Sazuna/UAT_keywords huggingface dataset:
Impact of Magnetorotational Instability on Grain Growth in Protoplanetary Disks. I. Relevant Turbulence Properties. Turbulence in protoplanetary disks induces collisions between dust grains, and thus facilitates grain growth. We investigate the two fundamental assumptions about the turbulence in obtaining grain collisional velocities—the kinetic energy spectrum and the turbulence autocorrelation time—in the context of the turbulence generated by the magnetorotational instability (MRI). We carry out numerical simulations of the MRI, as well as driven turbulence, for a range of physical and numerical parameters. We find that the convergence of the turbulence α-parameter does not necessarily imply the convergence of the energy spectrum. The MRI turbulence is largely solenoidal, for which we observe a persistent kinetic energy spectrum of k-4/3. The same is obtained for solenoidal driven turbulence with and without a magnetic field, over more than 1 dex near the dissipation scale. This power-law slope appears to be converged in terms of numerical resolution, and to be due to the bottleneck effect. The kinetic energy in the MRI turbulence peaks at the fastest growing mode of the MRI. In contrast, the magnetic energy peaks at the dissipation scale. The magnetic energy spectrum in the MRI turbulence does not show a clear power-law range, and is almost constant over approximately 1 dex near the dissipation scale. The turbulence autocorrelation time is nearly constant at large scales, limited by the shearing timescale, and shows a power-law drop close to k-1 at small scales, with a slope steeper than that of the eddy crossing time. The deviation from the standard picture of the Kolmogorov turbulence with the injection scale at the disk scale height can potentially have a significant impact on grain collisional velocities.

Keywords: Interstellar dust, Protoplanetary disks
The X-Ray Cavity Around Hotspot E in Cygnus A: Tunneled by a Deflected Jet. The powerful Fanaroff-Riley class II (FR II) radio galaxy Cygnus A exhibits primary and secondary hotspots in each lobe. A 2 Ms Chandra X-ray image of Cygnus A has revealed an approximately circular hole, with a radius of 3.9 kpc, centered on the primary hotspot in the eastern radio lobe, hotspot E. We infer the distribution of X-ray emission on our line of sight from an X-ray surface brightness profile of the radio lobe adjacent to the hole and use it to argue that the hole is excavated from the radio lobe. The surface brightness profile of the hole implies a depth at least 1.7 ± 0.3 times greater than its projected width, requiring a minimum depth of 13.3 ± 2.3 kpc. A similar hole observed in the 5 GHz Very Large Array radio map reinforces the argument for a cavity lying within the lobe. We argue that the jet encounters the shock compressed intracluster medium at hotspot E, passing through one or more shocks as it is deflected back into the radio lobe. The orientation of Cygnus A allows the outflow from hotspot E to travel almost directly away from us, creating an elongated cavity, as observed. These results favor models for multiple hotspots in which an FR II jet is deflected at a primary hotspot, then travels onward to deposit the bulk of its power at a secondary hotspot, rather than the dentist drill model.

Keywords: X-ray sources, Active galaxies, Galaxy jets, Cool cores
First SETI Observations with China's Five-hundred-meter Aperture Spherical Radio Telescope (FAST). The Search for Extraterrestrial Intelligence (SETI) attempts to address the possibility of the presence of technological civilizations beyond the Earth. Benefiting from high sensitivity, large sky coverage, and an innovative feed cabin for China's Five-hundred-meter Aperture Spherical radio Telescope (FAST), we performed SETI's first observations with FAST's newly commissioned 19 beam receiver; we report preliminary results in this paper. Using the data stream produced by the SERENDIP VI real-time multibeam SETI spectrometer installed at FAST, as well as its off-line data processing pipelines, we identify and remove four kinds of radio frequency interference (RFI): zone, broadband, multibeam, and drifting, utilizing the Nebula SETI software pipeline combined with machine-learning algorithms. After RFI mitigation, the Nebula pipeline identifies and ranks interesting narrowband candidate ET signals, scoring candidates by the number of times candidate signals have been seen at roughly the same sky position and same frequency, signal strength, proximity to a nearby star or object of interest, along with several other scoring criteria. We show four example candidate groups that demonstrate this RFI mitigation and candidate selection. This preliminary testing on FAST data helps to validate our SETI instrumentation techniques as well as our data processing pipeline.

