Sazuna/UAT_keywords huggingface dataset:
The Chemical Structure of Young High-mass Star-forming Clumps. II. Parsec-scale CO Depletion and Deuterium Fraction of HCO<SUP>+</SUP>. The physical and chemical properties of cold and dense molecular clouds are key to understanding how stars form. Using the IRAM 30 m and NRO 45 m telescopes, we carried out a Multiwavelength line-Imaging survey of the 70 μm-dArk and bright clOuds (MIAO). At a linear resolution of 0.1-0.5 pc, this work presents a detailed study of parsec-scale CO depletion and HCO+ deuterium (D-) fractionation toward four sources (G11.38+0.81, G15.22-0.43, G14.49-0.13, and G34.74-0.12) included in our full sample. In each source with T &lt; 20 K and nH ∼ 104-105 cm-3, we compared pairs of neighboring 70 μm bright and dark clumps and found that (1) the H2 column density and dust temperature of each source show strong spatial anticorrelation; (2) the spatial distribution of CO isotopologue lines and dense gas tracers, such as 1-0 lines of H13CO+ and DCO+, are anticorrelated; (3) the abundance ratio between C18O and DCO+ shows a strong correlation with the source temperature; (4) both the C18O depletion factor and D-fraction of HCO+ show a robust decrease from younger clumps to more evolved clumps by a factor of more than 3; and (5) preliminary chemical modeling indicates that chemical ages of our sources are ∼8 × 104 yr, which is comparable to their free-fall timescales and smaller than their contraction timescales, indicating that our sources are likely dynamically and chemically young.

Keywords: Interstellar molecules, Massive stars, Astrochemistry, Star formation, Interstellar medium
Horizontal Shear Instabilities at Low Prandtl Number. Turbulent mixing in the radiative regions of stars is usually either ignored or crudely accounted for in most stellar evolution models. However, there is growing evidence that such mixing is present and can affect various aspects of a star's life. Here, we present a first attempt at quantifying mixing by horizontal shear instabilities in stars using direct numerical simulations. The shear is driven by a body force, and rapidly becomes unstable. At saturation, we find that several distinct dynamical regimes exist, depending on the relative importance of stratification and thermal diffusion. In each of the regimes identified, we propose a certain number of theoretically motivated scaling laws for the turbulent vertical eddy scale, the turbulent diffusion coefficient, and the amplitude of temperature fluctuations (among other quantities). Based on our findings, we predict that the majority of stars should fall into one of two categories: high Péclet number stratified turbulence, and low Péclet number stratified turbulence. The latter is presented in a related paper by Cope et al., while the former is discussed here. Applying our results to the solar tachocline, we find that it should lie in the high Péclet number stratified turbulence regime, and predict a substantial amount of vertical mixing for temperature, momentum, and composition. Taken as is, the new turbulence model predictions are incompatible with the Spiegel &amp; Zahn model of the solar tachocline. However, rotation and magnetic fields are likely to affect the turbulence, and need to be taken into account in future studies.

Keywords: Hydrodynamical simulations, Stellar processes, Solar rotation, Hydrodynamics, Stellar physics, Stellar rotation, Astrophysical fluid dynamics, Stellar evolution
Localized Reconnection Heating Inferred from the Three-dimensional Locations of Bright Active Region Coronal Loops. Coronal loops observed in soft X-rays and extreme ultraviolet imaging data offer direct evidence that coronal plasma is heated by some mechanism. That mechanism appears to energize a particular bundle of field lines somehow selected from the magnetized coronal volume. Magnetic reconnection localized to a patch within a coronal current sheet is one mechanism that would select a flux bundle at the same time it energized it. Since magnetic reconnection occurs preferentially at topological boundaries, we would expect to find coronal loops concentrated there if it were at work. We explore this hypothesis using a data set, previously compiled by McCarthy et al., consisting of 301 coronal loops interconnecting a pair of active regions over a 48 hr period. That work computed the three-dimensional geometries and magnetic field strengths for most of the loops. This revealed many bright loops lying at the periphery of the interconnecting flux domain, possibly created and energized by the reconnection that created the interconnecting flux. There were, however, many loops well inside the domain which would be difficult to attribute to that mode of reconnection. Here we use detailed magnetic models of the interconnecting domain to show that these internal loops tend to occur along internal boundaries: separatrices. This offers a novel form of evidence that coronal loops are the products of patchy reconnection even under quiescent conditions.

