adsabs/SciX_UAT_keywords huggingface dataset:
Lessons on Star-forming Ultra-diffuse Galaxies from the Stacked Spectra of the Sloan Digital Sky Survey

We investigate the on-average properties for 28 star-forming ultra-diffuse galaxies (UDGs) located in low-density environments, by stacking their spectra from the Sloan Digital Sky Survey. These relatively isolated UDGs, with stellar masses of ${\mathrm{log}}_{10}({M}_{* }/{M}_{\odot })\sim 8.57\pm 0.29$ , have the on-average total stellar metallicity [M/H] ∼ -0.82 ± 0.14, iron metallicity [Fe/H] ∼ -1.00 ± 0.16, stellar age t* ∼ 5.2 ± 0.5 Gyr, α-enhancement [α/Fe] ∼ 0.24 ± 0.10, and oxygen abundance 12+log(O/H) ∼ 8.16 ± 0.06, as well as central stellar velocity dispersion 54 ± 12 km s-1. On the star formation rate versus stellar mass diagram, these UDGs are located lower than the extrapolated star-forming main sequence from the massive spirals, but roughly follow the main sequence of low-surface-brightness dwarf galaxies. We find that these star-forming UDGs are not particularly metal-poor or metal-rich for their stellar masses, as compared with the metallicity-mass relations of the nearby typical dwarfs. With the UDG data of this work and previous studies, we also find a coarse correlation between [Fe/H] and magnesium-element enhancement [Mg/Fe] for UDGs: [Mg/Fe] ≃ -0.43(±0.26) [Fe/H] -0.14(±0.40).

Keywords: dwarf galaxies; galaxy evolution; spectroscopy
Detection and Seismic Study of Gravity and Rossby Mode Pulsations in Four Contact Binaries

We report the detection of gravity (g) and Rossby (r) mode pulsations of four short-period eclipsing binaries, KIC 5439790, KIC 7501230, KIC 9350889, and KIC 9453192 based on the 4 yr Kepler high-precision photometry. Light-curve modeling reveals that the four binaries are all contact systems with small mass ratios. We study the short-term variability of the light-curve residuals after the removal of the binary model and attribute them to the g- and r-mode pulsations that stem from the primary stars. By introducing a new criterion, we attempt to identify period-spacing patterns in the Fourier spectra, which refers to the determination of the rotation rates of stellar interior and envelope as well as the asymptotic period spacings of the pulsating stars. It is interesting to find that the rotation rates of the stellar envelopes are all nearly equal to the orbits. The near-core rotations, however, are significantly slower by about 10%. Based on the derived asymptotic period spacings, stellar parameters were constrained from asteroseismology models. The pulsators are revealed to be evolved main-sequence stars with high metallicities.

Keywords: asteroseismology; contact binary stars
The First Flight of the Marshall Grazing Incidence X-Ray Spectrometer (MaGIXS)

The Marshall Grazing Incidence X-ray Spectrometer (MaGIXS) sounding rocket experiment launched on 2021 July 30 from the White Sands Missile Range in New Mexico. MaGIXS is a unique solar observing telescope developed to capture X-ray spectral images of coronal active regions in the 6-24 Å wavelength range. Its novel design takes advantage of recent technological advances related to fabricating and optimizing X-ray optical systems, as well as breakthroughs in inversion methodologies necessary to create spectrally pure maps from overlapping spectral images. MaGIXS is the first instrument of its kind to provide spatially resolved soft X-ray spectra across a wide field of view. The plasma diagnostics available in this spectral regime make this instrument a powerful tool for probing solar coronal heating. This paper presents details from the first MaGIXS flight, the captured observations, the data processing and inversion techniques, and the first science results.

Keywords: spectroscopy; solar active regions; solar x-ray emission; solar coronal heating; solar corona; active solar corona; solar atmosphere
The Origin of the Vanishing Soft X-Ray Excess in the Changing-look Active Galactic Nucleus Mrk 590

