and fifth-order moments) and two "viscosity tensors" (second- and fourth-order moments). The Braginskii model is then obtained as a particular case of a one ion-electron plasma with similar temperatures, with decoupled heat fluxes and viscosity tensors expressed in a quasistatic approximation. We provide all of the numerical values of the Braginskii model in a fully analytic form (together with the fourth- and fifth-order moments). For multispecies plasmas, the model makes the calculation of the transport coefficients straightforward. Formulation in fluid moments (instead of Hermite moments) is also suitable for implementation into existing numerical codes. It is emphasized that it is the quasistatic approximation that makes some Braginskii coefficients divergent in a weakly collisional regime. Importantly, we show that the heat fluxes and viscosity tensors are coupled even in the linear approximation, and that the fully contracted (scalar) perturbations of the fourth-order moment, which are accounted for in the 22-moment model, modify the energy exchange rates. We also provide several appendices, which can be useful as a guide for deriving the Braginskii model with the moment method of Grad.

Keywords: plasma physics; space plasmas
Solar Flare Ribbon Fronts. I. Constraining Flare Energy Deposition with IRIS Spectroscopy

Spectral lines formed at lower atmospheric layers show peculiar profiles at the "leading edge" of ribbons during solar flares. In particular, increased absorption of the BBSO/GST He I λ10830 line, as well as broad and centrally reversed profiles in the spectra of the Mg II and C II lines observed by the IRIS satellite, has been reported. In this work, we aim to understand the physical origin of such peculiar IRIS profiles, which seem to be common of many, if not all, flares. To achieve this, we quantify the spectral properties of the IRIS Mg II profiles at the ribbon leading edge during four large flares and perform a detailed comparison with a grid of radiative hydrodynamic models using the RADYN+FP code. We also studied their transition region (TR) counterparts, finding that these ribbon front locations are regions where TR emission and chromospheric evaporation are considerably weaker compared to other parts of the ribbons. Based on our comparison between the IRIS observations and modeling, our interpretation is that there are different heating regimes at play in the leading edge and the main bright part of the ribbons. More specifically, we suggest that bombardment of the chromosphere by more gradual and modest nonthermal electron energy fluxes can qualitatively explain the IRIS observations at the ribbon leading front, while stronger and more impulsive energy fluxes are required to drive chromospheric evaporation and more intense TR emission in the bright ribbon. Our results provide a possible physical origin for the peculiar behavior of the IRIS chromospheric lines in the ribbon leading edge and new constraints for the flare models.

Keywords: solar flares; solar atmosphere; solar chromosphere; solar activity
The Contribution and FIP Bias of Three Types of Materials inside ICMEs Associated with Different Flare Intensities

The relationship between coronal mass ejections (CMEs) and flares is an important issue in solar and stellar physics. The studies on the origination and generation mechanisms of interplanetary CME (ICME) materials are crucial for understanding the connection between CMEs and flares. The materials inside ICMEs can be classified into three types, coming from corona directly (corona materials), heated by magnetic reconnection in corona (heated corona materials), and generated by chromospheric evaporation (chromospheric evaporation materials). Here the contribution and first ionization potential (FIP) bias of three types of materials inside ICMEs associated with different flare intensities are analyzed and compared. We find that the speeds and scales of near-Earth ICMEs both increase with flare intensities. The proportions of heated corona materials are nearly constant with flare intensities. The contributions of corona materials (chromospheric evaporation materials) are significantly decreased (increased) with flare intensities. More than two-thirds of materials are chromospheric evaporation materials for ICMEs associated with strong flares. The FIP bias of corona materials and heated corona materials is almost the same. The FIP bias of chromospheric evaporation materials is significantly higher than that of corona materials and heated corona materials, and it is increased with flare intensities. The above characteristics of FIP bias can be explained reasonably by the origination and generation mechanisms of three types of ICME materials. The present study demonstrates that the origination and generation mechanisms of ICME materials are significantly influenced by flare intensities. The reasons for the elevation of FIP bias, if ICMEs are regarded as a whole, are that the FIP bias of chromospheric evaporation materials is much higher, and the chromospheric evaporation materials contributed significantly to the ICMEs that are associated with strong flares.

Keywords: solar abundances; solar flares; solar coronal mass ejections
Cosmic Ray Dissociation of Molecular Hydrogen and Dense Cloud Chemistry

Dissociation of molecular hydrogen by secondary electrons produced by cosmic ray or X-ray ionization plays a crucial role in the chemistry of the densest part of molecular clouds. Here we study the effect of the mean kinetic energy of secondary electrons on this process. We compare predictions using a range of secondary electron energies and predictions of the cross sections with the values in the UMIST database. We find that the predicted column densities change by nearly one dex.