Keywords: Solar coronal loops
Observations and Modeling of the Onset of Fast Reconnection in the Solar Transition Region. Magnetic reconnection is a fundamental plasma process that plays a critical role not only in energy release in the solar atmosphere, but also in fusion, astrophysics, and other space plasma environments. One of the challenges in explaining solar observations in which reconnection is thought to play a critical role is to account for the transition of the dynamics from a slow quasi-continuous phase to a fast and impulsive energetic burst of much shorter duration. Despite the theoretical progress in identifying mechanisms that might lead to rapid onset, a lack of observations of this transition has left models poorly constrained. High-resolution spectroscopic observations from NASA's Interface Region Imaging Spectrograph now reveal tell-tale signatures of the abrupt transition of reconnection from a slow phase to a fast, impulsive phase during UV bursts or explosive events in the Sun's atmosphere. Our observations are consistent with numerical simulations of the plasmoid instability, and provide evidence for the onset of fast reconnection mediated by plasmoids and new opportunities for remote-sensing diagnostics of reconnection mechanisms on the Sun.

Keywords: Solar magnetic fields, Solar chromosphere, Solar magnetic reconnection, Solar transition region
Radiation and Polarization Signatures from Magnetic Reconnection in Relativistic Jets. I. A Systematic Study. Blazars are relativistic magnetized plasma outflows from supermassive black holes that point very close to our line of sight. Their emission is nonthermal-dominated and highly variable across the entire electromagnetic spectrum. Relativistic magnetic reconnection has been proposed as the driver of particle acceleration during blazar flares. While recent particle-in-cell (PIC) simulations have self-consistently studied the evolution of magnetic reconnection and particle acceleration therein, the resulting radiation signatures have not been systematically explored. In particular, the polarization signatures, which directly reflect the characteristic strongly dynamical evolution of magnetic field during reconnection, have not been carefully investigated. In this paper, we present a systematic study of radiation and polarization signatures arising from magnetic reconnection in blazars, based on combined PIC and polarized radiation transfer simulations with various physical parameters. We identify a harder-when-brighter trend in the spectral evolution. Moreover, higher-frequency bands (ultraviolet to X-ray) tend to flare earlier than lower-frequency bands (infrared to optical) in the synchrotron spectral component. Most importantly, polarization signatures appear more variable with higher frequencies. We find that the variation in temporal polarization depends strongly on the guide field strength. Specifically, reconnection with a significant guide field component leads to a very high polarization degree that contradicts typical blazar observations, while large polarization angle rotations are unique signatures of magnetic reconnection between nearly antiparallel magnetic field lines. These rotations are at least 90° and can extend to &gt;180°, and they may be in either direction. These results imply that blazars that have shown large polarization angle rotations intrinsically have more nearly antiparallel magnetic field morphology.

Keywords: Jets, Blazars, Active galactic nuclei, Non-thermal radiation sources, Polarimetry
The Effect of Solar Wind Expansion and Nonequilibrium Ionization on the Broadening of Coronal Emission Lines. When observing spectral lines in the optically thin corona, line-of-sight (LOS) effects can strongly affect the interpretation of the data, especially in regions just above the limb. We present a semiempirical forward model, called the Global Heliospheric Optically thin Spectral Transport Simulation (GHOSTS), to characterize these effects. GHOSTS uses inputs from several other models to compute nonequilibrium ionization states (which include the solar-wind freezing-in effect) for many ions. These are used to generate ensembles of simulated spectral lines that are examined in detail, with emphasis on (1) relationships between quantities derived from observables and the radial variation of the observed quantities, (2) the behavior of thermal and nonthermal components of the line width, and (3) relative contributions of collisionally excited and radiatively scattered photons. We find that rapidly changing temperatures in the low corona can cause ion populations to vary dramatically with height. This can lead to line width measurements that are constant with height (a "plateau" effect) even when the temperature is increasing rapidly, as the plane of sky becomes evacuated and the foreground/background plasma dominates the observation. We find that LOS effects often drive the velocity width to be close to the plane-of-sky value of the wind speed, despite it flowing perpendicularly to the LOS there. The plateau effect can also cause the nonthermal component of the line width to greatly exceed the solar wind velocity at the observation height. Lastly, we study how much of the LOS is significant to the observation, and the importance of including continuum in the solar spectrum when computing the radiatively scattered emission.