We have studied the nature and origin of the soft X-ray excess detected in the interesting changing-look active galactic nucleus (CLAGN) Mrk 590 using two decades of multiwavelength observations from XMM-Newton, Suzaku, Swift, and NuSTAR. In light of vanishing soft excess in this CLAGN, we test two models, "the warm Comptonization" and "the ionized disk reflection," using extensive UV/X-ray spectral analysis. Our main findings are as follows: (1) the soft X-ray excess emission, last observed in 2004, vanished in 2011 and never reappeared in any of the later observations; (2) we detected a significant variability (~300%) in the observed optical-UV and power-law flux between observations with the lowest state (L bol = 4.4 × 1043 erg s-1, in 2016) and those with the highest state (L bol = 1.2 × 1044 erg s-1, in 2018); (3) the UV and power-law fluxes follow the same temporal pattern; (4) the photon index showed a significant variation ( ${\rm{\Gamma }}={1.88}_{-0.08}^{+0.02}$ and ${\rm{\Gamma }}={1.58}_{-0.03}^{+0.02}$ in 2002 and 2021, respectively) between observations; (5) no Compton hump was detected in the source spectra, but a narrow Fe Kα line is present in all observations; (6) we detected a high-energy cutoff in power-law continuum ( ${92}_{-25}^{+55}\,\mathrm{keV}$ and ${60}_{-08}^{+10}\,\mathrm{keV}$ ) with the latest NuSTAR observations; (7) the warm Comptonization model needs an additional diskbb component to describe the source UV bump; and (8) there is no correlation between the Eddington rate and the soft excess as found in other CLAGNs. We conclude that, given the spectral variability in UV/X-rays, the ionized disk reflection or the warm Comptonization models may not be adequate to describe the vanishing soft excess feature observed in Mrk 590.

Keywords: active galactic nuclei; x-ray active galactic nuclei; seyfert galaxies
Multiple Mg II Absorption Systems in the Lines of Sight to Quadruply Lensed Quasar H1413+1143

We find multiple Mg II absorption systems at redshift z = 1.66, 2.069, and 2.097 in the spatially resolved spectra of the quadruply gravitationally lensed quasar H1413+1143 utilizing the Kyoto tridimensional spectrograph II (Kyoto 3D II) spectrograph on board the Subaru telescope. Here we present the first measurement of differences in Mg II absorption strength of the multiple intervening absorbers, which include ones identified as damped Lyα (DLA) absorption systems. Our detection of the significant Mg II absorptions in the spatially resolved spectra reveals the inhomogeneous chemical enrichment on scales of about 12 kpc within the separation of the four sight lines. For the DLA system at z = 1.66, the rest equivalent widths (EWs) of the Mg II absorption lines between the four spatially resolved lines of sight change by factors of up to ~6, which trace the variations in the H I absorption strength. This suggests that inhomogeneous cold absorbers that give rise to the strong H I/Mg II absorptions dwell on a scale of about 6-12 kpc between the four lines of sight. We also investigate the degree of variation in the EW of the absorption lines between the lines of sight. We find that the systems giving rise to strong absorptions in the spectra of the quadruply lensed quasars tend to have a high degree of variation in absorption strength between the lines of sight toward the lensed quasars.

Keywords: quasar absorption line spectroscopy; galactic and extragalactic astronomy; intergalactic medium
First Constraints on Dense Molecular Gas at z = 7.5149 from the Quasar Pōniuā'ena

We report the detection of CO(6-5) and CO(7-6) and their underlying continua from the host galaxy of quasar J100758.264+211529.207 (Pōniuā'ena) at z = 7.5149, obtained with the NOrthern Extended Millimeter Array. Pōniuā'ena belongs to the HYPerluminous quasars at the Epoch of ReionizatION sample of 18 z > 6 quasars selected to be powered by supermassive black holes, which experienced the fastest mass growth in the first cosmic gigayear. The one reported here is the highest-redshift measurement of the cold and dense molecular gas to date. The host galaxy is unresolved, and the line luminosity implies a molecular reservoir of M(H2) = (2.2 ± 0.2) × 1010 M ⊙, assuming a CO spectral line energy distribution typical of high-redshift quasars and a conversion factor α = 0.8 ${M}_{\odot }{({\rm{K}}\,\mathrm{km}\,{{\rm{s}}}^{-1}\,{\mathrm{pc}}^{2})}^{-1}$ . We model the cold dust spectral energy distribution to derive a dust mass of M dust = (1.7 ± 0.6) × 108 M ⊙ and thus, a gas-to-dust ratio ~130. Both the gas and dust mass are remarkably similar to the reservoirs found for luminous quasars at z ~ 6-7. We use the CO detection to derive an estimate of the cosmic mass density of H2, ${{\rm{\Omega }}}_{{{\rm{H}}}_{2}}\simeq 1.31\times {10}^{-5}$ . This value is in line with the general trend suggested by literature estimates at z < 7 and agrees fairly well with the latest theoretical expectations of nonequilibrium molecular-chemistry cosmological simulations of cold gas at early times.