Keywords: Astrobiology, Sky surveys, Astronomical instrumentation
Observation of the Tailward Electron Flows Commonly Detected at the Flow Boundary of the Earthward Ion Bursty Bulk Flows in the Magnetotail. Using measurements of the Magnetospheric Multiscale mission in the magnetotail from -24 to -15RE, we identified 40 ion Bursty Bulk Flow events (BBFs) and investigated the electron behaviors during these BBFs. The ion flows peaked near the center of the plasma sheet and had a sharp flow boundary. The electron-flow profile is distinct from the ion flows of the BBFs. Inside the BBFs, the strongest Earthward electron flows are observed in the ion flow boundary, away from the current sheet center. Farther away from the peak of the Earthward electron flows, the tailward electron flows are observed in the edges of the ion flows, are mainly field-aligned with low energy, and are stronger than the Earthward flows. It seems that the tailward low-energy electrons are energized at some places tailward of the spacecraft and then ejected Earthward, consistent with the magnetic reconnection scenario in the magnetotail. We suggest this has implications for our understanding of astrophysical jets.

Keywords: Space plasmas, Interplanetary particle acceleration, Solar magnetic reconnection
Hα Distances to the Leading Arm of the Magellanic Stream. The Leading Arm (LA) is a tidal feature that is in front of the Magellanic Clouds (MCs) on their orbit through the Galaxy's halo. Many physical properties of the LA, such as its mass and size, are poorly constrained because it has few distance measurements. While Hα measurements have been used to estimate the distances to halo clouds, many studies have been unsuccessful in detecting Hα from the LA. In this study, we explore a group of H I clouds which lie 75°-90° from the MCs. Through ultraviolet and 21 cm radio spectroscopy, this region, dubbed the LA Extension, was found to have chemical and kinematic similarities to the LA. Using the Wisconsin Hα Mapper, we detect Hα emission in four out of seven of our targets. Assuming that this region is predominantly photoionized, we use a radiation model that incorporates the contributions of the Galaxy, MCs, and the extragalactic background at z = 0 to derive a heliocentric distance of d⊙ ≥ 13.4 kpc . We also use this model to rederive Hα distances of d⊙ ≥ 5.0 kpc and d⊙ ≥ 22.9 kpc to two clouds in the literature that might also be associated with the LA. Using these new measurements, and others in the literature, we provide a general trend of the variation of LA heliocentric distance as a function of Magellanic Stream longitude, and explore its implications for the origin and closest point of approach of the LA.

Keywords: High-velocity clouds, Dwarf galaxies, Magellanic Stream, Milky Way evolution, Galaxies
CHORUS. III. Photometric and Spectroscopic Properties of Lyα Blobs at z = 4.9-7.0. We report the Subaru Hyper Suprime-Cam (HSC) discovery of two Lyα blobs (LABs), dubbed z70-1 and z49-1 at z = 6.965 and z = 4.888, respectively, that are Lyα emitters with a bright (log{L}Lyα/[erg s-1]&gt; 43.4) and spatially extended Lyα emission, and present the photometric and spectroscopic properties of a total of seven LABs: the two new LABs and five previously known LABs at z = 5.7-6.6. The z70-1 LAB shows extended Lyα emission with a scale length of 1.4 ± 0.2 kpc, about three times larger than the UV continuum emission, making z70-1 the most distant LAB identified to date. All of the seven LABs, except z49-1, exhibit no active galactic nucleus (AGN) signatures such as X-ray emission, N V λ1240 emission, or Lyα line broadening, while z49-1 has a strong C IV λ1548 emission line indicating an AGN on the basis of the UV-line ratio diagnostics. We carefully model the point-spread functions of the HSC images and conduct two-component exponential profile fitting to the extended Lyα emission of the LABs. The Lyα scale lengths of the core (star-forming region) and halo components are rc = 0.6-1.2 kpc and rh = 2.0-13.8 kpc, respectively. The relations between the scale lengths and galaxy properties (Lyα luminosity LLyα, Lyα rest-frame equivalent width EW0, and UV continuum magnitude MUV) of our LABs are similar to those of Lyα halos (LAHs) identified around star-forming galaxies found previously by the Very Large Telescope/MUSE at similar redshifts, suggesting that our LABs are likely the bright version of high-z LAHs.

