Sazuna/UAT_keywords huggingface dataset:
Evidence for the Accretion of Gas in Star-forming Galaxies: High N/O Abundances in Regions of Anomalously Low Metallicity. While all models for the evolution of galaxies require the accretion of gas to sustain their growth via on-going star formation, it has proven difficult to directly detect this inflowing material. In this paper we use data of nearby star-forming galaxies in the SDSS IV Mapping Nearby Galaxies at Apache Point Observatory survey to search for evidence of accretion imprinted in the chemical composition of the interstellar medium. We measure both the O/H and N/O abundance ratios in regions previously identified as having anomalously low values of O/H. We show that the unusual locations of these regions in the N/O versus O/H plane indicate that they have been created through the mixing of disk gas having higher metallicity with accreted gas having lower metallicity. Taken together with previous analysis on these anomalously low-metallicity regions, these results imply that accretion of metal-poor gas can probably sustain star formation in present-day late-type galaxies.

Keywords: Surveys, Galaxy physics, Galaxy abundances, Spectroscopy
Timing Calibration of the NuSTAR X-Ray Telescope. The Nuclear Spectroscopic Telescope Array (NuSTAR) mission is the first focusing X-ray telescope in the hard X-ray (3-79 keV) band. Among the phenomena that can be studied in this energy band, some require high time resolution and stability: rotation-powered and accreting millisecond pulsars, fast variability from black holes and neutron stars, X-ray bursts, and more. Moreover, a good alignment of the timestamps of X-ray photons to UTC is key for multi-instrument studies of fast astrophysical processes. In this paper, we describe the timing calibration of the NuSTAR mission. In particular, we present a method to correct the temperature-dependent frequency response of the on-board temperature-compensated crystal oscillator. Together with measurements of the spacecraft clock offsets obtained during downlinks passes, this allows a precise characterization of the behavior of the oscillator. The calibrated NuSTAR event timestamps for a typical observation are shown to be accurate to a precision of ∼65 μs.

Keywords: X-ray astronomy, Cross-validation , Pulsar timing method, Millisecond pulsars, X-ray detectors, X-ray telescopes
A Large Population of Luminous Active Galactic Nuclei Lacking X-Ray Detections: Evidence for Heavy Obscuration?. We present a large sample of infrared-luminous candidate active galactic nuclei (AGNs) that lack X-ray detections in Chandra, XMM-Newton, and NuSTAR fields. We selected all optically detected SDSS sources with redshift measurements, combined additional broadband photometry from WISE, UKIDSS, 2MASS, and GALEX, and modeled the spectral energy distributions (SEDs) of our sample sources. We parameterize nuclear obscuration in our SEDs with $E{\left(B-V\right)}_{\mathrm{AGN}}$ and uncover thousands of powerful obscured AGNs that lack X-ray counterparts, many of which are identified as AGN candidates based on straightforward WISE photometric criteria. Using the observed luminosity correlation between rest-frame 2-10 keV ( ${L}_{{\rm{X}}}$ ) and rest-frame AGN $6\,\mu {\rm{m}}$ ( ${L}_{\mathrm{MIR}}$ ), we estimate the intrinsic X-ray luminosities of our sample sources and combine these data with flux limits from X-ray catalogs to determine lower limits on nuclear obscuration. Using the ratio of intrinsic-to-observed X-ray luminosity ( ${R}_{{L}_{{\rm{X}}}}$ ), we find a significant fraction of sources with column densities approaching ${N}_{{\rm{H}}}\gt {10}^{24}$ cm-2, suggesting that multiwavelength observations are necessary to account for the population of heavily obscured AGNs. We simulate the underlying ${N}_{{\rm{H}}}$ distribution for the X-ray non-detected sources in our sample through survival analysis, and confirm the presence of AGN activity via X-ray stacking. Our results point to a considerable population of extremely obscured AGNs undetected by current X-ray observatories.

