adsabs/SciX_UAT_keywords huggingface dataset:
Modeling the Strongest Silicate Emission Features of Local Type 1 AGNs

We measure the 10 and 18 μm silicate features in a sample of 67 local (z < 0.1) type 1 active galactic nuclei (AGN) with available Spitzer spectra dominated by nonstellar processes. We find that the 10 μm silicate feature peaks at ${10.3}_{-0.9}^{+0.7}\,\mu {\rm{m}}$ with a strength (Sip = ln fp(spectrum)/fp(continuum)) of ${0.11}_{-0.36}^{+0.15}$ , while the 18 μm one peaks at ${17.3}_{-0.7}^{+0.4}\,\mu {\rm{m}}$ with a strength of ${0.14}_{-0.06}^{+0.06}$ . We select from this sample sources with the strongest 10 μm silicate strength ( ${\sigma }_{{\mathrm{Si}}_{10\mu {\rm{m}}}}\gt 0.28$ , 10 objects). We carry out a detailed modeling of the infrared spectrometer/Spitzer spectra by comparing several models that assume different geometries and dust composition: a smooth torus model, two clumpy torus models, a two-phase medium torus model, and a disk+outflow clumpy model. We find that the silicate features are well modeled by the clumpy model of Nenkova et al., and among all models, those including outflows and complex dust composition are the best. We note that even in AGN-dominated galaxies, it is usually necessary to add stellar contributions to reproduce the emission at the shortest wavelengths.

Keywords: active galactic nuclei; infrared astronomy; dust continuum emission; active galaxies
Optical Variability of ICRF3 Quasars in the Pan-STARRS 3Pi Survey with Functional Principal Component Analysis

We make use of individual (epoch) detection data from the Pan-STARRS 3 survey for 2863 optical ICRF3 counterparts in the five wavelength bands g, r, i, z, and y, published as part of the Data Release 2. A dedicated method based on the Functional Principal Component Analysis is developed for these sparse and irregularly sampled data. With certain regularization and normalization constraints, it allows us to obtain uniform and compatible estimates of the variability amplitudes and average magnitudes between the passbands and objects. We find that the starting assumption of affinity of the light curves for a given object at different wavelengths is violated for several percent of the sample. The distributions of rms variability amplitudes are strongly skewed toward small values, peaking at 0.1 mag with tails stretching to 2 mag. Statistically, the lowest variability is found for the r band and the largest for the reddest y band. A small brighter-redder effect is present, with amplitudes in y greater than amplitudes in g in 57 of the sample. The variability versus redshift dependence shows a strong decline with z toward redshift 3, which we interpret as the time dilation of the dominant time frequencies. The colors of radio-loud ICRF3 quasars are correlated with redshift in a complicated, wavy pattern governed by the emergence of brightest emission lines within the five passbands.

Keywords: space astrometry; radio source catalogs; quasars
Toward Cosmological Simulations of the Magnetized Intracluster Medium with Resolved Coulomb Collision Scale

We present the first results of one extremely high-resolution, nonradiative magnetohydrodynamical cosmological zoom-in simulation of a massive cluster with a virial mass of M vir = 2.0 × 1015 solar masses. We adopt a mass resolution of 4 × 105 M ⊙ with a maximum spatial resolution of around 250 pc in the central regions of the cluster. We follow the detailed amplification process in a resolved small-scale turbulent dynamo in the intracluster medium (ICM) with strong exponential growth until redshift 4, after which the field grows weakly in the adiabatic compression limit until redshift 2. The energy in the field is slightly reduced as the system approaches redshift zero in agreement with adiabatic decompression. The field structure is highly turbulent in the center and shows field reversals on a length scale of a few tens of kiloparsecs and an anticorrelation between the radial and angular field components in the central region that is ordered by small-scale turbulent dynamo action. The large-scale field on megaparsec scales is almost isotropic, indicating that the structure formation process in massive galaxy cluster formation suppresses any memory of both the initial field configuration and the amplified morphology via the turbulent dynamo. We demonstrate that extremely high-resolution simulations of the magnetized ICM are within reach that can simultaneously resolve the small-scale magnetic field structure, which is of major importance for the injection of and transport of cosmic rays in the ICM. This work is a major cornerstone for follow-up studies with an on-the-fly treatment of cosmic rays to model in detail electron-synchrotron and gamma-ray emissions.

