The distribution of galactic IR dark clouds from MSX survey maps

M.P. Egan ¹, S.J. Carey ², S.D. Price ², & R.F. Shipman ¹

¹ Air Force Research Laboratory

² Boston College

Mid-infrared images of the Galactic plane taken in 1996 by the Midcourse Space Experiment (MSX) and by ISO revealed the presence of dark clouds in silhouette against the bright emission of the galactic plane. The lack of mid-IR emission, and the apparent high opacity of the clouds in the 6 to 25 micron region argued for clouds of high density and low temperature. Subsequent radio and sub-mm measurements have confirmed that the clouds have densities > 10⁵ particles per cubic centimeter, and temperatures of  10K. These dark clouds are a unique as they are either not currently forming stars or are in the earliest stages of star formation.

We have extracted positions and size measurements of dark clouds in quadrants I and IV from the MSX galactic plane survey images, using overlapping scans to confirm the cloud identifications. We examine the distribution of clouds as a function of both galactic latitude longitude. We shall also examine the size distribution of the clouds as a function of galactic longitude.