Sazuna/UAT_keywords huggingface dataset:
The Supernova Remnant Population of NGC 6946 as Observed in [Fe II] 1.644 μm with HST. NGC 6946 is a high-star-formation-rate, face-on, spiral galaxy that has hosted 10 supernovae since 1917. Not surprisingly, a large number of supernova remnants and candidates have been identified either as optical nebulae with high [S II]:Hα line ratios (147) or as compact non-thermal radio sources (35). However, there are only seven overlaps between these two samples. Here, we apply [Fe II] 1.644 μm emission as a new diagnostic to search for supernova remnants in an attempt to resolve this discrepancy. [Fe II] is expected to be relatively strong in the radiative shocks of supernova remnants and almost absent in H II regions. It is less susceptible to the effects of absorption along the line of sight than the optical lines normally used to identify remnants. Using data from the WFC3 camera on Hubble Space Telescope (HST), we identify 132 [Fe II] emission nebulae in NGC 6946 as likely supernova remnants. Of these, 54 align with previously known optical supernova remnants. The remaining 78 objects are new; of these 44 are visible in new HST imagery in Hα and [S II]. This brings the total number of supernova remnant candidates (from optical and/or IR data) in NGC 6946 to 225. A total of 14 coincidences with radio supernova remnant candidates (out of 30 in our search area) are found in this expanded list. The identification of so many new remnant candidates validates the use of [Fe II] imagery for finding remnants, and suggests that previous remnant searches in other galaxies may be far from complete. * Based on observations 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, Incorporated, under NASA contract NAS5-26555. Support for program numbers 14638 and 15216 was provided through a grant from the STScI under NASA contract NAS5-26555.

Keywords: Supernova remnants, Interstellar medium
Extracting the Cold Neutral Medium from H I Emission with Deep Learning: Implications for Galactic Foregrounds at High Latitude. Resolving the phase structure of neutral hydrogen (H I) is crucial for understanding the life cycle of the interstellar medium (ISM). However, accurate measurements of H I temperature and density are limited by the availability of background continuum sources for measuring H I absorption. Here we test the use of deep learning for extracting H I properties over large areas without optical depth information. We train a 1D convolutional neural network using synthetic observations of 3D numerical simulations of the ISM to predict the fraction ( ${f}_{\mathrm{CNM}}$ ) of cold neutral medium (CNM) and the correction to the optically thin H I column density for optical depth ( ${{ \mathcal R }}_{{\rm{H}}{\rm\small{I}}}$ ) from 21 cm emission alone. We restrict our analysis to high Galactic latitudes ( $| b| \gt 30^\circ $ ), where the complexity of spectral line profiles is minimized. We verify that the network accurately predicts ${f}_{\mathrm{CNM}}$ and ${{ \mathcal R }}_{{\rm{H}}{\rm\small{I}}}$ by comparing the results with direct constraints from 21 cm absorption. By applying the network to the GALFA-H I survey, we generate large-area maps of ${f}_{\mathrm{CNM}}$ and ${{ \mathcal R }}_{{\rm{H}}{\rm\small{I}}}$ . Although the overall contribution to the total H I column of CNM-rich structures is small (∼5%), we find that these structures are ubiquitous. Our results are consistent with the picture that small-scale structures observed in 21 cm emission aligned with the magnetic field are dominated by CNM. Finally, we demonstrate that the observed correlation between H I column density and dust reddening ( $E(B-V)$ ) declines with increasing ${{ \mathcal R }}_{{\rm{H}}{\rm\small{I}}}$ , indicating that future efforts to quantify foreground Galactic $E(B-V)$ using H I, even at high latitudes, should increase fidelity by accounting for H I phase structure.

