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<jats:title>Abstract</jats:title> <jats:p>We use Hubble Space Telescope Wide Field Camera 3 G102 and G141 grism spectroscopy to measure rest-frame optical emission-line ratios of 533 galaxies at <jats:italic>z</jats:italic> ∼ 1.5 in the CANDELS Ly<jats:italic>α</jats:italic> Emission at Reionization survey. We compare [O <jats:sc>iii</jats:sc>]/H<jats:italic>β</jats:italic> versus [S <jats:sc>ii</jats:sc>]/(H<jats:italic>α</jats:italic> + [N <jats:sc>ii</jats:sc>]) as an “unVO87” diagram for 461 galaxies and [O <jats:sc>iii</jats:sc>]/H<jats:italic>β</jats:italic> versus [Ne <jats:sc>iii</jats:sc>]/[O <jats:sc>ii</jats:sc>] as an “OHNO” diagram for 91 galaxies. The unVO87 diagram does not effectively separate active galactic nuclei (AGN) and [Ne <jats:sc>v</jats:sc>] sources from star-forming galaxies, indicating that the unVO87 properties of star-forming galaxies evolve with redshift and overlap with AGN emission-line signatures at <jats:italic>z</jats:italic> &gt; 1. The OHNO diagram does effectively separate X-ray AGN and [Ne <jats:sc>v</jats:sc>]-emitting galaxies from the rest of the population. We find that the [O <jats:sc>iii</jats:sc>]/H<jats:italic>β</jats:italic> line ratios are significantly anticorrelated with stellar mass and significantly correlated with <jats:inline-formula> <jats:tex-math> <?CDATA $\mathrm{log}({L}_{{\rm{H}}\beta })$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>log</mml:mi> <mml:mo stretchy="false">(</mml:mo> <mml:msub> <mml:mrow> <mml:mi>L</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">H</mml:mi> <mml:mi>β</mml:mi> </mml:mrow> </mml:msub> <mml:mo stretchy="false">)</mml:mo> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac3919ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>, while [S <jats:sc>ii</jats:sc>]/(H<jats:italic>α</jats:italic> + [N <jats:sc>ii</jats:sc>]) is significantly anticorrelated with <jats:inline-formula> <jats:tex-math> <?CDATA $\mathrm{log}({L}_{{\rm{H}}\beta })$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>log</mml:mi> <mml:mo stretchy="false">(</mml:mo> <mml:msub> <mml:mrow> <mml:mi>L</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">H</mml:mi> <mml:mi>β</mml:mi> </mml:mrow> </mml:msub> <mml:mo stretchy="false">)</mml:mo> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac3919ieqn2.gif" xlink:type="simple" /> </jats:inline-formula>. Comparison with MAPPINGS V photoionization models indicates that these trends are consistent with lower metallicity and higher ionization in low-mass and high-star formation rate (SFR) galaxies. We do not find evidence for redshift evolution of the emission-line ratios outside of the correlations with mass and SFR. Our results suggest that the OHNO diagram of [O <jats:sc>iii</jats:sc>]/H<jats:italic>β</jats:italic> versus [Ne <jats:sc>iii</jats:sc>]/[O <jats:sc>ii</jats:sc>] will be a useful indicator of AGN content and gas conditions in very high-redshift galaxies to be observed by the James Webb Space Telescope.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present a detailed physical analysis of the jet-launching mechanism of a circumstellar disk that is located in a binary system. Applying 3D resistive magnetohydrodynamics simulations, we investigate the local and global properties of the system, such as angular momentum transport and accretion and ejection mass fluxes. In comparison to previous works, for the first time we have considered the full magnetic torque, the presence of an outflow and thus the angular momentum transport by vertical motion, and the binary torque. We discuss its specific 3D structure and how it is affected by tidal effects. We find that the spiral structure evolving in the disk is launched into the outflow. We propose calling this newly discovered structure a jet spiral wall. These spiral features follow the same time evolution, with the jet spiral somewhat lagging the disk spiral. We find that the vertical transport of angular momentum has a significant role in the total angular momentum budget also in a binary system. The same holds for the magnetic torque; however, the contribution from the <jats:italic>ϕ</jats:italic>derivative of the magnetic pressure and<jats:italic> B</jats:italic> <jats:sub> <jats:italic>ϕ</jats:italic> </jats:sub> <jats:italic>B</jats:italic> <jats:sub> <jats:italic>r</jats:italic> </jats:sub> stresses are small. The gravity torque arising from the time-dependent 3D Roche potential becomes essential, as it constitutes the fundamental cause for all 3D effects appearing in our disk–jet system. Quantitatively, we find that the disk accretion rate in a binary system increases by 20% compared to a disk around a single star. The disk wind mass flux increases by even 50%.