adsabs/SciX_UAT_keywords huggingface dataset:
The Lyman Continuum Escape Survey. II. Ionizing Radiation as a Function of the [O III]/[O II] Line Ratio

We discuss the rest-frame optical emission line spectra of a large (∼50) sample of z ∼ 3.1 Lyα emitting galaxies (LAEs) whose physical properties suggest such sources are promising analogs of galaxies in the reionization era. Reliable Lyman continuum (LyC) escape fractions have now been determined for a large sample of such LAEs from the LymAn Continuum Escape Survey (LACES) undertaken via deep Hubble Space Telescope imaging in the SSA22 survey area reported in Fletcher et al. Using new measures of [O II] emission secured from Keck MOSFIRE spectra we re-examine, for a larger sample, earlier claims that LyC leakages may correlate with the nebular emission line ratio [O III]/[O II] as expected for density-bound H II regions. We find that a large [O III]/[O II] line ratio is indeed a necessary condition for LyC leakage, strengthening earlier claims made using smaller samples at various redshifts. However, not all LAEs with large [O III]/[O II] line ratios are leakers and leaking radiation appears not to be associated with differences in other spectral diagnostics. This suggests the detection of leaking radiation is modulated by an additional property, possibly the viewing angle for porous H II regions. We discuss our new results in the context of the striking bimodality of LAE leakers and non-leakers found in the LACES program and the implications for the sources of cosmic reionization.

Keywords: high-redshift galaxies; reionization; galaxy evolution
The Circumnuclear Disk Revealed by ALMA. I. Dense Clouds and Tides in the Galactic Center

Utilizing the Atacama Large Millimeter/submillimeter Array, we present CS line maps in five rotational lines (Ju = 7, 5, 4, 3, 2) toward the circumnuclear disk (CND) and streamers of the Galactic center. Our primary goal is to resolve the compact structures within the CND and the streamers, in order to understand the stability conditions of molecular cores in the vicinity of the supermassive black hole (SMBH) Sgr A*. Our data provide the first homogeneous high-resolution (1"3 = 0.05 pc) observations aiming at resolving density and temperature structures. The CS clouds have sizes of 0.05-0.2 pc with a broad range of velocity dispersion (σFWHM = 5-40 km s-1). The CS clouds are a mixture of warm (Tk ≥ 50-500 K, ${n}_{{{\rm{H}}}_{2}}$ = 103-105 cm-3) and cold gas (Tk ≤ 50 K, ${n}_{{{\rm{H}}}_{2}}$ = 106-108 cm-3). A stability analysis based on the unmagnetized virial theorem including tidal force shows that ${84}_{-37}^{+16} \% $ of the total gas mass is tidally stable, which accounts for the majority of gas mass. Turbulence dominates the internal energy and thereby sets the threshold densities 10-100 times higher than the tidal limit at distance ≥1.5 pc to Sgr A*, and therefore it inhibits the clouds from collapsing to form stars near the SMBH. However, within the central 1 pc, the tidal force overrides turbulence and the threshold densities for a gravitational collapse quickly grow to ≥ 108 cm-3.

Keywords: galactic center; interstellar molecules; radio interferometers
Correlated Read Noise Reduction in Infrared Arrays Using Deep Learning

We present a new procedure rooted in deep learning to construct science images from data cubes collected by astronomical instruments using HxRG detectors in low-flux regimes. It improves on the drawbacks of the conventional algorithms to construct 2D images from multiple readouts by using the readout scheme of the detectors to reduce the impact of correlated readout noise. We train a convolutional recurrent neural network on simulated astrophysical scenes added to laboratory darks to estimate the flux on each pixel of science images. This method achieves a reduction of the noise on constructed science images when compared to standard flux-measurement schemes (correlated double sampling, up-the-ramp sampling), which results in a reduction of the error on the spectrum extracted from these science images. Over simulated data cubes created in a low signal-to-noise ratio regime where this method could have the largest impact, we find that the error on our constructed science images falls faster than a $1/\sqrt{N}$ decay, and that the spectrum extracted from the images has, averaged over a test set of three images, a standard error reduced by a factor of 1.85 in comparison to the standard up-the-ramp pixel sampling scheme. The code used in this project is publicly available on GitHub 7 7 https://github.com/GuillaumePayeur/HxRG-denoiser

Keywords: astronomy data reduction; near infrared astronomy; neural networks; astronomical detectors
Are Electric-field-driven Magnetohydrodynamic Simulations of the Solar Corona Sensitive to the Initial Condition?