Keywords: Galaxy formation, Observational cosmology, High-redshift galaxies, Galaxy evolution
Corona-heated Accretion-disk Reprocessing: A Physical Model to Decipher the Melody of AGN UV/Optical Twinkling. Active galactic nuclei (AGNs) have long been observed to "twinkle" (I.e., their brightness varies with time) on timescales from days to years in the UV/optical bands. Such AGN UV/optical variability is essential for probing the physics of supermassive black holes (SMBHs), the accretion disk, and the broad-line region. Here, we show that the temperature fluctuations of an AGN accretion disk, which is magnetically coupled with the corona, can account for observed high-quality AGN optical light curves. We calculate the temperature fluctuations by considering the gas physics of the accreted matter near the SMBH. We find that the resulting simulated AGN UV/optical light curves share the same statistical properties as the observed ones as long as the dimensionless viscosity parameter α, which is widely believed to be controlled by magnetohydrodynamic (MHD) turbulence in the accretion disk, is about 0.01-0.2. Moreover, our model can simultaneously explain the larger-than-expected accretion disk sizes and the dependence of UV/optical variability upon wavelength for NGC 5548. Our model also has the potential to explain some other observational facts of AGN UV/optical variability, including the timescale-dependent bluer-when-brighter color variability and the dependence of UV/optical variability on AGN luminosity and black-hole mass. Our results also demonstrate a promising way to infer the black-hole mass, the accretion rate, and the radiative efficiency, thereby facilitating understanding of the gas physics and MHD turbulence near the SMBH and its cosmic mass growth history by fitting the AGN UV/optical light curves in the era of time-domain astronomy.

Keywords: Accretion, Supermassive black holes, Active galactic nuclei, Quasars
Neutrinos from the Galactic Center Hosting a Hypernova Remnant. Similar to star-forming galaxies or starburst galaxies, star-forming regions in our Galaxy can host cosmic-ray (CR) accelerators and rich gas as targets of hadronuclear interaction. By our estimations, the IceCube neutrino observatory might detect muon neutrinos from a CR accelerator associated with a molecular cloud complex in our Galaxy. The associated high-energy gamma-ray emission might be observed by the Cherenkov Telescope Array (CTA), High-Altitude Water Cherenkov Gamma-Ray Observatory (HAWC), and Large High Altitude Air Shower Observatory (LHAASO). Furthermore, taking the Galactic Center (GC) region as an example, we assume that a hypernova exploded in the past in the GC. We simulate the acceleration of CRs in the hypernova remnant (HNR) as well as their confinement and escape. The high-energy protons escape from the HNR, diffuse around the GC, interact with molecular clouds, and then produce gamma-rays and neutrinos. In the optimal cases, the GC would be a promising 100 TeV gamma-ray source for LHAASO's one-month observation. We propose that neutrino-induced searching for starting track-like and high-energy starting events (HESEs) observed by IceCube, from the GC region with a radius of 1°8, would help us discover the particle accelerator in the GC or constrain our models. Under the constraint from high-energy gamma-ray observations by the H.E.S.S. telescope, we estimate the exposure time needed to make a significant discovery for the optimal cases. The analysis combining observations of IceCube and ANTARES, starting track-like events and HESEs, future observations by neutrino detectors IceCube-Gen2 and KM3net, and gamma-ray telescopes CTA, HAWC, and LHAASO would help to constrain our models.

Keywords: Hydrodynamical simulations, Neutrino telescopes, Galactic center, High energy astrophysics, Hypernovae, Neutrino astronomy, Extended radiation sources, Molecular clouds, Gamma-ray telescopes, Supernova remnants, Gamma-ray astronomy, Cosmic rays
The Relationship between Chirality, Sense of Rotation, and Hemispheric Preference of Solar Eruptive Filaments. The orientation, chirality, and dynamics of solar eruptive filaments are key to our understanding of the magnetic field of coronal mass ejections (CMEs), and therefore to predicting the geoeffectiveness of CMEs arriving at Earth. However, confusion and contention remain over the relationship between the filament chirality, magnetic helicity, and the sense of rotation during eruption. To resolve the ambiguity in observations, in this paper we used stereoscopic observations to determine the rotation direction of filament apex and the method proposed by Chen et al. to determine the filament chirality. Our sample of 12 eruptive active-region filaments establishes a strong one-to-one relationship, I.e., during the eruption, sinistral/dextral filaments (located in the southern/northern hemisphere) rotate clockwise/counterclockwise when viewed from above, and corroborates a weak hemispheric preference, I.e., a filament and related sigmoid both exhibit a forward (reverse) S shape in the southern (northern) hemisphere, which suggests that the sigmoidal filament is associated with a low-lying magnetic flux rope with its axis dipped in the middle. As a result of rotation, the projected S shape of a filament is anticipated to be reversed during eruption.

