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<jats:title>Abstract</jats:title> <jats:p>We present the observation and analysis of newly discovered coherent structures in the L1688 region of Ophiuchus and the B18 region of Taurus. Using data from the Green Bank Ammonia Survey, we identify regions of high density and near-constant, almost-thermal velocity dispersion. We reveal 18 coherent structures are revealed, 12 in L1688 and 6 in B18, each of which shows a sharp “transition to coherence” in velocity dispersion around its periphery. The identification of these structures provides a chance to statistically study the coherent structures in molecular clouds. The identified coherent structures have a typical radius of 0.04 pc and a typical mass of 0.4 <jats:italic>M</jats:italic> <jats:sub>☉</jats:sub>, generally smaller than previously known coherent cores identified by Goodman et al., Caselli et al., and Pineda et al. We call these structures “droplets.” We find that, unlike previously known coherent cores, these structures are not virially bound by self-gravity and are instead predominantly confined by ambient pressure. The droplets have density profiles shallower than a critical Bonnor–Ebert sphere, and they have a velocity (<jats:italic>V</jats:italic> <jats:sub>LSR</jats:sub>) distribution consistent with the dense gas motions traced by NH<jats:sub>3</jats:sub> emission. These results point to a potential formation mechanism through pressure compression and turbulent processes in the dense gas. We present a comparison with a magnetohydrodynamic simulation of a star-forming region, and we speculate on the relationship of droplets with larger, gravitationally bound coherent cores, as well as on the role that droplets and other coherent structures play in the star formation process.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>A precise interstellar dust extinction law is critically important to interpret observations. There are two indicators of extinction: the color excess ratio (CER) and the relative extinction. Compared to the CER, the wavelength-dependent relative extinction is more challenging to be determined. In this work, we combine spectroscopic, astrometric, and photometric data to derive high-precision CERs and relative extinction from optical to mid-infrared (IR) bands. A group of 61,111 red clump (RC) stars are selected as tracers by stellar parameters from the Apache Point Observatory Galaxy Evolution Experiment survey. The multiband photometric data are collected from <jats:italic>Gaia</jats:italic>, APASS, Sloan Digital Sky Survey, Pan-STARRS1, Two Micron All Sky Survey, and <jats:italic>Wide-field Infrared Survey Explorer</jats:italic> surveys. For the first time, we calibrate the curvature of CERs in determining CERs <jats:italic>E</jats:italic>(<jats:italic>λ</jats:italic> − <jats:italic>G</jats:italic> <jats:sub>RP</jats:sub>)/<jats:italic>E</jats:italic>(<jats:italic>G</jats:italic> <jats:sub>BP</jats:sub> − <jats:italic>G</jats:italic> <jats:sub>RP</jats:sub>) from color excess–color excess diagrams. Through elaborate uncertainty analysis, we conclude that the precision of our CERs is significantly improved (<jats:italic>σ</jats:italic> &lt; 0.015). With parallaxes from <jats:italic>Gaia</jats:italic> DR2, we calculate the relative extinction <jats:inline-formula> <jats:tex-math> <?CDATA ${A}_{{G}_{\mathrm{BP}}}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjab1c61ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>/<jats:inline-formula> <jats:tex-math> <?CDATA ${A}_{{G}_{\mathrm{RP}}}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjab1c61ieqn2.gif" xlink:type="simple" /> </jats:inline-formula> for 5051 RC stars. By combining the CERs with the <jats:inline-formula> <jats:tex-math> <?CDATA ${A}_{{G}_{\mathrm{BP}}}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjab1c61ieqn3.gif" xlink:type="simple" /> </jats:inline-formula>/<jats:inline-formula> <jats:tex-math> <?CDATA ${A}_{{G}_{\mathrm{RP}}}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjab1c61ieqn4.gif" xlink:type="simple" /> </jats:inline-formula>, the optical–mid-IR extinction <jats:italic>A</jats:italic> <jats:sub> <jats:italic>λ</jats:italic> </jats:sub>/<jats:inline-formula> <jats:tex-math> <?CDATA ${A}_{{G}_{\mathrm{RP}}}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjab1c61ieqn5.gif" xlink:type="simple" /> </jats:inline-formula> has been determined in a total of 21 bands. Given no bias toward any specific environment, our extinction law represents the average extinction law with the total-to-selective extinction ratio <jats:italic>R</jats:italic> <jats:sub>V</jats:sub> = 3.16 ± 0.15. Our observed extinction law supports an adjustment in parameters of the CCM <jats:italic>R</jats:italic> <jats:sub>V</jats:sub> = 3.1 curve, together with the near-IR (NIR) power-law index <jats:italic>α</jats:italic> = 2.07 ± 0.03. The relative extinction values of the <jats:italic>Hubble Space Telescope</jats:italic> (<jats:italic>HST</jats:italic>) and the <jats:italic>James Webb Space Telescope</jats:italic> (<jats:italic>JWST</jats:italic>) NIR bandpasses are predicted in 2.5% precision. As the observed reddening/extinction tracks are curved, the curvature correction needs to be considered when applying extinction correction.