adsabs/SciX_UAT_keywords huggingface dataset:
Alfvén Number for the Richtmyer-Meshkov Instability in Magnetized Plasmas

The magnetohydrodynamical (MHD) evolution of the Richtmyer-Meshkov instability (RMI) is investigated using two-dimensional MHD simulations. The RMI is suppressed by a strong magnetic field, whereas the RMI amplifies an ambient magnetic field by many orders of magnitude if the seed field is weak. We have found that the suppression and amplification processes can be evaluated continuously along with the amplitude of the Alfvén number RA, which is defined as the ratio of the linear growth velocity of the RMI to the Alfvén speed at the interface. When the Alfvén number is less than unity, the Lorentz force acting on the fluid mitigates the unstable motion of the RMI significantly, and the interface oscillates stably in this limit. If RA ≳ 1, on the other hand, the surface modulation increases due to the growth of the RMI. The maximum strength of the magnetic field is enhanced up to by a factor of RA. This critical feature is universal and independent of the initial Mach number of the incident shock, the Atwood number, corrugation amplitude, and even the direction of the initial magnetic field.

Keywords: magnetohydrodynamical simulations; interstellar medium; interstellar magnetic fields; shocks
A Measurement of Circumgalactic Gas around Nearby Galaxies Using Fast Radio Bursts

The distribution of gas in the circumgalactic medium (CGM) of galaxies of all types is poorly constrained. Foreground CGMs contribute an extra amount to the dispersion measure (DM) of fast radio bursts (FRBs). We measure this DM excess for the CGMs of 1011-1013 M ⊙ halos using the CHIME/FRB first data release, a halo mass range that is challenging to probe in any other way. Because of the uncertainty in the FRBs' angular coordinates, only for nearby galaxies is the localization sufficient to confidently associate them with intersecting any foreground halo. Thus we stack on galaxies within 80 Mpc, optimizing the stacking scheme to approximately minimize the stack's variance and marginalize over uncertainties in FRB locations. The sample has 20-30 FRBs intersecting halos with masses of 1011-1012 M ⊙ and also of 1012-1013 M ⊙, and these intersections allow a marginal 1σ-2σ detection of the DM excess in both mass bins. The bin of 1011-1012 M ⊙ halos also shows a DM excess at 1-2 virial radii. By comparing data with different models for the CGM gas profile, we find that all models are favored by the data up to 2σ level compared to the null hypothesis of no DM excess. With 3000 more bursts from a future CHIME data release, we project a 4σ detection of the CGM. Distinguishing between viable CGM models by stacking FRBs with CHIME-like localization would require tens of thousands of bursts.

Keywords: radio bursts; radio transient sources; circumgalactic medium
First Cosmology Results using Supernovae Ia from the Dark Energy Survey: Survey Overview, Performance, and Supernova Spectroscopy

We present details on the observing strategy, data-processing techniques, and spectroscopic targeting algorithms for the first three years of operation for the Dark Energy Survey Supernova Program (DES-SN). This five-year program using the Dark Energy Camera mounted on the 4 m Blanco telescope in Chile was designed to discover and follow supernovae (SNe) Ia over a wide redshift range (0.05 < z < 1.2) to measure the equation-of-state parameter of dark energy. We describe the SN program in full: strategy, observations, data reduction, spectroscopic follow-up observations, and classification. From three seasons of data, we have discovered 12,015 likely SNe, 308 of which have been spectroscopically confirmed, including 251 SNe Ia over a redshift range of 0.017 < z < 0.85. We determine the effective spectroscopic selection function for our sample and use it to investigate the redshift-dependent bias on the distance moduli of SNe Ia we have classified. The data presented here are used for the first cosmology analysis by DES-SN ("DES-SN3YR"), the results of which are given in Dark Energy Survey Collaboration et al. The 489 spectra that are used to define the DES-SN3YR sample are publicly available at https://des.ncsa.illinois.edu/releases/sn.