Magnetohydrodynamic (MHD) simulations of the solar corona are often started from a potential field initial condition, which may be far from the true state of the coronal magnetic field. To test the sensitivity of the simulations to the initial condition, an electric-field-driven MHD code was initiated from three different initial conditions: the commonly used potential field, a nonlinear force-free field (NLFFF) extrapolation, which is believed to be a better representation of the true coronal magnetic field, and a purely vertical field. After relaxation, the magnetic field in the MHD simulations was compared. It was found that there is a tendency for all of the initial conditions to converge to a similar connectivity, particularly in areas of strong fields that are not close to the boundary, suggesting that the final state of the simulation is not particularly sensitive to the initial condition. The relaxed solution more closely resembles the NLFFF initial condition than the other initial conditions, but still exhibits substantial differences from it.

Keywords: magnetohydrodynamical simulations; solar corona; solar magnetic fields
UV Cooling via O VI Emission in the Superwind of M82 Observed with the Far Ultraviolet Spectroscopic Explorer (FUSE)

We examined archival Far Ultraviolet Spectroscopic Explorer data to search for far-ultraviolet emission lines in the starburst galaxy M82. The observations were made in an outflow region that extends beyond the galactic disk. We found the O VI λ λ 1032, 1038 emission lines from the galaxy's southern outflow region. The O VI lines suggest that the outflowing warm-hot gas is undergoing radiative cooling. We measured a radial velocity of ∼420 km s‑1 from the O VI lines, which is faster than the velocity seen in Hα observations. The O VI λ1038 emission line seems to be blended with the C II λ1037 emission line, which has a radial velocity of ∼300 km s‑1, similar to what is observed in Hα observations. The outflow medium of M82 appears to be composed of gas in multiple phases with varying temperatures and kinematics. Future spectroscopic observations in high energy regimes covering a wider spatial area are necessary to understand better the properties of the warm-hot gas medium in the outflow.

Keywords: ultraviolet spectroscopy; galaxies; starburst galaxies; circumgalactic medium; extragalactic astronomy
Effect of Transverse Magnetic Field on Kelvin–Helmholtz Instability in the Presence of a Radiation Field

The dispersion relation of the magnetized Kelvin–Helmholtz (KH) instability driven by shear flow with zero thickness of the shear layer is derived theoretically based on a set of magnetohydrodynamic equations in the presence of a transverse magnetic field and a radiation field. The influence of the magnetic field strength, the radiation field strength, and the density ratio of the two sides of the shear layer on KH instability is analyzed by solving the dispersion equation. The results indicate that the presence of radiation and transverse magnetic fields can destabilize the KH instability due to the resulting increase in Mach number, which in turn reduces the compressibility of the system. Also, the extent of the destabilizing effect of the magnetic field can be affected by the magnetoacoustic Mach number M 1f and the Mach number M 2. The growth rates vary more significantly for relatively small values of both parameters. Finally, the stabilizing effect of a large density ratio is considered, and it is found that as the density ratio increases, the effect of the radiation field is more significant at larger Mach number M 2. These results can be applied to astrophysical phenomena with velocity shear, such as flows across the transition layer between an H II region and a molecular cloud, accretion flows, and shear flows of cosmic plasmas.

Keywords: star clusters; radiative magnetohydrodynamics; magnetohydrodynamics; astrophysical fluid dynamics; hydrodynamics
Evidence of Third Dredge-up in Post-AGB Stars in Galactic Globular Clusters

