Sazuna/UAT_keywords huggingface dataset:
The 3D Kinematics of Gas in the Small Magellanic Cloud. We investigate the kinematics of neutral gas in the Small Magellanic Cloud (SMC) and test the hypothesis that it is rotating in a disk. To trace the 3D motions of the neutral gas distribution, we identify a sample of young, massive stars embedded within it. These are stars with radial velocity measurements from spectroscopic surveys and proper motion measurements from Gaia, whose radial velocities match with dominant H I components. We compare the observed radial and tangential velocities of these stars with predictions from the state-of-the-art rotating disk model based on high-resolution 21 cm observations of the SMC from the Australian Square Kilometer Array Pathfinder telescope. We find that the observed kinematics of gas-tracing stars are inconsistent with disk rotation. We conclude that the kinematics of gas in the SMC are more complex than can be inferred from the integrated radial velocity field. As a result of violent tidal interactions with the Large Magellanic Cloud, nonrotational motions are prevalent throughout the SMC, and it is likely composed of distinct substructures overlapping along the line of sight.

Keywords: Neutral hydrogen clouds, Magellanic Clouds, Galaxy kinematics, Interstellar medium, Magellanic irregular galaxies, Radio astronomy
Finding the Brightest Cosmic Beacons in the Southern Hemisphere. The study of absorptions along the lines of sight to bright high-z QSOs is an invaluable cosmological tool that provides a wealth of information on the inter-/circum-galactic medium, dark matter, primordial elements, reionization, fundamental constants, and general relativity. Unfortunately, the number of bright (i ≲ 18) QSOs at z ≳ 2 in the southern hemisphere is much lower than that in the north, due to the lack of wide multiwavelength surveys at decl. δ &lt; 0°, hampering the effectiveness of observations from southern observatories. In this work we present a new method based on Canonical Correlation Analysis to identify such objects, taking advantage of a number of available databases: Skymapper, Gaia DR2, WISE, and 2MASS. Our QSO candidate sample lists 1476 sources with i &lt; 18 over 12,400 square degrees in the southern hemisphere. With a preliminary campaign we observed spectroscopically 69 of them, confirming 54 new bright QSOs at z &gt; 2.5, corresponding to a success rate of our method of ∼80%. Furthermore, we estimate a completeness of ∼90% of our sample at completion of our observation campaign. The new QSOs confirmed by this first and the forthcoming campaigns (QUBRICS10 survey) will be the targets of subsequent studies using higher resolution spectrographs, like ESPRESSO, UVES, and (in the long term) ELT/HIRES.

Keywords: Sky surveys, Catalogs, Quasars
Asteroseismic Constraints on the Cosmic-time Variation of the Gravitational Constant from an Ancient Main-sequence Star. We investigate the variation of the gravitational constant G over the history of the universe by modeling the effects on the evolution and asteroseismology of the low-mass star KIC 7970740, which is one of the oldest (∼11 Gyr) and best-observed solar-like oscillators in the Galaxy. From these data we find \dot{G}/G=(2.1+/- 2.9)× 10-12 yr-1, that is, no evidence for any variation in G. We also find a Bayesian asteroseismic estimate of the age of the universe as well as astrophysical S-factors for five nuclear reactions obtained through a 12-dimensional stellar evolution Markov Chain Monte Carlo simulation.

Keywords: Stellar ages, Fundamental parameters of stars, Gravitation, Non-standard theories of gravity, Stellar evolutionary models, Stellar astronomy, Stellar physics, Main sequence stars, Stellar oscillations, Asteroseismology, Stellar evolutionary tracks, Stellar evolution
Heavy Ion Acceleration by Super-Alfvénic Waves. A generation mechanism of super-Alfvénic (SPA) waves in multi-ion species plasma is proposed, and the associated heavy ion acceleration process is discussed. The SPA waves are thought to play important roles in particle acceleration since they have large wave electric fields because of their high phase velocity. It is demonstrated by using full particle-in-cell simulations that large amplitude proton cyclotron waves, excited due to proton temperature anisotropy, nonlinearly destabilize SPA waves through parametric decay instability in a three-component plasma composed of electrons, protons, and α particles. At the same time, α cyclotron waves get excited via another decay instability. A pre-accelerated α particle resonates simultaneously with the two daughter waves, the SPA waves and the α cyclotron waves, and it is further accelerated perpendicular to the ambient magnetic field. The process may work in astrophysical environments where a sufficiently large temperature anisotropy of lower mass ions occurs.