Keywords: quasars
Near-infrared Studies of Nova V1674 Herculis: A Shocking Record Breaker

We present near-infrared spectroscopy of Nova Herculis 2021 (V1674 Her), obtained over the first 70 days of its evolution. This fastest nova on record displays a rich emission line spectrum, including strong coronal line emission with complex structures. The hydrogen line fluxes, combined with a distance of ${4.7}_{-1.0}^{+1.3}$ kpc, give an upper limit to the hydrogen ejected mass of ${M}_{\mathrm{ej}}={1.4}_{-1.2}^{+0.8}\times {10}^{-3}$ M⊙. The coronal lines appeared at day 11.5, the earliest onset yet observed for any classical nova, before there was an obvious source of ionizing radiation. We argue that the gas cannot be photoionized, at least in the earliest phase, and must be shocked. Its temperature is estimated to be 105.57±0.05 K on day 11.5. Tentative analysis indicates a solar abundance of aluminum and an underabundance of calcium, relative to silicon, with respect to solar values in the ejecta. Further, we show that the vexing problem of whether collisional ionization or photoionization is responsible for coronal emission in classical novae can be resolved by correlating the temporal sequence in which the X-ray supersoft phase and the near-infrared coronal line emission appear.

Keywords: classical novae; chemical abundances; spectroscopy; explosive nucleosynthesis
Reoriented Memory of Galaxy Spins for the Early Universe

Galaxy spins are believed to retain the initially acquired tendency of being aligned with the intermediate principal axis of the linear tidal field, which disseminates the prospect of using them as a probe of early universe physics. This roseate prospect, however, is contingent upon the key assumption that the observable stellar spins of present galaxies measured at inner radii have the same alignment tendency toward the initial tidal field as their dark matter counterparts measured at virial limits. We test this assumption directly against a high-resolution hydrodynamical simulation by tracing the galaxy component particles back to the protogalactic stage. It is discovered that the galaxy stellar spins at z = 0 have strong but reoriented memory for the early universe, exhibiting a significant signal of cross-correlation with the major principal axis of the initial tidal field at z = 127. An analytic single-parameter model for this reorientation of the present galaxy stellar spins relative to the initial tidal field is devised and shown to be in good accord with the numerical results.

Keywords: cosmology; large-scale structure of the universe
Evidence of Grain Alignment by Magnetically Enhanced Radiative Torques from Multiwavelength Dust Polarization Modeling of HL Tau

The Atacama Large Millimeter/Submillimeter Array has revolutionized the field of dust polarization in protoplanetary disks across multiple wavelengths. Previous observations and empirical modeling have suggested multiple mechanisms of dust polarization toward HL Tau, including grain alignment and dust scattering. However, a detailed modeling of dust polarization based on grain alignment physics is not yet available. Here, using an updated POLARIS code, we perform numerical modeling of dust polarization arising from both grain alignment by the magnetically enhanced radiative torque mechanism and self-scattering to reproduce the HL Tau polarization observed at three wavelengths of 0.87, 1.3, and 3.1 mm. Our modeling results show that the observed multiwavelength polarization could be reproduced only when large grains contain embedded iron inclusions and those with slow internal relaxation must have wrong internal alignment (i.e., the grain's major axis parallel to its angular momentum). The abundance of iron embedded inside grains in the form of clusters is constrained to be ≳16%, and the number of iron atoms per cluster is N cl ∼ 9 × 102. Maximum grain sizes probed at wavelengths of λ = 0.87, 1.3, and 3.1 mm are constrained at ∼60, 80, and 90 μm, respectively.

Keywords: protoplanetary disks; polarimetry; radio astronomy; circumstellar dust; magnetic fields
Onset of Cosmic Reionization: Evidence of an Ionized Bubble Merely 680 Myr after the Big Bang

While most of the intergalactic medium (IGM) today is permeated by ionized hydrogen, it was largely filled with neutral hydrogen for the first 700 million years after the big bang. The process that ionized the IGM (cosmic reionization) is expected to be spatially inhomogeneous, with fainter galaxies likely playing a significant role. However, we still have only a few direct constraints on the reionization process. Here we report spectroscopic confirmation of two galaxies and very likely a third galaxy in a group (hereafter EGS77) at redshift z = 7.7, merely 680 Myr after the big bang. The physical separation among the three members is <0.7 Mpc. We estimate the radius of ionized bubble of the brightest galaxy to be about 1.02 Mpc, and show that the individual ionized bubbles formed by all three galaxies likely overlap significantly, forming a large yet localized ionized region, indicative of inhomogeneity in the reionization process. It is striking that two of three galaxies in EGS77 are quite faint in the continuum, thanks to our selection using their Lyα line emission in the narrowband filter. Indeed, one is the faintest spectroscopically confirmed galaxy yet discovered at such high redshifts. Our observations provide direct constraints on the process of cosmic reionization, and allow us to investigate the properties of sources responsible for reionizing the universe.

