Sazuna/UAT_keywords huggingface dataset:
Density of Neutral Hydrogen in the Sun's Interstellar Neighborhood. Interstellar neutral atoms, unlike charged particles, freely penetrate the heliosphere, allowing us to sample the physical state of the interstellar matter directly. Most interstellar hydrogen atoms are ionized before reaching the inner heliosphere and become energetic protons picked up by the solar wind and transported away from the Sun. Consequently, observations of interstellar hydrogen atoms by missions operating within a few astronomical units from the Sun are subject to significant systematic uncertainties. We analyze observations from the Solar Wind Around Pluto instrument on New Horizons, the first experiment to provide extensive measurements of the picked-up protons far from the Sun. Analyzing the density of these protons, we find an interstellar neutral hydrogen density at the termination shock of 0.127 ± 0.015 cm-3, i.e., ∼40% higher than previously thought. We show that the Voyager observations of the slowdown of the solar wind further support this value. This result resolves a problem of why energetic neutral atom fluxes, created from pickup ions by charge exchange with hydrogen atoms, are roughly twice that expected from numerical models. Our result also implies higher charge exchange rates at the heliospheric boundaries and, consequently, a less asymmetric shape of the heliosphere. Based on a previous study of the atom filtration in the heliospheric boundaries, we estimate the neutral hydrogen density in the unperturbed local interstellar medium of 0.195 ± 0.033 cm-3. This value agrees with astrophysical observations of the interstellar clouds in the Sun proximity.

Keywords: Space plasmas, Heliosphere, Interstellar atomic gas, Solar wind, Pickup ions, Interstellar clouds, Interstellar medium
Piercing through Highly Obscured and Compton-thick AGNs in the Chandra Deep Fields. II. Are Highly Obscured AGNs the Missing Link in the Merger-triggered AGN-Galaxy Coevolution Models?. By using a large, highly obscured ( ${N}_{{\rm{H}}}\gt {10}^{23}\ {\mathrm{cm}}^{-2}$ ) active galactic nucleus (AGN) sample (294 sources at z ∼ 0-5) selected from detailed X-ray spectral analyses in the deepest Chandra surveys, we explore distributions of these X-ray sources in various optical/infrared/X-ray color-color diagrams and their host-galaxy properties, aiming at characterizing the nuclear obscuration environment and the triggering mechanism of highly obscured AGNs. We find that the refined Infrared Array Camera (IRAC) color-color diagram fails to identify the majority of X-ray-selected, highly obscured AGNs, even for the most luminous sources with $\mathrm{log}\,{L}_{{\rm{X}}}(\mathrm{erg}\ {{\rm{s}}}^{-1})\gt 44$ . Over 80% of our sources will not be selected as heavily obscured candidates using the flux ratio of ${f}_{24\mu {\rm{m}}}/{f}_{R}\gt 1000$ and R - K &gt; 4.5 criteria, implying complex origins and conditions for the obscuring materials that are responsible for the heavy X-ray obscuration. The average star formation rate (SFR) of highly obscured AGNs is similar to that of stellar mass- (M*-) and z-controlled normal galaxies, while a lack of quiescent hosts is observed for the former. Partial correlation analyses imply that highly obscured AGN activity (traced by ${L}_{{\rm{X}}}$ ) appears to be more fundamentally related to M*, and no dependence of ${N}_{{\rm{H}}}$ on either M* or SFR is detected. Morphology analyses reveal that 61% of our sources have a significant disk component, while only ∼27% of them exhibit irregular morphological signatures. These findings together point toward a scenario where secular processes (e.g., galactic-disk instabilities), instead of mergers, are most probable to be the leading mechanism that triggers accretion activities of X-ray-selected, highly obscured AGNs.