Keywords: Solar ultraviolet emission, Solar wind, Solar coronal holes, Spectroscopy, Ionization, Radiative transfer simulations
Molecular Gas Outflow in the Starburst Galaxy NGC 1482. Galactic winds are essential to the regulation of star formation in galaxies. To study the distribution and dynamics of molecular gas in wind, we imaged the nearby starburst galaxy NGC 1482 in CO (J = 1 → 0) at a resolution of 1″ (≈100 pc) using the Atacama Large Millimeter/submillimeter Array. Molecular gas is detected in a nearly edge-on disk with a radius of 3 kpc and a biconical outflow emerging from the central 1 kpc starburst and extending to at least 1.5 kpc perpendicular to the disk. In the outflow, CO gas is distributed approximately as a cylindrically symmetrical envelope surrounding the warm and hot ionized gas traced by Hα and soft X-rays. The velocity, mass outflow rate, and kinetic energy of the molecular outflow are ${v}_{{\rm{w}}}\sim 100\,\mathrm{km}\,{{\rm{s}}}^{-1}$ , ${\dot{M}}_{{\rm{w}}}\sim 7\,{M}_{\odot }\,{\mathrm{yr}}^{-1}$ , and ${E}_{{\rm{w}}}\sim 7\times {10}^{54}\,\mathrm{erg}$ , respectively. ${\dot{M}}_{{\rm{w}}}$ is comparable to the star formation rate ( ${\dot{M}}_{{\rm{w}}}/\mathrm{SFR}\sim 2$ ) and Ew is ∼1% of the total energy released by stellar feedback in the past $1\times {10}^{7}\,\mathrm{yr}$ , which is the dynamical timescale of the outflow. The results indicate that the wind is starburst driven.

Keywords: Starburst galaxies, Molecular gas, Galactic winds, Galaxy fountains, Stellar feedback, Interstellar phases, Star formation, Galaxy evolution, Galaxy kinematics, Cold neutral medium
A Machine-learning Approach to Integral Field Unit Spectroscopy Observations. I. H ii Region Kinematics. SITELLE is a novel integral field unit spectroscopy instrument that has an impressive spatial (11 by 11 arcmin), spectral coverage, and spectral resolution (R ∼ 1-20,000). SIGNALS is anticipated to obtain deep observations (down to 3.6 × 10-17erg s-1 cm-2) of 40 galaxies, each needing complex and substantial time to extract spectral information. We present a method that uses Convolution Neural Networks (CNN) for estimating emission-line parameters in optical spectra obtained with SITELLE as part of the SIGNALS large program. Our algorithm is trained and tested on synthetic data representing typical emission spectra for H ii regions based on Mexican Million Models database (3MdB) BOND simulations. The network's activation map demonstrates its ability to extract the dynamical (broadening and velocity) parameters from a set of five emission lines (e.g., Hα, N [ii] doublet, and S [ii] doublet) in the SN3 (651-685 nm) filter of SITELLE. Once trained, the algorithm was tested on real SITELLE observations in the SIGNALS program of one of the southwest fields of M33. The CNN recovers the dynamical parameters with an accuracy better than 5 $\mathrm{km}\,{{\rm{s}}}^{-1}$ in regions with a signal-to-noise ratio greater than 15 over the Hα line. More importantly, our CNN method reduces calculation time by over an order of magnitude on the spectral cube with native spatial resolution when compared with standard fitting procedures. These results clearly illustrate the power of machine-learning algorithms for the use in future IFU-based missions. Subsequent work will explore the applicability of the methodology to other spectral parameters such as the flux of key emission lines.

