Sazuna/UAT_keywords huggingface dataset:
The KMOS<SUP>3D</SUP> Survey: Investigating the Origin of the Elevated Electron Densities in Star-forming Galaxies at 1 ≲ z ≲ 3. We investigate what drives the redshift evolution of the typical electron density (ne) in star-forming galaxies, using a sample of 140 galaxies drawn primarily from KMOS3D (0.6 &lt; z &lt; 2.6) and 471 galaxies from SAMI (z &lt; 0.113). We select galaxies that do not show evidence of active galactic nucleus activity or outflows to constrain the average conditions within H II regions. Measurements of the [S II]λ6716/[S II]λ6731 ratio in four redshift bins indicate that the local ne in the line-emitting material decreases from 187 ${}_{-132}^{+140}$ cm-3 at z ∼ 2.2 to 32 ${}_{-9}^{+4}$ cm-3 at z ∼ 0, consistent with previous results. We use the Hα luminosity to estimate the rms ne averaged over the volumes of star-forming disks at each redshift. The local and volume-averaged ne evolve at similar rates, hinting that the volume filling factor of the line-emitting gas may be approximately constant across 0 ≲ z ≲ 2.6. The KMOS3D and SAMI galaxies follow a roughly monotonic trend between ne and star formation rate, but the KMOS3D galaxies have systematically higher ne than the SAMI galaxies at a fixed offset from the star-forming main sequence, suggesting a link between the ne evolution and the evolving main sequence normalization. We quantitatively test potential drivers of the density evolution and find that ne(rms) $\simeq {n}_{{{\rm{H}}}_{2}}$ , suggesting that the elevated ne in high-z H II regions could plausibly be the direct result of higher densities in the parent molecular clouds. There is also tentative evidence that ne could be influenced by the balance between stellar feedback, which drives the expansion of H II regions, and the ambient pressure, which resists their expansion.

Keywords: High-redshift galaxies, Galaxy evolution, Interstellar medium
Einstein@Home All-sky Search for Continuous Gravitational Waves in LIGO O2 Public Data. We conduct an all-sky search for continuous gravitational waves in the LIGO O2 data from the Hanford and Livingston detectors. We search for nearly monochromatic signals with frequency 20.0 Hz ≤ f ≤ 585.15 Hz and spin-down $-2.6\times {10}^{-9}\,\mathrm{Hz}\,{{\rm{s}}}^{-1}\leqslant \dot{f}\leqslant 2.6\times {10}^{-10}$ Hz s-1. We deploy the search on the Einstein@Home volunteer-computing project and follow-up the waveforms associated with the most significant results with eight further search stages, reaching the best sensitivity ever achieved by an all-sky survey up to 500 Hz. Six of the inspected waveforms pass all the stages but they are all associated with hardware injections, which are fake signals simulated at the LIGO detector for validation purposes. We recover all these fake signals with consistent parameters. No other waveform survives, so we find no evidence of a continuous gravitational wave signal at the detectability level of our search. We constrain the h0 amplitude of continuous gravitational waves at the detector as a function of the signal frequency, in half-Hz bins. The most constraining upper limit at 163.0 Hz is h0 = 1.3 × 10-25, at the 90% confidence level. Our results exclude neutron stars rotating faster than 5 ms with equatorial ellipticities larger than 10-7 closer than 100 pc. These are deformations that neutron star crusts could easily support, according to some models.