Keywords: AGN host galaxies, Active galaxies, X-ray active galactic nuclei
Super Star Clusters in the Central Starburst of NGC 4945. The nearby (3.8 Mpc) galaxy NGC 4945 hosts a nuclear starburst and Seyfert type 2 active galactic nucleus (AGN). We use the Atacama Large Millimeter/submillimeter Array (ALMA) to image the 93 GHz (3.2 mm) free-free continuum and hydrogen recombination line emission (H40α and H42α) at 2.2 pc (0"12) resolution. Our observations reveal 27 bright, compact sources with FWHM sizes of 1.4-4.0 pc, which we identify as candidate super star clusters. Recombination line emission, tracing the ionizing photon rate of the candidate clusters, is detected in 15 sources, six of which have a significant synchrotron component to the 93 GHz continuum. Adopting an age of ∼5 Myr, the stellar masses implied by the ionizing photon luminosities are ${\mathrm{log}}_{10}$ (M⋆/M⊙) ≈ 4.7-6.1. We fit a slope to the cluster mass distribution and find β = -1.8 ± 0.4. The gas masses associated with these clusters, derived from the dust continuum at 350 GHz, are typically an order of magnitude lower than the stellar mass. These candidate clusters appear to have already converted a large fraction of their dense natal material into stars and, given their small freefall times of ∼0.05 Myr, are surviving an early volatile phase. We identify a pointlike source in 93 GHz continuum emission that is presumed to be the AGN. We do not detect recombination line emission from the AGN and place an upper limit on the ionizing photons that leak into the starburst region of Q0 &lt; 1052 s-1.

Keywords: Starburst galaxies, Star formation, Galaxies, Star clusters
The Sloan Digital Sky Survey Reverberation Mapping Project: How Broad Emission Line Widths Change When Luminosity Changes. Quasar broad emission lines are largely powered by photoionization from the accretion continuum. Increased central luminosity will enhance line emissivity in more distant clouds, leading to increased average distance of the broad-line-emitting clouds and decreased averaged line width, which is known as the "breathing" broad-line region. However, different lines breathe differently, and some high-ionization lines, such as C IV, can even show "anti-breathing" where the line broadens when luminosity increases. Using multi-year photometric and spectroscopic monitoring data from the Sloan Digital Sky Survey Reverberation Mapping project, we quantify the breathing effect ( ${\rm{\Delta }}\mathrm{log}W=\alpha {\rm{\Delta }}\mathrm{log}L$ ) of broad Hα, Hβ, Mg II, C IV, and C III] for statistical quasar samples over z ≈ 0.1-2.5. We find that Hβ displays the most consistent normal breathing expected from the virial relation (α ∼ -0.25), Mg II and Hα on average show no breathing (α ∼ 0), and C IV (and similarly C III] and Si IV) mostly shows anti-breathing (α &gt; 0). The anti-breathing of C IV can be well understood by the presence of a non-varying core component in addition to a reverberating broad-base component, which is consistent with earlier findings. The deviation from canonical breathing introduces extra scatter (a luminosity-dependent bias) in single-epoch virial BH mass estimates due to intrinsic quasar variability, which underlies the long-argued caveats of C IV single-epoch masses. Using the line dispersion instead of FWHM leads to fewer, albeit still substantial, deviations from canonical breathing in most cases. Our results strengthen the need for reverberation mapping to provide reliable quasar BH masses and to quantify the level of variability-induced bias in single-epoch BH masses based on various lines.

Keywords: Supermassive black holes, Reverberation mapping, Quasars
Local and Global Gas Metallicity versus Stellar Age Relation in MaNGA Galaxies. The search for new global scaling relations linking the physical properties of galaxies has a fundamental interest. Furthermore, their recovery from spatially resolved relations has been in the spotlight of integral field spectroscopy (IFS). In this study, we investigate the existence of global and local relations between stellar age (Age⋆) and gas-phase metallicity (Zg). To this aim, we analyze IFS data for a sample of 736 star-forming disk galaxies from the MaNGA survey. We report a positive correlation between the global Zg and D(4000) (an indicator of stellar age), with a slope that decreases with increasing galaxy mass. Locally, a similar trend is found when analyzing the Zg and D(4000) of the star-forming regions, as well as the residuals resulting from removing the radial gradients of both parameters. The local laws have systematically smaller slopes than the global one. We ascribe this difference to random errors that cause the true slope of the Age⋆-Zg relation to be systematically underestimated when performing a least-squares fitting. The explored relation is intimately linked with the already known relation between gas metallicity and star formation rate at fixed mass, both presenting a common physical origin.