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>In order for the <jats:italic>Wide-Field Infrared Survey Telescope</jats:italic> (<jats:italic>WFIRST</jats:italic>) and other stage IV dark energy experiments (e.g., Large Synoptic Survey Telescope, LSST; and <jats:italic>Euclid</jats:italic>) to infer cosmological parameters not limited by systematic errors, accurate redshift measurements are needed. This accuracy can be met by using spectroscopic subsamples to calibrate the photometric redshifts for the full sample. In this work, we find the minimal number of spectra required for the <jats:italic>WFIRST</jats:italic> weak-lensing redshift calibration by employing the Self-Organizing Map (SOM) spectroscopic sampling technique. We use galaxies from the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS) to build the LSST+<jats:italic>WFIRST</jats:italic> lensing analog sample of ∼36,000 objects and to train the LSST+<jats:italic>WFIRST</jats:italic> SOM. We find that 26% of the <jats:italic>WFIRST</jats:italic> lensing sample consists of sources fainter than the <jats:italic>Euclid</jats:italic> depth in the optical, 91% of which live in color cells already occupied by brighter galaxies. We demonstrate the similarity between faint and bright galaxies as well as the feasibility of redshift measurements at different brightness levels. Our results suggest that the spectroscopic sample acquired for calibration to the <jats:italic>Euclid</jats:italic> depth is sufficient for calibrating the majority of the <jats:italic>WFIRST</jats:italic> color space. For the spectroscopic sample to fully represent the synthetic color space of <jats:italic>WFIRST</jats:italic>, we recommend obtaining additional spectroscopy of ∼0.2–1.2k new sources in cells occupied by mostly faint galaxies. We argue that either the small area of the CANDELS fields and the small overall sample size or the large photometric errors might be the reason for no/fewer bright galaxies mapped to these cells. Acquiring the spectra of these sources will confirm the above findings and will enable the comprehensive calibration of the <jats:italic>WFIRST</jats:italic> color–redshift relation.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The Space Telescope and Optical Reverberation Mapping Project (AGN STORM) on NGC 5548 in 2014 is one of the most intensive multiwavelength AGN monitoring campaigns ever. For most of the campaign, the emission-line variations followed changes in the continuum with a time lag, as expected. However, the lines varied independently of the observed UV-optical continuum during a 60–70 day “holiday,” suggesting that unobserved changes to the ionizing continuum were present. To understand this remarkable phenomenon and to obtain an independent assessment of the ionizing continuum variations, we study the intrinsic absorption lines present in NGC 5548. We identify a novel cycle that reproduces the absorption line variability and thus identify the physics that allows the holiday to occur. In this cycle, variations in this obscurer’s line-of-sight covering factor modify the soft X-ray continuum, changing the ionization of helium. Ionizing radiation produced by recombining helium then affects the level of ionization of some ions seen by the <jats:italic>Hubble Space Telescope</jats:italic>. In particular, high-ionization species are affected by changes in the obscurer covering factor, which does not affect the optical or UV continuum, and thus appear as uncorrelated changes, a “holiday.” It is likely that any other model that selectively changes the soft X-ray part of the continuum during the holiday can also explain the anomalous emission-line behavior observed.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present observations of the <jats:italic>C</jats:italic>-band 1<jats:sub>10</jats:sub>–1<jats:sub>11</jats:sub> (4.8 GHz) and <jats:italic>Ku</jats:italic>-band 2<jats:sub>11</jats:sub>–2<jats:sub>12</jats:sub> (14.5 GHz) K-doublet lines of H<jats:sub>2</jats:sub>CO and the <jats:italic>C</jats:italic>-band 1<jats:sub>10</jats:sub>–1<jats:sub>11</jats:sub> (4.6 GHz) line of H<jats:sub>2</jats:sub> <jats:sup>13</jats:sup>CO toward a large sample of Galactic molecular clouds, through the Shanghai Tianma 65 m radio telescope (TMRT). Our sample with 112 sources includes strong H<jats:sub>2</jats:sub>CO sources from the TMRT molecular line survey at <jats:italic>C</jats:italic>-band and other known H<jats:sub>2</jats:sub>CO sources. All three lines are detected toward 38 objects (43 radial velocity components) yielding a detection rate of 34%. Complementary observations of their continuum emission at both <jats:italic>C</jats:italic>- and <jats:italic>Ku</jats:italic>-bands were performed. Combining spectral line parameters and continuum data, we calculate the column densities, the optical depths and the isotope ratio H<jats:sub>2</jats:sub> <jats:sup>12</jats:sup>CO/H<jats:sub>2</jats:sub> <jats:sup>13</jats:sup>CO for each source. To evaluate photon trapping caused by sometimes significant opacities in the main isotopologue’s rotational mm-wave lines connecting our measured K-doublets, and to obtain <jats:sup>12</jats:sup>C/<jats:sup>13</jats:sup>C abundance ratios, we used the RADEX non-LTE model accounting for radiative transfer effects. This implied the use of the new collision rates from Wiesenfeld &amp; Faure. Also implementing distance values from trigonometric parallax measurements for our sources, we obtain a linear fit of <jats:sup>12</jats:sup>C/<jats:sup>13</jats:sup>C = (5.08 ± 1.10)<jats:italic>D</jats:italic> <jats:sub>GC</jats:sub> + (11.86 ± 6.60), with a correlation coefficient of 0.58. <jats:italic>D</jats:italic> <jats:sub>GC</jats:sub> refers to Galactocentric distances. Our <jats:sup>12</jats:sup>C/<jats:sup>13</jats:sup>C ratios agree very well with the ones deduced from CN and C<jats:sup>18</jats:sup>O but are lower than those previously reported on the basis of H<jats:sub>2</jats:sub>CO, tending to suggest that the bulk of the H<jats:sub>2</jats:sub>CO in our sources was formed on dust grain mantles and not in the gas phase.</jats:p>