adsabs/SciX_UAT_keywords huggingface dataset:
Gas-rich, Field Ultra-diffuse Galaxies Host Few Globular Clusters

We present Hubble Space Telescope imaging of 14 gas-rich, low-surface-brightness galaxies in the field at distances of 25-36 Mpc, with mean effective radii and g-band central surface brightnesses of 1.9 kpc and 24.2 mag arcsec-2. Nine meet the standard criteria to be considered ultra-diffuse galaxies (UDGs). An inspection of point-like sources brighter than the turnover magnitude of the globular cluster luminosity function and within twice the half-light radii of each galaxy reveals that, unlike those in denser environments, gas-rich, field UDGs host very few old globular clusters (GCs). Most of the targets (nine) have zero candidate GCs, with the remainder having one or two candidates each. These findings are broadly consistent with expectations for normal dwarf galaxies of similar stellar mass. This rules out gas-rich, field UDGs as potential progenitors of the GC-rich UDGs that are typically found in galaxy clusters. However, some in galaxy groups may be directly accreted from the field. In line with other recent results, this strongly suggests that there must be at least two distinct formation pathways for UDGs, and that this subpopulation is simply an extreme low surface brightness extension of the underlying dwarf galaxy population. The root cause of their diffuse stellar distributions remains unclear, but the formation mechanism appears to only impact the distribution of stars (and potentially dark matter), without strongly impacting the distribution of neutral gas, the overall stellar mass, or the number of GCs.

Keywords: low surface brightness galaxies; dwarf galaxies; galaxy formation; globular star clusters
Simulated Observations of Star Formation Regions: Infrared Evolution of Globally Collapsing Clouds

A direct comparison between hydrodynamical simulations and observations is needed to improve the physics included in the former and to test biases in the latter. Post-processing radiative transfer and synthetic observations are now the standard way to do this. We report on the first application of the SKIRT radiative-transfer code to simulations of a star-forming cloud. The synthetic observations are then analyzed following traditional observational workflows. We find that in the early stages of the simulation, stellar radiation is inefficient in heating dust to the temperatures that are observed in Galactic clouds, thus the addition of an interstellar radiation field is necessary. The spectral energy distribution of the cloud settles rather quickly after ~3 Myr of evolution from the onset of star formation, but its morphology continues to evolve for ~8 Myr due to the expansion of H II regions and the respective creation of cavities, filaments, and ridges. Modeling synthetic Herschel fluxes with one- or two-component modified blackbodies underestimates total dust masses by a factor of ~2. However, spatially resolved fitting recovers up to about 70% of the intrinsic value. This "missing mass" is located in a very cold dust component with temperatures below 10 K, which does not contribute appreciably to the far-infrared flux. This effect could bias real observations if this dust exists in large amounts. Finally, we tested observational calibrations of the SFR based on infrared fluxes and concluded that they are in agreement when compared to the intrinsic SFR of the simulation averaged over ~100 Myr.

Keywords: star forming regions; interstellar medium; interstellar radiation field; computational methods; radiative transfer simulations
Targeting Bright Metal-poor Stars in the Disk and Halo Systems of the Galaxy

We present the results of spectroscopic follow-up for 1897 low-metallicity star candidates, selected from the Best & Brightest (B&B) Survey, carried out with the GMOS-N/S (Gemini North/South telescopes) and Goodman (SOAR Telescope) spectrographs. From these low-resolution (R ∼ 2000) spectra, we estimate stellar atmospheric parameters, as well as carbon and magnesium abundance ratios. We confirm that 56% of our program stars are metal-poor ([Fe/H] < - 1.0), 30% are very metal-poor (VMP; [Fe/H] < - 2.0), and 2% are extremely metal-poor (EMP; [Fe/H] < - 3.0). There are 191 carbon-enhanced metal-poor (CEMP) stars, resulting in CEMP fractions of 19% and 43% for the VMP and EMP regimes, respectively. A total of 94 confirmed CEMP stars belong to Group I (A(C) ≳ 7.25) and 97 to Group II (A(C) ≲ 7.25) in the Yoon-Beers A(C)-[Fe/H] diagram. Moreover, we combine these data with Gaia EDR3 astrometric information to delineate new target-selection criteria, which have been applied to the Goodman/SOAR candidates, to more than double the efficiency for identification of bona fide VMP and EMP stars in comparison to random draws from the B&B catalog. We demonstrate that this target-selection approach can achieve success rates of 96%, 76%, 28%, and 4% for [Fe/H] ≤ - 1.5, ≤ - 2.0, ≤ - 2.5 and ≤ - 3.0, respectively. Finally, we investigate the presence of dynamically interesting stars in our sample. We find that several VMP/EMP ([Fe/H] ≤ - 2.5) stars can be associated with either the disk system or halo substructures like Gaia-Sausage/Enceladus and Sequoia.