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Current observational evidence suggests that all large galaxies contain globular clusters (GCs), while the smallest galaxies do not. Over what galaxy mass range does the transition from GCs to no GCs occur? We investigate this question using galaxies in the Local Group (LG), nearby dwarf galaxies, and galaxies in the Virgo Cluster Survey. We consider four types of statistical model: (1) logistic regression to model the probability that a galaxy of stellar mass <jats:italic>M</jats:italic> <jats:sub>*</jats:sub> has any number of GCs; (2) Poisson regression to model the number of GCs versus <jats:italic>M</jats:italic> <jats:sub>*</jats:sub>; (3) linear regression to model the relation between GC system mass (<jats:inline-formula> <jats:tex-math> <?CDATA $\mathrm{log}{M}_{\mathrm{gcs}}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>log</mml:mi> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>gcs</mml:mi> </mml:mrow> </mml:msub> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac33b0ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>) and host galaxy mass (<jats:inline-formula> <jats:tex-math> <?CDATA $\mathrm{log}{M}_{\star }$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>log</mml:mi> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>⋆</mml:mo> </mml:mrow> </mml:msub> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac33b0ieqn2.gif" xlink:type="simple" /> </jats:inline-formula>); and (4) a Bayesian lognormal hurdle model of the GC system mass as a function of galaxy stellar mass for the entire data sample. From the logistic regression, we find that the 50% probability point for a galaxy to contain GCs is <jats:italic>M</jats:italic> <jats:sub>*</jats:sub> = 10<jats:sup>6.8</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>. From postfit diagnostics, we find that Poisson regression is an inappropriate description of the data. Ultimately, we find that the Bayesian lognormal hurdle model, which is able to describe how the mass of the GC system varies with <jats:italic>M</jats:italic> <jats:sub>*</jats:sub> even in the presence of many galaxies with no GCs, is the most appropriate model over the range of our data. In an Appendix, we also present photometry for the little-known GC in the LG dwarf Ursa Major II.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Dual supermassive black holes (SMBHs) at ∼kiloparsec scales are the progenitor population of SMBH mergers and play an important role in understanding the pairing and dynamical evolution of massive black holes in galaxy mergers. Because of the stringent resolution requirement and the apparent rareness of these small-separation pairs, there are scarce observational constraints on this population, with few confirmed dual SMBHs at &lt;10 kpc separations at <jats:italic>z</jats:italic> &gt; 1. Here we present results from a pilot search for kiloparsec-scale dual quasars selected with Gaia Data release 2 (DR2) astrometry and followed up with Hubble Space Telescope (HST) Wide Field Camera 3 dual-band (F475W and F814W) snapshot imaging. Our targets are quasars primarily selected with the varstrometry technique, i.e., light centroid jitter caused by asynchronous variability from both members in an unresolved quasar pair, supplemented by subarcsecond pairs already resolved by Gaia DR2. We find an overall high fraction of HST-resolved pairs among the varstrometry-selected quasars (unresolved in Gaia DR2), ∼30%–50%, increasing toward high redshift (∼60%–80% at <jats:italic>z</jats:italic> &gt; 1.5). We discuss the nature of the 45 resolved subarcsecond pairs based on HST and supplementary data. A substantial fraction (∼40%) of these pairs are likely physical quasar pairs or gravitationally lensed quasars. We also discover a triple quasar candidate and a quadruply lensed quasar, which is among the smallest-separation quadruple lenses. These results provide important guidelines to improve varstrometry selection and follow-up confirmation of ~kiloparsec-scale dual SMBHs at high redshift.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present 850 <jats:italic>μ</jats:italic>m polarimetric observations toward the Serpens Main molecular cloud obtained using the POL-2 polarimeter on the James Clerk Maxwell Telescope as part of the B-fields In STar-forming Region Observations survey. These observations probe the magnetic field morphology of the Serpens Main molecular cloud on about 6000 au scales, which consists of cores and six filaments with different physical properties such as density and star formation activity. Using the histogram of relative orientation (HRO) technique, we find that magnetic fields are parallel to filaments in less-dense filamentary structures where <jats:inline-formula> <jats:tex-math> <?CDATA ${N}_{{{\rm{H}}}_{2}}\lt 0.93\times {10}^{22}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>N</mml:mi> </mml:mrow> <mml:mrow> <mml:msub> <mml:mrow> <mml:mi mathvariant="normal">H</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msub> </mml:mrow> </mml:msub> <mml:mo>&lt;</mml:mo> <mml:mn>0.93</mml:mn> <mml:mo>×</mml:mo> <mml:msup> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> <mml:mrow> <mml:mn>22</mml:mn> </mml:mrow> </mml:msup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac4bbeieqn1.gif" xlink:type="simple" /> </jats:inline-formula> cm<jats:sup>−2</jats:sup> (magnetic fields perpendicular to density gradients), while they are perpendicular to filaments (magnetic fields parallel to density gradients) in dense filamentary