Keywords: interstellar medium
Solar Electron Beam-Langmuir Wave Interactions and How They Modify Solar Electron Beam Spectra: Solar Orbiter Observations of a Match Made in the Heliosphere

Solar Orbiter's four in situ instruments have recorded numerous energetic electron events at heliocentric distances between 0.5 and 1 au. We analyze energetic electron fluxes, spectra, pitch-angle distributions, associated Langmuir waves, and type III solar radio bursts for three events to understand what causes modifications in the electron flux and identify the origin and characteristics of features observed in the electron spectrum. We investigate what electron beam properties and solar wind conditions are associated with Langmuir wave growth and spectral breaks in the electron peak flux as a function of energy. We observe velocity dispersion and quasilinear relaxation in the electron flux caused by the resonant wave-particle interactions in the deca-keV range, at the energies at which we observe breaks in the electron spectrum, cotemporal with the local generation of Langmuir waves. We show, via the evolution of the electron flux at the time of the event, that these interactions are responsible for the spectral signatures observed around 10 and 50 keV, confirming the results of simulations by Kontar and Reid. These signatures are independent of pitch-angle scattering. Our findings highlight the importance of using overlapping FOVs when working with data from different sensors. In this work, we exploit observations from all in situ instruments to address, for the first time, how the energetic electron flux is modified by the beam-plasma interactions and results in specific feature appearing in the local spectrum. Our results, corroborated with numerical simulations, can be extended to a wider range of heliocentric distances.

Keywords: interplanetary particle acceleration; space plasmas; solar particle emission; solar energetic particles; radio bursts; solar physics
FIRST J1419+3940 as the First Observed Radio Flare from a Neutron Star Merger

During their violent merger, two neutron stars can shed a few percent of their mass. As this ejecta expands, it collides with the surrounding interstellar gas, producing a slowly fading radio flare that lasts for years. Radio flares uniquely probe the neutron star merger populations as many events from past decades could still be detectable. Nonetheless, no radio flare observation has been reported to date. Here we show that the radio transient FIRST J1419+3940, first observed in 1993 and still detectable, could have originated from a neutron star merger. We carry out numerical simulations of neutron star merger ejecta to demonstrate that the observed radio light curve is well reproduced by a merger model with astrophysically expected parameters. We examine the observed radio data, as well as the host galaxy, to find clues that could differentiate the transient's neutron star merger origin from the alternative explanation—the afterglow of an off-axis long gamma-ray burst. Near-future observations could find further evidence for the FIRST J1419+3940 radio transient's origin. We show that existing radio surveys likely already recorded multiple radio flares, informing us of the origin and properties of neutron star mergers and their role in the nucleosynthesis of the heaviest elements in the universe.

Keywords: neutron stars; extragalactic radio sources; gravitational wave sources
Brightest Cluster Galaxy Formation in the z = 4.3 Protocluster SPT 2349-56: Discovery of a Radio-loud Active Galactic Nucleus

We have observed the z = 4.3 protocluster SPT2349-56 with the Australia Telescope Compact Array (ATCA) with the aim of detecting radio-loud active galactic nuclei (AGNs) among the ~30 submillimeter (submm) galaxies (SMGs) identified in the structure. We detect the central complex of submm sources at 2.2 GHz with a luminosity of L 2.2 = (4.42 ± 0.56) × 1025 W Hz-1. MeerKAT and the Australian Square Kilometre Array Pathfinder also detect the source at 816 MHz and 888 MHz, respectively, constraining the radio spectral index to α = -1.45 ± 0.16, implying L 1.4,rest = (2.2 ± 0.2) × 1026 W Hz-1. The radio observations do not have sufficient spatial resolution to uniquely identify one of the three Atacama Large Millimeter/submillimeter Array (ALMA) galaxies as the AGN, however the ALMA source properties themselves suggest a likely host. This radio luminosity is ~100× higher than expected from star formation, assuming the usual far-infrared-radio correlation, indicating an AGN driven by a forming brightest cluster galaxy. None of the SMGs in SPT2349-56 show signs of AGNs in any other diagnostics available to us, highlighting the radio continuum as a powerful probe of obscured AGNs. We compare these results to field samples of radio sources and SMGs, along with the 22 gravitationally lensed SPT-SMGs also observed in the ATCA program, as well as powerful radio galaxies at high redshifts. The (3.3 ± 0.7) × 1038 W of power from the radio-loud AGN sustained over 100 Myr is comparable to the binding energy of the gas mass of the central halo, and similar to the instantaneous energy injection from supernova feedback from the SMGs in the core region. The SPT2349-56 radio-loud AGNs may be providing strong feedback on a nascent intracluster medium.