To better understand the mixing and mass loss experienced by low-mass stars as they ascend the asymptotic giant branch (AGB), I have gathered from the literature the abundances of CNO and s-process elements in post-AGB stars in Galactic globular clusters. These species are mixed to the surface during third dredge-up (3DU) events, so their abundance should increase as the star ascends the AGB. Of the 17 stars in this sample, CNO abundances are available for 11. Of these, four are enhanced in CNO relative to the red giant branch stars from which they descended, which I take as evidence of 3DU on the AGB. The enhancement is mainly in the form of carbon. Of the six stars for which only heavy-element abundances are available, one shows s-process enhancements that previous authors have interpreted as evidence of 3DU. Combining these 17 stars with other recent samples reveals that most globular-cluster post-AGB stars have luminosities $\mathrm{log}(L/{L}_{\odot })\sim 3.25$ . They are the progeny of blue horizontal-branch (HB) stars in clusters with intermediate metallicity ([Fe/H] ~ -1.5). A second group consists of sub-luminous stars associated with high-metallicity clusters ([Fe/H] ~ -1.0) with red HBs. They may be burning helium, rather than hydrogen. A third group of hot, super-luminous stars is evolving quickly across the Hertzsprung-Russell diagram. Some of them may be merger remnants.

Keywords: stellar abundances; asymptotic giant branch stars; post-asymptotic giant branch stars; stellar atmospheres
Multifluid MHD Studies of the Ionospheric Magnetic Flux Ropes at Mars

We use a multifluid MHD model to study the formation of the small-scale magnetic flux rope (MFR) in the ionosphere of Mars. It is found that a straight flux tube can turn into a twisted MFR during its sinking into the lower ionosphere, caused by the differential compression at different parts of the tube. Further studies show that the MFR is not a force-free structure, in which there is always a pressure gradient force to balance the magnetic force. Moreover, we find that the ionospheric ions inside the MFR can be squeezed out from the two ends of the MFR, with an outflow flux of about 3.5 × 107 cm-2 s-1, which can play an important role for the ion escape from Mars. In addition, we find that both the sinking speed and the ratio of the ion gyroradius to the tube radius can affect the characteristics of MFR. An MFR can be more quickly formed for a larger sinking speed, but it can be also more quickly filled by the ambient ions. Oppositely, the MFR is more difficult to be filled when the ratio of the ion gyroradius to the tube radius is smaller. Once the MFR is filled, the compression is prevented by an outward pressure gradient force, and both the field strength and the rope helicity begin to decrease. Our results can explain the different altitude dependences of MFRs observed at Mars and Venus.

Keywords: space plasmas; planetary magnetospheres
Estimating the Convective Turnover Time

The introduction of the Rossby number (R0), which incorporates the convective turnover time (τ), in 1984 was a pioneering idea for understanding the correlation between stellar rotation and activity. The convective turnover time, which cannot be measured directly, is often inferred using existing τ-mass or τ-color relations, typically established based on an ensemble of different types of stars by assuming that τ is a function of mass. In this work, we use Gaia Early Data Release 3 to demonstrate that the masses used to establish one of the most cited τ-mass relations are overestimated for G-type dwarfs and significantly underestimated for late M dwarfs, offsets that affect studies using this τ-mass relation to draw conclusions. We discuss the challenges of creating such relations then and now. In the era of Gaia and other large data sets, stars used to establish these relations require characterization in a multidimensional space, rather than via the single-characteristic relations of the past. We propose that new multidimensional relations should be established based on updated theoretical models and all available stellar parameters for different interior structures from a set of carefully vetted single stars, so that the convective turnover time can be estimated more accurately.

Keywords: hertzsprung russell diagram; m dwarf stars; stellar activity
A Radio Technosignature Search of Six Resonant Sub-Neptunes Orbiting HD 110067

We describe archival observations and analysis of the HD 110067 planetary system using the Green Bank Telescope (GBT) as part of the Breakthrough Listen search for technosignatures. The star hosts six sub-Neptune planets in resonant orbits, and we tune the drift rate range of our search to match the properties of the system derived by Luque et al. Our observations cover frequencies from 1 to 11.2 GHz, using the GBT's L, S, C, and X-band receivers, to an equivalent isotropic radiated power limit of ∼3 × 1012 W. No technosignatures were found, but this unusual system remains an interesting target for future technosignature searches.