structures with star formation activity. Moreover, applying the HRO technique to denser core regions, we find that magnetic field orientations change to become perpendicular to density gradients again at <jats:inline-formula> <jats:tex-math> <?CDATA ${N}_{{{\rm{H}}}_{2}}\approx 4.6\times {10}^{22}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>N</mml:mi> </mml:mrow> <mml:mrow> <mml:msub> <mml:mrow> <mml:mi mathvariant="normal">H</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msub> </mml:mrow> </mml:msub> <mml:mo>≈</mml:mo> <mml:mn>4.6</mml:mn> <mml:mo>×</mml:mo> <mml:msup> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> <mml:mrow> <mml:mn>22</mml:mn> </mml:mrow> </mml:msup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac4bbeieqn2.gif" xlink:type="simple" /> </jats:inline-formula> cm<jats:sup>−2</jats:sup>. This can be interpreted as a signature of core formation. At <jats:inline-formula> <jats:tex-math> <?CDATA ${N}_{{{\rm{H}}}_{2}}\approx 16\times {10}^{22}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>N</mml:mi> </mml:mrow> <mml:mrow> <mml:msub> <mml:mrow> <mml:mi mathvariant="normal">H</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msub> </mml:mrow> </mml:msub> <mml:mo>≈</mml:mo> <mml:mn>16</mml:mn> <mml:mo>×</mml:mo> <mml:msup> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> <mml:mrow> <mml:mn>22</mml:mn> </mml:mrow> </mml:msup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac4bbeieqn3.gif" xlink:type="simple" /> </jats:inline-formula> cm<jats:sup>−2</jats:sup>, magnetic fields change back to being parallel to density gradients once again, which can be understood to be due to magnetic fields being dragged in by infalling material. In addition, we estimate the magnetic field strengths of the filaments (<jats:italic>B</jats:italic> <jats:sub>POS</jats:sub> = 60–300 <jats:italic>μ</jats:italic>G)) using the Davis–Chandrasekhar–Fermi method and discuss whether the filaments are gravitationally unstable based on magnetic field and turbulence energy densities.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We perform three-dimensional smoothed-particle hydrodynamics simulations of warped, non-coplanar gravitationally unstable discs to show that as the warp propagates through the self-gravitating disk, it heats up the disk rendering it gravitationally stable, thus losing their spiral structure and appearing completely axisymmetric. In their youth, protoplanetary discs are expected to be massive and self-gravitating, which results in nonaxisymmetric spiral structures. However recent observations of young protoplanetary discs with the Atacama Large Millimeter/submillimeter Array have revealed that discs with large-scale spiral structure are rarely observed in the midplane. Instead, axisymmetric discs, with some also having ring and gap structures, are more commonly observed. Our work invloving warps, non-coplanar disk structures that are expected to commonly occur in young discs, potentially resolves this discrepancy between observations and theoretical predictions. We demonstrate that they are able to suppress the large-scale spiral structure of self-gravitating protoplanetary discs.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Observations of solar flare reconnection at very high spatial and temporal resolution can be made indirectly at the footpoints of reconnected loops into which flare energy is deposited. The response of the lower atmosphere to this energy input includes a downward-propagating shock called chromospheric condensation, which can be observed in the UV and visible. In order to characterize reconnection using high-resolution observations of this response, one must develop a quantitative relationship between the two. Such a relation was recently developed, and here we test it on observations of chromospheric condensation in a single footpoint from a flare ribbon of the X1.0 flare on 2014 October 25 (SOL2014-10-25T16:56:36). Measurements taken of Si <jats:sc>iv</jats:sc> 1402.77 Å emission spectra using the Interface Region Imaging Spectrograph (IRIS) in a single pixel show the redshifted component undergoing characteristic condensation evolution. We apply the technique called the Ultraviolet Footpoint Calorimeter to infer energy deposition into one footpoint. This energy profile, persisting much longer than the observed condensation, is input into a one-dimensional, hydrodynamic simulation to compute the chromospheric response, which contains a very brief condensation episode. From this simulation, we synthesize Si <jats:sc>iv</jats:sc> spectra and compute the time-evolving Doppler velocity. The synthetic velocity evolution is found to compare reasonably well with the IRIS observation, thus corroborating our reconnection–condensation relationship. The exercise reveals that the chromospheric condensation characterizes a particular portion of the reconnection energy release rather than its entirety, and that the timescale of condensation does not necessarily reflect the timescale of energy input.