Keywords: Galaxy formation, Galaxy abundances, Star formation, Galaxy chemical evolution
Examining the Magnetic Geometry of Magnetic Flux Ropes from the View of Single-point Analysis. Magnetic flux ropes, characterized as magnetic field lines that wrap and rotate around a central axis, are observed ubiquitously in the space-plasma environment. Accurately examining the physical parameters (e.g., axis orientation, helical handedness, current density, curvature radius, and size) of flux ropes is essential for studying their evolution and associated dynamics. The geometric parameters of flux ropes can be resolved by a cluster of at least four spacecraft with the separation scale much smaller than the flux ropes. However, most spacecraft missions are of single-point measurements, especially for the missions on other planets (e.g., Mars, Venus, Mercury), thus, the method for investigating the flux ropes based on single-point measurements becomes particularly important. A single-point method that infers the axis orientation of flux ropes was recently developed by Rong et al. Here, we apply this method to study two flux ropes observed by the Magnetospheric Multiscale Mission (MMS), one close to the force-free field and the other close to the non-force-free field, by comparing them with the multipoint analysis of MMS. Our study demonstrates that, apart from axis orientation, the method of Rong et al. can reasonably infer the current density, curvature radius of magnetic field, and the transverse size of flux ropes. We discussed the main error sources of calculated parameters, and suggest that it is worthwhile to widely apply the method by Rong et al. to single-point spacecraft missions for the purpose of examining the geometry and dynamics of flux ropes.

Keywords: Space plasmas, Planetary boundary layers, Astrophysical magnetism, Solar coronal mass ejections, Planetary science, Planetary magnetospheres, Magnetic fields
Deep Modeling of Quasar Variability. Quasars have long been known as intrinsically variable sources, but the physical mechanism underlying the temporal optical/UV variability is still not well understood. We propose a novel nonparametric method for modeling and forecasting the optical variability of quasars utilizing an AE neural network to gain insight into the underlying processes. The AE is trained with ∼15,000 decade-long quasar light curves obtained by the Catalina Real-time Transient Survey selected with negligible flux contamination from the host galaxy. The AE&amp;'s performance in forecasting the temporal flux variation of quasars is superior to that of the damped random walk process. We find a temporal asymmetry in the optical variability and a novel relation—the amplitude of the variability asymmetry decreases as luminosity and/or black hole mass increases—is suggested with the help of autoencoded features. The characteristics of the variability asymmetry are in agreement with those from the self-organized disk instability model, which predicts that the magnitude of the variability asymmetry decreases as the ratio of the diffusion mass to inflow mass in the accretion disk increases.

Keywords: Neural networks, Galaxy accretion disks, Active galaxies, Astrostatistics
Open Cluster Chemical Homogeneity throughout the Milky Way. The chemical homogeneity of surviving stellar clusters contains important clues about interstellar medium (ISM) mixing efficiency, star formation, and the enrichment history of the Galaxy. Existing measurements in a handful of open clusters suggest homogeneity in several elements at the 0.03 dex level. Here we present (i) a new cluster member catalog based only on APOGEE radial velocities and Gaia-DR2 proper motions, (ii) improved abundance uncertainties for APOGEE cluster members, and (iii) the dependence of cluster homogeneity on Galactic and cluster properties, using abundances of eight elements from the APOGEE survey for 10 high-quality clusters. We find that cluster homogeneity is uncorrelated with Galactocentric distance, $| Z| $ , age, and metallicity. However, velocity dispersion, which is a proxy for cluster mass, is positively correlated with intrinsic scatter at relatively high levels of significance for [Ca/Fe] and [Mg/Fe]. We also see a possible positive correlation at a low level of significance for [Ni/Fe], [Si/Fe], [Al/Fe], and [Fe/H], while [Cr/Fe] and [Mn/Fe] are uncorrelated. The elements that show a correlation with velocity dispersion are those that are predominantly produced by core-collapse supernovae (CCSNe). However, the small sample size and relatively low correlation significance highlight the need for follow-up studies. If borne out by future studies, these findings would suggest a quantitative difference between the correlation lengths of elements produced predominantly by Type Ia SNe versus CCSNe, which would have implications for Galactic chemical evolution models and the feasibility of chemical tagging.

