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Low-mass stars like our Sun begin their evolution within cold (10 K) and dense ($\sim 10^5$ cm$^{-3}$) cores of gas and dust. The physical structure of starless cores is best probed by thermal emission of dust grains. We present a high resolution dust continuum study of the starless cores in the B10 region of the Taurus Molecular Cloud. New observations at 1.2mm and 2.0mm ($12^{"}$ and $18^{"}$ resolution) with the NIKA2 instrument on the IRAM 30m have probed the inner regions of 14 low-mass starless cores. We perform sophisticated 3D radiative transfer modelling for each of these cores through the radiative transfer framework $\textit{pandora}$, which utilizes RADMC-3D. Model best-fits constrain each cores' central density, density slope, aspect ratio, opacity, and interstellar radiation field strength. These `typical' cores in B10 span central densities from $5 \times 10^4 - 1 \times 10^6$ cm$^{-3}$, with a mean value of $2.6 \times 10^5$ cm$^{-3}$. We find the dust opacity laws assumed in the 3D modelling, as well as the estimates from $\textit{Herschel}$, have dust emissivity indices, $\beta$'s, on the lower end of the distribution constrained directly from the NIKA2 maps, which averages to $\beta = 2.01\pm0.48$. From our 3D density structures and archival NH$_3$ data, we perform a self-consistent virial analysis to assess each core's stability. Ignoring magnetic field contributions, we find 9 out of the 14 cores ($64\%$) are either in virial equilibrium or are bound by gravity and external pressure. To push the bounded cores back to equilibrium, an effective magnetic field difference of only $\sim 15 \mu$G is needed., Comment: Accepted to MNRAS. 19 pages, 20 figures

(Abridged) The initial physical conditions of high-mass stars and protoclusters remain poorly characterized. To this end we present the first targeted ALMA 1.3mm continuum and spectral line survey towards high-mass starless clump candidates, selecting a sample of 12 of the most massive candidates ($400-4000\, M_\odot$) within 5 kpc. The joint 12+7m array maps have a high spatial resolution of $\sim 3000\, \mathrm{au}$ ($\sim 0.8^{\prime\prime}$) and have point source mass-completeness down to $\sim 0.3\, M_\odot$ at $6\sigma$ (or $1\sigma$ column density sensitivity of $1.1\times10^{22}\, \mathrm{cm^{-2}}$). We discover previously undetected signposts of low-luminosity star formation from CO (2-1) and SiO (5-4) bipolar outflows and other signatures towards 11 out of 12 clumps, showing that current MIR/FIR Galactic Plane surveys are incomplete to low- and intermediate-mass protostars ($\lesssim 50\, L_\odot$). We compare a subset of the observed cores with a suite of radiative transfer models of starless cores. We find a high-mass starless core candidate with a model-derived mass consistent with $29^{52}_{15}\, M_\odot$ when integrated over size scales of $2\times10^4\, \mathrm{au}$. Unresolved cores are poorly fit by starless core models, supporting the interpretation that they are protostellar even without detection of outflows. Substantial fragmentation is observed towards 10 out of 12 clumps. We extract sources from the maps using a dendrogram to study the characteristic fragmentation length scale. Nearest neighbor separations when corrected for projection are consistent with being equal to the clump average thermal Jeans length. Our findings support a hierarchical fragmentation process, where the highest density regions are not strongly supported against thermal gravitational fragmentation by turbulence or magnetic fields., Comment: 32 pages, 17 figures, and 6 tables. Accepted for publication in ApJ (August 26, 2019)

