The molecular gas toward Cassiopeia A.

Fully sampled 20″ resolution maps of Cassiopeia A in the J = 1 − 0 line of 13 CO, and additional observations of the J = 1 − 0 and J = 2 − 1 lines of 12 CO and 13 CO are presented. From the peak 12 CO line intensity, the kinetic temperature of the molecular gas reaches 20K. The warmest clouds are in the SE part of the region mapped. From the 13 CO data, there are at least eleven molecular clouds. Ten clouds are in the Perseus spiral arm, ∼ 3 kpc from the sun; one is in the solar neighborhood. For the Perseus arm clouds, a Large Velocity Gradient analysis of J = 2 − 1 and J = 1 − 0 lines of 13 CO gives H 2 densities <4000 CM −3 . For these clouds, masses from CO data are significantly smaller than obtained from the virial theorem if only gravity is important; the clouds toward the SE of Cas A are closest to being bound