Sazuna/UAT_keywords huggingface dataset:
2 mm Observations and the Search for High-redshift Dusty Star-forming Galaxies. Finding high-redshift (z ≫ 4) dusty star-forming galaxies is extremely challenging. It has recently been suggested that millimeter selections may be the best approach since the negative K-correction makes galaxies at a given far-infrared luminosity brighter at z ≳ 4 than those at z = 2-3. Here we analyze this issue using a deep Atacama Large Millimeter/submillimeter Array (ALMA) 2 mm sample obtained by targeting ALMA 870 μm priors (these priors were the result of targeting SCUBA-2 850 μm sources) in the GOODS-S. We construct prior-based 2 mm galaxy number counts and compare them with published blank field-based 2 mm counts, finding good agreement down to 0.2 mJy. Only a fraction of the current 2 mm extragalactic background light is resolved, and we estimate what observational depths may be needed to resolve it fully. By complementing the 2 mm ALMA data with a deep SCUBA-2 450 μm sample, we exploit the steep gradient with a redshift of the 2 mm-450 μm flux density ratio to estimate redshifts for those galaxies without spectroscopic or robust optical/near-infrared photometric redshifts. Our observations measure galaxies with star formation rates in excess of 250 M ☉ yr-1. For these galaxies, the star formation rate densities fall by a factor of 9 from z = 2-3 to z = 5-6.

Keywords: Millimeter astronomy, Starburst galaxies, Submillimeter astronomy, Galaxies
The JCMT BISTRO Survey: Studying the Complex Magnetic Field of L43. We present observations of polarized dust emission at 850 μm from the L43 molecular cloud, which sits in the Ophiuchus cloud complex. The data were taken using SCUBA-2/POL-2 on the James Clerk Maxwell Telescope as a part of the BISTRO large program. L43 is a dense ( ${N}_{{{\rm{H}}}_{2}}\sim {10}^{22}$ -1023 cm-2) complex molecular cloud with a submillimeter-bright starless core and two protostellar sources. There appears to be an evolutionary gradient along the isolated filament that L43 is embedded within, with the most evolved source closest to the Sco OB2 association. One of the protostars drives a CO outflow that has created a cavity to the southeast. We see a magnetic field that appears to be aligned with the cavity walls of the outflow, suggesting interaction with the outflow. We also find a magnetic field strength of up to ~160 ± 30 μG in the main starless core and up to ~90 ± 40 μG in the more diffuse, extended region. These field strengths give magnetically super- and subcritical values, respectively, and both are found to be roughly trans-Alfvénic. We also present a new method of data reduction for these denser but fainter objects like starless cores.

Keywords: Stellar-interstellar interactions, Molecular clouds, Interstellar magnetic fields, Young stellar objects, Starlight polarization, Dust continuum emission
Understanding the Level of Turbulence by Asymmetric Distributions: A Motivation for Measurements in Space Plasmas. In this article, on the basis of the Langevin equation applied to velocity fluctuations, we numerically model the partial variance of increments, which is a useful tool to measure time and spatial correlations in space plasmas. We consider a coupled map lattice model to relate the spatial scale of fluctuations, k, to some macro parameters of the systems, such as the Reynolds number, R  λ , the κ parameter of Kappa distributions, and a skewness parameter, δ. To do so, we compute the velocity probability density function (pdf) for each spatial scale and different values of Reynolds number in the simulations. We fit the pdf with a Skew-Kappa distribution, and we obtain a numerical relationship between the level of turbulence of the plasma and the skewness of obtained distributions, namely, $\langle \delta \rangle \sim {R}_{\lambda }^{-1/2}$ . We expect the results exposed in this paper to be useful as a tool to characterize the turbulence in the context of space plasma and other environments.