We present an expanded distance catalog for 1,710 molecular cloud structures identified in the Bolocam Galactic Plane Survey (BGPS) version 2, representing a nearly threefold increase over the previous BGPS distance catalog. We additionally present a new method for incorporating extant data sets into our Bayesian distance probability density function (DPDF) methodology. To augment the dense-gas tracers (e.g., HCO+(3-2), NH3(1,1)) used to derive line-of-sight velocities for kinematic distances, we utilize the Galactic Ring Survey 13CO(1-0) data to morphologically extract velocities for BGPS sources. The outline of a BGPS source is used to select a region of the GRS 13CO data, along with a reference region to subtract enveloping diffuse emission, to produce a line profile of 13CO matched to the BGPS source. For objects with a HCO+(3-2) velocity, \approx 95% of the new 13CO(1-0) velocities agree with that of the dense gas. A new prior DPDF for kinematic distance ambiguity (KDA) resolution, based on a validated formalism for associating molecular cloud structures with known objects from the literature, is presented. We demonstrate this prior using catalogs of masers with trigonometric parallaxes and HII regions with robust KDA resolutions. The distance catalog presented here contains well-constrained distance estimates for 20% of BGPS V2 sources, with typical distance uncertainties \lesssim 0.5 kpc. Approximately 75% of the well-constrained sources lie within 6 kpc of the Sun, concentrated in the Scutum-Centarus arm. Galactocentric positions of objects additionally trace out portions of the Sagittarius, Perseus, and Outer arms in the first and second Galactic quadrants, and we also find evidence for significant regions of interarm dense gas., Comment: 28 pages, 19 figures. Accepted for publication in ApJ. Distance-Omnibus code available at https://github.com/BGPS/distance-omnibus

We sort $4683$ molecular clouds between $10^\circ< \ell 1$ dex) progressions when sorted by star formation indicator. The median starless clump candidate is marginally sub-virial ($��\sim 0.7$) with $>75\%$ of clumps with known distance being gravitationally bound ($��< 2$). These samples show a statistically significant increase in the median clump mass of $��M \sim 170-370$ M$_\odot$ from the starless candidates to clumps associated with protostars. This trend could be due to (i) mass growth of the clumps at $\dot{M}\sim200-440$ Msun Myr$^{-1}$ for an average free-fall $0.8$ Myr time-scale, (ii) a systematic factor of two increase in dust opacity from starless to protostellar phases, (iii) and/or a variation in the ratio of starless to protostellar clump lifetime that scales as $\sim M^{-0.4}$. By comparing to the observed number of ${\rm CH_3OH}$ maser containing clumps we estimate the phase-lifetime of massive ($M>10^3$ M$_\odot$) starless clumps to be $0.37 \pm 0.08 \ {\rm Myr} \ (M/10^3 \ {\rm M}_\odot)^{-1}$; the majority ($M, Accepted for publication in ApJ; 33 pages; 22 figures; 7 tables

With a goal toward deriving the physical conditions in external galaxies, we present a study of the ammonia (NH$_3$) emission and absorption in a sample of star forming systems. Using the unique sensitivities to kinetic temperature afforded by the excitation characteristics of several inversion transitions of NH$_3$, we have continued our characterization of the dense gas in star forming galaxies by measuring the kinetic temperature in a sample of 23 galaxies and one galaxy offset position selected for their high infrared luminosity. We derive kinetic temperatures toward 13 galaxies, 9 of which possess multiple kinetic temperature and/or velocity components. Eight of these galaxies exhibit kinetic temperatures $>100$ K, which are in many cases at least a factor of two larger than kinetic temperatures derived previously. Furthermore, the derived kinetic temperatures in our galaxy sample, which are in many cases at least a factor of two larger than derived dust temperatures, point to a problem with the common assumption that dust and gas kinetic temperatures are equivalent. As previously suggested, the use of dust emission at wavelengths greater than 160 $��$m to derive dust temperatures, or dust heating from older stellar populations, may be skewing derived dust temperatures in these galaxies to lower values. We confirm the detection of high-excitation OH $^2��_{3/2}$ J=9/2 absorption toward Arp220 (Ott et. al. 2011). We also report the first detections of non-metastable NH$_3$ inversion transitions toward external galaxies in the (2,1) (NGC253, NGC660, IC342, and IC860), (3,1), (3,2), (4,3), (5,4) (all in NGC660) and (10,9) (Arp220) transitions., 29 pages, 22 figures, final version following proof corrections accepted for publication in ApJ