Keywords: population ii stars; milky way stellar halo; milky way disk; cemp stars; spectroscopy; chemical abundances; stellar atmospheres; milky way dynamics; milky way evolution; milky way formation
Variations of the Plasma Environment Revealed by the Evolution of the Supra-arcade Fan in the 2017 September 10 Flare

Based on observations from the Interface Region Imaging Spectrograph and Hinode, we analyze the thermodynamic evolution of the supra-arcade fan (SAF) in the 2017 September 10 flare. The SAF presents discontinuous characters during the rising process, indicating a nonuniform process of magnetic reconnection in the solar eruption. The intensity peaks of the high-temperature spectral lines (Fe XXI 1354.08 Å, Fe XXIII 263.76 Å, and Fe XXIV 255.10 Å) basically correspond to the valley of the Doppler velocity and Doppler width. The temperature and density increase spatially at the upper boundary of the SAF. These results indicate that a compressed interface may exist in the SAF, where the plasma environment shows remarkable changes in density, temperature, and turbulence. In view of the fact that the height of the SAF is close to the hard X-ray source, we conclude that the interface could be related to termination shocks (TSs), taking into account the synthetic spectral profiles obtained from numerical experiments. In turn, the variations of the spectral profiles might be useful tools for identifying TSs from EUV spectral observations.

Keywords: solar flares; solar magnetic reconnection; termination shock
Void Lensing in Cubic Galileon Gravity

Weak-lensing studies via cosmic voids are a promising probe of modified gravity (MG). The excess surface mass density (ESD) is widely used as a lensing statistic in weak-lensing research. In this paper, we use the ray-tracing method to study the ESD around voids in simulations based on cubic Galileon (CG) gravity. With the compilation of an N-body simulation and the ray-tracing method, changes in structure formation and deflection angle resulting from MG can both be considered, making the extraction of lensing signals more realistic. We find good agreements between the measurement and theoretical prediction of ESD for CG gravity. However, the lensing signals are much less affected by the change in the deflection angle than by the change in the structure formation, indicating a good approximation of the ESD (statistics) as the projection of the 3D dark matter density field. Finally, we demonstrate that it is impossible to distinguish CG and general relativity in our simulation, but in the next-generation survey, thanks to the large survey area and the increased galaxy number density, detecting the differences between these two models is possible. The method employed in this paper, which combines an N-body simulation and the ray-tracing method, can be a robust way to measure the lensing signals from simulations based on the MGs, and especially on that which significantly modifies the deflection angle.

Keywords: weak gravitational lensing; cosmology; voids; non-standard theories of gravity
Influence of C/O Ratio on Hot Jupiter Atmospheric Chemistry

We conducted laboratory experiments to study the chemistry in hot Jupiter atmospheres with a C/O ratio of 0.35. We compared our results with the ones obtained previously for atmospheres with a C/O ratio of 1 to investigate the influence of the C/O ratio on the chemistry and formation of photochemical organic aerosol. We found that the C/O ratio and the gas mixture compositions strongly influence the pathways responsible for the formation of CO2. Thermochemical reactions are primarily responsible for the formation of CO2 in low C/O ratio atmospheres, while photochemistry is the dominant process in high C/O ratio atmospheres even if the final CO2 concentration is the same in both cases. Our results show that low C/O atmospheres at the thermochemical equilibrium contain a higher water abundance, while high C/O atmospheres are significantly depleted in water. However, in low C/O atmospheres, the water abundance is not affected by UV photolysis, while our previous work demonstrated that a significant amount of water can be produced in high C/O ratio atmospheres. This contrast in water production suggests that photochemistry should be considered when interpreting exoplanet transit spectra. Finally, we did not observe the formation of a detectable amount of nonvolatile photochemical aerosols in low C/O atmospheres, in contrast to our previous study. We infer that for a C/O ratio < 1, water likely inhibits organic growth and aerosol formation, suggesting that photochemical organic aerosols are likely to be observed in planets presenting a carbon enrichment compared to their host stars.