Keywords: Interstellar atomic gas, Convolutional neural networks, Interstellar absorption, Cold neutral medium, Interstellar medium, Radio astronomy, Milky Way Galaxy
Statistical Detection of IGM Structures during Cosmic Reionization Using Absorption of the Redshifted 21 cm line by H I against Compact Background Radio Sources. Detecting neutral hydrogen structures in the intergalactic medium (IGM) during cosmic reionization via absorption (21 cm forest) against a background radiation is considered independent and complementary to the three-dimensional tomography and power spectrum techniques. The direct detection of this absorption requires very bright (≳10-100 mJy) background sources at high redshifts (z ≳ 8), which are evidently rare; very long times of integration; or instruments of very high sensitivity. This motivates a statistical one-dimensional (1D) power spectrum approach along narrow sightlines but with fainter background objects (∼1-10 mJy), which are likely to be more abundant and significant contributors at high redshifts. The 1D power spectrum reduces cosmic variance and improves sensitivity especially on small spatial scales. Using standard radiative transfer and fiducial models for the instrument, the background sources, and the evolution of IGM structures during cosmic reionization, the potential of the 1D power spectrum along selected narrow directions is investigated against uncertainties from thermal noise and the chromatic synthesized point spread function (PSF) response. Minimum requirements on the number of high-redshift background sources, the telescope sensitivity, and the PSF quality are estimated for a range of instrumental, background source, and reionization model parameters. The 1D power spectrum is intrinsically stronger at higher redshifts. A ∼1000 hr observing campaign targeting ∼100 narrow sightlines to radio-faint, high-redshift background objects with modern radio telescopes, especially the Square Kilometre Array, can detect the 1D power spectrum on a range of spatial scales and redshifts, and potentially discriminate between models of cosmic reionization.

Keywords: Radio spectroscopy, Early universe, Aperture synthesis, Large-scale structure of the universe, Intergalactic medium, Observational cosmology, H I line emission, Radiative transfer equation, Radio interferometers, Discrete radio sources, Reionization, High-redshift galaxies
Herschel SPIRE Discovery of Far-infrared Excess Synchrotron Emission from the West Hot Spot of the Radio Galaxy Pictor A. A far-infrared counterpart to the west hot spot of the radio galaxy Pictor A is discovered with the Spectral and Photometric Imaging REceiver (SPIRE) on board Herschel. The color-corrected flux density of the source is measured as 70.0 ± 9.9 mJy at the wavelength of 350 μm. A close investigation into its radio-to-optical spectrum indicates that the mid-infrared excess over the radio synchrotron component, detected with Wide-field Infrared Survey Explorer and Spitzer, significantly contributes to the far-infrared band. Thanks to the SPIRE data, it is revealed that the spectrum of the excess is described by a broken power-law model subjected to a high-energy cutoff. By applying the radiative cooling break under continuous energy injection (Δα = 0.5), the broken power-law model supports an idea that the excess originates in 10 pc scale substructures within the hot spot. From the break frequency, ${\nu }_{{\rm{b}}}={1.6}_{-1.0}^{+3.0}\times {10}^{12}$ Hz, the magnetic field was estimated as B ≃ 1-4 mG. This is higher than the minimum-energy magnetic field of the substructures by a factor of 3-10. Even if the origin of the excess is larger than ∼100 pc, the magnetic field stronger than the minimum-energy field is confirmed. It is proposed that regions with a magnetic field locally boosted via plasma turbulence are observed as the substructures. The derived energy index below the break, α ∼ 0.22 (conservatively &lt;0.42), is difficult to be attributed to the strong-shock acceleration (α = 0.5). Stochastic acceleration and magnetic reconnection are considered as a plausible alternative mechanism.

Keywords: High energy astrophysics, Active galaxies, Galaxy jets, Far infrared astronomy, Non-thermal radiation sources, Fanaroff-Riley radio galaxies, Radio hot spots
Isomers of Hydrogenated Polycyclic Aromatic Hydrocarbons Explain the Presence of Infrared Bands in the 3 μm Region. A large number of hydrogenated coronene, circumcoronene, and circumcircumcoronene isomers have been investigated by means of density functional theory calculations. The computation of their IR spectra puts forward significant differences between the different isomers in the 3 μm region and shows that hydrogenated polycyclic aromatic hydrocarbons can account for the aromatic infrared bands resulting from the absorption of light by the interstellar medium. In particular, the intense 3.3 μm band, as well as the weak features observed at 3.40, 3.46, 3.51, and 3.56 μm are reasonably reproduced by the present calculations. The latter two are only observed when hydrogenation takes place in tertiary carbon atoms, showing that the frequencies at which these IR bands appear are a consequence of their position and chemical environment within the molecule.

