adsabs/SciX_UAT_keywords huggingface dataset:
Lyman Continuum Leakers in the AstroSat Ultraviolet Deep Field: Extreme-ultraviolet Emitters at the Cosmic Noon

We report the direct detection of Lyman continuum (LyC) emission from nine galaxies and one active galactic nucleus at z ∼ 1.1–1.6 in the GOODS-North field using deep observations from the Ultraviolet Imaging Telescope (UVIT) on board AstroSat. The absolute escape fraction of the sources estimated from the far-ultraviolet and Hα-line luminosities using Monte Carlo analysis of two intergalactic medium models span a range ∼10%–55%. The rest-frame UV wavelength of the sources falls in the extreme-ultraviolet regime ∼550–700 Å, the shortest LyC wavelength range probed so far. This redshift range remains devoid of direct detections of LyC emission due to the instrumental limitations of previously available facilities. With UVIT having very low detector noise, each of these sources is detected with an individual signal-to-noise ratio (S/N) > 3, while for the stack of six sources, we achieve an S/N ∼ 7.4. The LyC emission is seen to be offset from the optical centroids and extended beyond the UVIT point-spread function of 1.″6 in most of the sources. This sample fills an important niche between GALEX and Cosmic Origins Spectrograph at low z and Hubble Space Telescope's Wide Field Camera 3 at high z and is crucial in understanding the evolution of LyC leakers.

Keywords: emission line galaxies; reionization; ultraviolet astronomy
Preatmospheric Detection of a Meter-sized Earth Impactor

On 2020 September 18 U.S. Government (USG) sensors detected a bolide with peak bolometric magnitude of -19 over the Western Pacific. The impact was also detected by the Geostationary Lightning Mapper instrument on the GOES-17 satellite and infrasound sensors in Hawaii. The USG measurements reported a steep entry angle of 67° from horizontal from a radiant 13° east of north and an impact speed of 11.7 km s-1. Interpretation of all energy yields produces a preferred energy estimate of 0.4 kt TNT, corresponding to a 23,000 kg, 3 m diameter meteoroid. A postimpact search of telescopic images found that the Asteroid Terrestrial-impact Last Alert System survey captured the object just 10 minutes prior to impact at an Earth-centered distance of nearly 11,900 km with apparent magnitude m = 12.5. The object appears as a 0.44° streak originating on the eastern edge of the image, extending one-third of the USG state-vector-based prediction of 1.26° over the 30 s exposure. The streak shows brightness variability consistent with small asteroid rotation. The position of Earth's shadow, the object's size, and its consistency with the reported USG state vector confirm the object is likely natural. This is the eighth preatmospheric detection of a near-Earth asteroid (NEA) impactor and the closest initial telescopic detection prior to impact. The high altitude of peak fireball brightness suggests it was a weak object comparable in many respects with 2008 TC3 (the Almahata Sitta meteorite), with an absolute magnitude H = 32.5 and likely low albedo. Therefore, we suggest the NEA was a C-complex asteroid.

Keywords: bolides; sky surveys; near-earth objects
A White Dwarf-Main-sequence Binary Unveiled by Time-domain Observations from LAMOST and TESS

We report a single-lined white dwarf-main-sequence binary system, LAMOST J172900.17+652952.8, which is discovered by the Large Sky Area Multi-Object Fibre Spectroscopic Telescope (LAMOST)'s medium-resolution time-domain surveys. The radial-velocity semi-amplitude and orbital period of the optical visible star are measured by using follow-up observations with the Palomar 200 inch telescope and light curves from the Transiting Exoplanet Survey Satellite (TESS). Thus the mass function of the invisible candidate white dwarf is derived, f(M 2) = 0.120 ± 0.003 M ⊙. The mass of the visible star is measured based on a spectral energy distribution fitting, M 1 = ${0.81}_{-0.06}^{+0.07}\,{M}_{\odot }$ . Hence, the mass of its invisible companion is M 2 ≳ 0.63 M ⊙. The companion ought to be a compact object rather than a main-sequence star owing to the mass ratio q = M 2/M 1 ≳ 0.78 and the single-lined spectra. The compact object is likely to be a white dwarf if the inclination angle is not small, i ≳ 40°. By using the Galaxy Evolution Explorer (GALEX) near-UV flux, the effective temperature of the white dwarf candidate is constrained as ${T}_{\mathrm{eff}}^{\mathrm{WD}}$ ≲ 12,000-13,500 K. It is difficult to detect white dwarfs which are outshone by their bright companions via single-epoch optical spectroscopic surveys. Therefore, optical time-domain surveys can play an important role in unveiling invisible white dwarfs and other compact objects in binaries.