Keywords: type ia supernovae; supernovae; cosmology; cosmological parameters; observational cosmology; sky surveys
High-resolution He I 10830 Å Narrowband Imaging for a Small-scale Chromospheric Jet

Solar jets are ubiquitous phenomena in the solar atmosphere. They are important in mass and energy transport to the upper atmosphere and interplanetary space. Here, we report a detailed analysis of a small-scale chromospheric jet with high-resolution He I 10830 Å and TiO 7057 Å images observed by the 1.6 m aperture Goode Solar Telescope at the Big Bear Solar Observatory. The observation reveals the finest dark threads inside the jet are rooted in the intergranular lanes. Their width is equal to the telescope's diffraction limit at 10830 Å (∼100 km). The jet is recurrent and its association with the emergence and convergence of magnetic flux is observed. Together with other important features like photospheric flow toward the magnetic polarity inversion line, a bald-patch magnetic configuration, and earlier excitation of helium atoms, we propose that the jet might be initiated by magnetic reconnection in a U-shaped loop configuration. The plasmoid configuration results from the possible buoyancy of the magnetic reconnection, which reoccurs in a second step with an overlying magnetic field line. Notably, the second-step magnetic reconnection produces not only bidirectional cool or hot flows but also a new U-shaped loop configuration. The feature may be used to explain the recurrent behavior of the jet, since the new U-shaped loop can be driven to reconnect again.

Keywords: solar chromosphere; solar magnetic reconnection
Nine Localized Deviations from Keplerian Rotation in the DSHARP Circumstellar Disks: Kinematic Evidence for Protoplanets Carving the Gaps

We present evidence for localized deviations from Keplerian rotation, I.e., velocity "kinks," in 8 of the 18 circumstellar disks observed by the DSHARP program: DoAr 25, Elias 2-27, GW Lup, HD 143006, HD 163296, IM Lup, Sz 129, and WaOph 6. Most of the kinks are detected over a small range in both radial extent and velocity, suggesting a planetary origin, but for some of them foreground contamination prevents us from measuring their spatial and velocity extent. Because of the DSHARP limited spectral resolution and signal to noise in the 12CO J = 2-1 line, as well as cloud contamination, the kinks are usually detected in only one spectral channel, and will require confirmation. The strongest circumstantial evidence for protoplanets in the absence of higher spectral resolution data and additional tracers is that, upon deprojection, we find that all of the candidate planets lie within a gap and/or at the end of a spiral detected in dust continuum emission. This suggests that a significant fraction of the dust gaps and spirals observed by Atacama Large Millimeter/submillimeter Array in disks are caused by embedded protoplanets.

Keywords: protoplanetary disks; planet formation; submillimeter astronomy
Molecular Deuterations in Massive Starless Clump Candidates

Deuterated molecules are valuable probes for investigating the evolution and the kinematics in the earliest stages of star formation. In this study, we conduct a comprehensive investigation by performing a single-point survey of 101 starless clump candidates, and carrying out on-the-fly (OTF) observations of 11 selected sources, focusing on deuterated molecular lines using the IRAM 30 m telescope. In the single-point observation, we make 46 detections for DCO+ J = 1‑0, 12 for DCN J = 1‑0, 51 for DNC J = 1‑0, 7 for N2D+ J = 1‑0, 20 for DCO+ J = 2‑1, and 10 for DCN J = 2‑1. The starless clump candidates with deuterated molecule detections exhibit lower median kinetic temperatures and a narrower H2CO (1(0,1)‑0(0,0)) median full width at half maximum compared to those without such detections, while simultaneously displaying similar median values of 1.1 mm intensity, mass, and distance. Furthermore, our OTF observations reveal that deuterated molecules predominantly have peaks near the 1.1 mm continuum peaks, with the DCO+ J = 1‑0 emission demonstrating higher intensity in the deuterated peak region compared to the DCN and DNC J = 1‑0 emissions. Additionally, the majority of emissions from deuterated molecules and 13C isotopologues exhibit peak positions close to those of the 1.1 mm continuum peaks. By analyzing the 20″ × 20″ regions with strongest deuterated emissions in the OTF observations, we estimated deuterated abundances of 0.004‑0.045, 0.011‑0.040, and 0.004‑0.038 for D frac(HCN), D frac(HCO+), and D frac(HNC), respectively. The differential detection of deuterated molecular lines in our OTF observations could be attributed to variations in critical densities and formation pathways.