Keywords: Neutron stars, Astronomy data analysis, Gravitational waves, Compact objects
The Discovery of a Highly Accreting, Radio-loud Quasar at z = 6.82. Radio sources at the highest redshifts can provide unique information on the first massive galaxies and black holes, the densest primordial environments, and the epoch of reionization. The number of astronomical objects identified at z &gt; 6 has increased dramatically over the last few years, but previously only three radio-loud (R2500 = fν,5 GHz/fν,2500 Å &gt; 10) sources had been reported at z &gt; 6, with the most distant being a quasar at z = 6.18. Here we present the discovery and characterization of PSO J172.3556+18.7734, a radio-loud quasar at z = 6.823. This source has an Mg II-based black hole mass of ∼3 × 108 M☉ and is one of the fastest accreting quasars, consistent with super-Eddington accretion. The ionized region around the quasar is among the largest measured at these redshifts, implying an active phase longer than the average lifetime of the z ≳ 6 quasar population. From archival data, there is evidence that its 1.4 GHz emission has decreased by a factor of two over the last two decades. The quasar's radio spectrum between 1.4 and 3.0 GHz is steep (α = -1.31). Assuming the measured radio slope and extrapolating to rest-frame 5 GHz, the quasar has a radio-loudness parameter R2500 ∼ 90. A second steep radio source (α = -0.83) of comparable brightness to the quasar is only 23"1 away (∼120 kpc at z = 6.82; projection probability &lt;2%), but shows no optical or near-infrared counterpart. Further follow-up is required to establish whether these two sources are physically associated.

Keywords: Supermassive black holes, Quasars, Extragalactic radio sources, Radio loud quasars, Active galactic nuclei
Disk Tearing: Numerical Investigation of Warped Disk Instability. We present numerical simulations of misaligned disks around a spinning black hole covering a range of parameters. Previous simulations have shown that disks that are strongly warped by a forced precession—in this case, the Lense-Thirring effect from the spinning black hole—can break apart into discrete disks or rings that can behave quasi-independently for short timescales. With the simulations we present here, we confirm that thin and highly inclined disks are more susceptible to disk tearing than thicker disks or those with lower inclination, and we show that lower values of the disk viscosity parameter lead to instability at lower warp amplitudes. This is consistent with detailed stability analysis of the warped disk equations. We find that the growth rates of the instability seen in the numerical simulations are similar across a broad range of parameters, and are of the same order as the predicted growth rates. However, we did not find the expected trend of growth rates with viscosity parameter. This may indicate that the growth rates are affected by numerical resolution, or that the wavelength of the fastest-growing mode is a function of local disk parameters. Finally, we also find that disk tearing can occur for disks with a viscosity parameter that is higher than predicted by a local stability analysis of the warped disk equations. In this case, the instability manifests differently, producing large changes in the disk tilt locally in the disk, rather than the large changes in disk twist that typically occur in lower-viscosity disks.

Keywords: Accretion, Hydrodynamical simulations, Black hole physics, Hydrodynamics, Circumstellar disks, Stellar accretion disks, Relativistic disks
Disk Tearing: Implications for Black Hole Accretion and AGN Variability. Accretion disks around black holes power some of the most luminous objects in the universe. Disks that are misaligned to the black hole spin can become warped over time by Lense-Thirring precession. Recent work has shown that strongly warped disks can become unstable, causing the disk to break into discrete rings producing a more dynamic and variable accretion flow. In a companion paper, we present numerical simulations of this instability and the resulting dynamics. In this paper, we discuss the implications of this dynamics for accreting black hole systems, with particular focus on the variability of active galactic nuclei (AGN). We discuss the timescales on which variability might manifest, as well as the impact of the observer orientation with respect to the black hole spin axis. When the disk warp is unstable near the inner edge of the disk, we find quasi-periodic behavior of the inner disk, which may explain the recent quasi-periodic eruptions observed in, for example, the Seyfert 2 galaxy GSN 069 and in the galactic nucleus of RX J1301.9+2747. These eruptions are thought to be similar to the "heartbeat" modes observed in some X-ray binaries (e.g., GRS 1915+105 and IGR J17091-3624). When the instability manifests at larger radii in the disk, we find that the central accretion rate can vary on timescales that may be commensurate with, e.g., changing-look AGN. We therefore suggest that some of the variability properties of accreting black hole systems may be explained by the disk being significantly warped, leading to disk tearing.