Keywords: galaxy clusters
Energetic Electron Pitch-angle Distributions in the Martian Space Environment: Pancake

We perform a statistical investigation of the occurrence rates of energetic electron (100-500 eV) pancake pitch-angle distributions (PADs) in the Martian space environment by utilizing 6 yr of MAVEN data. In the Martian ionosphere, we find the following: (1) at the same altitude in the terminator and night regions, the occurrences rates in the center of the southern magnetic anomaly regions are very low, but at the edges of strong magnetic fields, they increase significantly; (2) the occurrence rates of energetic electron perpendicular anisotropies on the Martian dayside increase with altitude; and (3) some closed magnetic lines in the 10°S-55°S, 30°W-125°W region at 400-800 km altitude gradually become open during the rotation of Mars from duskside to dawnside, while more closed magnetic lines are produced in the 40°S-65°S, 35°E-90°E region. In the Martian induced magnetosphere, we find the following: (1) the high-energy electron perpendicular anisotropy in the magnetosheath is the most significant; (2) the occurrence rates in the southern (Z MSO ≤-1 R M) magnetosheath are higher than those in the northern (Z MSO ≥ 1 R M) magnetosheath; (3) in the region of ∣Z MSO∣ < 0.5 R M, these high-energy electron pancake PADs are mainly concentrated in the magnetosheath region with Y MSO ∈ [-1.4RM, 2R M]; (4) the occurrence rates in the dawnside (Y MSO ≤-1 R M) magnetosheath are higher than those in the duskside (Y MSO ≥ 1 R M) magnetosheath; and (5) in the region of ∣Y MSO∣ < 0.5 R M, the occurrence rates throughout the magnetosheath are very high.

Keywords: mars; planetary magnetospheres; planetary dynamics; magnetic fields; space plasmas
Contribution of Dark Matter Annihilation to Gamma-Ray Burst Afterglows near Massive Galaxy Centers

Gamma-ray bursts (GRBs) are believed to be powered by ultrarelativistic jets. If these jets encounter and accelerate excess electrons and positrons produced by particle dark matter (DM) annihilation, the observed electromagnetic radiation would be enhanced. In this paper, we study GRB afterglow emission with the presence of abundant DM under the weakly interacting massive particle annihilation conditions. We calculate the light curves and spectra of the GRB afterglows with different parameters, i.e., DM density, particle DM mass, annihilation channel, and electron density of the interstellar medium. We find that the effect of DM may become noticeable in the afterglow spectra if the circumburst has a low electron number density ( $n\lesssim 0.1\,{\mathrm{cm}}^{-3}$ ) and if the DM has a high number density ( ${\rho }_{\chi }\gtrsim {10}^{3}\,\mathrm{GeV}\,{\mathrm{cm}}^{-3}$ ). According to the standard galaxy DM density profile, GRB afterglows with DM contribution might occur at distances of several to tens of parsecs from the centers of massive galaxies.

Keywords: dark matter; gamma-ray bursts; galaxy dark matter halos; relativistic jets; shocks
X-Ray Emission from Isolated Neutron Stars Revisited: 3D Magnetothermal Simulations

X-ray emission from the surface of isolated neutron stars (NSs) has been now observed in a variety of sources. The ubiquitous presence of pulsations clearly indicates that thermal photons either come from a limited area, possibly heated by some external mechanism, or from the entire (cooling) surface but with an inhomogeneous temperature distribution. In an NS the thermal map is shaped by the magnetic field topology since heat flows in the crust mostly along the magnetic field lines. Self-consistent surface thermal maps can hence be produced by simulating the coupled magnetic and thermal evolution of the star. We compute the evolution of the NS crust in three dimensions for different initial configurations of the magnetic field and use the ensuing thermal surface maps to derive the spectrum and the pulse profile as seen by an observer at infinity, accounting for general-relativistic effects. In particular, we compare cases with a high degree of symmetry with inherently 3D ones, obtained by adding a quadrupole to the initial dipolar field. Axially symmetric fields result in rather small pulsed fractions (≲5%), while more complex configurations produce higher pulsed fractions, up to ~25%. We find that the spectral properties of our axisymmetric model are close to those of the bright isolated NS RX J1856.5-3754 at an evolutionary time comparable with the inferred dynamical age of the source.