Keywords: galaxy clusters; magnetohydrodynamical simulations; intracluster medium; magnetic fields; extragalactic magnetic fields; cosmic magnetic fields theory
SN 2020bio: A Double-peaked, H-poor Type IIb Supernova with Evidence of Circumstellar Interaction

We present photometric and spectroscopic observations of SN 2020bio, a double-peaked Type IIb supernova (SN) discovered within a day of explosion, primarily obtained by Las Cumbres Observatory and Swift. SN 2020bio displays a rapid and long-lasting initial decline throughout the first week of its light curve, similarly to other well-studied Type IIb SNe. This early-time emission is thought to originate from the cooling of the extended outer hydrogen-rich (H-rich) envelope of the progenitor star that is shock heated by the SN explosion. We compare SN 2020bio to a sample of other double-peaked Type IIb SNe in order to investigate its progenitor properties. Analytical model fits to the early-time emission give progenitor radius (≈100-1500 R ⊙) and H-rich envelope mass (≈0.01-0.5 M ⊙) estimates that are consistent with other Type IIb SNe. However, SN 2020bio displays several peculiarities, including (1) weak H spectral features indicating a greater amount of mass loss than other Type IIb progenitors; (2) an underluminous secondary light-curve peak that implies a small amount of synthesized 56Ni (M Ni ≈0.02 M ⊙); and (3) low-luminosity nebular [O I] and interaction-powered nebular features. These observations are more consistent with a lower-mass progenitor (M ZAMS ≈ 12 M ⊙) that was stripped of most of its H-rich envelope before exploding. This study adds to the growing diversity in the observed properties of Type IIb SNe and their progenitors.

Keywords: circumstellar matter; core-collapse supernovae; supernovae
Less Effective Hydrodynamic Escape of H2-H2O Atmospheres on Terrestrial Planets Orbiting Pre-main-sequence M Dwarfs

Terrestrial planets currently in the habitable zones around M dwarfs likely experienced a long-term runaway-greenhouse condition because of a slow decline in host-star luminosity in its pre-main-sequence phase. Accordingly, they might have lost significant portions of their atmospheres including water vapor at high concentration by hydrodynamic escape induced by the strong stellar X-ray and extreme ultraviolet (XUV) irradiation. However, the atmospheric escape rates remain highly uncertain due partly to a lack of understanding of the effect of radiative cooling in the escape outflows. Here we carry out 1D hydrodynamic escape simulations for an H2-H2O atmosphere on a planet with mass of 1M ⊕ considering radiative and chemical processes to estimate the atmospheric escape rate and follow the atmospheric evolution during the early runaway-greenhouse phase. We find that the atmospheric escape rate decreases with the basal H2O/H2 ratio due to the energy loss by the radiative cooling of H2O and chemical products such as OH and OH+: the escape rate of H2 becomes one order of magnitude smaller when the basal H2O/H2 = 0.1 than that of the pure hydrogen atmosphere. The timescale for H2 escape exceeds the duration of the early runaway-greenhouse phase, depending on the initial atmospheric amount and composition, indicating that H2 and H2O could be left behind after the end of the runaway-greenhouse phase. Our results suggest that temperate and reducing environments with oceans could be formed on some terrestrial planets around M dwarfs.

Keywords: exoplanet evolution; exoplanet atmospheres; upper atmosphere
Kinetic Alfvén Waves Excited by Multiple Free Energy Sources in the Magnetotail

The generation of kinetic Alfvén waves (KAWs) is investigated through a three-component theoretical model incorporating ion beam and velocity shear as the sources of free energy in a non-Maxwellian κ-distributed plasmas. The model considers Maxwellian distributed background ions, drifting-Maxwellian beam ions, and κ-electrons as its constituent species. It is found that the combination of either positive velocity shear with counter-streaming beam ions or parallel streaming beam ions with negative velocity shear favors the excitation of KAWs. The effect of the κ-parameter on the excitation of KAWs under the combined energy sources is explored. The effect of plasma parameters such as number density, propagation angle, and temperature of plasma species on the real frequency and the growth rate of KAWs are examined. For the plasma parameters pertinent to the magnetotail region of Earth's magnetosphere, the model is able to produce KAWs in the frequency range of ≈(5-67) mHz, which matches well with the recent 'Time History of Events and Macroscale Interactions during Substorms (THEMIS)' observations in the near-Earth magnetotail region.