Keywords: star formation; massive stars; interstellar molecules; interstellar abundances
Very Large Telescope Spectroscopy of Ultra-faint Dwarf Galaxies. I. Boötes I, Leo IV, and Leo V

We perform consistent reductions and measurements for three ultra-faint dwarf galaxies (UFDs): Boötes I, Leo IV, and Leo V. Using the public archival data from the GIRAFFE spectrograph on the Very Large Telescope (VLT), we locate new members and provide refined measurements of physical parameters for these dwarf galaxies. We identify nine new Leo IV members and four new Leo V members, and perform a comparative analysis of previously discovered members. Additionally, we identify one new binary star in both Leo IV and Leo V. After removing binary stars, we recalculate the velocity dispersions of Boötes I and Leo IV to be ${5.1}_{-0.8}^{+0.7}$ and ${3.4}_{-0.9}^{+1.3}$ km s-1, respectively; we do not resolve the Leo V velocity dispersion. We identify a weak velocity gradient in Leo V that is ~4× smaller than the previously calculated gradient and that has a corresponding position angle that differs from the value in the literature by ~120°. Combining the VLT data with previous values from the literature, we reanalyze the Boötes I metallicity distribution function and find that a model including infall of pristine gas, while Boötes I was forming stars' best fits the data. Our analysis of Leo IV, Leo V, and other UFDs will enhance our understanding of these enigmatic stellar populations and contribute to future dark matter studies. This is the first in a series of papers examining 13 UDFs observed with VLT/GIRAFFE between 2009 and 2017. Similar analyses of the remaining 10 UFDs will be presented in forthcoming papers.

Keywords: dwarf galaxies; local group; stellar kinematics; dark matter; stellar abundances; stellar populations; binary stars; metallicity
Disk Masses and Dust Evolution of Protoplanetary Disks around Brown Dwarfs

We present the largest sample of brown dwarf (BD) protoplanetary disk spectral energy distributions modeled to date. We compile 49 objects with ALMA observations from four star-forming regions: ρ Ophiuchus, Taurus, Lupus, and Upper Scorpius. Studying multiple regions with various ages enables us to probe disk evolution over time. Specifically, from our models, we obtain values for dust grain sizes, dust settling, and disk mass; we compare how each of these parameters vary between the regions. We find that disk mass decreases with age. We also find evidence of disk evolution (i.e., grain growth and significant dust settling) in all four regions, indicating that planet formation and disk evolution may begin to occur at earlier stages. We generally find that these disks contain too little mass to form planetary companions, though we cannot rule out that planet formation may have already occurred. Finally, we examine the disk mass-host mass relationship and find that BD disks are largely consistent with previously determined relationships for disks around T Tauri stars.

Keywords: brown dwarfs; exoplanet formation; protoplanetary disks; star formation
The Timescales of Star Cluster Emergence: The Case of NGC 4449

We survey the young star cluster population in the dwarf galaxy NGC 4449 with the goal of investigating how stellar feedback may depend on the clusters' properties. Using ultraviolet (UV)–optical–near-infrared photometry obtained with the Hubble Space Telescope, we have recovered 99 compact sources exhibiting emission in the Paβ hydrogen recombination line. Our analysis reveals these sources possess masses of 102 < M ⊙ < 105, ages of 1–20 Myr, and a color excess E(B ‑ V) in the range 0–1.4. After selecting clusters with masses above 3000 M ⊙ to mitigate stochastic sampling of the stellar initial mass function, we find that our IR-selected clusters have a median mass ∼ 7 × 103 M ⊙ and remain embedded in their surrounding gas and dust for 5–6 Myr. In contrast, line-emitting sources selected from existing UV/optical catalogs have a median mass ∼ 3.5 × 104 M ⊙ and have cleared their surroundings by 4 Myr. We further find that the environment in NGC 4449 has too low pressure to drive these differences. We interpret these findings as evidence that the clearing timescale from presupernova and supernova feedback is cluster mass dependent. Even in clusters with masses ∼ 7000 M ⊙, stochastic sampling of the upper end of the stellar initial mass function is present, randomly decreasing the number of massive stars available to inject energy and momentum into the surrounding medium. This effect may increase the clearing timescales in these clusters by decreasing the effectiveness of both presupernova and supernova feedback; neither models nor observations have so far explored such dependence explicitly. Future studies and observations with, e.g., the JWST, will fill this gap.