Keywords: Interstellar molecules, Cosmochemistry, Polycyclic aromatic hydrocarbons, Line positions, Spectral line identification, Molecular spectroscopy, Infrared sources
Coronal Mini-jets in an Activated Solar Tornado-like Prominence. High-resolution observations from the Interface Region Imaging Spectrometer reveal the existence of a particular type of small solar jet, which arose singly or in clusters from a tornado-like prominence suspended in the corona. In this study, we perform a detailed statistical analysis of 43 selected mini-jets in the tornado event. Our results show that the mini-jets typically have (1) a projected length of 1.0-6.0 Mm, (2) a width of 0.2-1.0 Mm, (3) a lifetime of 10-50 s, (4) a velocity of 100-350 km s-1, and (5) an acceleration of 3-20 km s-2. Based on spectral diagnostics and EM-Loci analysis, these jets seem to be multithermal small-scale plasma ejections with an estimated average electron density of ∼2.4 × 1010 cm-3 and an approximate mean temperature of ∼2.6 × 105 K. Their mean kinetic energy density, thermal energy density, and dissipated magnetic field strength are roughly estimated to be ∼9 erg cm-3, 3 erg cm-3, and 16 G, respectively. The accelerations of the mini-jets, the UV and EUV brightenings at the footpoints of some mini-jets, and the activation of the host prominence suggest that the tornado mini-jets are probably created by fine-scale external or internal magnetic reconnections (a) between the prominence field and the enveloping or background field or (b) between twisted or braided flux tubes within the prominence. The observations provide insight into the geometry of such reconnection events in the corona and have implications for the structure of the prominence magnetic field and the instability that is responsible for the eruption of prominences and coronal mass ejections.

Keywords: Solar activity, The Sun, Solar prominences
Electromagnetic Ion-Ion Instabilities in Space Plasmas: Effects of Suprathermal Populations. In collision-poor plasmas from space, three distinct ion-ion instabilities can be driven by the proton beams streaming along the background magnetic field: left-hand resonant, nonresonant, and right-hand resonant instabilities. These instabilities are in general investigated considering only idealized proton beams with Maxwellian velocity distributions, and ignoring the implications of suprathermal populations, usually reproduced by the Kappa power laws. Moreover, the existing theories minimize the kinetic effects of electrons, assuming them isotropic and Maxwellian distributed. In an attempt to overcome these limitations, in the present paper we present the results of an extended investigation of ion-ion instabilities, which show that their dispersion and stability properties (e.g., growth rates, wave frequencies, and the unstable wavenumbers) are highly sensitive to the influence of suprathermal populations and anisotropic electrons. These results offer valuable explanations for the origin of the enhanced low-frequency fluctuations, frequently observed in space plasmas and associated with proton beams.

Keywords: Interplanetary medium, Space plasmas, Shocks, Solar wind
High-cadence Dispersed Spectral Analysis of Supernova Remnant 1987A. We present an analysis of the dispersed spectral data from 11 epochs (2011 March-2018 September) of supernova remnant (SNR) 1987A observations performed with Chandra. These observations were performed with the High Energy Transmission Grating (HETG) as part of our ongoing Chandra monitoring campaign of SNR 1987A, whose first-order dispersed spectrum provides a significantly greater energy resolution than the previously published zeroth-order spectrum. Our data sets with moderate exposure times of ∼50-70 ks per epoch cover the time period between deep Chandra HETG observations (with individual exposures &gt;∼200 ks) taken in 2011 March and 2018 March. These data have a much higher cadence than the widely spaced deep high-resolution spectra, at the expense of total exposure time. While statistical uncertainties are large due to low photon count statistics in the observed first-order spectra, we find that spectral model parameters are generally in line with the shock wave propagating into the medium beyond the dense inner ring, as suggested by Frank et al. (2016). As the reverse shock begins ionizing the heavier elements of the supernova ejecta interior to the equatorial ring, spectral fit parameters are expected to change as the chemical makeup and physical properties of the shocked gas evolve. Based on our broadband spectral model fits, we find that abundance values appear to be constant in this time period. While our results are somewhat limited due to photon statistics, we demonstrate the utility of the dispersed HETG spectral analysis that can be performed with our regular Chandra monitoring observations of SNR 1987A.

