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Session 42 - Molecular Clouds: Models and Observations.
Display session, Tuesday, June 11
Great Hall,
We report the results of a search for diffuse Galactic HII regions using radio recombination lines. Unlike previous surveys, which have been directed toward fairly bright, compact radio continuum sources, we observed unprepossessing objects that might be optically obscured analogs to the Rosette nebula, typically a factoor of two fainter in the continuum than could have been detected before. One hundred thirty nebulae have been detected in radio recombination lines for the first time; most require at least one main sequence O star to provide their ionization. The diffuse HII regions appear to have essentially the same distribution in the Galaxy as compact HII regions, and track the surface density of CO fairly closely. There is some indication that the diffuse nebulae have a low abundance of ionized helium, possibly due to their low excitation. We also find that several newly discovered nebulae are associated with peculiar kinematic features in the Galactic nucleus.