Keywords: Neural networks, Convolutional neural networks, Supernova remnants, Emission nebulae, Interstellar medium, H II regions
The Completed SDSS-IV Extended Baryon Oscillation Spectroscopic Survey: Baryon Acoustic Oscillations with Lyα Forests. We present a measurement of baryonic acoustic oscillations (BAOs) from Lyα absorption and quasars at an effective redshift $z=2.33$ using the complete extended Baryonic Oscillation Spectroscopic Survey (eBOSS). The 16th and final eBOSS data release (SDSS DR16) contains all data from eBOSS and its predecessor, the Baryonic Oscillation Spectroscopic Survey (BOSS), providing 210,005 quasars with zq &gt; 2.10 that are used to measure Lyα absorption. We measure the BAO scale both in the autocorrelation of Lyα absorption and in its cross-correlation with 341,468 quasars with redshift zq &gt; 1.77. Apart from the statistical gain from new quasars and deeper observations, the main improvements over previous work come from more accurate modeling of physical and instrumental correlations and the use of new sets of mock data. Combining the BAO measurement from the auto- and cross-correlation yields the constraints of the two ratios ${D}_{H}(z\,=2.33)/{r}_{d}=8.99\pm 0.19$ and ${D}_{M}(z=2.33)/{r}_{d}=37.5\pm 1.1$ , where the error bars are statistical. These results are within 1.5σ of the prediction of the flat-ΛCDM cosmology of Planck (2016). The analysis code, picca, the catalog of the flux transmission field measurements, and the Δχ2 surfaces are publicly available.

Keywords: Cosmology, Lyman alpha forest, Large-scale structure of the universe, Baryon acoustic oscillations, Dark energy
Carnegie Supernova Project: Classification of Type Ia Supernovae. We use the spectroscopy and homogeneous photometry of 97 Type Ia supernovae (SNe Ia) obtained by the Carnegie Supernova Project as well as a subset of 36 SNe Ia presented by Zheng et al. to examine maximum-light correlations in a four-dimensional (4D) parameter space: B-band absolute magnitude, MB, Si ii λ6355 velocity, ${v}_{\mathrm{Si}{\rm\small{II}}}$ , and Si ii pseudo-equivalent widths pEW(Si ii λ6355) and pEW(Si ii λ5972). It is shown using Gaussian mixture models (GMMs) that the original four groups in the Branch diagram are well-defined and robust in this parameterization. We find three continuous groups that describe the behavior of our sample in [MB, ${v}_{\mathrm{Si}{\rm\small{II}}}$ ] space. Extending the GMM into the full 4D space yields a grouping system that only slightly alters group definitions in the [MB, ${v}_{\mathrm{Si}{\rm\small{II}}}$ ] projection, showing that most of the clustering information in [MB, ${v}_{\mathrm{Si}{\rm\small{II}}}$ ] is already contained in the 2D GMM groupings. However, the full 4D space does divide group membership for faster objects between core-normal and broad-line objects in the Branch diagram. A significant correlation between MB and pseudo-equivalent width (Si ii λ5972) is found, which implies that Branch group membership can be well-constrained by spectroscopic quantities alone. In general, we find that higher-dimensional GMMs reduce the uncertainty of group membership for objects between the originally defined Branch groups. We also find that the broad-line Branch group becomes nearly distinct with the inclusion of ${v}_{\mathrm{Si}{\rm\small{II}}}$ , indicating that this subclass of SNe Ia may be somehow different from the other groups.

Keywords: Type Ia supernovae
Equation of State Constraints from Nuclear Physics, Neutron Star Masses, and Future Moment of Inertia Measurements. We explore constraints on the equation of state (EOS) of neutron-rich matter based on microscopic calculations up to nuclear densities and observations of neutron stars. In a previous work we showed that predictions based on modern nuclear interactions derived within chiral effective field theory and the observation of two-solar-mass neutron stars result in a robust uncertainty range for neutron star radii and the EOS over a wide range of densities. In this work we extend this study, employing both the piecewise polytrope extension from Hebeler et al. as well as the speed of sound model of Greif et al., and show that moment of inertia measurements of neutron stars can significantly improve the constraints on the EOS and neutron star radii.