Keywords: Accretion, Hydrodynamical simulations, Black hole physics, Hydrodynamics, Circumstellar disks, Stellar accretion disks, Relativistic disks
Possible Periodic Activity in the Short Bursts of SGR 1806-20: Connection to Fast Radio Bursts. Magnetars are highly magnetized neutron stars that are characterized by recurrent emission of short-duration bursts in soft gamma-rays/hard X-rays. Recently, FRB 200428 was found to be associated with an X-ray burst from a Galactic magnetar. Two fast radio bursts show mysterious periodic activity. However, it is unclear whether magnetar X-ray bursts are periodic phenomena. In this paper, we investigate the activity period of SGR 1806-20. More than 3000 short bursts observed by different telescopes are collected, including the observations of RXTE, HETE-2, ICE, and Konus. We consider the observation windows and divide the data into two subsamples to alleviate the effect of uneven sampling. The epoch-folding and Lomb-Scargle methods are used to derive the period of the short bursts. We find a possible period of about 398.20 ± 25.45 days, but other peaks exist in the periodograms. If the period is real, the connection between short bursts of magnetars and fast radio bursts should be investigated extensively.

Keywords: Magnetars, Soft gamma-ray repeaters, Radio transient sources
Internal Structure of Molecular Gas in a Main-sequence Galaxy With a UV Clump at z = 1.45. We present results of subarcsec Atacama Large Millimeter/submillimeter Array observations of CO(2-1) and CO(5-4) toward a massive main-sequence galaxy at z = 1.45 in the Subaru-XMM/Newton Deep Survey/UDS field, aiming at examining the internal distribution and properties of molecular gas in the galaxy. Our target galaxy consists of the bulge and disk, and has a UV clump in the Hubble Space Telescope images. The CO emission lines are clearly detected, and the CO(5-4)/CO(2-1) flux ratio (R52) is ∼1, similar to that of the Milky Way. Assuming a metallicity-dependent CO-to-H2 conversion factor and a CO(2-1)/CO(1-0) flux ratio of 2 (the Milky Way value), the molecular gas mass and the gas-mass fraction (fgas = ratio of the molecular gas mass to the molecular gas mass + stellar mass) are estimated to be ∼1.5 × 1011M⊙ and ∼0.55, respectively. We find that R52 peak coincides with the position of the UV clump and that its value is approximately twice higher than the galactic average. This result implies a high gas density and/or high temperature in the UV clump, which qualitatively agrees with a numerical simulation of a clumpy galaxy. The CO(2-1) distribution is well represented by a rotating-disk model, and its half-light radius is ∼2.3 kpc. Compared to the stellar distribution, the molecular gas is more concentrated in the central region of the galaxy. We also find that fgas decreases from ∼0.6 at the galactic center to ∼0.2 at three times the half-light radius, indicating that the molecular gas is distributed in the more central region of the galaxy than stars and seems to be associated with the bulge rather than with the stellar disk.

Keywords: Molecular gas, Galaxy formation, Galaxy properties, Galaxy physics, Galaxy evolution, High-redshift galaxies
Signatures of Clouds in Hot Jupiter Atmospheres: Modeled High-resolution Emission Spectra from 3D General Circulation Models. Observations of scattered light and thermal emission from hot Jupiter exoplanets have suggested the presence of inhomogeneous aerosols in their atmospheres. 3D general circulation models (GCMs) that attempt to model the effects of aerosols have been developed to understand the physical processes that underlie their dynamical structures. In this work, we investigate how different approaches to aerosol modeling in GCMs of hot Jupiters affect high-resolution thermal emission spectra throughout the duration of the planet's orbit. Using results from a GCM with temperature-dependent cloud formation, we calculate spectra of a representative hot Jupiter with different assumptions regarding the vertical extent and thickness of clouds. We then compare these spectra to models in which clouds are absent or simply post-processed (i.e., added subsequently to the completed clear model). We show that the temperature-dependent treatment of clouds in the GCM produces high-resolution emission spectra that are markedly different from the clear and post-processed cases—both in the continuum flux levels and line profiles—and that increasing the vertical extent and thickness of clouds leads to bigger changes in these features. We evaluate the net Doppler shifts of the spectra induced by global winds and the planet's rotation and show that they are strongly phase dependent, especially for models with thicker and more extended clouds. This work further demonstrates the importance of radiative feedback in cloudy atmospheric models of hot Jupiters, as this can have a significant impact on interpreting spectroscopic observations of exoplanet atmospheres.