Keywords: Chemical enrichment, Milky Way evolution, Chemical abundances, Star clusters
A New Parameterization of the Star Formation Rate Dense Gas Mass Relation: Embracing Gas Density Gradients. It is well established that a gas density gradient inside molecular clouds and clumps raises their star formation rate (SFR) compared with what they would experience from a gas reservoir of uniform density. This effect should be observed in the relation between dense-gas mass Mdg and SFR of molecular clouds and clumps, with steeper gas density gradients yielding higher SFR/Mdg ratios. The content of this paper is twofold. First, we build on the notion of a magnification factor introduced by Parmentier to redefine the dense-gas relation (i.e., the relation between Mdg and SFR). Not only does the SFR/Mdg ratio depend on the mean freefall time of the gas and on its (intrinsic) star formation efficiency per freefall time, but it also depends on the clump density profile (e.g., the logarithmic slope $-p$ of the gas density profile and on the relative extent of the constant-density region at the clump center). Second, we show that nearby molecular clouds follow the newly defined dense-gas relation, provided that their dense-gas mass is defined based on a volume density criterion. We also find the same trend for the dense molecular clouds of the Central Molecular Zone (CMZ) of the Galaxy, although this one is scaled down by a factor of 10 compared with nearby clouds, even when including the Sgr C and Sgr B2 clouds. The respective locii of both nearby and CMZ clouds in the $(p,{SFR}/{M}_{{dg}})$ parameter space is discussed.

Keywords: Star formation, Molecular clouds, Star clusters
Quasi-adiabatic and Stochastic Heating and Particle Acceleration at Quasi-perpendicular Shocks. Based on Magnetospheric Multiscale observations from the Earth&amp;'s bow shock, we have identified two plasma heating processes that operate at quasi-perpendicular shocks. Ions are subject to stochastic heating in a process controlled by the heating function ${\chi }_{j}={m}_{j}{q}_{j}^{-1}{B}^{-2}\mathrm{div}({{\boldsymbol{E}}}_{\perp })$ for particles with mass mj and charge qj in the electric and magnetic fields ${\boldsymbol{E}}$ and ${\boldsymbol{B}}$ . Test-particle simulations are employed to identify the parameter ranges for bulk heating and stochastic acceleration of particles in the tail of the distribution function. The simulation results are used to show that ion heating and acceleration in the studied bow shock crossings is accomplished by waves at frequencies (2-10)fcp (proton gyrofrequency) for the bulk heating, and $f\gt 10{f}_{{cp}}$ for the tail acceleration. When electrons are not in the stochastic heating regime, $| {\chi }_{e}| \lt 1$ , they undergo a quasi-adiabatic heating process characterized by the isotropic temperature relation $T/B={({T}_{0}/{B}_{0})({B}_{0}/B)}^{1/3}$ . This is obtained when the energy gain from the conservation of the magnetic moment is redistributed to the parallel energy component through the scattering by waves. The results reported in this paper may be applicable also to particle heating and acceleration at astrophysical shocks.

Keywords: Shocks, Interplanetary physics
Stellar Populations of a Sample of Optically Selected AGN-host Dwarf Galaxies. In this paper we present our studies on the stellar populations and star formation histories (SFHs) for the Reines et al. sample of 136 dwarf galaxies that host active galactic nuclei (AGNs), selected from the Sloan Digital Sky Survey Data Release 8. We derive stellar populations and reconstruct SFHs for these AGN-host dwarfs using the stellar population synthesis code STARLIGHT. Our results suggest that these AGN-host dwarfs have assembled their stellar masses within a narrow period of time with the stellar mass-weighted ages in the range of 109-1010 yr, but show a wide diversity of SFHs with the luminosity-weighted stellar ages in the range of 107-1010 yr. The old population (t &gt; 109 yr) contributes most to the galaxy light for the majority of the sample; the young population (t &lt; 108 yr) also appears in significant but widely varying fractions, while the intermediate-age population (108 &lt; t &lt; 109 yr) in general contributes less to the optical continuum at 4020 Å. We also find that these dwarfs follow a similar mass-metallicity relation to normal star-forming galaxies, indicating that AGNs have little effect on the chemical evolution of the host galaxy. We further investigate the relation between the derived SFHs and morphology of the host galaxy, and find no correlation. Comparing the SFHs with the luminosity of the [O III] λ5007 line ( ${L}_{[{\rm{O}}{\rm\small{III}}]}$ ), we find a mild correlation exists when ${L}_{[{\rm{O}}{\rm\small{III}}]}\gt {10}^{39}$ erg s-1, indicating a physical connection between star formation and AGN activities in these dwarf galaxies.