Keywords: interstellar dust; young star clusters; dwarf galaxies; interstellar dust extinction
Discovery of Calm Astronomical Sites Over the Antarctic Continent

A calm astronomical site means a site where astronomical observation would be less likely to be interfered with by optical turbulence. Previous turbulence measurements at a few sites in Antarctica have demonstrated very calm atmospheric conditions here. So far, to realize a wide range of measurements of the turbulence conditions above the Antarctic plateau will be a great hardship. Thus, in this study, the numerical weather model outputs provided by the Antarctic Mesoscale Prediction System (AMPS) have been used. Based on the AMPS outputs, the boundary layer height and the atmospheric Richardson number were obtained, from which the turbulence conditions above the Antarctic plateau have been evaluated. Finally, a statistical conclusion evaluating the total atmospheric turbulence above the whole Antarctic continent for an entire year is first reported. We find some sites (or regions) have a calmer atmosphere than Dome A; this is of great instructional significance for planning the next generation of ground-based optical astronomical telescopes.

Keywords: atmospheric effects; astronomical seeing
Hadronic Processes at Work in 5BZB J0630-2406

Recent observations are shedding light on the important role that active galactic nuclei play in the production of high-energy neutrinos. In this study, we focus on one object, 5BZB J0630-2406, which is among the blazars recently proposed as associated with neutrino emission during the first 7 yr of IceCube observations. Modeling the quasi-simultaneous, broadband spectral energy distribution, we explore various scenarios from purely leptonic to leptohadronic models, testing the inclusion of external photon fields. This theoretical study provides a complementary testing ground for the proposed neutrino-blazar association. Despite being historically classified as a BL Lac, our study shows that 5BZB J0630-2406 belongs to the relatively rare subclass of high-power flat-spectrum radio quasars. Our results indicate that interactions between protons and external radiation fields can produce a neutrino flux that is within the reach of the IceCube detector. Furthermore, the spectral shape of the X-ray emission suggests the imprint of hadronic processes related to very energetic protons.

Keywords: bl lacertae objects; gamma-rays; neutrino astronomy; non-thermal radiation sources
Yonder: A Python Package for Data Denoising and Reconstruction

We present a standalone implementation of a data-deconvolution method based on singular value decomposition. The tool is written in python and packaged in the open-source yonder package. yonder receives as input two matrices, one for the data and another for the errors, and outputs a denoised version of the original dataset. In this Research Note, we briefly describe the methodology and show a demonstration of the yonder on a simulated dataset.

Keywords: astrostatistics techniques; astronomy software; astronomy data analysis
Constraints on the Very High Energy Gamma-Ray Emission from Short GRBs with HAWC

Many gamma-ray bursts (GRBs) have been observed from radio wavelengths, and a few at very high energies (VHEs, >100 GeV). The High Altitude Water Cherenkov (HAWC) gamma-ray observatory is well suited to study transient phenomena at VHEs owing to its large field of view and duty cycle. These features allow for searches of VHE emission and can probe different model assumptions of duration and spectra. In this paper, we use data collected by HAWC between 2014 December and 2020 May to search for emission in the energy range from 80 to 800 GeV coming from a sample of 47 short GRBs that triggered the Fermi, Swift, and Konus satellites during this period. This analysis is optimized to search for delayed and extended VHE emission within the first 20 s of each burst. We find no evidence of VHE emission, either simultaneous or delayed, with respect to the prompt emission. Upper limits (90% confidence level) derived on the GRB fluence are used to constrain the synchrotron self-Compton forward-shock model. Constraints for the interstellar density as low as 10-2 cm-3 are obtained when assuming z = 0.3 for bursts with the highest keV fluences such as GRB 170206A and GRB 181222841. Such a low density makes observing VHE emission mainly from the fast-cooling regime challenging.

