Molecular clouds and cloud cores in the inner Galaxy

A compilation of CO emission regions and their measured parameters is presented which represents a nearly complete accounting of the molecular clouds in the first quadrant of the Galaxy. Emission regions associated with radio H II regions have systematically brighter CO peaks that are a factor of two to three times larger and have twice the mean velocity dispersion as the general cloud population. Both the H II region clouds and the hot core regions have a Galactic distribution characteristic of a spiral arm population, whereas the colder clouds are much less confined in Galactic azimuthal angle. Virial masses are obtained for the large sample of clouds with assigned kinematic distances. The mean H2 density for a GMC of diameter 40 pc is 180/cm. For these clouds, a linear relationship is found between the H2 column density and the integrated CO emission. The variation in the Z-dispersion of clouds as a function of cloud mass suggests that more massive GMCs have smaller random velocities.