Keywords: Supernova remnants, Supernovae, X-ray astronomy, Circumstellar gas
Abundance Analysis of New r-process-enhanced Stars from the HESP-GOMPA Survey. We present a study on the detailed chemical abundances of five new relatively bright r-process-enhanced stars that were initially observed as part of the SDSS/MARVELS pre-survey. These stars were selected, on the basis of their metallicities and carbon abundances, among a total of 60 stars, for high-resolution spectroscopic follow-up as part of the HESP-GOMPA survey (Hanle Echelle SPectrograph—Galactic survey Of Metal Poor stArs). Here we discuss the three new r-I and two new r-II stars found in this survey. We have carried out a detailed abundance analysis for each of these stars, at a resolving power of R ∼ 30,000, and we compare our results to the existing literature. We could measure three of the first r-process-peak elements (Sr, Y, and Zr) in all five stars, while Ba, Ce, Nd, Sm, Eu, and Dy could be detected among the second r-process-peak elements. Thorium could also be detected in one of the targets, which is found to be an actinide-boost star. We have carried out a comparative study among the subpopulations of the r-process-enhanced stars and other stars of the Milky Way halo population to constrain the origin of this class of objects. These bright r-process-enhanced stars provide an excellent opportunity to study the nucleosynthesis history of this population in great detail, and shed light on their chemical-enrichment histories.

Keywords: High resolution spectroscopy, R-process, Chemical abundances, Nucleosynthesis
Herschel 158 μm [{C} {II}}] Observations of "CO-dark" Gas in the Perseus Giant Molecular Cloud. We present observations of velocity-resolved [C II] 158 μm emission from both a dense and a more diffuse photodissociation region (PDR) in the Perseus giant molecular cloud using the Heterodyne Instrument for the Far-Infrared on board the Herschel Space Telescope. We detect [C II] emission from 80% of the total positions, with a 95% detection rate from the dense boundary region. The integrated intensity of the [C II] emission remains relatively constant across each boundary, despite the observed range in optical extinction between 1 and 10 mag. This flat profile indicates a constant heating and cooling rate within both regions observed. The integrated intensity of [C II] emission is reasonably well correlated with the neutral hydrogen (H I) column density, as well as the total gas column density. This, in addition to the 80' (7 pc) extent of the [C II] emission from the cloud center, suggests that the H I envelope plays a dominant role in explaining the [C II] emission emanating from Perseus. We compare the [C II] and 12CO integrated intensities with predictions from a 1D, two-sided slab PDR model and show that a simple core + envelope, equilibrium model without an additional "CO-dark" H2 component can reproduce observations well. Additional observations are needed to disentangle how much of the [C II] emission is associated with the "CO-dark" H2 gas, as well as constrain spatial variations of the dust-to-gas ratio across Perseus.

Keywords: Molecular gas, Astronomy data modeling, Astronomy data analysis, Photodissociation regions, Far infrared astronomy, Giant molecular clouds, Dark interstellar clouds, Interstellar clouds, Diffuse molecular clouds
Composition Effects on Kilonova Spectra and Light Curves. I. The merger of neutron star binaries is believed to eject a wide range of heavy elements into the universe. By observing the emission from this ejecta, scientists can probe the ejecta properties (mass, velocity, and composition distributions). The emission (a.k.a. kilonova) is powered by the radioactive decay of the heavy isotopes produced in the merger and this emission is reprocessed by atomic opacities to optical and infrared wavelengths. Understanding the ejecta properties requires calculating the dependence of this emission on these opacities. The strong lines in the optical and infrared in lanthanide opacities have been shown to significantly alter the light curves and spectra in these wavelength bands, arguing that the emission in these wavelengths can probe the composition of this ejecta. Here we study variations in the kilonova emission by varying individual lanthanide (and the actinide uranium) concentrations in the ejecta. The broad forest of lanthanide lines makes it difficult to determine the exact fraction of individual lanthanides. Nd is an exception. Its opacities above 1 μm are higher than other lanthanides and observations of kilonovae can potentially probe increased abundances of Nd. Similarly, at early times when the ejecta is still hot (first day), the U opacity is strong in the 0.2-1 μm wavelength range and kilonova observations may also be able to constrain these abundances.