Keywords: close binary stars; radial velocity; white dwarf stars; light curves
Magnetic Braking during Direct Collapse Black Hole Formation

Magnetic fields are expected to be efficiently amplified during the formation of the first massive black holes via the small-scale dynamo and in the presence of strong accretion shocks occurring during gravitational collapse. Here, we analyze high-resolution cosmological magnetohydrodynamical simulations of gravitational collapse in atomic cooling halos, exploring the dynamical role of magnetic fields, particularly concerning the effect of magnetic braking and angular momentum transport. We find that after the initial amplification, magnetic fields contribute to the transport of angular momentum and reduce it compared to pure hydrodynamical simulations. However, the magnetic and Reynolds torques do not fully compensate for the inward advection of angular momentum, which still accumulates over timescales of ~1 Myr. A Jeans analysis further shows that magnetic pressure strongly contributes to suppressing fragmentation on scales of 0.1-10 pc. Overall, the presence of magnetic fields thus aids in the transport of angular momentum and favors the formation of massive objects.

Keywords: population iii stars; early universe; supermassive black holes
An Early-warning System for Electromagnetic Follow-up of Gravitational-wave Events

Binary neutron stars (BNSs) will spend ≃10-15 minutes in the band of Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO) and Virgo detectors at design sensitivity. Matched-filtering of gravitational-wave (GW) data could in principle accumulate enough signal-to-noise ratio (S/N) to identify a forthcoming event tens of seconds before the companions collide and merge. Here we report on the design and testing of an early-warning GW detection pipeline. Early-warning alerts can be produced for sources that are at low enough redshift so that a large enough S/N accumulates ∼10-60 s before merger. We find that about 7% (49%) of the total detectable BNS mergers will be detected 60 s (10 s) before the merger. About 2% of the total detectable BNS mergers will be detected before merger and localized to within 100 deg2 (90% credible interval). Coordinated observing by several wide-field telescopes could capture the event seconds before or after the merger. LIGO-Virgo detectors at design sensitivity could facilitate observing at least one event at the onset of merger.

Keywords: neutron stars; gravitational waves
An Empirical Approach to Selecting the First Growing Black Hole Seeds with JWST/NIRCam

The James Webb Space Telescope (JWST) will have the sensitivity to detect early low-mass black holes (BHs) as they transition from "seeds" to supermassive BHs. Based on the JAGUAR mock catalog of galaxies, we present a clean color selection that takes advantage of the unique UV slope of accreting supermassive BHs with a relatively low mass and high accretion rates. We show that those galaxies hosting ~106 M ⊙ BHs radiating at >10% of their Eddington luminosity separate in color space from inactive systems for a range of host stellar masses. Here we propose a set of 3-band, 2-color selection boxes (with 90% completeness; 90% purity; balanced purity/completeness) with JWST/NIRCam to identify the most promising growing BH candidates at z ~ 7-10.

Keywords: active galactic nuclei; high-redshift galaxies; intermediate-mass black holes; early universe
Discriminating between Neutron Stars and Black Holes with Imperfect Knowledge of the Maximum Neutron Star Mass

Although gravitational-wave signals from exceptional low-mass compact binary coalescences, like GW170817, may carry matter signatures that differentiate the source from a binary black hole system, only one out of every eight events detected by the current Advanced LIGO and Virgo observatories are likely to have signal-to-noise ratios large enough to measure matter effects, even if they are present. Nonetheless, the systems' component masses will generally be constrained precisely. Constructing an explicit mixture model for the total rate density of merging compact objects, we develop a hierarchical Bayesian analysis to classify gravitational-wave sources according to the posterior odds that their component masses are drawn from different subpopulations. Accounting for current uncertainty in the maximum neutron star mass and adopting a power-law mass distribution with or without a mass gap and either random or mass-ratio-dependent pairing, we examine two recent events from the LIGO-Virgo Collaboration's third observing run, GW190425 and GW190814. For population models with no overlap between the neutron star and black hole mass distributions, we typically find that there is a $\gtrsim 70 \% $ chance, depending on the exact population model, that GW190425 was a binary neutron star merger rather than a neutron-star-black-hole merger. On the other hand, we find that there is a $\lesssim 6 \% $ chance that GW190814 involved a slowly spinning neutron star, regardless of our assumed population model.