Keywords: exoplanet atmospheres; exoplanet atmospheric composition; planetary atmospheres; laboratory astrophysics
High-energy Neutrinos from the Inner Circumnuclear Region of NGC 1068

High-energy neutrinos are detected by the IceCube Observatory in the direction of NGC 1068, the archetypical type II Seyfert galaxy. The neutrino flux, surprisingly, is more than an order of magnitude higher than the γ-ray upper limits at measured TeV energy, posing tight constraints on the physical conditions of a neutrino production site. We report an analysis of the submillimeter, mid-infrared, and ultraviolet observations of the central 50 pc of NGC 1068 and suggest that the inner dusty torus and the region where the jet interacts with the surrounding interstellar medium (ISM) may be a potential neutrino production site. Based on radiation and magnetic field properties derived from observations, we calculate the electromagnetic cascade of the γ-rays accompanying the neutrinos. When injecting protons with a hard spectrum, our model may explain the observed neutrino flux above ~10 TeV. It predicts a unique sub-TeV γ-ray component, which could be identified by a future observation. Jet-ISM interactions are commonly observed in the proximity of jets of both supermassive and stellar-mass black holes. Our results imply that such interaction regions could be γ-ray-obscured neutrino production sites, which are needed to explain the IceCube diffuse neutrino flux.

Keywords: seyfert galaxies; radio hot spots; high-energy cosmic radiation; gamma-ray sources
Fermi-GBM Observations of GRB 210812A: Signatures of a Million Solar Mass Gravitational Lens

Observing gravitationally lensed objects in the time domain is difficult, and well-observed time-varying sources are rare. Lensed gamma-ray bursts (GRBs) offer improved timing precision for this class of objects, complementing observations of quasars and supernovae. The rate of lensed GRBs is highly uncertain, approximately one in 1000. The Gamma-ray Burst Monitor on board the Fermi Gamma-ray Space Telescope has observed more than 3000 GRBs, making it an ideal instrument to uncover lensed bursts. Here we present observations of GRB 210812A showing two emission episodes, separated by 33.3 s and with a flux ratio of about 4.5. An exhaustive temporal and spectral analysis shows that the two emission episodes have the same pulse and spectral shape, which poses challenges to GRB models. We report multiple lines of evidence for a gravitational lens origin. In particular, modeling the lightcurve using nested sampling, we uncover strong evidence in favor of the lensing scenario. Assuming a point-mass lens, the mass of the lensing object is about 1 million solar masses. High-resolution radio imaging is needed for future lens candidates to derive tighter constraints.

Keywords: gamma-ray bursts; gravitational lensing
The Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) Quasar Survey: Quasar Properties from Data Releases 6 to 9

We report the fourth installment in the series of the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) quasar survey, which includes quasars observed between 2017 September and 2021 June. There are in total 13,066 quasars reliably identified, of which 6685 are newly discovered that are not reported in the Sloan Digital Sky Survey (SDSS) DR14 quasar catalog or Million Quasars catalog. Because LAMOST does not provide accurate absolute flux calibration, we recalibrate the spectra with the SDSS/Pan-STARRS1 multiband photometric data. The emission-line properties of Hα, Hβ, Mg II, and C IV and the continuum luminosities are measured by fitting the recalibrated spectra. We also estimate the single-epoch virial black hole masses (M BH) using the derived emission-line and continuum parameters. This is the first time that the emission-line and continuum fluxes were estimated based on LAMOST recalibrated quasar spectra. The catalog and spectra for these quasars are available online. After the 9 yr LAMOST quasar survey, there are in total 56,175 identified quasars, of which 24,127 are newly discovered. The LAMOST quasar survey not only discovers a great number of new quasars but also provides a database for investigating the spectral variability of the quasars observed by both LAMOST and SDSS and finding rare quasars, including changing-look quasars and broad absorption line quasars.