Keywords: Solar filaments, Solar filament eruptions
The Leoncino Dwarf Galaxy: Exploring the Low-metallicity End of the Luminosity-Metallicity and Mass-Metallicity Relations. Extremely metal-poor (XMP) galaxies are low-mass, star-forming galaxies with gas-phase oxygen abundances below 12 + log(O/H) = 7.35 (∼ 1/20 Z⊙). Galaxy evolution scenarios suggest three pathways to form an XMP: (1) secular evolution at low galaxy masses, (2) slow evolution in voids, or (3) dilution of measured abundances from infall of pristine gas. The recently discovered XMP galaxy Leoncino, with an oxygen abundance below 3% Z {}⊙, provides an opportunity to explore these different scenarios. Using Hubble Space Telescope imaging of the resolved stellar populations of Leoncino, we measure the distance to the galaxy to be D={12.1}-3.4+1.7 Mpc and find that Leoncino is located in an underdense environment. Leoncino has a compact morphology, hosts a population of young, massive stars, has a high gas-to-star mass ratio, and shows signs of interaction with a galaxy nearby on the sky, UGC 5186. Similar to nearly all XMP galaxies known in the nearby universe, Leoncino is offset from the Luminosity-Metallicity (LZ) relation. However, Leoncino is consistent with the stellar Mass-Metallicity (MZ) relation defined by Local Volume galaxies. Thus, our results suggest that the offset from the LZ relation is due to higher recent star formation, likely triggered by a minor interaction, while the low oxygen abundance is consistent with the expectation that low-mass galaxies will undergo secular evolution marked by inefficient star formation and metal loss via galactic winds. This is in contrast to XMP galaxies that are outliers in both the LZ and MZ relations; in such cases, the low oxygen abundances are best explained by dilution due to the infall of pristine gas. We also discuss why quiescent XMP galaxies are underrepresented in current surveys.

Keywords: Dwarf irregular galaxies, Distance measure, Metallicity
Time-domain Study of the Young Massive Cluster Westerlund 2 with the Hubble Space Telescope. I. Time-domain studies of pre-main-sequence (PMS) stars have long been used to investigate star properties during their early evolutionary phases and to trace the evolution of circumstellar environments. Historically these studies have been confined to the nearest, low-density, star-forming regions. We used the Wide Field Camera 3 on board the Hubble Space Telescope to extend, for the first time, the study of PMS variability to one of the few young massive clusters in the Milky Way, Westerlund 2. Our analysis reveals that at least one-third of the intermediate- and low-mass PMS stars in Westerlund 2 are variable. Based on the characteristics of their light curves, we classified ∼11% of the variable stars as weak-line T Tauri candidates, ∼52% as classical T Tauri candidates, ∼5% as dippers, and ∼26% as bursters. In addition, we found that 2% of the stars below 6 M⊙ (∼6% of the variables) are eclipsing binaries, with orbital periods shorter than 80 days. The spatial distribution of the different populations of variable PMS stars suggests that stellar feedback and UV radiation from massive stars play an important role in the evolution of circumstellar and planetary disks.

Keywords: Star forming regions, Young star clusters, Weak-line T Tauri stars, T Tauri stars, Pre-main sequence stars, Star formation, Variable stars, Eclipsing binary stars
The Megamaser Cosmology Project. XIII. Combined Hubble Constant Constraints. We present a measurement of the Hubble constant made using geometric distance measurements to megamaser-hosting galaxies. We have applied an improved approach for fitting maser data and obtained better distance estimates for four galaxies previously published by the Megamaser Cosmology Project: UGC 3789, NGC 6264, NGC 6323, and NGC 5765b. Combining these updated distance measurements with those for the maser galaxies CGCG 074-064 and NGC 4258, and assuming a fixed velocity uncertainty of 250 km s-1 associated with peculiar motions, we constrain the Hubble constant to be H0 = 73.9 ± 3.0 km s-1 Mpc-1 independent of distance ladders and the cosmic microwave background. This best value relies solely on maser-based distance and velocity measurements, and it does not use any peculiar velocity corrections. Different approaches for correcting peculiar velocities do not modify H0 by more than ±1σ, with the full range of best-fit Hubble constant values spanning 71.8-76.9 km s-1 Mpc-1. We corroborate prior indications that the local value of H0 exceeds the early-universe value, with a confidence level varying from 95% to 99% for different treatments of the peculiar velocities.