Keywords: solar wind; space plasmas; alfven waves
COMAP Early Science. I. Overview

The CO Mapping Array Project (COMAP) aims to use line-intensity mapping of carbon monoxide (CO) to trace the distribution and global properties of galaxies over cosmic time, back to the Epoch of Reionization (EoR). To validate the technologies and techniques needed for this goal, a Pathfinder instrument has been constructed and fielded. Sensitive to CO(1-0) emission from z = 2.4-3.4 and a fainter contribution from CO(2-1) at z = 6-8, the Pathfinder is surveying 12 deg2 in a 5 yr observing campaign to detect the CO signal from z ~ 3. Using data from the first 13 months of observing, we estimate P CO(k) = -2.7 ± 1.7 × 104 μK2 Mpc3 on scales k = 0.051 -0.62 Mpc-1, the first direct three-dimensional constraint on the clustering component of the CO(1-0) power spectrum. Based on these observations alone, we obtain a constraint on the amplitude of the clustering component (the squared mean CO line temperature bias product) of ${\left\langle {Tb}\right\rangle }^{2}\lt 49$ μK2, nearly an order-of-magnitude improvement on the previous best measurement. These constraints allow us to rule out two models from the literature. We forecast a detection of the power spectrum after 5 yr with signal-to-noise ratio (S/N) 9-17. Cross-correlation with an overlapping galaxy survey will yield a detection of the CO-galaxy power spectrum with S/N of 19. We are also conducting a 30 GHz survey of the Galactic plane and present a preliminary map. Looking to the future of COMAP, we examine the prospects for future phases of the experiment to detect and characterize the CO signal from the EoR.

Keywords: co line emission; cosmological evolution; high-redshift galaxy clusters; molecular gas; radio astronomy; astronomical instrumentation
Detecting the Effect of Nonthermal Sources on the Warm-hot Galactic Halo

We report the first detection of nonthermal broadening of O VII lines in the warm-hot ≈106 K circumgalactic medium of the Milky Way. We use z = 0 absorption of O VII Kα, O VII Kβ, and O VIII Kα lines in archival grating data of b > 15° quasar sightlines from Chandra and XMM-Newton. Nonthermal line broadening is evident in two-thirds of the sightlines considered, and on average is constrained at 4.6σ significance. Nonthermal line broadening dominates over thermal broadening. We extensively test whether the appearance of nonthermal line broadening could instead be because of multiple thermally broadened velocity components and robustly rule it out. Nonthermal line broadening is more evident toward sightlines at lower galactic latitude indicating the Galactic disk origin of the nonthermal sources. There is weak/no correlation between nonthermal line broadening and the angular separation of sightlines from the Galactic center, indicating that the nuclear region might not be a major source of nonthermal factors.

Keywords: circumgalactic medium; x-ray astronomy; quasar absorption line spectroscopy; hot ionized medium; non-thermal radiation sources; galaxy evolution; galaxy environments; galaxy processes; milky way galaxy; milky way evolution; milky way galaxy physics
C IV Emission-line Properties and Uncertainties in Black Hole Mass Estimates of z ∼ 3.5 Quasars

