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K.B. McQuinn, R. Simon, J.M. Jackson, T.M Bania (Boston University IAR)
As part of the Boston University-Five College Radio Astronomy Observatory Galactic Ring Survey (GRS), we compare 13CO emission in the l = 40 - 47 degrees range with corresponding optical extinction seen in the Palomar Digital Sky Survey. We also compare our cloud positions with the Lynds catalog of dark nebulae. For many GRS molecular clouds, we find a direct correlation between 13CO emission and optical extinction. As dust clouds are within the roughly 3 kpc optical horizon, the corresponding emission in 13CO must lie at the near kinematic distance. We also check for HI self-absorption features in these objects in the BU-Arecibo Galactic Plane HI Survey. HI self-absorption occurs when cold, foreground gas at the near kinematic distance absorbs hotter, background radiation from gas located at the far kinematic distance. All near clouds should therefore display HI self-absorption features and our results confirm that HI self-absorption can be used to resolve the near-far kinematic distance ambiguity.
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