The spatial and mass distributions of molecular clouds and spiral structure

Abstract

The authors model the growth of molecular clouds resulting from cloud-cloud collisions and coalescence in the Galactic ring between 4 and 8 kpc, taking into account the presence of a spiral potential and the mutual cloud-cloud gravitational attraction. The mean lifetime of molecular clouds is determined to be ≡2×108yr. The clouds are present in both spiral arm and interarm regions, but a spiral pattern in their spatial distribution is clearly discernible, with the more massive clouds showing a stronger correlation with the spiral arms. As viewed from within the Galactic disk, however, it is very difficult to ascertain that the molecular cloud distribution in longitude-velocity space has a spiral pattern.