Keywords: High resolution spectroscopy, Theoretical models, Exoplanet atmospheres
Migration of Solar Polar Crown Filaments in the Past 100 Years. Polar crown filaments (PCFs) are formed above the polarity inversion line, which separates unipolar polar fields and the nearest dispersed fields. They are important features in studying solar polar fields and their cyclical variations. Due to the relatively weak field strength and projection effects, measuring polar magnetic fields is more difficult than obtaining the field strengths concentrated in active regions at lower latitudes. "Rush-to-the-pole" of PCFs represent the progress of unipolar polar fields from the previous solar cycle being canceled by the dispersed fields generated in the current cycle. Such progress is a good indicator of the polarity reversal in the polar areas and a precursor for the solar maximum. In this study, PCFs are identified from a 100 yr archive, covering cycles 16-24. This archive consists of full-disk Hα images obtained from the Kodaikanal Solar Observatory of the Indian Institute of Astrophysics, Kanzelhöhe Solar Observatory, and Big Bear Solar Observatory. The poleward migration speeds are measured and show an obvious asymmetry in the northern and southern hemispheres. In addition, our results show that the PCFs usually reach their highest latitudes first in the northern hemisphere, except cycle 17. Similarly, previous studies show that the magnetic field reversed first at the north pole in six out of nine cycles. We also compare the temporal variations of PCF migration and the latitude gradient factor of the differential rotation, which shows a trend in the southern hemisphere. Moreover, the migration speed of PCFs does not seem to be well correlated with the maximum sunspot numbers.

Keywords: Solar filaments, Solar magnetic fields, Solar evolution
The Polar Precursor Method for Solar Cycle Prediction: Comparison of Predictors and Their Temporal Range. The polar precursor method is widely considered to be the most robust physically motivated method to predict the amplitude of an upcoming solar cycle. It uses indicators of the magnetic field concentrated near the poles around the sunspot minimum. Here, we present an extensive analysis of the performance of various such predictors, based on both observational data (Wilcox Solar Observatory (WSO) magnetograms, Mount Wilson Observatory polar faculae counts, and Pulkovo A(t) index) and outputs (polar cap magnetic flux and global dipole moment) of various existing flux transport dynamo models. We calculate Pearson correlation coefficients (r) of the predictors with the next cycle amplitude as a function of time measured from several solar cycle landmarks: setting r = 0.8 as a lower limit for acceptable predictions, we find that observations and models alike indicate that the earliest time when the polar predictor can be safely used is 4 yr after the polar field reversal. This is typically 2-3 yr before the solar minimum and about 7 yr before the predicted maximum, considerably extending the usual temporal scope of the polar precursor method. Reevaluating the predictors another 3 yr later, at the time of the solar minimum, further increases the correlation level to r ≳ 0.9. As an illustration of the result, we determine the predicted amplitude of Cycle 25 based on the value of the WSO polar field at the now official minimum date of 2019 December as 126 ± 3. A forecast based on the value in early 2017, 4 yr after the polar reversal would have only differed from this final prediction by 3.1 ± 14.7%.

Keywords: Solar cycle, Solar magnetic fields, Sunspot cycle, Solar dynamo
Exploring the Energy-dependent Radiation Properties in Dissipative Magnetospheres with Fermi Pulsars. The equatorial current sheets outside the light cylinder (LC) are thought to be promising sites of high-energy emission based on the results of recent numerical simulations. We explore the pulsar light curves and energy spectra by computing the curvature radiation based on the FIDO magnetospheres. The FIDO magnetospheres with a near force-free regime inside the LC and a finite but high conductivity outside the LC are constructed using a spectral algorithm. The pulsar high-energy emission properties are explored by integrating the trajectories of the test particles under the influence of both the accelerating electric field and the curvature radiation losses. As an application, we compare the predicted energy-dependent light curves and energy spectra with those of the Crab and Vela pulsars published in the Fermi 2PC catalog. We find that the observed characteristics of the light curves and energy spectra from the Crab and Vela pulsars can be well reproduced by the FIDO model.