Keywords: Space plasmas, Plasma astrophysics, Interplanetary particle acceleration, Solar coronal waves, Alfven waves
No Snowball Cycles at the Outer Edge of the Habitable Zone for Habitable Tidally Locked Planets. Planets orbiting within the habitable zones of M stars are prime targets for future observations, which motivates a greater understanding of how tidal locking can affect planetary habitability. In this Letter we will consider the effect of tidal locking on limit cycling between snowball and warm climate states, which has been suggested could occur for rapidly rotating planets in the outer regions of the habitable zone with low CO2 outgassing rates. Here, we use a 3D Global Climate Model that calculates silicate-weathering to show that tidally locked planets with an active carbon cycle will not experience limit cycling between warm and snowball states. Instead, they smoothly settle into “Eyeball” states with a small unglaciated substellar region. The size of this unglaciated region depends on the stellar irradiation, the CO2 outgassing rate, and the continental configuration. Furthermore, we argue that a tidally locked habitable zone planet cannot stay in a snowball state for a geologically significant time. This may be beneficial to the survival of complex life on tidally locked planets orbiting the outer edge of their stars, but might also make it less likely for complex life to arise.

Keywords: Exoplanets, Exoplanet astronomy, Astrobiology, Habitable planets, Exoplanet atmospheres
Cold Giant Planets Evaporated by Hot White Dwarfs. Atmospheric escape from close-in Neptunes and hot Jupiters around Sun-like stars driven by extreme ultraviolet (EUV) irradiation plays an important role in the evolution of exoplanets and in shaping their ensemble properties. Intermediate and low mass stars are brightest at EUV wavelengths at the very end of their lives, after they have expelled their envelopes and evolved into hot white dwarfs. Yet the effect of the intense EUV irradiation of giant planets orbiting young white dwarfs has not been assessed. We show that the giant planets in the solar system will experience significant hydrodynamic escape caused by the EUV irradiation from the white dwarf left behind by the Sun. A fraction of the evaporated volatiles will be accreted by the solar white dwarf, resulting in detectable photospheric absorption lines. As a large number of the currently known extrasolar giant planets will survive the metamorphosis of their host stars into white dwarfs, observational signatures of accretion from evaporating planetary atmospheres are expected to be common. In fact, one-third of the known hot single white dwarfs show photospheric absorption lines of volatile elements, which we argue are indicative of ongoing accretion from evaporating planets. The fraction of volatile contaminated hot white dwarfs strongly decreases as they cool. We show that accretion from evaporating planetary atmospheres naturally explains this temperature dependence if more than 50% of hot white dwarfs still host giant planets.

Keywords: White dwarf stars, Solar system, Extrasolar gaseous giant planets, Exoplanet atmospheres
Where Do Quasar Hosts Lie with Respect to the Size-Mass Relation of Galaxies?. The evolution of the galaxy size-mass relation has been a puzzle for over a decade. High-redshift galaxies are significantly more compact than galaxies observed today at an equivalent mass, but how much of this apparent growth is driven by progenitor bias, minor mergers, secular processes, or feedback from active galactic nuclei (AGNs) is unclear. To help disentangle the physical mechanisms at work by addressing the latter, we study the size-M stellar relation of 32 carefully selected broad-line AGN hosts at 1.2 &lt; z &lt; 1.7 (7.5 &lt; log M BH &lt; 8.5; L bol/L Edd ≳ 0.1). Using the Hubble Space Telescope with multiband photometry and state-of-the-art modeling techniques, we measure half-light radii while accounting for uncertainties from subtracting bright central point sources. We find AGN hosts to have sizes ranging from ∼1 to 6 kpc at M stellar ∼ (0.3-1) × 1011 M ⊙. Thus, many hosts have intermediate sizes as compared to equal-mass star-forming and quiescent galaxies. While inconsistent with the idea that AGN feedback may induce an increase in galaxy sizes, this finding is consistent with hypotheses in which AGNs preferentially occur in systems with prior concentrated gas reservoirs, or are involved in a secular compaction processes perhaps responsible for building their bulges. If driven by minor mergers that do not grow central black holes as fast as they do bulge-like stellar structures, such a process would explain both the galaxy size-mass relation observed here and the evolution in the black hole-bulge mass relation described in a companion paper.