Keywords: Neutron stars, Stellar mergers, R-process, Stellar atmospheric opacity, Compact binary stars, Interacting binary stars
Dark Matter Deficient Galaxies Produced via High-velocity Galaxy Collisions in High-resolution Numerical Simulations. The recent discovery of diffuse dwarf galaxies that are deficient in dark matter appears to challenge the current paradigm of structure formation in our universe. We describe numerical experiments to determine if so-called dark matter deficient galaxies (DMDGs) could be produced when two gas-rich, dwarf-sized galaxies collide with a high relative velocity of ∼300 km s-1. Using idealized high-resolution simulations with both mesh-based and particle-based gravito-hydrodynamics codes, we find that DMDGs can form as high-velocity galaxy collisions and separate dark matter from the warm disk gas, which subsequently is compressed by shock and tidal interaction to form stars. Then using the large simulated universe IlLUSTRISTNG, we discover a number of high-velocity galaxy collision events in which DMDGs are expected to form. However, we did not find evidence that these types of collisions actually produced DMDGs in the TNG100-1 run. We argue that the resolution of the numerical experiment is critical to realizing the "collision-induced" DMDG formation scenario. Our results demonstrate one of many routes in which galaxies could form with unconventional dark matter fractions.

Keywords: Cosmology, Hydrodynamical simulations, Galaxy formation, Large-scale structure of the universe, Galaxy evolution, Dark matter
Spin Evolution of Stellar-mass Black Hole Binaries in Active Galactic Nuclei. The astrophysical origin of gravitational-wave (GW) events is one of the most timely problems in the wake of the LIGO/Virgo discoveries. In active galactic nuclei (AGNs), binaries form and evolve efficiently by dynamical interactions and gaseous dissipation. Previous studies have suggested that binary black hole (BBH) mergers in AGN disks can contribute significantly to BBH mergers observed by GW interferometers. Here we examine the distribution of the effective spin parameter χeff of this GW source population. We extend our semi-analytical model of binary formation and evolution in AGN disks by following the evolution of the binary orbital angular momenta and black hole (BH) spins. BH spins change due to gas accretion and BH mergers, while the binary orbital angular momenta evolve due to gas accretion and binary-single interactions. We find that the distribution of χeff predicted by our AGN model is similar to the distribution observed during LIGO/Virgo O1 and O2. On the other hand, if radial migration of BHs is inefficient, χeff is skewed toward higher values than the observed distribution, because of the paucity of scattering events that would randomize spin directions relative to the orbital plane. We suggest that high binary masses and the positive correlation between binary mass and the standard deviation of χeff for chirp masses up to $\approx 20\,{M}_{\odot }$ can be possible signatures for mergers originating in AGN disks. Finally, hierarchical mergers in AGN disks naturally produce properties of the recent GW event GW190412, including a low mass ratio, a high primary BH spin, and a significant spin component in the orbital plane.

Keywords: Active galactic nuclei, Stellar mass black holes, Gravitational wave sources
PLATON II: New Capabilities and a Comprehensive Retrieval on HD 189733b Transit and Eclipse Data. Recently, we introduced PLanetary Atmospheric Tool for Observer Noobs (PLATON), a Python package that calculates model transmission spectra for exoplanets and retrieves atmospheric characteristics based on observed spectra. We now expand its capabilities to include the ability to compute secondary eclipse depths. We have also added the option to calculate models using the correlated-k method for radiative transfer, which improves accuracy without sacrificing speed. Additionally, we update the opacities in PLATON—many of which were generated using old or proprietary line lists—using the most recent and complete public line lists. These opacities are made available at R = 1000 and R = 10,000 over the 0.3-30 μm range, and at R = 375,000 in select near-IR bands, making it possible to utilize PLATON for ground-based high-resolution cross-correlation studies. To demonstrate PLATON's new capabilities, we perform a retrieval on published Hubble Space Telescope (HST) and Spitzer transmission and emission spectra of the archetypal hot Jupiter HD 189733b. This is the first joint transit and secondary eclipse retrieval for this planet in the literature, as well as the most comprehensive set of both transit and eclipse data assembled for a retrieval to date. We find that these high signal-to-noise data are well matched by atmosphere models with a C/O ratio of ${0.66}_{-0.09}^{+0.05}$ and a metallicity of ${12}_{-5}^{+8}$ times solar where the terminator is dominated by extended nanometer-sized haze particles at optical wavelengths. These are among the smallest uncertainties reported to date for an exoplanet, demonstrating both the power and the limitations of HST and Spitzer exoplanet observations.

Keywords: Exoplanet atmospheric composition , Astronomical models, Exoplanet atmospheres, Transmission spectroscopy