Keywords: reionization; early universe; high-redshift galaxies; lyman-alpha galaxies; galaxy groups; intergalactic medium
The Population of Massive Stars in Active Galactic Nuclei Disks

Gravitational instability in the outskirts of active galactic nuclei (AGN) disks leads to disk fragmentation and formation of ∼300 M ⊙ supermassive stars with potentially long lifetimes. Alternatively, stars can be captured ex situ and grow from gas accretion in the AGN disk. However, the number density distribution throughout the disk is limited by thermal feedback as their luminosities provide the dominant heating source. We derive equilibrium stellar surface density profiles under two limiting contexts: in the case where the stellar lifetimes are prolonged, due to the recycling of hydrogen-rich disk gas, only the fraction of gas converted into heat is removed from the disk accretion flow. Alternatively, if stellar composition recycling is inefficient and stars can evolve off the main sequence, the disk accretion rate is quenched toward smaller radii resembling a classical starburst disk, albeit the effective removal rate depends not only on the stellar lifetime, but also the mass of stellar remnants. For AGNs with central supermassive black hole masses of ∼106–108 M ⊙ accreting at ∼0.1 Eddington efficiency, we estimate a total number of 103–105 massive stars and the rate of stellar mergers to be 10‑3 to 1 yr‑1. We initiate the detailed study of the interaction between a swarm of massive stars through hydro and N-body simulations to provide better prescriptions of dynamical processes in AGN disks, and to constrain more accurate estimates of the stellar population.

Keywords: active galactic nuclei; galaxy accretion disks; massive stars; stellar mergers; stellar evolution
Untangling the Galaxy. IV. Empirical Constraints on Angular Momentum Evolution and Gyrochronology for Young Stars in the Field

We present a catalog of ~100,000 periodic variable stars in Transiting Exoplanet Survey Satellite (TESS) full-frame image data among members of widely distributed moving groups identified with Gaia in the previous papers in the series. By combining the periods from our catalog attributable to rotation with previously derived rotation periods for benchmark open clusters, we develop an empirical gyrochronology relation of angular momentum evolution that is valid for stars with ages 10-1000 Myr. Excluding stars rotating faster than 2 days, which we find are predominantly binaries, we achieve a typical age precision of ≈0.2-0.3 dex and improving at older ages. Importantly, these empirical relations apply to not only FGK-type stars but also M-type stars, due to the angular momentum distribution being much smoother, simpler, continuous, and monotonic as compared to the rotation period distribution. As a result, we are also able to begin tracing in fine detail the nature of angular momentum loss in low-mass stars as functions of mass and age. We characterize the stellar variability amplitudes of the cool stars as functions of mass and age, which may correlate with the starspot covering fractions. We also identify pulsating variables among the hotter stars in the catalog, including δ Scuti, γ Dor, and slowly pulsating B-type variables. These data represent an important step forward in being able to estimate precise ages of FGK- and M-type stars in the field, starting as early as the pre-main-sequence phase of evolution.

Keywords: variable stars; stellar rotation; intrinsic variable stars; pulsating variable stars; stellar populations
The Ultraluminous Lyα Luminosity Function at z = 6.6