Keywords: Neutron stars, Rotation powered pulsars, Magnetohydrodynamical simulations
Coronal Heating Law Constrained by Microwave Gyroresonant Emission. The question why the solar corona is much hotter than the visible solar surface still puzzles solar researchers. Most theories of the coronal heating involve a tight coupling between the coronal magnetic field and the associated thermal structure. This coupling is based on two facts: (i) the magnetic field is the main source of the energy in the corona and (ii) the heat transfer preferentially happens along the magnetic field, while is suppressed across it. However, most of the information about the coronal heating is derived from the analysis of extreme ultraviolet or soft X-ray emissions, which are not explicitly sensitive to the magnetic field. This paper employs another electromagnetic channel—the sunspot-associated microwave gyroresonant emission, which is explicitly sensitive to both the magnetic field and thermal plasma. We use nonlinear force-free field reconstructions of the magnetic skeleton dressed with a thermal structure as prescribed by a field-aligned hydrodynamics to constrain the coronal heating model. We demonstrate that the microwave gyroresonant emission is extraordinarily sensitive to details of the coronal heating. We infer heating model parameters consistent with observations.

Keywords: Solar coronal radio emission, Solar coronal heating, Solar magnetic fields
First Phase Space Portrait of a Hierarchical Stellar Structure in the Milky Way. We present the first detailed observational picture of a possible ongoing massive cluster hierarchical assembly in the Galactic disk as revealed by the analysis of the stellar full phase space (3D positions and kinematics and spectro-photometric properties) of an extended area (6° diameter) surrounding the well-known h and χ Persei double stellar cluster in the Perseus Arm. Gaia-EDR3 shows that the area is populated by seven comoving clusters, three of which were previously unknown, and by an extended and quite massive (M ∼ 105 M⊙) halo. All stars and clusters define a complex structure with evidence of possible mutual interactions in the form of intra-cluster overdensities and/or bridges. They share the same chemical abundances (half-solar metallicity) and age (t ∼ 20 Myr) within a small confidence interval and the stellar density distribution of the surrounding diffuse stellar halo resembles that of a cluster-like stellar system. The combination of these pieces of evidence suggests that stars distributed within a few degrees from h and χ Persei are part of a common, substructured stellar complex that we named LISCA I. Comparison with results obtained through direct N-body simulations suggest that LISCA I may be at an intermediate stage of an ongoing cluster assembly that can eventually evolve in a relatively massive (a few times 105 M⊙) stellar system. We argue that such a cluster formation mechanism may be quite efficient in the Milky Way and disk-like galaxies and, as a consequence, it has a relevant impact on our understanding of cluster formation efficiency as a function of the environment and redshift.

Keywords: Dynamical evolution, Astrometry, Photometry, Star clusters
Nonequilibrium Flux Rope Formation by Confined Flares Preceding a Solar Coronal Mass Ejection. We present evidence that a magnetic flux rope was formed before a coronal mass ejection (CME) and its associated long-duration flare during a pair of preceding confined eruptions and associated impulsive flares in a compound event in NOAA Active Region 12371. Extreme-ultraviolet images and the extrapolated nonlinear force-free field show that the first two (impulsive) flares, SOL2015-06-21T01:42, result from the confined eruption of highly sheared low-lying flux, presumably a seed flux rope. The eruption spawns a vertical current sheet, where magnetic reconnection creates flare ribbons and loops, a nonthermal microwave source, and a sigmoidal hot channel that can only be interpreted as a magnetic flux rope. Until the subsequent long-duration flare, SOL2015-06-21T02:36, the sigmoid's elbows expand, while its center remains stationary, suggesting nonequilibrium but not yet instability. The "flare reconnection" during the confined eruptions acts like "tether-cutting reconnection" whose flux feeding of the rope leads to instability. The subsequent full eruption is seen as an accelerated rise of the entire hot channel, seamlessly evolving into the fast halo CME. Both the confined and ejective eruptions are consistent with the onset of the torus instability in the dipped decay index profile that results from the region's two-scale magnetic structure. We suggest that the formation or enhancement of a nonequilibrium but stable flux rope by confined eruptions is a generic process occurring prior to many CMEs.

Keywords: Solar flares, Solar magnetic reconnection, Solar coronal mass ejections, Solar magnetic fields, Active solar corona