Keywords: Surveys, Active galaxies, Infrared galaxies, Quasars
Thermal and Turbulent Properties of the Warm Neutral Medium in the Solar Neighborhood. The transition from the diffuse warm neutral medium (WNM) to the dense cold neutral medium (CNM) is what set the initial conditions to the formation of molecular clouds. The properties of the turbulent cascade in the WNM, essential to describe this radiative condensation process, have remained elusive in part due to the difficulty in mapping out the structure and kinematics of each H I thermal phase. Here we present an analysis of a 21 cm hyper-spectral data cube from the GHIGLS H I survey where the contribution of the WNM is extracted using ROHSA, a Gaussian decomposition tool that includes spatial regularization. The distance and volume of the WNM emission is estimated using 3D dust extinction map information. The thermal and turbulent contributions to the Doppler line width of the WNM were disentangled using two techniques, one based on the statistical properties of the column density and centroid velocity fields, and the other on the relative motions of CNM structures as a probe of turbulent motions. We found that the volume of WNM sampled here (5.2 × 105 pc3), located at the outer edge of the Local Bubble, shows thermal properties in accordance with expected values for heating and cooling processes typical of the solar neighborhood: Pth/kB = (4.4 ± 2.6) × 103 K cm-3, n = 0.74 ± 0.41 cm-3, and Tk = (6.0 ± 1.3) × 103 K. The WNM has the properties of sub/trans-sonic turbulence, with a turbulent Mach number at the largest scale probed here (l = 130 pc) of ${{ \mathcal M }}_{s}=0.87\pm 0.15$ , a density contrast of ${\sigma }_{\rho /{\rho }_{0}}=0.6\pm 0.2$ , and velocity and density power spectra compatible with k-11/3. The low Mach number of the WNM provides dynamical conditions that allow the condensation mode of thermal instability to grow freely and form CNM structures, as predicted by theory.

Keywords: Warm neutral medium, Solar neighborhood, Interstellar atomic gas
Aurora Sightings Observed in Chinese History Caused by CIRs or Great-storm CMEs. Auroras observed at middle and low geographic latitudes are related to external inputs and varying geomagnetic fields. This work aims to exclude corotating interaction region (CIR) storms and identify strong coronal mass ejection (CME) storms according to historical auroral records when the geomagnetic field varies substantially. An existing catalog of the aurora records in Chinese history reported by Zeng &amp; Jin from 193 B.C. to 1911 A.D. is used. Archaeomagnetic field models are adopted to estimate the variation of the dipole field. According to the empirical relation between the equatorward boundary of the auroral oval, Dst index, and geomagnetic field intensity, the auroras caused by CIRs can be excluded, and those caused by strong CMEs are identified. After 1500 A.D., China's magnetic latitude decreased substantially due to the pole shift. This shift provides a better opportunity to investigate the existence of great-level storms. These great-storm CMEs occurred in both solar maximum and minimum. The space weather modeling framework is used to calculate the cusp area and the downward ion flux through the cusp for varied geomagnetic field and solar wind. For the present solar wind condition and tilt angle &lt;15°, stronger geomagnetic field tends to generate a larger cusp area and higher ion flux through the cusp. For the weaker solar wind in the Maunder minimum, the ion flux is lower, but the cusp area is similar to that at present.

Keywords: Geomagnetic fields, Solar coronal mass ejections
A Long Stream of Metal-poor Cool Gas around a Massive Starburst Galaxy at z = 2.67. We present the first detailed dissection of the circumgalactic medium (CGM) of massive starburst galaxies at z &gt; 2. Our target is a submillimeter galaxy (SMG) at z = 2.674 that has a star formation rate of 1200 M☉ yr-1 and a molecular gas reservoir of 1.3 × 1011 M☉. We characterize its CGM with two background QSOs at impact parameters of 93 kpc and 176 kpc. We detect strong H I and metal-line absorption near the redshift of the SMG toward both QSOs, each consisting of three main subsystems spanning over 1500 km s-1. The absorbers show remarkable kinematic and metallicity coherence across a separation of ∼86 kpc. In particular, the cool gas in the CGM of the SMG exhibits high H I column densities ( ${\rm{log}}({N}_{{\rm{H}}{\rm\small{I}}}/{{\rm{cm}}}^{-2})=20.2,18.6$ ), a low metallicity ([M/H] ≍ -2.0), and nearly the same radial velocity (δv ∼ -300 km s-1). While the H I column densities match previous results on the massive halos hosting QSOs, the metallicity is lower by more than an order of magnitude, making it an outlier in the line width-metallicity relation of damped Lyα absorbers. The large physical extent, the velocity coherence, the high surface densities, and the low metallicity are all consistent with the cool, inflowing, and near-pristine gas streams predicted to penetrate hot massive halos at z &gt; 1.5. We estimate a total gas accretion rate of ∼100 M☉ yr-1 from three such streams. At this rate, it takes only a gigayear to acquire the molecular gas reservoir of the central starburst.

