[112.21] MSX Infrared Dark Clouds in the BU-FCRAO Galactic Ring Survey: A Galactic Ring Population

R. Simon, J.M. Jackson, R.Y. Shah, T.M. Bania, D.P. Clemens (IAR, Boston University), M.H. Heyer (FCRAO, UMass Amherst)

Recent high resolution surveys with the ISO and MSX satellites have revealed a large number of Galactic clouds with significant extinction in the mid-infrared. The infrared dark clouds are characterized by their high masses, high column densities, and low temperatures. Little is known, however, about their origin and distribution in the Galaxy.

The BU-FCRAO Galactic Ring Survey (GRS), a high resolution survey of 13CO emission in the inner Milky Way, makes it possible to derive physical parameters of IR dark clouds and their parental molecular clouds, such as sizes and masses, by spectroscopically determining their distances. Based on morphological correlation of IR extinction and BU-FCRAO Galactic Ring Survey (GRS) 13CO emission in velocity channel maps, we assign radial velocities to the IR dark clouds throughout the first Galactic quadrant and, assuming they are at the near kinematic distance, determine their location in the Galaxy. We find that the majority of the IR dark clouds is concentrated in the Galactic Ring at a Galactocentric radius of 5 kpc. We suggest that the condensations in the most massive IR dark clouds represent high mass proto-clusters, or OB-associations in the making.