Keywords: Interplanetary turbulence, Space plasmas, Non-Gaussianity
Afterglow Polarizations in a Stratified Medium with Effect of the Equal Arrival Time Surface. The environment of a γ-ray burst has an important influence on the evolution of jet dynamics and its afterglow. Here we investigate the afterglow polarizations in a stratified medium with the equal arrival time surface (EATS) effect. Polarizations of multiband afterglows are predicted. The effects of the parameters of the stratified medium on the afterglow polarizations are also investigated. We found the influences of the EATS effect on the afterglow polarizations become important for off-axis detections and polarization degree (PD) bumps move to later times with the EATS effect. Even if the magnetic field configurations, jet structure, and observational angles are fixed, polarization properties of the jet emission could still evolve. Here, we assume a large-scale ordered magnetic field in the reverse-shock region and a two-dimensional random field in the forward-shock region. Then, PD evolution is mainly determined by the evolution of the f 32 parameter (the flux ratio between the reverse-shock region and forward-shock region) at the early stage and by the evolution of the bulk Lorentz factor γ at the late stage. Through the influences on the f 32 or γ, the observational energy band, observational angles, and the parameters of the stratified medium will finally affect the afterglow polarizations.

Keywords: Gamma-ray bursts, Magnetic fields
Application of the Disk Instability Model to All Quasiperiodic Eruptions. After the first quasiperiodic eruption (QPE; GSN 069) was reported in 2019, four other sources have been identified as a QPE or a candidate. However, the physics behind QPEs is still unclear, although several models have been proposed. Pan et al. proposed an instability model for an accretion disk with magnetically driven outflows in the first QPE of GSN 069, which is able to reproduce both the light curve and the evolution of the spectra fairly well. In this work, we extend this model to all QPEs. We improve the calculations of the spectrum of the disk by introducing a hardening factor, which is caused by a deviation of opacity from a blackbody. We find that the light curves and evolution of the spectra of the four QPEs and candidates can all be well reproduced by our model calculations.

Keywords: Active galactic nuclei, Galaxy accretion disks, Magnetic fields
The Structure and Origin of Switchbacks: Parker Solar Probe Observations. Switchbacks are rapid magnetic field reversals that last from seconds to hours. Current Parker Solar Probe (PSP) observations pose many open questions in regard to the nature of switchbacks. For example, are they stable as they propagate through the inner heliosphere, and how are they formed? In this work, we aim to investigate the structure and origin of switchbacks. In order to study the stability of switchbacks, we suppose the small-scale current sheets therein are generated by magnetic braiding, and they should work to stabilize the switchbacks. With more than 1000 switchbacks identified with PSP observations in seven encounters, we find many more current sheets inside than outside switchbacks, indicating that these microstructures should work to stabilize the S-shape structures of switchbacks. Additionally, we study the helium variations to trace the switchbacks to their origins. We find both helium-rich and helium-poor populations in switchbacks, implying that the switchbacks could originate from both closed and open magnetic field regions in the Sun. Moreover, we observe that the alpha-proton differential speeds also show complex variations as compared to the local Alfvén speed. The joint distributions of both parameters show that low helium abundance together with low differential speed is the dominant state in switchbacks. The presence of small-scale current sheets in switchbacks along with the helium features are in line with the hypothesis that switchbacks could originate from the Sun via interchange reconnection process. However, other formation mechanisms are not excluded.

Keywords: Solar wind, Interplanetary magnetic fields
RadioAstron Space VLBI Imaging of the Jet in M87. I. Detection of High Brightness Temperature at 22 GHz. We present results from the first 22 GHz space very long baseline interferometric (VLBI) imaging observations of M87 by RadioAstron. As a part of the Nearby AGN Key Science Program, the source was observed in 2014 February at 22 GHz with 21 ground stations, reaching projected (u, v) spacings up to ~11 Gλ. The imaging experiment was complemented by snapshot RadioAstron data of M87 obtained during 2013-2016 from the AGN Survey Key Science Program. Their longest baselines extend up to ~25 Gλ. For all of these measurements, fringes are detected only up to ~2.8 Earth diameter or ~3 Gλ baseline lengths, resulting in a new image with angular resolution of ~150 μas or ~20 Schwarzschild radii spatial resolution. The new image not only shows edge-brightened jet and counterjet structures down to submilliarcsecond scales but also clearly resolves the VLBI core region. While the overall size of the core is comparable to those reported in the literature, the ground-space fringe detection and slightly superresolved RadioAstron image suggest the presence of substructures in the nucleus, whose minimum brightness temperature exceeds ${T}_{{\rm{B}},\min }\sim {10}^{12}\,$ K. It is challenging to explain the origin of this record-high ${T}_{{\rm{B}},\min }$ value for M87 by pure Doppler boosting effect with a simple conical jet geometry and known jet speed. Therefore, this can be evidence for more extreme Doppler boosting due to a blazar-like small jet viewing angle or highly efficient particle acceleration processes occurring already at the base of the outflow.

