Browsing by Subject "inner galaxy"
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Item The Bolocam Galactic Plane Survey. V. HCO+ and N2H+ Spectroscopy of 1.1 mm Dust Continuum Sources(2011-08) Schlingman, Wayne M.; Shirley, Yancy L.; Schenk, David E.; Rosolowsky, Erik; Bally, John; Battersby, Cara; Dunham, Miranda K.; Ellsworth-Bowers, Timothy P.; Evans, Neal J., II; Ginsburg, Adam; Stringfellow, Guy; Evans, Neal J., IIWe present the results of observations of 1882 sources in the Bolocam Galactic Plane Survey (BGPS) at 1.1 mm with the 10 m Henrich Hertz Telescope simultaneously in HCO+ J = 3-2 and N2H+ J = 3-2. We detect 77% of these sources in HCO+ and 51% in N2H+ at greater than 3 sigma. We find a strong correlation between the integrated intensity of both dense gas tracers and the 1.1 mm dust emission of BGPS sources. We determine kinematic distances for 529 sources (440 in the first quadrant breaking the distance ambiguity and 89 in the second quadrant). We derive the size, mass, and average density for this subset of clumps. The median size of BGPS clumps is 0.75 pc with a median mass of 330M(circle dot) (assuming T-Dust = 20 K). The median HCO+ linewidth is 2.9 km s(-1) indicating that BGPS clumps are dominated by supersonic turbulence or unresolved kinematic motions. We find no evidence for a size-linewidth relationship for BGPS clumps. We analyze the effects of the assumed dust temperature on the derived clump properties with a Monte Carlo simulation and find that changing the temperature distribution will change the median source properties (mass, volume-averaged number density, surface density) by factors of a few. The observed differential mass distribution has a power-law slope that is intermediate between that observed for diffuse CO clouds and the stellar initial mass function. BGPS clumps represent a wide range of objects (from dense cores to more diffuse clumps) and are typically characterized by larger sizes and lower densities than previously published surveys of high-mass star-forming regions. This collection of objects is a less-biased sample of star-forming regions in the Milky Way that likely span a wide range of evolutionary states.Item The Bolocam Galactic Plane Survey. VIII. A Mid-Infrared Kinematic Distance Discrimination Method(2013-06) Ellsworth-Bowers, Timothy P.; Glenn, Jason; Rosolowsky, Erik; Mairs, Steven; Evans, Neal J.; Battersby, Cara; Ginsburg, Adam; Shirley, Yancy L.; Bally, John; Evans, Neal J.We present a new distance estimation method for dust-continuum-identified molecular cloud clumps. Recent (sub-)millimeter Galactic plane surveys have cataloged tens of thousands of these objects, plausible precursors to stellar clusters, but detailed study of their physical properties requires robust distance determinations. We derive Bayesian distance probability density functions (DPDFs) for 770 objects from the Bolocam Galactic Plane Survey in the Galactic longitude range 7 degrees.5 <= l <= 65 degrees.. The DPDF formalism is based on kinematic distances, and uses any number of external data sets to place prior distance probabilities to resolve the kinematic distance ambiguity (KDA) for objects in the inner Galaxy. We present here priors related to the mid-infrared absorption of dust in dense molecular regions and the distribution of molecular gas in the Galactic disk. By assuming a numerical model of Galactic mid-infrared emission and simple radiative transfer, we match the morphology of (sub-) millimeter thermal dust emission with mid-infrared absorption to compute a prior DPDF for distance discrimination. Selecting objects first from (sub-) millimeter source catalogs avoids a bias towards the darkest infrared dark clouds (IRDCs) and extends the range of heliocentric distance probed by mid-infrared extinction and includes lower-contrast sources. We derive well-constrained KDA resolutions for 618 molecular cloud clumps, with approximately 15% placed at or beyond the tangent distance. Objects with mid-infrared contrast sufficient to be cataloged as IRDCs are generally placed at the near kinematic distance. Distance comparisons with Galactic Ring Survey KDA resolutions yield a 92% agreement. A face-on view of the Milky Way using resolved distances reveals sections of the Sagittarius and Scutum-Centaurus Arms. This KDA-resolution method for large catalogs of sources through the combination of (sub-) millimeter and mid-infrared observations of molecular cloud clumps is generally applicable to other dust-continuum Galactic plane surveys.