Using a high-luminosity (Lbol ∼ 1047.5-1048.3 erg s-1), high-redshift (3.2 < z < 3.8) quasar sample of 19 quasars with optical and near-infrared spectroscopy, we investigate the reliability of the C IV-based black hole mass estimates (MBH). The median logarithm of the C IV- and Hβ-based MBH ratios is 0.110 dex, with a scatter of 0.647 dex. The C IV-to-Hβ BH mass differences are significantly correlated with the C IV FWHMs, blueshifts, and asymmetries. Corrections of the C IV FWHM using the blueshift and asymmetry reduce the scatter of the mass differences by ∼0.04-0.2 dex. Quasars in our sample accrete at the Eddington ratio REDD > 0.3 and cover a considerable range of blueshifts, with 18/19 of the quasars showing C IV blueshifts (with the median value of 1126 km s-1) and 14/19 of the quasars showing C IV blueshifts larger than 500 km s-1. It suggests that not all quasars with high Eddington ratios show large blueshifts. The Baldwin effect between the C IV rest-frame equivalent width (REW) and the continuum luminosity at 1350 Å is not seen, likely due to the limited luminosity range of our sample. We find a lack of flux in the red wing of the composite spectrum with larger C IV blueshift and detect a higher ratio of [O III] quasars with REW[O III] > 5 Å in the subsample with lower C IV blueshift. It is more likely that they are caused by the combination of the Eddington ratio and the orientation effect.

Keywords: black hole physics; quasars
Optical Flux and Spectral Variability of BL Lacertae during Its Historical High Outburst in 2020

BL Lacertae underwent a series of historical high flux activity over a year from 2020 August in the optical to VHE γ-rays. In this paper, we report on optical flux and spectral variability of the first historical maxima outburst event during October-November in the g, r, and i bands with the 1.26 m telescope at the Xinglong Observatory, China. We detected significant intranight variations with amplitude rising up to ~30%, where the fastest variability timescale was found to be a few tens of minutes, giving an emitting region size of the order 10-3 pc, which corresponds to ~100 Schwarzschild radius of the central black hole, likely coming from some jet mini-structures. Unlike on the intranight timescale, a clear frequency-dependent pattern along symmetric timescales (~11 days) of flux variation is detected on a long timescale. The spectral evolution was predominated by flattening of the spectra with increasing brightness i.e., a bluer-when-brighter trend in 96% of the cases. On the night before the outburst peak, the color indices shown in a color-magnitude diagram, clustered into two distinct branches, within a period of ~6 hr, which is connected to a hard-soft-hard spectral evolution trend extracted from time-resolved spectra. To the best of our knowledge, such a trend has never been seen in BL Lac or any other blazars before. The results obtained in this study can be explained in the context of shock-induced particle acceleration or magnetic reconnection in the jet where turbulent processes most likely resulted in the asymmetric flux variation on a nightly timescale.

Keywords: active galactic nuclei; blazars
In Situ Observation of Solar-flare-induced Proton Cyclotron Waves Upstream from Mars

Proton cyclotron waves (PCWs) upstream from Mars are usually interpreted as waves generated by ion/ion instabilities due to the interaction between the solar wind plasma and the pickup protons, originating from the extended hydrogen (H) exosphere of Mars. Their generation mainly depends on the solar wind properties and the relative density of the newborn protons with respect to the background solar wind. Under stable solar wind conditions, a higher solar irradiance leads to both increased exospheric H density and ionization rate of H atoms, and therefore a higher relative density, which tends to increase the linear wave growth rate. Here we show that the solar irradiance is likely to contribute significantly to PCW generation. Specifically, we present observations from the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft indicating that, around the peak of the X8.2 flare on 2017 September 10, the increased solar irradiance gave rise to higher pickup H+ fluxes, which in turn excited PCWs. This result has implications for inferring the loss of hydrogen to space in early Martian history with more intense and frequent X-class flares as well as their contributions to the total loss.