Keywords: gravitational waves; neutron stars; black holes; compact objects
Bayesian Dynamic Mapping of an Exo-Earth from Photometric Variability

Photometric variability of a directly imaged exo-Earth conveys spatial information on its surface and can be used to retrieve a two-dimensional geography and axial tilt of the planet (spin-orbit tomography). In this study, we relax the assumption of the static geography and present a computationally tractable framework for dynamic spin-orbit tomography applicable to time-varying geography. First, a Bayesian framework of static spin-orbit tomography is revisited using analytic expressions of the Bayesian inverse problem with a Gaussian prior. We then extend this analytic framework to a time-varying one through a Gaussian process in the time domain, and present analytic expressions that enable efficient sampling from a full joint posterior distribution of geography, axial tilt, spin rotation period, and hyperparameters in the Gaussian process priors. Consequently, it only takes 0.3 s for a laptop computer to sample one posterior dynamic map conditioned on the other parameters with 3072 pixels and 1024 time grids, for a total of ∼3 × 106 parameters. We applied our dynamic mapping method to a toy model and found that the time-varying geography was accurately retrieved along with the axial tilt and spin rotation period. In addition, we demonstrated the use of dynamic spin-orbit tomography with a real multicolor light curve of the Earth as observed by the Deep Space Climate Observatory. We found that the resultant snapshots from the dominant component of a principal component analysis roughly captured the large-scale, seasonal variations of the clear-sky and cloudy areas on the Earth.

Keywords: exoplanet surface characteristics; exoplanet surface variability; exoplanet astronomy; direct imaging; bayesian statistics; computational methods
GW170817A as a Hierarchical Black Hole Merger

Despite the rapidly growing number of stellar-mass binary black hole mergers discovered through gravitational waves, the origin of these binaries is still not known. In galactic centers, black holes can be brought to each others' proximity by dynamical processes, resulting in mergers. It is also possible that black holes formed in previous mergers encounter new black holes, resulting in so-called hierarchical mergers. Hierarchical events carry signatures such as higher-than-usual black hole mass and spin. Here we show that the recently reported gravitational-wave candidate, GW170817A, could be the result of such a hierarchical merger. In particular, its chirp mass ∼40 M⊙ and effective spin of χeff ∼ 0.5 are the typically expected values from hierarchical mergers within the disks of active galactic nuclei. We find that the reconstructed parameters of GW170817A strongly favor a hierarchical merger origin over having been produced by an isolated binary origin (with an odds ratio of > 103).

Keywords: gravitational waves; black holes; active galactic nuclei
Properties of Compact Faint Radio Sources as a Function of Angular Size from Stacking

The polarization properties of radio sources powered by an Active Galactic Nucleus (AGN) have attracted considerable attention because of the significance of magnetic fields in the physics of these sources, their use as probes of plasma along the line of sight, and as a possible contaminant of polarization measurements of the cosmic microwave background. For each of these applications, a better understanding of the statistics of polarization in relation to source characteristics is crucial. In this paper, we derive the median fractional polarization, Π0,med, of large samples of radio sources with 1.4 GHz flux density 6.6 < S1.4 < 70 mJy, by stacking 1.4 GHz NVSS polarized intensity as a function of angular size derived from the FIRST survey. Five samples with deconvolved mean angular size 1"8 to 8"2 and two samples of symmetric double sources are analyzed. These samples represent most sources smaller than or near the median angular size of the mJy radio source population We find that the median fractional polarization Π0,med at 1.4 GHz is a strong function of source angular size ≲5″ and a weak function of angular size for larger sources up to ∼8″. We interpret our results as depolarization inside the AGN host galaxy and its circumgalactic medium. The curvature of the low-frequency radio spectrum is found to anticorrelate with Π0,med, a further sign that depolarization is related to the source.

