CO in Galactic HII regions

We analyze all sources within the BU-FCRAO Galactic Ring Survey (GRS) of ^13^CO emission known to be HII regions based upon the presence of radio continuum and cm-wavelength radio recombination line emission. Unlike all previous large area coverage ^13^CO surveys, the GRS is fully sampled in angle and yet covers ~75deg^2^ of the Inner Galaxy.

The angular resolution of the GRS (46") allows us to associate molecular gas with HII regions without ambiguity and to investigate the physical properties of this molecular gas. We find clear CO/HII morphological associations in position and velocity for ~80% of the nebular sample. Compact HII region molecular gas clouds are on average larger than UC clouds: 2.2' compared to 1.7'.