Keywords: AGN host galaxies, Supermassive black holes, Active galactic nuclei, Quasars
Search for Astronomical Neutrinos from Blazar TXS 0506+056 in Super-Kamiokande. We report a search for astronomical neutrinos in the energy region from several GeV to TeV in the direction of the blazar TXS 0506+056 using the Super-Kamiokande detector following the detection of a 100 TeV neutrinos from the same location by the IceCube collaboration. Using Super-Kamiokande neutrino data across several data samples observed from 1996 April to 2018 February we have searched for both a total excess above known backgrounds across the entire period as well as localized excesses on smaller timescales in that interval. No significant excess nor significant variation in the observed event rate are found in the blazar direction. Upper limits are placed on the electron- and muon-neutrino fluxes at the 90% confidence level as 6.0 × 10-7 and 4.5 × 10-7-9.3 × 10-10 [erg cm-2 s-1], respectively.

Keywords: Blazars, Neutrino astronomy, BL Lacertae objects
Strong Excess Faraday Rotation on the Inside of the Sagittarius Spiral Arm. We present first results for Faraday rotation of compact polarized sources (1-2 GHz continuum) in The H I/OH/Recombination line (THOR) survey of the inner Galaxy. In the Galactic longitude range 39° &lt; ℓ &lt; 52°, we find rotation measures (RMs) in the range -310 rad m-2 ≤ RM ≤ +4219 rad m-2, with the highest values concentrated within a degree of ℓ = 48° at the Sagittarius arm tangent. Most of the high RMs arise in diffuse plasma, along lines of sight that do not intersect H II regions. For ℓ &gt; 49°, RM drops off rapidly, while at ℓ &lt; 47°, the mean RM is higher with a larger standard deviation than at ℓ &gt; 49°. We attribute the RM structure to the compressed diffuse warm ionized medium in the spiral arm, upstream of the major star formation regions. The Sagittarius arm acts as a significant Faraday screen inside the Galaxy. This has implications for models of the Galactic magnetic field and the expected amount of Faraday rotation of fast radio bursts from their host galaxies. We emphasize the importance of sensitivity to high Faraday depth in future polarization surveys.

Keywords: Galaxy magnetic fields, Transient sources, Spiral arms, H II regions, Interstellar medium, Polarimetry, Radio pulsars
Hi-C 2.1 Observations of Jetlet-like Events at Edges of Solar Magnetic Network Lanes. We present high-resolution, high-cadence observations of six, fine-scale, on-disk jet-like events observed by the High-resolution Coronal Imager 2.1 (Hi-C 2.1) during its sounding-rocket flight. We combine the Hi-C 2.1 images with images from the Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly (AIA) and the Interface Region Imaging Spectrograph (IRIS), and investigate each event’s magnetic setting with co-aligned line-of-sight magnetograms from the SDO/Helioseismic and Magnetic Imager (HMI). We find that (i) all six events are jetlet-like (having apparent properties of jetlets), (ii) all six are rooted at edges of magnetic network lanes, (iii) four of the jetlet-like events stem from sites of flux cancelation between majority-polarity network flux and merging minority-polarity flux, and (iv) four of the jetlet-like events show brightenings at their bases reminiscent of the base brightenings in coronal jets. The average spire length of the six jetlet-like events (9000 ± 3000 km) is three times shorter than that for IRIS jetlets (27,000 ± 8000 km). While not ruling out other generation mechanisms, the observations suggest that at least four of these events may be miniature versions of both larger-scale coronal jets that are driven by minifilament eruptions and still-larger-scale solar eruptions that are driven by filament eruptions. Therefore, we propose that our Hi-C events are driven by the eruption of a tiny sheared-field flux rope, and that the flux rope field is built and triggered to erupt by flux cancelation.