Keywords: Neutron stars, Nuclear astrophysics
Exploiting Orbital Constraints from Optical Data to Detect Binary Gamma-Ray Pulsars. It is difficult to discover pulsars via their gamma-ray emission because current instruments typically detect fewer than one photon per million rotations. This creates a significant computing challenge for isolated pulsars, where the typical parameter search space spans wide ranges in four dimensions. It is even more demanding when the pulsar is in a binary system, where the orbital motion introduces several additional unknown parameters. Building on earlier work by Pletsch &amp; Clark, we present optimal methods for such searches. These can also incorporate external constraints on the parameter space to be searched, for example, from optical observations of a presumed binary companion. The solution has two parts. The first is the construction of optimal search grids in parameter space via a parameter space metric, for initial semicoherent searches and subsequent fully coherent follow-ups. The second is a method to demodulate and detect the periodic pulsations. These methods have different sensitivity properties than traditional radio searches for binary pulsars and might unveil new populations of pulsars.

Keywords: Gamma-ray sources, Astronomy data analysis, Binary pulsars, Millisecond pulsars
Chandra Monitoring of the J1809-1917 Pulsar Wind Nebula and Its Field. PSR J1809-1917 is a young (τ = 51 kyr) and energetic ( $\dot{E}=1.8\times {10}^{36}$ erg s-1) radio pulsar powering an X-ray pulsar wind nebula (PWN) that exhibits morphological variability. We report on the results of a new monitoring campaign by the Chandra X-ray Observatory (Chandra), carried out across six epochs with a ∼7 week cadence. The compact nebula can be interpreted as a jet-dominated outflow along the pulsar's spin axis. Its variability can be the result of Doppler boosting in the kinked jet, whose shape changes with time (akin to the Vela pulsar jet). The deep X-ray image, composed of 405 ks of new and 131 ks of archival Chandra data, reveals an arcminute-scale extended nebula (EN) whose axis of symmetry aligns with both the axis of the compact nebula and the direction toward the peak of the nearby TeV source HESS J1809-193. The EN's morphology and extent suggest that the pulsar is likely moving through the ambient medium at a transonic velocity. We also resolved a faint 7' long nonthermal collimated structure protruding from the PWN. It is possibly another instance of a "misaligned outflow" (also known as a "kinetic jet") produced by high-energy particles escaping the PWN's confinement and tracing the interstellar magnetic field lines. Finally, taking advantage of the 536 ks exposure, we analyzed the point sources in the J1809 field and classified them using multiwavelength data. None of the classified sources in the field can reasonably be expected to produce the extended TeV flux in the region, suggesting that PSR J1809-1917 is indeed the counterpart to HESS/eHWC J1809-193.

Keywords: Neutron stars, X-ray astronomy, Rotation powered pulsars, Extended radiation sources, Pulsars, Interstellar magnetic fields, Non-thermal radiation sources, Interstellar medium, Radio pulsars
GeV γ-Ray Emission from M33 and Arp 299. Star-forming galaxies are huge reservoirs of cosmic rays (CRs) and these CRs convert a significant fraction of their energy into γ-rays by colliding with the interstellar medium (ISM). Several nearby star-forming galaxies have been detected in GeV-TeV γ-rays. It is also found that the γ-ray luminosities in 0.1-100 GeV correlate well with indicators of the star-formation rates of the galaxies, such as the total infrared (IR) luminosity. In this paper, we report a systematic search for possible γ-ray emission from galaxies in the IRAS Revised Bright Galaxies Sample, using 11.4 yr of γ-ray data taken by the Fermi Large Area Telescope. Two new galaxies, M33 and Arp 299, are detected significantly. The two galaxies are consistent with the empirical correlation between the γ-ray luminosity and IR luminosity, suggesting that their γ-ray emissions should mainly originate from CRs interacting with ISM. Nevertheless, there is tentative evidence that the flux of the γ-ray emission from Arp 299 is variable. If the variability is true, part of the emission from Arp 299 should originate from the obscured active galactic nucleus in this interacting galaxy system. In addition, we find that the γ-ray excess from M33 is located at the northeast region of the galaxy, where a supergiant H ii region, NGC 604, resides. This indicates that some bright star-forming regions in spiral galaxies could play a dominant role in the galaxy in producing γ-ray emission.

Keywords: Gamma-ray sources, Starburst galaxies