Keywords: exoplanets; technosignatures; search for extraterrestrial intelligence; radio astronomy
The Q Branch Cooling Anomaly Can Be Explained by Mergers of White Dwarfs and Subgiant Stars

Gaia's exquisite parallax measurements allowed for the discovery and characterization of the Q branch in the Hertzsprung-Russell diagram, where massive C/O white dwarfs (WDs) pause their dimming due to energy released during crystallization. Interestingly, the fraction of old stars on the Q branch is significantly higher than in the population of WDs that will become Q branch stars or that were Q branch stars in the past. From this, Cheng et al. inferred that ~6% of WDs passing through the Q branch experience a much longer cooling delay than that of standard crystallizing WDs. Previous attempts to explain this cooling anomaly have invoked mechanisms involving supersolar initial metallicities. In this paper, we describe a novel scenario in which a standard composition WD merges with a subgiant star. The evolution of the resulting merger remnant leads to the creation of a large amount of 26Mg, which, along with the existing 22Ne, undergoes a distillation process that can release enough energy to explain the Q branch cooling problem without the need for atypical initial abundances. The anomalously high number of old stars on the Q branch may thus be evidence that mass transfer from subgiants to WDs leads to unstable mergers.

Keywords: binary stars; cosmochronology; nucleosynthesis; white dwarf stars
Physical Properties of the Young Asteroid Pair 2010 UM26 and 2010 RN221

The main belt asteroids 458271 (2010 UM26) and 2010 RN221 share almost identical orbital elements, and currently appear as comoving objects ~30″ apart in the plane of the sky. They are products of the breakup of a parent object, or the splitting of a binary, with a separation age measured in decades rather than thousands or millions of years as for most other asteroid pairs. The nature of the precursor body and the details of the breakup and separation of the components are unknown. We obtained deep, high-resolution imaging using the Hubble Space Telescope to characterize the pair and to search for material in addition to the main components that might have been released upon breakup. The primary and secondary have absolute magnitudes H = 17.98 and 19.69, respectively, and effective diameters 760 and 350 m (assuming geometric albedo 0.20). The secondary/primary mass ratio is 0.1, assuming equal densities. Time-series photometry shows that the primary rotates with period ~5.9 hr and has a small photometric range (0.15 mag), while the period of the secondary is undetermined (but ≳20 hr) and its lightcurve range is at least 1 mag. The primary rotation period and component mass ratio are consistent with a simple model for the breakup of a rotationally unstable precursor. However, unlike other observationally supported instances of asteroid breakup, neither macroscopic fragments nor unresolved material are found remaining in the vicinity of this asteroid pair. We suggest that the pair is a recently dissociated binary, itself formed earlier by rotational instability of 2010 UM26.

Keywords: asteroids; asteroid rotation; asteroid satellites
ALMA Measures Rapidly Depleted Molecular Gas Reservoirs in Massive Quiescent Galaxies at z ∼ 1.5

We present Atacama Large Millimeter/submillimeter Array (ALMA) CO(2-1) spectroscopy of six massive (log10 ${M}_{* }$ / ${M}_{\odot }$ > 11.3) quiescent galaxies at z ∼ 1.5. These data represent the largest sample using CO emission to trace molecular gas in quiescent galaxies above z > 1, achieving an average 3σ sensitivity of ${M}_{{{\rm{H}}}_{2}}$ ∼ 1010 ${M}_{\odot }$ . We detect one galaxy at 4σ significance and place upper limits on the molecular gas reservoirs of the other five, finding molecular gas mass fractions ${M}_{{{\rm{H}}}_{2}}/{M}_{* }={f}_{{{\rm{H}}}_{2}}\lt 2 \% \mbox{--}6 \% $ (3σ upper limits). This is 1-2 orders of magnitude lower than coeval star-forming galaxies at similar stellar mass, and comparable to galaxies at z = 0 with similarly low specific star formation rate (sSFR). This indicates that their molecular gas reservoirs were rapidly and efficiently used up or destroyed, and that gas fractions are uniformly low (<6%) despite the structural diversity of our sample. The implied rapid depletion time of molecular gas ( ${t}_{\mathrm{dep}}$ < 0.6 Gyr) disagrees with extrapolations of empirical scaling relations to low sSFR. We find that our low gas fractions are instead in agreement with predictions from both the recent SIMBA cosmological simulation, and from analytical "bathtub" models for gas accretion onto galaxies in massive dark matter halos (log ${}_{10}{M}_{\mathrm{halo}}/{M}_{\odot }\sim 14$ at z = 0). Such high mass halos reach a critical mass of log ${}_{10}{M}_{\mathrm{halo}}/{M}_{\odot }\gt 12$ by z ∼ 4 that halt the accretion of baryons early in the universe. Our data are consistent with a simple picture where galaxies truncate accretion and then consume the existing gas at or faster than typical main-sequence rates. Alternatively, we cannot rule out that these galaxies reside in lower mass halos, and low gas fractions may instead reflect either stronger feedback, or more efficient gas consumption.