Keywords: Very long baseline interferometry, Relativistic jets, Active galactic nuclei, Radio galaxies
Analytic Post-Newtonian Astrometric and Spectroscopic Models of Orbits around Black Holes. Observations of the S stars, the cluster of young stars in the inner 0.1 pc of the Galactic center, have been crucial in providing conclusive evidence for a supermassive black hole at the center of our galaxy. Since some of the stars have orbits less than that of a typical human lifetime, it is possible to observe multiple orbits and test the weak-field regime of general relativity. Current calculations of orbits require relatively slow and expensive computations in order to perform numerical integrations for the position and momentum of each star at each observing time. In this paper, we present a computationally efficient, first-order post-Newtonian model for the astrometric and spectroscopic data gathered for the S stars. We find that future, 30 m class telescopes-and potentially even current large telescopes with very high spectroscopic resolution-may be able to detect the Shapiro effect for an S star in the next decade or so.

Keywords: Orbital motion, Supermassive black holes, Galactic center, Two-body problem, General relativity
Kinetic Equilibrium of Two-dimensional Force-free Current Sheets. Force-free current sheets are local plasma structures with field-aligned electric currents and approximately uniform plasma pressures. Such structures, widely found throughout the heliosphere, are sites for plasma instabilities and magnetic reconnection, the growth rate of which is controlled by the structure's current-sheet configuration. Despite the fact that many kinetic equilibrium models have been developed for one-dimensional force-free current sheets, their two-dimensional (2D) counterparts, which have a magnetic field component normal to the current sheets, have not received sufficient attention to date. Here, using particle-in-cell simulations, we search for such 2D force-free current sheets through relaxation from an initial, magnetohydrodynamic equilibrium. Kinetic equilibria are established toward the end of our simulations, thus demonstrating the existence of kinetic force-free current sheets. Although the system currents in the late equilibrium state remain field aligned as in the initial configuration, the velocity distribution functions of both ions and electrons systematically evolve from their initial drifting Maxwellians to their final time-stationary Vlasov state. The existence of 2D force-free current sheets at kinetic equilibrium necessitates future work in discovering additional integrals of motion of the system, constructing the kinetic distribution functions, and eventually investigating their stability properties.

Keywords: Space plasmas, Interplanetary discontinuities, Magnetic fields, Heliosphere
MAVEN Observations of the Interloop Magnetic Reconnections at Mars. Magnetic reconnection between neighboring magnetic field loops, the so-called interloop reconnection, is a common process to drive flares in the solar atmosphere. However, there is no direct evidence that a similar but less explosive process can take place on planets. The strong crustal fields on Mars generate plenty of magnetic loops in the near-Mars regions, providing a unique environment to research the interloop reconnection on a planet. Here, we report magnetic reconnection events between crustal field loops in the Martian ionosphere observed by Mars Atmosphere and Volatile EvolutioN (MAVEN) for the first time. During the current layer crossing, MAVEN recorded the characteristic signals of collisionless magnetic reconnection, including the Hall magnetic field, Alfvénic outflow, and electron energization. This finding implies that the interloop reconnection in the Martian ionosphere could contribute to the localized energy deposition and particle energization, which provides the seed source for aurora in the Martian atmosphere.