Keywords: gamma-ray bursts; gamma-ray detectors; high energy astrophysics; gamma-ray transient sources; theoretical models; extragalactic astronomy
High-resolution, High-sensitivity, Low-frequency uGMRT View of Coma Cluster of Galaxies

We present high-resolution, high-sensitivity upgraded Giant Metrewave Radio Telescope observations of the Coma cluster (A1656) at 250-500 MHz and 550-850 MHz. At 250-500 MHz, 135 sources have extensions >0.'45 (with peak-to-local-noise ratio >4). Of these, 24 sources are associated with Coma-member galaxies. In addition, we supplement this sample of 24 galaxies with 20 ram pressure stripped (RPS) galaxies from (Chen et al. 2020, eight are included in the original extended radio source sample) and an additional five are detected and extended. We present radio morphologies, radio spectra, spectral index maps, and equipartition properties for these two samples. In general, we find the equipartition properties lie within a narrow range (e.g., ${P}_{\min }$ = 1-3 × 10- 13 dynes cm-2). Only NGC 4874, one of the two brightest central Coma cluster galaxies, has a central energy density and pressure about five times higher and a radio source age about 50% lower than that of the other Coma galaxies. We find a diffuse tail of radio emission trailing the dominant galaxy of the merging NGC 4839 group that coincides with the slingshot tail seen in X-rays. The southwestern radio relic, B1253+275, has a large extent ≈32' × 10' (≃1.08 × 0.34 Mpc2). For NGC 4789, whose long radio tails merge into the relic and may be a source of its relativistic seed electrons, we find a transverse radio spectral gradient, a steepening from southwest to northeast across the width of the radio source. Finally, radio morphologies of the extended and RPS samples suggest that these galaxies are on their first infall into Coma on (predominantly) radial orbits.

Keywords: coma cluster; astrophysical black holes; galaxy clusters; high energy astrophysics; intracluster medium; radio continuum emission; radio galaxies; supermassive black holes; tailed radio galaxies; x-ray active galactic nuclei
Stellar Transits across a Magnetized Accretion Torus as a Mechanism for Plasmoid Ejection

The close neighborhood of a supermassive black hole contains not only the accreting gas and dust but also stellar-sized objects, such as late-type and early-type stars and compact remnants that belong to the nuclear star cluster. When passing through the accretion flow, these objects perturb it by the direct action of stellar winds, as well as their magnetic and gravitational effects. By performing general-relativistic magnetohydrodynamic simulations, we investigate how the passages of a star can influence the supermassive black hole gaseous environment. We focus on the changes in the accretion rate and the emergence of blobs of plasma in the funnel of an accretion torus. We compare results from 2D and 3D numerical computations that have been started with comparable initial conditions. We find that a quasi-stationary inflow can be temporarily inhibited by a transiting star, and the plasmoids can be ejected along the magnetic field lines near the rotation axis. We observe the characteristic signatures of the perturbing motion in the power spectrum of the accretion variability, which provides an avenue for a multi-messenger detection of these transient events. Finally, we discuss the connection of our results to multiwavelength observations of galactic nuclei, with the emphasis on ten promising sources (Sgr A*, OJ 287, J0849+5108, RE J1034+396, 1ES 1927+65, ESO 253-G003, GSN 069, RX J1301.9+2747, eRO-QPE1, and eRO-QPE2).

Keywords: magnetohydrodynamical simulations; supermassive black holes; accretion; low-luminosity active galactic nuclei
Multi-spacecraft Observations of the 2022 March 25 CME and EUV Wave: An Analysis of Their Propagation and Interrelation

This paper reports on a well-defined EUV wave associated with a coronal mass ejection (CME) observed on 2022 March 25. The CME was observed by Solar Orbiter (SolO) during its first close perihelion (0.32 au) and by several other spacecraft from different viewpoints. The EUV wave was visible by the Extreme Ultraviolet Imager on board the Solar Terrestrial Relations Observatory (STEREO-A/STA) in near quadrature to SolO. We perform a detailed analysis of the early phase of this CME in relation to the evolution of the associated EUV wave. The kinematics of the EUV wave and CME are derived via visual identification of the fronts using both the STA and SolO data. The analysis of an associated metric type II radio burst provides information on the early phase of the CME and wave propagation. Finally, we compare the EUV speed to the local magnetic field and Alfvén speed using standard models of the corona. The analysis of the decoupling between the EUV wave and the CME driver via imaging, kinematic study, radio data analysis, and comparison with maps/models clearly indicates that the EUV front is consistent with a wave initially driven by the lateral expansion of the CME, which evolves into a fast-mode magnetosonic wave after decoupling from the CME.

Keywords: solar physics; the sun; solar extreme ultraviolet emission; solar coronal mass ejections