Keywords: quasars; catalogs; surveys
Not So Fast, Not So Furious: Just Magnetic

WD 0810-353 is a white dwarf within the 20 pc volume around the Sun. Using Gaia astrometric distance and proper motions, and a radial velocity derived from Gaia spectroscopy, it has been predicted that this star will pass within 1 pc of the solar system in about 30 kyr. However, WD 0810-353 has been also shown to host a magnetic field with a strength of the order of 30 MG. Its spectrum is therefore not like those of normal DA stars of similar effective temperature. We have obtained and analyzed new polarized spectra of the star around Hα. Our analysis suggests that the visible surface of the star shows two regions of different field strength (~30 and ~45 MG, respectively), and opposite polarity. The spectra do not change over a 4 yr time span, meaning that either the stellar rotation period is no shorter than several decades, or that the field is symmetric about the rotation axis. Taking into account magnetic shift and splitting, we obtain an estimate of the radial velocity of the star (+83 ± 140 km s-1); we reject both the value and the claimed precision deduced from the Gaia DR3 spectroscopy (-373.7 ± 8.2 km s-1), and we conclude that there will probably be no close encounter between the solar system and WD 0810-353. We also reject the suggestion that the star is a hypervelocity runaway star, a survivor of a Type Ia supernova explosion. It is just a stellar remnant in the solar neighborhood with a very strong and complex magnetic field.

Keywords: white dwarf stars; spectropolarimetry; stellar magnetic fields; close encounters; solar neighborhood
Common Envelope Shaping of Planetary Nebulae. III. The Launching of Jets in Proto-Planetary Nebulae

We compute successfully the launching of two magnetic winds from two circumbinary disks formed after a common envelope event. The launching is produced by the increase of magnetic pressure due to the collapse of the disks. The collapse is due to internal torques produced by a weak poloidal magnetic field. The first wind can be described as a wide jet, with an average mass-loss rate of ~1.3 × 10-7 M⊙ yr-1 and a maximum radial velocity of ~230 km s-1. The outflow has a half-opening angle of ~20°. Narrow jets are also formed intermittently with velocities up to 3000 km s-1, with mass-loss rates of ~6 × 10-12 M⊙ yr-1 during short periods of time. The second wind can be described as a wide X-wind, with an average mass-loss rate of ~1.68 × 10-7 M⊙ yr-1 and a velocity of ~30 km s-1. A narrow jet is also formed with a velocity of 250 km s-1 and a mass-loss rate of ~10-12 M⊙ yr-1. The computed jets are used to provide inflow boundary conditions for simulations of proto-planetary nebulae. The wide jet evolves into a molecular collimated outflow within a few astronomical units, producing proto-planetary nebulae with bipolar, elongated shapes, whose kinetic energies reach ~4 × 1045 erg at 1000 yr. Similarities with observed features in W43A, OH 231.8+4.2, and Hen 3-1475 are discussed. The computed wide X-wind produces proto-planetary nebulae with slower expansion velocities, bipolar and elliptical shapes, and possible starfish-type and quadrupolar morphology.

Keywords: protoplanetary nebulae; planetary nebulae; stellar evolution; asymptotic giant branch stars; common envelope binary stars; post-asymptotic giant branch stars
The Physical Properties of Low-redshift FeLoBAL Quasars. I. Spectral-synthesis Analysis of the Broad Absorption-line (BAL) Outflows Using SimBAL

We present the first systematic study of 50 low-redshift (0.66 < z < 1.63) iron low-ionization broad absorption-line quasars (FeLoBALQs) using SimBAL, which represents a more than five-fold increase in the number of FeLoBALQs with detailed absorption line spectral analyses. We found the outflows have a wide range of ionization parameters, $-4\lesssim \mathrm{log}U\lesssim 1.2$ and densities, $2.8\lesssim \mathrm{log}n\lesssim 8\ [{\mathrm{cm}}^{-3}]$ . The objects in our sample showed FeLoBAL gas located at a wide range of distances $0\lesssim \mathrm{log}R\lesssim 4.4$ [pc], although we do not find any evidence for disk winds (with R ≪ 0.01 pc) in our sample. The outflow strength primarily depends on the outflow velocity with faster outflows found in quasars that are luminous or that have flat or redder spectral energy distributions. We found that ~18% of the FeLoBALQs in the sample have the significantly powerful outflows needed for quasar feedback. Eight objects showed overlapping troughs in the spectra, and we identified eleven loitering outflow objects, a new class of FeLoBALQs that are characterized by low outflow velocities and high column density winds located $\mathrm{log}R\lesssim 1$ [pc] from the central engine. The FeLoBALs in loitering outflows objects do not show properties expected for radiatively driven winds, and these objects may represent a distinct population among FeLoBALQs. We discuss how the potential acceleration mechanisms and the origins of the FeLoBAL winds may differ for outflows at different locations in quasars.