Keywords: The Sun, Quiet sun, Solar magnetic fields, Solar chromospheric heating, Solar chromosphere
First Evidence of Enhanced Recombination in Astrophysical Environments and the Implications for Plasma Diagnostics. We report the first unambiguous observational evidence of Rydberg Enhanced Recombination (RER), a potentially important recombination mechanism that has hitherto been unexplored in low-temperature photoionized plasmas. RER shares similarities with dielectronic recombination, with the difference that the electron is captured into a highly excited state below the ionization threshold—rather than above the threshold—of the recombining ion. We predict transitions of carbon and oxygen ions that are formed via the RER process, and their relative strengths with collisional-radiative spectral models. Optical C II RER features are detected in published high-resolution spectra of eight planetary nebulae, and a C III transition has been found in the ultraviolet spectrum in a symbiotic star system. The relative intensities of these lines are consistent with their production by this recombination mechanism. Because RER has not previously been accounted for in photoionized plasmas, its inclusion in models can significantly impact the predicted ionization balance and hence abundance calculations of important astrophysical species. Calculations for {C}+ suggest that the enhancement in the total recombination rate can amount to a factor of 2.2 at 8100 K, increasing to 7.5 at T = 3500 K. These results demonstrate the importance of including RER in models of photoionized astrophysical plasmas and in elemental abundance determinations.

Keywords: Radiative transfer simulations, Atomic spectroscopy, Symbiotic binary stars, Planetary nebulae
Feature Matching Conditional GAN for Fast Radio Burst Localization with Cluster-fed Telescope. For the real-time transient localization, there are large uncertainties of the fast radio burst (FRB) positions due to the undersampled focal plane in cluster-fed telescopes. A novel focal-field feature matching algorithm based on a conditional generative adversarial network, F3M-cGAN, is proposed for FRB localization. By exploiting the multiple frequency characteristics of FRBs, an improved three-dimensional convolution autoencoder is developed to jointly synthesize focal-field distribution (FFD) features. Meanwhile, the received signals are input as a condition to the discriminator to strengthen the mapping relation. Moreover, an estimator based on a deep neural network is introduced to estimate the position of the FRBs, and a position encoder is designed to enhance the position precision according to the energy distribution. For pattern reconstruction, texture loss is used as feedback for the generator. Based on the alternate training process of the F3M-cGAN framework, effective reconstruction and position estimation could be achieved. A scale model of the Five-hundred-meter Aperture Spherical radio Telescope is used to verify the effectiveness of the proposed method. The simulation results demonstrate that this approach can accurately reconstruct FFD features with limited feeds, and realize a higher real-time localizing precision than the angular resolution of a radio telescope. Furthermore, the proposed method can increase the search area for transients.

Keywords: Reflecting telescopes, Radio bursts, Radio telescopes, Field of view, Radio astronomy
A Mirage of the Cosmic Shoreline: Venus-like Clouds as a Statistical False Positive for Exoplanet Atmospheric Erosion. Near-term studies of Venus-like atmospheres with James Webb Space Telescope (JWST) promise to advance our knowledge of terrestrial planet evolution. However, the remote study of Venus in the solar system and the ongoing efforts to characterize gaseous exoplanets both suggest that high altitude aerosols can limit observational studies of lower atmospheres, and potentially make it challenging to recognize exoplanets as “Venus-like.” To support practical approaches for exo-Venus characterization with JWST, we use Venus-like atmospheric models with self-consistent cloud formation of the seven TRAPPIST-1 exoplanets to investigate the atmospheric depth that can be probed using both transmission and emission spectroscopy. We find that JWST/Mid-IR Instrument Low Resolution Spectrometer secondary eclipse emission spectroscopy in the 6 μm opacity window could probe at least an order of magnitude deeper pressures than transmission spectroscopy, potentially allowing access to the subcloud atmosphere for the two hot innermost TRAPPIST-1 planets. In addition, we identify two confounding effects of sulfuric acid aerosols that may carry strong implications for the characterization of terrestrial exoplanets with transmission spectroscopy: (1) there exists an ambiguity between cloud-top and solid surface in producing the observed spectral continuum; and (2) the cloud-forming region drops in altitude with semimajor axis, causing an increase in the observable cloud-top pressure with decreasing stellar insolation. Taken together, these effects could produce a trend of thicker atmospheres observed at lower stellar insolation—a convincing false positive for atmospheric escape and an empirical “cosmic shoreline.” However, developing observational and theoretical techniques to identify Venus-like exoplanets and discriminate them from stellar windswept worlds will enable advances in the emerging field of terrestrial comparative planetology.