Keywords: extragalactic radio sources; extragalactic magnetic fields; radio galaxies; polarimetry; radio jets; spectral index
The Distribution of Radio Quiet Active Galactic Nuclei in the Star Formation Rate-stellar Mass Plane

That active galactic nuclei (AGN) with jets can alternately enhance as well as suppress star formation rates, explains the location and slope of radio loud AGN on the star formation rate-stellar mass plane. Here, we explore 860 type 1 and 2 AGN at z < 0.2 from the ROSAT-2RXS survey in order to understand both different location and lower slopes for non-jetted AGN in the star formation rate-stellar mass plane. We describe the nature of these differences in terms of different degrees of black hole feedback, with relatively weak negative feedback from non-jetted AGN compared to both relatively strong positive and negative feedback from jetted AGN. The validity of these ideas brings us a step closer towards understanding the black hole scaling relations across space and time.

Keywords: active galaxies; radio quiet quasars; black holes; agn host galaxies
Observational Signatures of Cosmic-Ray Interactions in Molecular Clouds

We investigate ionization and heating of gas in the dense, shielded clumps/cores of molecular clouds bathed by an influx of energetic, charged cosmic rays (CRs). These molecular clouds have complex structures, with substantial variation in their physical properties over a wide range of length scales. The propagation and distribution of CRs is thus regulated accordingly, in particular, by the magnetic fields threaded through the clouds and into the dense regions within. We have found that a specific heating rate reaching 10-26 erg cm-3 s-1 can be sustained in the dense clumps/cores for Galactic environments, and this rate increases with CR energy density. The propagation of CRs and heating rates in some star-forming filaments identified in IC 5146 are calculated, with the CR diffusion coefficients in these structures determined from magnetic field fluctuations inferred from optical and near-infrared polarizations of starlight, which is presumably a magnetic field tracer. Our calculations indicate that CR heating can vary by nearly three orders of magnitude between different filaments within a cloud due to different levels of CR penetration. The CR ionization rate among these filaments is similar. The equilibrium temperature that could be maintained by CR heating alone is of order 1 K in a Galactic environment, but this value would be higher in strongly star-forming environments, thus causing an increase in the Jeans mass of their molecular clouds.

Keywords: interstellar clouds; cosmic rays; galactic cosmic rays; interstellar magnetic fields; star formation
Neutral Heating Efficiency in the Dayside Martian Upper Atmosphere

The neutral heating efficiency is commonly defined as the fraction of the solar extreme ultraviolet and X-ray energy absorbed by a planetary atmosphere that ends up as local heat. It is a crucial parameter that determines the upper atmospheric temperature and, consequently, the thermal escape rate on both solar system bodies and exoplanets. Combining the Mars Atmosphere and Volatile Evolution measurements of a variety of atmospheric parameters, we calculate the neutral heating efficiency in the dayside Martian upper atmosphere based on a complicated network of microscopic processes, including photon and photoelectron impact processes, as well as exothermic chemical reactions. Our calculations indicate that neutral heating is mainly contributed by photon impact at low altitudes, of which the bulk occurs via CO2 photodissociation, and exothermic chemistry at high altitudes, of which the bulk occurs via {{{O}}}2+ and {CO}}2+ dissociative recombination. Collisional quenching of metastable neutrals and ions, which is of great interest in the literature, contributes to local heating by no more than 10% at all altitudes. In the dayside median sense, the neutral heating efficiency remains roughly constant at 20% from 150 to 200 km and increases steadily to 32% near 250 km. The heating efficiency at 150-200 km shows a weak correlation with solar zenith angle, increases modestly with increasing solar activity, and is clearly enhanced over strong crustal magnetic anomalies. Throughout the study, strict local heating is assumed, but nonlocal heating does not affect our results near or below 200 km.