Keywords: galaxy evolution; galaxy quenching; quenched galaxies; molecular gas; co line emission; galaxy formation; high-redshift galaxies; compact galaxies; early-type galaxies
Black Hole Mass Measurements of Early-type Galaxies NGC 1380 and NGC 6861 through ALMA and HST Observations and Gas-dynamical Modeling

We present Atacama Large Millimeter/submillimeter Array (ALMA) Cycle 2 observations of CO(2-1) emission from the circumnuclear disks in two early-type galaxies, NGC 1380 and NGC 6861. The disk in each galaxy is highly inclined (i ~ 75°), and the projected velocities of the molecular gas near the galaxy centers are ~300 km s-1 in NGC 1380 and ~500 km s-1 in NGC 6861. We fit thin disk dynamical models to the ALMA data cubes to constrain the masses of the central black holes (BHs). We created host galaxy models using Hubble Space Telescope images for the extended stellar mass distributions and incorporated a range of plausible central dust extinction values. For NGC 1380, our best-fit model yields M BH = 1.47 × 108 M ⊙ with a ~40% uncertainty. For NGC 6861, the lack of dynamical tracers within the BH's sphere of influence due to a central hole in the gas distribution precludes a precise measurement of M BH. However, our model fits require a value for M BH in the range of (1-3) × 109 M ⊙ in NGC 6861 to reproduce the observations. The BH masses are generally consistent with predictions from local BH-host galaxy scaling relations. Systematic uncertainties associated with dust extinction of the host galaxy light and choice of host galaxy mass model dominate the error budget of both measurements. Despite these limitations, the measurements demonstrate ALMA's ability to provide constraints on BH masses in cases where the BH's projected radius of influence is marginally resolved or the gas distribution has a central hole. * Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. These observations are associated with programs 15226 and 11712.

Keywords: lenticular galaxies; elliptical galaxies; supermassive black holes
Ultradiffuse Galaxies (UDGs) with Hyper Suprime-Cam. I. Revised Catalog of Coma Cluster UDGs

This is the first in a series of papers on the properties of ultradiffuse galaxies (UDGs) in clusters of galaxies. We present an updated catalog of UDGs in the Coma Cluster using g- and r-band images obtained with Hyper Suprime-Cam (HSC) of the Subaru telescope. We develop a method to find UDGs even in the presence of contaminating objects, such as halos and background galaxies. This study expands upon our previous works that covered about half the area of the Coma Cluster. The HSC observations covered the whole Coma Cluster up to the virial radius and beyond (an area twice as large as the previous studies) and doubled the numbers of UDGs (r eff, r ≥ 1.5 kpc) and sub-UDGs (1.0 ≤ r eff, r < 1.5 kpc) to 774 and 729, respectively. The new UDGs show internal properties consistent with those of previous studies (e.g., a Sérsic index of approximately 1), and are distributed across the cluster, with a concentration around the cluster center. The whole cluster coverage clearly revealed an excess of their distribution toward the east to southwest direction along the cluster center, where Coma connects to other large-scale structure, and where a known substructure exists (the NGC 4839 subgroup). The alignment of the UDG distribution along the large-scale structure around Coma supports the interpretation that most of them lie at the distance of the Coma Cluster and the NGC 4839 subgroup. * This research is based on data collected at the Subaru Telescope, which is operated by the National Astronomical Observatory of Japan. We are honored and grateful for the opportunity of observing the universe from Maunakea, which has cultural, historical, and natural significance in Hawaii.

Keywords: low surface brightness galaxies; galaxies; galactic and extragalactic astronomy; galaxy clusters; coma cluster; galaxy structure