Keywords: Starburst galaxies, Circumgalactic medium
Ensuring Robustness in Training-set-based Global 21 cm Cosmology Analysis. We present a methodology for ensuring the robustness of our analysis pipeline in separating the global 21 cm hydrogen cosmology signal from large systematics based on singular value decomposition (SVD) of training sets. We show how traditional goodness-of-fit metrics such as the χ2 statistic that assess the fit to the full data may not be able to detect a suboptimal extraction of the 21 cm signal when it is fit alongside one or more additional components owing to significant covariance between them. However, we find that comparing the number of SVD eigenmodes for each component chosen by the pipeline for a given fit to the distribution of eigenmodes chosen for synthetic data realizations created from training set curves can detect when one or more of the training sets is insufficient to optimally extract the signal. Furthermore, this test can distinguish which training set (e.g., foreground, 21 cm signal) needs to be modified in order to better describe the data and improve the quality of the 21 cm signal extraction. We also extend this goodness-of-fit testing to cases where a prior distribution derived from the training sets is applied and find that, in this case, the χ2 statistic and the recently introduced ψ2 statistic are able to detect inadequacies in the training sets due to the increased restrictions imposed by the prior. Crucially, the tests described in this paper can be performed when analyzing any type of observations with our pipeline.

Keywords: Cosmology, Astronomy data modeling, Observational cosmology, Astronomy data analysis, H I line emission, Reionization, Radio astronomy
Projected Cosmological Constraints from Strongly Lensed Supernovae with the Roman Space Telescope. One of the primary mission objectives of the Roman Space Telescope is to investigate the nature of dark energy with a variety of methods. Observations of Type I supernovae (SNe Ia) will be one of the principal anchors of the Roman cosmology program through traditional luminosity distance measurements. This SNe Ia cosmology program can provide another valuable cosmological probe, without altering the strategy of the mission: time delay cosmography with gravitationally lensed supernova (SN). In this work, we forecast lensed SN cosmology constraints with the Roman Space Telescope, while providing useful tools for future work. Using the anticipated characteristics of the Roman SNe Ia survey, we have constructed mock catalogs of expected resolved lensing systems, as well as strongly lensed Type Ia and core-collapse (CC) SN light curves, including microlensing effects. We predict Roman will find ∼11 lensed SNe Ia and ∼20 CCSNe, depending on the survey strategy. Next, we estimate the time delay precision obtainable with Roman (Ia: ∼2 days, CC: ∼3 days), and use a Fisher matrix analysis to derive projected constraints on H0,Ωm, and the dark energy equation of state, w, for each SNe Ia survey strategy. A strategy optimized for the discovery of high-redshift SNe Ia is preferred when considering the constraints possible from both SNe Ia and lensed SN cosmology, also delivering ∼1.5 times more lensed SNe than other proposed survey strategies.

Keywords: Gravitational microlensing, Strong gravitational lensing, Cosmology, Supernovae
The Nature of the Milky Way's Stellar Halo Revealed by the Three Integrals of Motion. We developed a new selection method of halo stars in the phase-space distribution defined by the three integrals of motion in an axisymmetric Galactic potential (E, Lz, I3), where I3 is the third integral of motion. The method is used to explore the general chemodynamical structure of the halo based on stellar samples from SDSS-SEGUE DR7 and APOGEE DR16, matched with Gaia DR2. We found the following. (a) Halo stars can be separated from disk stars by selecting over (1) 0 &lt; Lz &lt; 1500 kpc km s-1, ${(2{I}_{3})}^{1/2}\gt 1000$ kpc km s-1 (orbital angle θorb &gt; 15-20 deg), and E &lt; -1.5 × 105 km2 s-2, and (2) Lz &lt; 0 kpc km s-1. These selection criteria are free from kinematical biases introduced by the simple high-velocity cuts adopted in recent literature. (b) The averaged, or coarse-grained, halo phase-space distribution shows a monotonic, exponential decrease with increasing E and I3 like the Michie-Bodenheimer models. (c) The inner stellar halo described in Carollo et al. is found to comprise a combination of Gaia Enceladus debris (GE), lowest-E stars (likely in situ stars), and metal-poor prograde stars missed by the high-velocity cut selection. (d) The very metal-poor outer halo, ([Fe/H] &lt; -2.2), exhibits both retrograde and prograde rotation, with an asymmetric Lz distribution toward high retrograde motions and larger θorb than those possessed by the GE-dominated inner halo. (e) The Sgr dSph galaxy could induce a long-range dynamical effect on local halo stars. Implications for the formation of the stellar halo are also discussed.