Keywords: Mars, Magnetic fields, Plasma physics
Evidence of Electron Acceleration via Nonlinear Resonant Interactions with Whistler-mode Waves at Foreshock Transients. Shock waves are sites of intense plasma heating and charged particle acceleration. In collisionless solar wind plasmas, such acceleration is attributed to shock drift or Fermi acceleration but also to wave-particle resonant interactions. We examine the latter for the case of electrons interacting with one of the most commonly observed wave modes in shock environments, the whistler mode. Such waves are particularly intense in dynamic, localized regions upstream of shocks, arising from the kinetic interaction of the shock with solar wind discontinuities. These regions, known as foreshock transients, are also sites of significant electron acceleration by mechanisms not fully understood. Using in situ observations of such transients in the Earth's foreshock, we demonstrate that intense whistler-mode waves can resonate nonlinearly with &gt;25 eV solar wind electrons and accelerate them to ~100-500 eV. This acceleration is mostly effective for the 50-250 eV energy range, where the accelerated electron population exhibits a characteristic butterfly pitch-angle distribution consistent with theoretical predictions. Such nonlinear resonant acceleration is very fast, implying that this mechanism may be important for injecting suprathermal electrons of solar wind origin into the shock region, where they can undergo further, efficient shock-drift acceleration to even higher energies.

Keywords: Planetary bow shocks
Soft X-Ray-induced Dimerization of Methane. Carbon 1s excitation of methane, CH4, has been studied in the gas phase using the ion trap integrated with the photon-ion instrument at PETRA III/DESY and soft X-rays from the beamline P04. The created photoions are stored within the ion trap so that in further steps the photoions can undergo reactions with neutral methane molecules. The ionic photoproducts as well as reaction products created thereby are mass-over-charge analyzed by an ion time-of-flight spectrometer. Besides the photoions, product ions with up to three carbon atoms are found. In contrast to experiments using vacuum ultraviolet radiation, especially highly reactive product ions with a small number of hydrogen atoms such as ${{\rm{C}}}_{2}{{\rm{H}}}_{2}^{+}$ and ${{\rm{C}}}_{2}{{\rm{H}}}_{3}^{+}$ are found, which are important precursors for larger hydrocarbons such as C6H6. Possible production routes of the product ions are analyzed on the basis of a model that considers the probabilities for photofragmentation and the first subsequent chemical reaction step. The model indicates that the high degree of fragmentation by photons with energies around 280 eV is favoring these products. The results of the measurements show that the products like ${{\rm{C}}}_{2}{{\rm{H}}}_{2}^{+}$ and ${{\rm{C}}}_{2}{{\rm{H}}}_{3}^{+}$ can be generated by a single collision of the ionization product with neutral methane. The results suggest that soft X-rays might be important for chemical reactions in planetary atmospheres, which has usually not been taken into account. However, due to the high degree of fragmentation and large cross sections involved, they can have a large influence even when the corresponding photon flux is rather small.

Keywords: Planetary atmospheres
Characterizing 3D Magnetic Structures in Sunspot Light Bridges. Light bridges (LBs) are narrow structures dividing sunspot umbra, and their role in active region evolution is yet to be explored. We investigated the magnetic structure of the two LBs: a narrow LB (with width ~810 km) and a considerably wider LB (2475 km) in the active region NOAA 12371. We employed: (1) the high-spatial-resolution spectropolarimetric data obtained by the Near InfraRed Imaging Spectropolarimeter (NIRIS) of the 1.6 m Goode Solar Telescope (GST) for studying the magnetic structure at the photosphere, and (2) the nonlinear force-free field (NLFFF) models, extrapolated from both the photospheric magnetogram from GST/NIRIS and from the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory, for studying the three-dimensional (3D) magnetic structure on a larger scale. Our observations reveal the presence of a field-free (or, more precisely, weak-field) region and the different velocity structures inside the two LBs. Analysis of the 3D NLFFF model shows a low-lying magnetic canopy as well as the enhanced current system above the LBs. The substantial difference between the LBs and the umbrae is found in the overall magnetic topology in that the field lines emanating from the two LBs are more twisted than that from the neighboring umbrae.