Keywords: neutron stars; magnetars; magnetohydrodynamical simulations; stellar magnetic fields
Where Binary Neutron Stars Merge: Predictions from IllustrisTNG

The rate and location of binary neutron star (BNS) mergers are determined by a combination of the star formation history and the delay-time distribution (DTD) function. In this paper, we couple the star formation rate histories from the IllustrisTNG model to a series of varied assumptions for the BNS DTD to make predictions for the BNS merger host galaxy mass function. These predictions offer two outcomes: (i) in the near term they influence the BNS merger event follow-up strategy by scrutinizing where most BNS merger events are expected to occur, and (ii) in the long term they constrain the DTD for BNS merger events once the host galaxy mass function is observationally well determined. From our fiducial model analysis, we predict that 50% of BNS mergers will occur in host galaxies with stellar mass between 1010 and 1011 M⊙, 68% between 4 × 109 and 3 × 1011 M⊙, and 95% between 4 × 108 and 2 × 1012 M⊙. We find that the details of the DTD employed do not have a strong effect on the peak of the host mass function. However, varying the DTD provides enough spread that the true DTD can be determined from enough electromagnetic observations of BNS mergers. Knowing the true DTD can help us determine the prevalence of BNS systems formed through highly eccentric and short-separation fast-merging channels and can constrain the dominant source of r-process material.

Keywords: neutron stars; compact objects; gravitational waves; stellar mergers; magnetohydrodynamical simulations; close binary stars
Variable and Supersonic Winds in the Atmosphere of an Ultrahot Giant Planet

Hot Jupiters (HJs) receive intense irradiation from their stellar hosts. The resulting extreme environments in their atmospheres allow us to study the conditions that drive planetary atmospheric dynamics, e.g., global-scale winds. General circulation models predict day-to-nightside winds and equatorial jets with speeds of the order of a few km s-1. To test these models, we apply high-resolution transmission spectroscopy using the Potsdam Echelle Polarimetric and Spectroscopic Instrument (PEPSI) spectrograph on the Large Binocular Telescope to study the atmosphere of KELT-9 b, an ultrahot Jupiter and currently the hottest known planet. We measure ~10 km s-1 day-to-nightside winds traced by Fe II features in the planet's atmosphere. This is at odds with previous literature (including data taken with PEPSI), which report no significant day-to-nightside winds on KELT-9 b. We identify the cause of this discrepancy as due to an inaccurate ephemeris for KELT-9 b in previous literature. We update the ephemeris, which shifts the midtransit time by up to 10 minutes for previous data sets, resulting in consistent detections of blueshifts in all the data sets analyzed here. Furthermore, a comparison with archival data sets from the High-accuracy Radial velocity Planet Searcher for the Northern hemisphere suggests a temporal wind variability of ~5-8 km s-1 over timescales between weeks to years. Temporal variability of atmospheric dynamics on HJs is a phenomenon anticipated by certain general circulation models that has not been observed over these timescales until now. However, such large variability as we measure on KELT-9 b challenges general circulation models, which predict much lower amplitudes of wind variability over timescales between days to weeks.

Keywords: exoplanet astronomy; exoplanet atmospheres; exoplanet atmospheric variability; exoplanets
The Hidden Past of M92: Detection and Characterization of a Newly Formed 17° Long Stellar Stream Using the Canada-France Imaging Survey

We present an analysis of the structure, kinematics, and orbit of a newly found stellar stream emanating from the globular cluster M92 (NGC 6341). This stream was discovered in an improved matched-filter map of the outer Galaxy, based on a "color-color-magnitude" diagram, created using photometry from the Canada-France Imaging Survey and the Pan-STARRS 1 3π survey. We find the stream to have a length of 17° (2.5 kpc at the distance of M92), a width dispersion of 0°29(42 pc), and a stellar mass of [3.17 ± 0.89] × 104 M⊙ (10% of the stellar mass of the current main body of M92). We examine the kinematics of main-sequence, red giant, and blue horizontal branch stars belonging to the stream and that have proper motion measurements from the second data release of Gaia. N-body simulations suggest that the stream was likely formed very recently (during the last ∼500 Myr) forcing us to question the orbital origin of this ancient, metal-poor globular cluster.

Keywords: globular star clusters; milky way dynamics; milky way stellar halo; galaxy formation