Keywords: Stellar abundances, Milky Way stellar halo, Milky Way dynamics, Milky Way formation
ALMA 1.3 mm Survey of Lensed Submillimeter Galaxies Selected by Herschel: Discovery of Spatially Extended SMGs and Implications. We present an ALMA 1.3 mm (Band 6) continuum survey of lensed submillimeter galaxies (SMGs) at z = 1.0 to ∼3.2 with an angular resolution of ∼0"2. These galaxies were uncovered by the Herschel Lensing Survey and feature exceptionally bright far-infrared continuum emission (Speak ≳ 90 mJy) owing to their lensing magnification. We detect 29 sources in 20 fields of massive galaxy clusters with ALMA. Using both the Spitzer/IRAC (3.6/4.5 μm) and ALMA data, we have successfully modeled the surface brightness profiles of 26 sources in the rest-frame near- and far-infrared. Similar to previous studies, we find the median dust-to-stellar continuum size ratio to be small (Re,dust/Re,star = 0.38 ± 0.14) for the observed SMGs, indicating that star formation is centrally concentrated. This is, however, not the case for two spatially extended main-sequence SMGs with a low surface brightness at 1.3 mm (≲0.1 mJy arcsec-2), in which the star formation is distributed over the entire galaxy (Re,dust/Re,star &gt; 1). As a whole, our SMG sample shows a tight anticorrelation between (Re,dust/Re,star) and far-infrared surface brightness (ΣIR) over a factor of ≃1000 in ΣIR. This indicates that SMGs with less vigorous star formation (i.e., lower ΣIR) lack central starburst and are likely to retain a broader spatial distribution of star formation over the whole galaxies (i.e., larger Re,dust/Re,star). The same trend can be reproduced with cosmological simulations as a result of central starburst and potentially subsequent "inside-out" quenching, which likely accounts for the emergence of compact quiescent galaxies at z ∼ 2.

Keywords: Starburst galaxies, Galaxy evolution, Infrared galaxies, Submillimeter astronomy, High-redshift galaxies
Particle Acceleration by Relativistic Magnetic Reconnection Driven by Kink Instability Turbulence in Poynting Flux-Dominated Jets. Particle acceleration in magnetized relativistic jets still puzzles theorists. In this work, we investigate the acceleration of particles injected into a three-dimensional relativistic magnetohydrodynamical jet subject to current-driven kink (CDK) instability. We find that, once turbulence driven by CDK fully develops, achieving a nearly stationary state, the amplitude of excited wiggles along the jet spine attains maximum growth, causing disruption of the magnetic field lines and the formation of several sites of fast reconnection. Low-energy protons injected into the jet at this state experience exponential acceleration, mostly in directions parallel to the local magnetic field, up to maximum energies $E\sim {10}^{16}$ eV for $B\sim 0.1$ G and $E\sim {10}^{18}$ eV for $B\sim 10$ G. The Larmor radius of the particles attaining these energies corresponds to the size of the acceleration region (∼the diameter of the perturbed jet). There is a clear association of the accelerated particles with regions of fast reconnection. In the early nonlinear growth stage of the CDK, when there are no sites of fast reconnection yet, injected particles with initially much larger energy are accelerated by magnetic curvature drift. We have also obtained the acceleration time due to reconnection with a dependence on the particles' energy, ${t}_{A}\propto {E}^{0.1}$ . The energy spectrum of the accelerated particles develops a power-law index $p$ ∼ -1.2 in the beginning, in agreement with earlier works. Our results provide a multidimensional framework for exploring this process in real systems and explain their emission patterns, especially at very high energies, and associated neutrino emission recently detected in some blazars.