Keywords: solar wind; mars; pickup ions; plasma physics
Application of the Thermodynamics of Radiation to Dyson Spheres as Work Extractors and Computational Engines and Their Observational Consequences

I apply the thermodynamics of radiation to Dyson spheres as machines that do work or computation and examine their observational consequences. I identify four properties of Dyson spheres that complicate typical analyses: globally, they may do no work in the usual sense; they use radiation as the source and sink of energy; they accept radiation from a limited range of solid angles; and they conserve energy flux globally. I consider three kinds of activities: computation at the Landauer limit; dissipative activities, in which the energy of a sphere's activities cascades into waste heat, as for a biosphere; and "traditional" work that leaves the sphere, such as radio emission. I apply the Landsberg formalism to derive efficiency limits in all three cases and show that optical circulators provide an "existence proof" that greatly simplifies the problem and allows the Landsberg limit to be plausibly approached. I find that for computation and traditional work, there is little to no advantage to nesting shells (as in a "Matrioshka Brain"); that the optimal use of mass is generally to make very small and hot Dyson spheres; that for "complete" Dyson spheres, we expect optical depths of several; and that in all cases the Landsberg limit corresponds to a form of the Carnot limit. I explore how these conclusions might change in the face of complications, such as the sphere having practical efficiencies below the Landsberg limit (using the endoreversible limit as an example), no use of optical circulators, and swarms of materials instead of shells.

Keywords: chemical thermodynamics; search for extraterrestrial intelligence; astrobiology; technosignatures
AstroSat UVIT Survey of M31: Point-source Catalog

An ultraviolet survey of M31 has been carried out during 2017-19 with the UltraViolet Imaging Telescope (UVIT) instrument on board the AstroSat Observatory. Here we analyze far- and near-ultraviolet (FUV and NUV) observations from the M31 UVIT survey, which covers a sky area of ≃3° × 1° with spatial resolution of ≃1″. The observations included six filter bands in the wavelength range of 120-280 nm. The limiting magnitude (AB) in the FUV band (CaF2 filter), which has the largest number of detected sources, is ∼23. The primary product of this work is the M31 UVIT point-source catalog containing positions and photometry. In total ≃75,000 sources were detected at FUV or NUV wavelengths.

Keywords: ultraviolet astronomy; ultraviolet sources; andromeda galaxy
High-velocity Stars in SDSS/APOGEE DR17

We report 23 stars having Galactocentric velocities larger than 450 km s-1 in the final data release of the APOGEE survey. This sample was generated using space velocities derived by complementing the high-quality radial velocities from the APOGEE project in Sloan Digital Sky Survey's Data Release 17 (DR17) with distances and proper motions from Gaia early Data Release 3 (eDR3). We analyze the observed kinematics and derived dynamics of these stars, considering different potential models for the Galaxy. We find that three stars could be unbound depending on the adopted potential, but in general all of the stars show typical kinematics of halo stars. The APOGEE DR17 spectroscopic results and Gaia eDR3 photometry are used to assess the stellar parameters and chemical properties of the stars. All of the stars belong to the red giant branch, and, in general, they follow the abundance pattern of typical halo stars. There are a few exceptions that would deserve further analysis through high-resolution spectroscopy. In particular, we identify a high-velocity Carbon-Enhanced Metal-Poor star, with a Galactocentric velocity of 482 km s-1. We do not confirm any hypervelocity star in the sample, but this result is very sensitive to the adopted distances and less sensitive to the Galactic potential.

Keywords: milky way dynamics; stellar kinematics; stellar abundances
Optical Spectropolarimetry of Binary Asteroid Didymos-Dimorphos before and after the DART Impact

We have monitored the Didymos-Dimorphos binary asteroid in spectropolarimetric mode in the optical range before and after the DART impact. The ultimate goal was to obtain constraints on the characteristics of the ejected dust for modeling purposes. Before impact, Didymos exhibited a linear polarization rapidly increasing with phase angle, reaching a level of ~5% in the blue and ~4.5% in the red. The shape of the polarization spectrum was anticorrelated with that of its reflectance spectrum, which appeared typical of an S-class asteroid. After impact, the level of polarization dropped by about 1 percentage point (pp) in the blue band and about 0.5 pp in the red band, then continued to linearly increase with phase angle, with a slope similar to that measured prior to impact. The polarization spectra, once normalized by their values at an arbitrary wavelength, show very little or no change over the course of all observations before and after impact. The lack of any remarkable change in the shape of the polarization spectrum after impact suggests that the way in which polarization varies with wavelength depends on the composition of the scattering material, rather than on its structure, be this a surface or a debris cloud.

Keywords: near-earth objects; spectropolarimetry