Keywords: upper atmosphere; mars; aeronomy; planetary atmospheres; photoionization; photodissociation regions; astrochemistry
Three-dimensional Simulations of Massive Stars. II. Age Dependence

We present 3D full star simulations, reaching up to 90% of the total stellar radius, for three 7 M ⊙ stars of different ages: zero-age main sequence (ZAMS), mid-main sequence (midMS), and terminal-age main sequence (TAMS). A comparison with several theoretical prescriptions shows that the generation spectra for all three ages are dominated by convective plumes. Two distinct overshooting layers are observed, with most plumes stopped within the layer situated directly above the convective boundary; overshooting to the second, deeper layer becomes progressively more infrequent with increasing stellar age. Internal gravity wave (IGW) propagation is significantly impacted in the midMS and TAMS models as a result of some IGWs getting trapped within their Brunt-Väisälä frequency spikes. A fundamental change in the wave structure across radius is also observed, driven by the effect of density stratification on IGW propagation causing waves to become evanescent within the radiative zone, with older stars being affected more strongly. We find that the steepness of the frequency spectrum at the surface increases from ZAMS to the older models, with older stars also showing more modes in their spectra.

Keywords: stellar dynamics; stellar evolution; stellar ages; stellar properties; internal waves; stellar convective zones
The 2175 Å Dust Feature in Star-forming Galaxies at 1.3 ≤ z ≤ 1.8: The Dependence on Stellar Mass and Specific Star Formation Rate

We present direct spectroscopic measurements of the broad 2175 Å absorption feature in 505 star-forming main-sequence galaxies at 1.3 ≤ z ≤ 1.8 using individual and stacked spectra from the zCOSMOS-deep survey. Significant 2175 Å excess absorption features of moderate strength are measured, especially in the composite spectra. The excess absorption is well described by a Drude profile. The bump amplitude expressed in units of k(λ) = A(λ)/E(B - V), relative to the featureless Calzetti et al. law, has a range Bk ≈ 0.2-0.8. The bump amplitude decreases with the specific star formation rate (sSFR), while it increases moderately with the stellar mass. However, a comparison with local "starburst" galaxies shows that the high-redshift main-sequence galaxies have stronger bump features, despite having a higher sSFR than the local sample. Plotting the bump strength against the ${\rm{\Delta }}\mathrm{logsSFR}\equiv \mathrm{log}\left(\mathrm{SFR}/{\mathrm{SFR}}_{\mathrm{MS}}\right)$ relative to the main sequence, however, brings the two samples into much better concordance. This may indicate that it is the recent star formation history of the galaxies that determines the bump strength through the destruction of small carbonaceous grains by supernovae and intense radiation fields coupled with the time delay of ∼1 Gyr in the appearance of carbon-rich asymptotic giant branch stars.

Keywords: galaxy evolution; interstellar medium; interstellar dust; interstellar dust extinction
An Extended Theoretical Scenario for Classical Cepheids. I. Modeling Galactic Cepheids in the Gaia Photometric System

We present a new extended and detailed set of models for classical Cepheid pulsators at solar chemical composition (Z = 0.02, Y = 0.28) based on a well-tested nonlinear hydrodynamical approach. In order to model the possible dependence on crucial assumptions such as the mass-luminosity relation of central helium burning intermediate-mass stars or the efficiency of superadiabatic convection, the model set was computed by varying not only the pulsation mode and the stellar mass but also the mass-luminosity relation and the mixing length parameter that is used to close the system of nonlinear hydrodynamical and convective equations. The dependence of the predicted boundaries of the instability strip as well as of both light and radial velocity curves on the assumed mass-luminosity and the efficiency of superadiabatic convection is discussed. Nonlinear period-mass-luminosity-temperature, period-radius, and period-mass-radius relations are also computed. The theoretical atlas of bolometric light curves for both the fundamental and first overtone mode has been converted in the Gaia filters G, GBP, and GBR and the corresponding mean magnitudes have been derived. Finally, the first theoretical period-luminosity-color and period-Wesenheit relations in the Gaia filters are provided and the resulting theoretical parallaxes are compared with Gaia Data Release 2 results for both fundamental and first overtone Galactic Cepheids.

Keywords: cepheid variable stars; cepheid distance; stellar pulsations; theoretical models; hubble constant; stellar parallax; distance indicators