Keywords: Magnetohydrodynamics, High energy astrophysics, Magnetohydrodynamical simulations, Particle astrophysics, Cosmic rays
Mass-gap Mergers in Active Galactic Nuclei. The recently discovered gravitational wave sources GW190521 and GW190814 have shown evidence of BH mergers with masses and spins outside of the range expected from isolated stellar evolution. These merging objects could have undergone previous mergers. Such hierarchical mergers are predicted to be frequent in active galactic nuclei (AGNs) disks, where binaries form and evolve efficiently by dynamical interactions and gaseous dissipation. Here we compare the properties of these observed events to the theoretical models of mergers in AGN disks, which are obtained by performing one-dimensional N-body simulations combined with semi-analytical prescriptions. The high BH masses in GW190521 are consistent with mergers of high-generation (high-g) BHs where the initial progenitor stars had high metallicity, 2g BHs if the original progenitors were metal-poor, or 1g BHs that had gained mass via super-Eddington accretion. Other measured properties related to spin parameters in GW190521 are also consistent with mergers in AGN disks. Furthermore, mergers in the lower mass gap or those with low mass ratio as found in GW190814 and GW190412 are also reproduced by mergers of 2g-1g or 1g-1g objects with significant accretion in AGN disks. Finally, due to gas accretion, the massive neutron star merger reported in GW190425 can be produced in an AGN disk.

Keywords: Neutron stars, Black holes, Close binary stars, Gravitational wave sources, Gravitational wave astronomy, Active galactic nuclei, N-body simulations
Peeking Between the Pulses: The Far-UV Spectrum of the Previously Unseen White Dwarf in AR Scorpii. The compact object in the interacting binary AR Sco has widely been presumed to be a rapidly rotating, magnetized white dwarf (WD), but it has never been detected directly. Isolating its spectrum has proven difficult because the spin-down of the WD generates pulsed synchrotron radiation that far outshines the WD's photosphere. As a result, a previous study of AR Sco was unable to detect the WD in the averaged far-ultraviolet spectrum from a Hubble Space Telescope (HST) observation. In an effort to unveil the WD's spectrum, we reanalyze these HST observations by calculating the average spectrum in the troughs between synchrotron pulses. We identify weak spectral features from the previously unseen WD and estimate its surface temperature to be 11,500 ± 500 K. Additionally, during the synchrotron pulses, we detect broad Lyα absorption consistent with hot WD spectral models. We infer the presence of a pair of hotspots, with temperatures between 23,000 and 28,000 K, near the magnetic poles of the WD. As the WD is not expected to be accreting from its companion, we describe two possible mechanisms for heating the magnetic poles. The Lyα absorption of the hotspots appears relatively undistorted by Zeeman splitting, constraining the WD's field strength to be ≲100 MG, but the data are insufficient to search for the subtle Zeeman splits expected at lower field strengths.

Keywords: Rotation powered pulsars, White dwarf stars, DQ Herculis stars, Magnetic variable stars, Cataclysmic variable stars
Inspiraling Double Compact Object Detection and Lensing Rate: Forecast for DECIGO and B-DECIGO. Emergence of gravitational wave (GW) astronomy revived the interest in exploring the low-frequency GW spectrum inaccessible from the ground. Satellite GW observatory DECihertz Interferometer Gravitational wave Observatory (DECIGO) in its original configuration and the currently proposed smaller-scale B-DECIGO are aimed to cover the decihertz part of the GW spectrum, which fills the gap between LISA millihertz and deca- to kilohertz range probed by ground-based detectors. In this paper we forecast the detection rates of inspiraling double compact objects (DCOs) and the unresolved confusion noise from these sources in DECIGO and B-DECIGO. In the context of DECIGO we use, for the first time, the population synthesis intrinsic inspiral rates of NS-NS, BH-NS and BH-BH systems. We also estimate the expected gravitational lensing rates of such sources for DECIGO and B-DECIGO. The result is that yearly detection of resolvable DCOs inspirals for the DECIGO is of the order of 102-105, while for a much smaller-scale B-DECIGO they are about 10-105 depending on the DCO population considered. Taking into account that a considerable part of these events would be detectable by ground-based GW observatories, the significance of DECIGO/B-DECIGO could be substantial. Due to contamination by unresolved sources, both DECIGO and B-DECIGO will not be able to register lensed NS-NS or BH-NS systems, but the lensed BH-BH systems could be observed at the rate of about 50 per year in DECIGO. Smaller-scale B-DECIGO will be able to detect a few lensed BH-BH systems per year. We also address the question of the magnification bias in the GW event catalogs of DECIGO and B-DECIGO.

Keywords: Strong gravitational lensing, Gravitational wave detectors, Gravitational waves