Arecibo-Green Bank Carbon Radio Recombination Line Study of HI Clouds

In order to sustain star formation in the Galaxy, the molecular clouds from which stars form must be continuously renewed. Several mechanisms have been proposed for the formation of molecular clouds. Although the details differ, all require a converging flow to enhance the local gas density. Among the most effective converging flows are those driven by (a) stellar feedback or turbulence, (b) the agglomeration of cloudlets, (c) gravitational instability, and (d) magneto-gravitational instability. Here we investigate the first of these; namely the role of stellar feedback from supernovae and HII region expansion on the formation of molecular clouds. We have used the Arecibo and Green Bank telescopes to measure low-frequency. (< 1 GHz) carbon recombination line (CRRL) emission in six cloud forming regions. We combine these data with measurements of HI self-absorption to set stringent constraints on the physical properties and evolution of the cloud forming regions.