Keywords: broad-absorption line quasar; spectroscopy; high-luminosity active galactic nuclei; active galactic nuclei; galaxies; quasars
Extending the Frequency Reach of Pulsar Timing Array-based Gravitational Wave Search without High-cadence Observations

Gravitational wave (GW) searches using pulsar timing arrays (PTAs) are assumed to be limited by the typical average observational cadence of 1/(2 weeks) for a single pulsar to GW frequencies ≲4 × 10-7 Hz. We show that this assumption is incorrect and that a PTA can detect signals with much higher frequencies, which are preserved in the data due to aliasing, by exploiting asynchronous observations from multiple pulsars. This allows an observation strategy that is scalable to future large-scale PTAs containing O(103) pulsars, enabled by the Five-hundred meter Aperture Spherical Telescope and the Square Kilometer Array, without requiring a higher per-pulsar observation cadence. We show that higher frequency GW observations, reaching up to 4 × 10-4 Hz with an Square Kilometer Array-era PTA, have significant astrophysical implications, such as (i) a three orders of magnitude better constraint than current high-cadence observations on GW strain in the [10, 400] μHz band, and (ii) sensitive tests of the no-hair theorem in the mass range of supermassive black hole binaries using their inspiral, merger, and ringdown signals.

Keywords: pulsar timing method; gravitational wave astronomy
An Ultralong-wavelength Sky Model with Absorption Effect

The radio sky at frequencies below ~10 MHz is still largely unknown; this remains the last unexplored part of the electromagnetic spectrum in astronomy. The upcoming space experiments aiming at such low frequencies (ultralong wavelengths or ultralow frequencies) would benefit from reasonable expectations of the sky brightness distribution at relevant frequencies. In this work, we develop a radio sky model that is valid down to ~1 MHz. In addition to discrete H II objects, we take into account the free-free absorption by thermal electrons in the Milky Way's warm ionized medium. This absorption effect becomes obvious at ≲10 MHz, and could make the global radio spectrum turn over at ~3 MHz. Our sky map shows unique features at the ultralong wavelengths, including a darker Galactic plane in contrast to the sky at higher frequencies, and huge shadows of the spiral arms on the sky map. It will be a useful guide for designing future ultralong-wavelength observations. Our Ultralong-wavelength Sky Model with Absorption (ULSA) model can be downloaded at doi:10.5281/zenodo.4454153.

Keywords: radio continuum emission; interstellar emissions; galaxy structure; h ii regions; extragalactic radio sources
The Pre-He White Dwarfs in Eclipsing Binaries. II. WASP 0843-11

We present the Transiting Exoplanet Survey Satellite (TESS) photometry and our high-resolution spectra of the EL CVn-type star 1SWASP J084356.46-113327.5 (WASP 0843-11), which consists of an F-type main-sequence (MS) star and a hotter low-mass helium white dwarf precursor (pre-He WD). In a spectral analysis, double-lined radial velocities (RVs) were obtained for the first time. From a simultaneous analysis of the TESS light and RV curves, the masses, radii, and temperatures of each component were determined to be M1 = 1.733 ± 0.031 M⊙, M2 = 0.220 ± 0.008 M⊙, R1 = 2.094 ± 0.013 R⊙, R2 = 0.331 ± 0.003 R⊙, T1 = 6960 ± 120 K, and T2 =9870 ± 310 K, respectively. According to their physical properties, the primary and secondary stars are located on the instability strips of δ Sct/γ Dor hybrids and extremely low-mass WDs, respectively. We applied multiple frequency analyses to the residual light curve after subtracting the binarity effects and detected a total of four independent frequencies. A frequency of f3 = 1.6356 day-1 in the low-frequency region was reminiscent of γ Dor stars, while the other three frequencies of f2, f15, and f18 in the high-frequency region (150-196 day-1) are probably related to pre-He WD components. Our results demonstrate that the more massive MS primary star of WASP 0843-11 is a γ Dor pulsator, whereas the hotter secondary component is a pre-He WD with high-frequency pulsations.

Keywords: eclipsing binary stars; fundamental parameters of stars; stellar oscillations; spectroscopy; multi-periodic pulsation; asteroseismology; stellar evolution; white dwarf stars