Keywords: Very long baseline interferometry, Observational cosmology, Hubble constant, Megamasers, Water masers
In-situ Switchback Formation in the Expanding Solar Wind. Recent near-Sun solar-wind observations from Parker Solar Probe have found a highly dynamic magnetic environment, permeated by abrupt radial-field reversals, or "switchbacks." We show that many features of the observed turbulence are reproduced by a spectrum of Alfvénic fluctuations advected by a radially expanding flow. Starting from simple superpositions of low-amplitude outward-propagating waves, our expanding-box compressible magnetohydrodynamic simulations naturally develop switchbacks because (I) the normalized amplitude of waves grows due to expansion and (II) fluctuations evolve toward spherical polarization (I.e., nearly constant field strength). These results suggest that switchbacks form in situ in the expanding solar wind and are not indicative of impulsive processes in the chromosphere or corona.

Keywords: Space plasmas, Interplanetary turbulence, Solar wind, Alfven waves, Solar magnetic fields
Detecting Interstellar Objects through Stellar Occultations. Stellar occultations have been used to search for Kuiper Belt and Oort Cloud objects. We propose a search for interstellar objects based on the characteristic durations (∼0.1 s) of their stellar occultation signals and high inclination relative to the ecliptic plane. An all-sky monitoring program of all ∼7 × 106 stars with R ≲ 12.5 using 1-m telescopes with 0.1 s cadences is predicted to discover ∼1 interstellar object per year.

Keywords: Meteors, Stellar occultation, Asteroids
De-noising SDO/HMI Solar Magnetograms by Image Translation Method Based on Deep Learning. In astronomy, long-exposure observations are one of the important ways to improve signal-to-noise ratios (S/Ns). In this Letter, we apply a deep-learning model to de-noise solar magnetograms. This model is based on a deep convolutional generative adversarial network with a conditional loss for image-to-image translation from a single magnetogram (input) to a stacked magnetogram (target). For the input magnetogram, we use Solar Dynamics Observatory (SDO)/Helioseismic and Magnetic Imager (HMI) line-of-sight magnetograms at the center of the solar disk. For the target magnetogram, we make 21-frame-stacked magnetograms, taking into account solar rotation at the same position. We train a model using 7004 pairs of the input and target magnetograms from 2013 January to 2013 October. We then validate the model using 707 pairs from 2013 November and test the model using 736 pairs from 2013 December. Our results from this study are as follows. First, our model successfully de-noises SDO/HMI magnetograms, and the de-noised magnetograms from our model are mostly consistent with the target magnetograms. Second, the average noise level of the de-noised magnetograms is greatly reduced from 8.66 to 3.21 G, and it is consistent with that of the target magnetograms, 3.21 G. Third, the average pixel-to-pixel correlation coefficient value increases from 0.88 (input) to 0.94 (de-noised), which means that the de-noised magnetograms are more consistent with the target ones than the input ones. Our results can be applied to many scientific fields in which the integration of many frames (or long-exposure observations) are used to improve the S/N.

Keywords: The Sun, Astronomy data analysis, Solar magnetic fields
Is GW190425 Consistent with Being a Neutron Star-Black Hole Merger?. GW190425 is the second neutron star merger event detected by the Advanced LIGO/Virgo detectors. If interpreted as a double neutron star merger, the total gravitational mass is substantially larger than that of the binary systems identified in the Galaxy. In this work we analyze the gravitational-wave data within the neutron star-black hole merger scenario. For the black hole, we yield a mass of 2.40M-0.32+0.36 M_{⊙} and an aligned spin of 0.141-0.064+0.067. As for the neutron star we find a mass of 1.15-0.13+0.15 M_{⊙} and the dimensionless tidal deformability of 1.4-1.2+3.8 × 103. These parameter ranges are for 90% credibility. The inferred masses of the neutron star and the black hole are not in tension with current observations and we suggest that GW190425 is a viable candidate of a neutron star-black hole merger event. Benefitting from the continual enhancement of the sensitivities of the advanced gravitational detectors and the increase of the number of the observatories, similar events are anticipated to be much more precisely measured in the future and the presence of black holes below the so-called mass gap will be unambiguously clarified. If confirmed, the mergers of neutron stars with (quickly rotating) low-mass black holes are likely important production sites of the heaviest r-process elements.

Keywords: Gravitational waves