We present the luminosity function (LF) for ultraluminous Lyα emitting galaxies (LAEs) at z = 6.6. We define ultraluminous LAEs (ULLAEs) as galaxies with $\mathrm{log}L(\mathrm{Ly}\alpha )\gt 43.5$ erg s-1. We select our main sample using the g', r', I', z', and NB921 observations of a wide-area (30 deg2) Hyper Suprime-Cam survey of the north ecliptic pole (NEP) field. We select candidates with $g^{\prime} ,r^{\prime} ,I^{\prime} \gt 26$ , NB921 ≤ 23.5, and $\mathrm{NB}921-z^{\prime} \leqslant 1.3$ . Using the DEIMOS spectrograph on Keck II, we confirm 9 of our 14 candidates as ULLAEs at z = 6.6 and the remaining 5 as an active galactic nucleus at z = 6.6, two [O III]λ5007 emitting galaxies at z = 0.84 and z = 0.85, and two nondetections. This emphasizes the need for full spectroscopic follow-up to determine accurate LFs. In constructing the ULLAE LF at z = 6.6, we combine our nine NEP ULLAEs with two previously discovered and confirmed ULLAEs in the COSMOS field: CR7 and COLA1. We apply rigorous corrections for incompleteness based on simulations. We compare our ULLAE LF at z = 6.6 with LFs at z = 5.7 and z = 6.6 from the literature. Our data reject some previous LF normalizations and power-law indices, but they are broadly consistent with others. Indeed, a comparative analysis of the different literature LFs suggests that no LF is fully consistent with any of the others, making it critical to determine the evolution from z = 5.7 to z = 6.6 using LFs constructed in exactly the same way at both redshifts.

Keywords: emission line galaxies; lyman-alpha galaxies; observational cosmology; high-redshift galaxies
NOEMA High-fidelity Imaging of the Molecular Gas in and around M82

We present a 154 pointing IRAM NOEMA mosaic of the CO(1-0) line emission in and around the nearby starburst galaxy M82. The observations, complemented by zero-spacing observations, reach a spatial resolution of ~30 pc (~1"9) at 5.0 km s-1 spectral resolution, sufficient to resolve the molecular gas in the central starburst disk, the outflow, and the tidal streamers. The resulting moment and peak brightness maps show a striking amount of structure. Using a clump decomposition algorithm, we analyze the physical properties (e.g., radii R, line widths σ, and masses M) of ~2000 molecular clouds. To first order, the clouds' properties are very similar, irrespective of their environment. This also holds for the size-line width relations of the clouds. The distribution of clouds in the σ2/R versus column density Σ space suggests that external pressure does not play a significant role in setting their physical parameters in the outflow and streamers. We find that the clouds in the streamers stay approximately constant in size (R ~ 50 pc) and mass (M ~ 105 M⊙) and do not vary with their projected distance from M82's center. The clouds in the outflow, on the other hand, appear to decrease in size and mass with distance toward the southern outflow. The reduction in the molecular gas luminosity could be indicative of cloud evaporation of embedded clouds in the hot outflow.

Keywords: molecular gas; molecular clouds; tidal tails; galactic winds; interstellar medium; starburst galaxies
The Evolution of the Luminosity Function for Luminous Compact Blue Galaxies to z = 1

Luminous compact blue galaxies (LCBGs) are compact, star-forming galaxies that are rarely observed in the local universe but abundant at z = 1. This increase in LCBG number density over cosmic lookback time roughly follows the increase in the star formation rate density of the universe over the same period. We use publicly available data in the COSMOS field to study the evolution of the largest homogeneous sample of LCBGs to date by deriving their luminosity function in four redshift bins over the range 0.1 ≤ z ≤ 1. We find that over this redshift range, the characteristic luminosity (M*) increases by ∼0.2 mag, and the number density increases by a factor of 4. While LCBGs make up only about 18% of galaxies more luminous than MB = -18.5 at z ∼ 0.2, they constitute roughly 54% at z ∼ 0.9. The strong evolution in number density indicates that LCBGs are an important population of galaxies to study in order to better understand the decrease in the star formation rate density of the universe since z ∼ 1.

Keywords: galaxy evolution
Determination of the Abundance of Mercury from the Hg II Line at 5677.10 Å in Late B-type Stars. IV. HD 149121 (28 Her) and HD 178065

The weak line of Hg II located at 5677.10 Å is used to measure the mercury abundance in two HgMn stars, HD 149121 (28 Her) and HD 178065. This line is detected at 3σ above the noise in the adjacent continuum in both stars. The synthesis of this line confirms a large overabundance of mercury, about +4.57 dex in HD 149121, and +3.70 dex in HD 178065, which is less than the excesses derived from the 3983.93 Å line in earlier studies. The presence of previously reported weak emission lines of Ti II at 6106.50 Å and of Cr II at 6158.62 and 6182.30 Å in the spectrum of HD 178065 is confirmed. The synthesis of other lines close to the Hg II line yields estimates of the abundance deficiencies or excesses relative to solar abundances. Oxygen has a solar abundance (0.00 dex), silicon is deficient (‑0.48 dex), iron also (‑0.22 dex) and chromium is overabundant in HD 178065.

Keywords: chemically peculiar stars; mercury-manganese stars