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Accurate determinations of stellar parameters and distances for large complete samples of stars are keys for conducting detailed studies of the formation and evolution of our Galaxy. Here we present stellar atmospheric parameters (effective temperature, luminosity classifications, and metallicity) estimates for some 24 million stars determined from the stellar colors of SMSS DR2 and Gaia EDR3, based on training data sets with available spectroscopic measurements from previous high/medium/low-resolution spectroscopic surveys. The number of stars with photometric-metallicity estimates is 4–5 times larger than that collected by the current largest spectroscopic survey to date—LAMOST—over the course of the past decade. External checks indicate that the precision of the photometric-metallicity estimates are quite high, comparable to or slightly better than that derived from spectroscopy, with typical values around 0.05–0.15 dex for both dwarf and giant stars with [Fe/H] &gt; −2.01.0, 0.10–0.20 dex for giant stars with −2.0 &lt; [Fe/H] ≤ −1.0, and 0.20–0.25 dex for giant stars with [Fe/H] ≤ −2.0, and include estimates for stars as metal-poor as [Fe/H] ∼ −3.5, substantially lower than previous photometric techniques. Photometric-metallicity estimates are obtained for an unprecedented number of metal-poor stars, including a total of over three million metal-poor (MP; [Fe/H] ≤ −1.0) stars, over half a million very metal-poor (VMP; [Fe/H] ≤ −2.0) stars, and over 25,000 extremely metal-poor (EMP; [Fe/H] ≤ −3.0) stars. Moreover, distances are determined for over 20 million stars in our sample. For the over 18 million sample stars with accurate Gaia parallaxes, stellar ages are estimated by comparing with theoretical isochrones. Astrometric information is provided for the stars in our catalog, along with radial velocities for ∼10% of our sample stars, taken from completed/ongoing large-scale spectroscopic surveys.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present a study of narrow filaments toward a massive infrared dark cloud, NGC 6334S, using the Atacama Large Millimeter/submillimeter Array. Thirteen gas filaments are identified using the H<jats:sup>13</jats:sup>CO<jats:sup>+</jats:sup> line, while a single continuum filament is revealed by the continuum emission. The filaments present a compact radial distribution with a median filament width of ∼0.04 pc, narrower than the previously proposed “quasi-universal” 0.1 pc filament width. The higher spatial resolution observations and higher density gas tracer tend to identify even narrower and lower mass filaments. The filament widths are roughly twice the size of embedded cores. The gas filaments are largely supported by thermal motions. The nonthermal motions are predominantly subsonic and transonic in both identified gas filaments and embedded cores, which may imply that stars are likely born in environments of low turbulence. A fraction of embedded objects show a narrower velocity dispersion compared with their corresponding natal filaments, which may indicate that turbulent dissipation is taking place in these embedded cores. The physical properties (mass, mass per unit length, gas kinematics, and width) of gas filaments are analogous to those of narrow filaments found in low- to high-mass star-forming regions. The more evolved sources are found to be farther away from the filaments, a situation that may have resulted from the relative motions between the young stellar objects and their natal filaments.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The inner ∼200 pc region of the Galaxy contains a 4 million M<jats:sub>⊙</jats:sub> supermassive black hole (SMBH), significant quantities of molecular gas, and star formation and cosmic-ray energy densities that are roughly two orders of magnitude higher than the corresponding levels in the Galactic disk. At a distance of only 8.2 kpc, the region presents astronomers with a unique opportunity to study a diverse range of energetic astrophysical phenomena, from stellar objects in extreme environments, to the SMBH and star-formation-driven feedback processes that are known to influence the evolution of galaxies as a whole. We present a new survey of the Galactic center conducted with the South African MeerKAT radio telescope. Radio imaging offers a view that is unaffected by the large quantities of dust that obscure the region at other wavelengths, and a scene of striking complexity is revealed. We produce total-intensity and spectral-index mosaics of the region from 20 pointings (144 hr on-target in total), covering 6.5 square degrees with an angular resolution of 4″ at a central frequency of 1.28 GHz. Many new features are revealed for the first time due to a combination of MeerKAT’s high sensitivity, exceptional <jats:italic>u</jats:italic>, <jats:italic>v</jats:italic>-plane coverage, and geographical vantage point. We highlight some initial survey results, including new supernova remnant candidates, many new nonthermal filament complexes, and enhanced views of the Radio Arc bubble, Sagittarius A, and Sagittarius B regions. This project is a South African Radio Astronomy Observatory public legacy survey, and the image products are made available with this article.</jats:p>