Keywords: Solar active region magnetic fields, Sunspots
The Hot Circumgalactic Medium of the Milky Way: New Insights from XMM-Newton Observations. We present XMM-Newton observations around the sight line of Mrk 421. The emission spectrum of the Milky Way (MW) circumgalactic medium (CGM) shows that a two-phase model is a better fit to the data compared to a single-phase model; in addition to the warm-hot virial phase at log (T/K) = 6.30 ± 0.02, a hot super-virial phase at log (T/K) = ${6.88}_{-0.06}^{+0.07}$ is required. Furthermore, we present observations of five fields within 5 degrees of the primary field. Their spectra also require a two-phase model at warm-hot and hot temperatures. The hot phase, which was first discovered in Das et al. in 2019, appears to be widespread. By chemical tagging, we show that the emission from the supevirial phase comes from the L-shell transitions of Fe XVIII-Fe XXII, and that the range of temperatures probed in emission is distinct from that in absorption. We detect scatter in temperature and emission measure in both the phases, and deduce that there is small-scale density inhomogeneity in the MW CGM. The emitting gas likely has higher density, possibly from regions close to the disk of the MW, while the absorption in the virial phase may arise from low-density gas extended out to the virial radius of the MW. The presence of the super-virial phase far from the regions around the Galactic center implicates physical processes unrelated to the activity at the Galactic center. Hot outflows resulting from star formation activity throughout the Galactic disk are likely to be responsible for producing this phase.

Keywords: Diffuse x-ray background, Milky Way Galaxy, Circumgalactic medium
Solar Cycle Variation of 0.3-1.29 MeV Nucleon<SUP>-1</SUP> Heavy Ion Composition During Quiet Times Near 1 au in Solar Cycles 23 and 24. We report on the annual variation of quiet-time suprathermal ion composition for C through Fe using Advanced Composition Explorer (ACE)/Ultra-Low Energy Isotope Spectrometer data over the energy range 0.3-1.28 MeV nuc-1 from 1998 through 2019, covering solar cycle 23's rising phase through Solar Cycle 24's declining phase. Our findings are: (1) quiet-time suprathermal abundances resemble CIR-associated particles during solar minima; (2) quiet-time suprathermals are M/Q fractionated in a manner that is consistent with M/Q fractionation in large gradual solar energetic particle events (GSEP) during solar maxima; and (3) variability within the quiet-time suprathermal pool increases as a function of M/Q and is consistent with the analogous variability in GSEP events. From these observations, we infer that quiet-time suprathermal ions are remnants of CIRs in solar minima and GSEP events in solar maxima. Coincident with these results, we also unexpectedly show that S behaves like a low FIP ion in the suprathermal regime, and is therefore drawn from low FIP solar sources.

Keywords: Solar energetic particles, Sunspot number
The Formation of a U-shaped Filament Due to the Successive Magnetic Reconnection between a Filament and Its Nearby Chromospheric Fibrils. Although magnetic reconnection plays a key role in the formation of a solar filament, the detailed formation process is still ambiguous. Combining the observational data from the New Vacuum Solar Telescope and the Solar Dynamics Observatory, we analyzed the formation of a U-shaped filament via successive magnetic reconnection in the AR NOAA 11598 on 2012 October 25. The successive reconnection occurred between a filament (F) and its nearby chromospheric fibrils (CF). The associated brightening and magnetic cancellation were observed. The changes in appearance of the CF at the reconnection site were accompanied by the formation and accumulation of some new magnetic loops, as well as plasmas propagated along the formed magnetic loops from the reconnection site, indicating the changes in the topology of the F and CF. These can provide comprehensive observational evidence for successive reconnection. After the reconnection, a longer U-shaped filament was formed. During the formation of the U-shaped filament, two major magnetic energy releases took place. While in the two energy release processes, the injected plasma from the reconnection site can provide part of the material for the formation of the U-shaped filament. Therefore, we conclude that the successive reconnection results in both the dynamical evolution and the subsequent formation associated with the U-shaped filament. And the results of nonlinear force-free field extrapolation demonstrated that the magnetic topology of the F was changed significantly; this is consistent with the observational results and further confirms the formation of the U-shaped filament.

Keywords: Solar active regions, Solar filaments, Solar magnetic reconnection