Keywords: Active galaxies, Dwarf galaxies, Galaxy stellar content, Galaxies
The H I Structure of the Local Volume Dwarf Galaxy Pisces A. Dedicated H I surveys have recently led to a growing category of low-mass galaxies found in the Local Volume. We present synthesis imaging of one such galaxy, Pisces A, a low-mass dwarf originally confirmed via optical imaging and spectroscopy of neutral hydrogen (H I) sources in the Galactic Arecibo L-band Feed Array H I survey. Using H I observations taken with the Karl G. Jansky Very Large Array, we characterize the kinematic structure of the gas and connect it to the galaxy&amp;'s environment and evolutionary history. While the galaxy shows overall ordered rotation, a number of kinematic features indicate a disturbed gas morphology. These features are suggestive of a tumultuous recent history and represent $\sim 3.5$ % of the total baryonic mass. We find a total baryon fraction ${f}_{\mathrm{bary}}=0.13$ if we include these features. We also quantify the cosmic environment of Pisces A, finding an apparent alignment of the disturbed gas with nearby, large-scale filamentary structure at the edge of the Local Void. We consider several scenarios for the origin of the disturbed gas, including gas stripping via ram pressure or galaxy-galaxy interactions, as well as accretion and ram pressure compression. Though we cannot rule out a past interaction with a companion, our observations best support the suggestion that the neutral gas morphology and recent star formation in Pisces A are a direct result of its interactions with the intergalactic medium.

Keywords: Dwarf galaxies, Radio galaxies, Galaxies
Subaru High-z Exploration of Low-luminosity Quasars (SHELLQs). XI. Proximity Zone Analysis for Faint Quasar Spectra at z ∼ 6. We present measurements of the size of the quasar proximity zone (Rp) for 11 low-luminosity ( $-26.16\leqslant {M}_{1450}\leqslant -22.83$ ) quasars at z ∼ 6, discovered by the Subaru High-z Exploration of Low-Luminosity Quasars project. Our faint quasar sample expands the Rp measurement down to ${M}_{1450}=-22.83$ mag, where more common quasar populations dominate at the epoch. We restrict the sample to quasars whose systemic redshifts have been precisely measured by [C II] 158 μm or Mg II λ2798 emission lines. We also update the Rp measurements for 26 luminous quasars presented in Eilers et al. by using the latest systemic redshift results. The luminosity dependence on Rp is found to be consistent with the theoretical prediction assuming a highly ionized intergalactic medium. We find a shallow redshift evolution of the luminosity-corrected Rp, ${R}_{p,\mathrm{corr}}^{-25}$ ( ${R}_{p,\mathrm{corr}}^{-25}\propto {(1+z)}^{-3.79\pm 1.72}$ ) over $5.8\lesssim z\lesssim 6.6$ . This trend is steeper than that of Eilers et al., but significantly shallower than those of the earlier studies. Our results suggest that Rp,corr is insensitive to the neutral fraction of the universe at z ∼ 6. Four quasars show exceptionally small ${R}_{p,\mathrm{corr}}^{-25}$ ( $\lesssim 0.90$ proper Mpc), which could be the result of their young age (&lt;104 yr) in the reionization epoch, though statistics on this are still scarce.

Keywords: Reionization, Quasar absorption line spectroscopy, Intergalactic medium
Spectral Signatures of PeVatrons. We analyze the energy distributions of final (stable) products—gamma rays, neutrinos, and electrons—produced in inelastic proton-proton collisions in the PeV energy regime. We also calculate the energy spectrum of synchrotron radiation from secondary electrons, assuming that these are promptly cooled in the surrounding magnetic field. We show that the synchrotron radiation has an energy distribution much shallower than that of primary protons, hence we suggest taking advantage of such a feature in the spectral analysis of the highest-energy (cutoff) emission region from particle accelerators. For a broad range of energy distributions in the parent protons, we propose simple analytical presentations for the spectra of secondaries in the cutoff region. These results can be used in the interpretation of high-energy radiation from PeVatrons—cosmic-ray factories accelerating protons to energies up to 1 PeV.

Keywords: High-energy cosmic radiation, Spectral energy distribution, Particle astrophysics, Gamma-rays