Keywords: Extrasolar rocky planets, Exoplanets, Exoplanet astronomy, Exoplanet evolution, Exoplanet atmospheres
Exploring the Outskirts of Globular Clusters: The Peculiar Kinematics of NGC 3201. The outskirts of globular clusters (GCs) simultaneously retain crucial information about their formation mechanism and the properties of their host galaxy. Thanks to the advent of precision astrometry both their morphological and kinematic properties are now accessible. Here we present the first dynamical study of the outskirts of the retrograde GC NGC 3201 until twice its Jacobi radius (&lt;100 pc), using specifically selected high-quality astrometric data from Gaia DR2. We report the discovery of a stellar overdensity along the southeast/northwest direction that we identify as tidal tails. The GC is characterized globally by radial anisotropy and a hint of isotropy in the outer parts, with an excess of tangential orbits around the lobes corresponding to the tidal tails, in qualitative agreement with an N-body simulation. Moreover, we measure flat velocity dispersion profiles, reaching values of 3.5 ± 0.9 km s-1 until beyond the Jacobi radius. While tidal tails could contribute to such a flattening, this high velocity dispersion value is in disagreement with the expectation from the sole presence of potential escapers. To explain this puzzling observation, we discuss the possibility of an accreted origin of the GC, the presence of a dark matter halo—leftover of its formation at high redshift—and the possible effects of non-Newtonian dynamics. Our study uncovers a new path for the study of GC formation and of the properties of the Milky Way potential in the era of precision astrometry.

Keywords: Globular star clusters, Stellar dynamics, Tidal tails, Proper motions, Milky Way Galaxy, Dynamical evolution
An ASKAP Search for a Radio Counterpart to the First High-significance Neutron Star-Black Hole Merger LIGO/Virgo S190814bv. We present results from a search for a radio transient associated with the LIGO/Virgo source S190814bv, a likely neutron star-black hole (NSBH) merger, with the Australian Square Kilometre Array Pathfinder. We imaged a 30 deg2 field at ΔT = 2, 9, and 33 days post-merger at a frequency of 944 MHz, comparing them to reference images from the Rapid ASKAP Continuum Survey observed 110 days prior to the event. Each epoch of our observations covers 89% of the LIGO/Virgo localization region. We conducted an untargeted search for radio transients in this field, resulting in 21 candidates. For one of these, AT2019osy, we performed multiwavelength follow-up and ultimately ruled out the association with S190814bv. All other candidates are likely unrelated variables, but we cannot conclusively rule them out. We discuss our results in the context of model predictions for radio emission from NSBH mergers and place constrains on the circum-merger density and inclination angle of the merger. This survey is simultaneously the first large-scale radio follow-up of an NSBH merger, and the most sensitive widefield radio transients search to-date.

Keywords: Transient sources, Radio astronomy, Gravitational waves, Radio transient sources
Water Vapor and Clouds on the Habitable-zone Sub-Neptune Exoplanet K2-18b. Results from the Kepler mission indicate that the occurrence rate of small planets (&lt;3 R ⊕) in the habitable zone of nearby low-mass stars may be as high as 80%. Despite this abundance, probing the conditions and atmospheric properties on any habitable-zone planet is extremely difficult and has remained elusive to date. Here, we report the detection of water vapor and the likely presence of liquid and icy water clouds in the atmosphere of the 2.6 R ⊕ habitable-zone planet K2-18b. The simultaneous detection of water vapor and clouds in the mid-atmosphere of K2-18b is particularly intriguing because K2-18b receives virtually the same amount of total insolation from its host star ({1368}-107+114 W m-2) as the Earth receives from the Sun (1361 W m-2), resulting in the right conditions for water vapor to condense and explain the detected clouds. In this study we observed nine transits of K2-18b using Hubble Space Telescope/WFC3 in order to achieve the necessary sensitivity to detect the water vapor, and we supplement this data set with Spitzer and K2 observations to obtain a broader wavelength coverage. While the thick hydrogen-dominated envelope we detect on K2-18b means that the planet is not a true Earth analog, our observations demonstrate that low-mass habitable-zone planets with the right conditions for liquid water are accessible with state-of-the-art telescopes.

Keywords: Mini Neptunes, Exoplanet atmospheres, Planetary atmospheres, Exoplanets