A CO survey of giant molecular clouds near Cassiopeia A and NGC 7538

With the 1.2 m telescope at the Center for Astrophysics we have undertaken a survey of the J = 1 --> 0 CO line toward the conspicuous complex of giant molecular clouds (GMCs) in the Perseus arm in the region of Cas A and NGC 7538. The survey, at a spectral resolution of 250 kHz (0.65 km s(-1)), on a uniform grid of points spaced every 0.degrees 125 in latitude and longitud e, covers 55 deg(2) between I = 107 degrees and 116 degrees A smaller area of approximate to 15 deg(2) between l = 108 degrees and 113 degrees was sim ilarly surveyed in (CO)-C-13. I, the region covered in both isotopic specie s we find at least seven GMCs with masses on the order of 10(5) M-circle do t. An intensity-weighted radius gives a more meaningful measure of cloud si ze than the simple geometrical area and is best used to estimate the virial mass. The ratio of total cloud luminosities in CO and (CO)-C-13, S-12/S-13 , ranges from 6 to 10, with a mean of 8.5. The distribution of molecular ga s is very similar in CO and (CO)-C-13, and the velocity-integrated intensit ies at each point are closely correlated. In the (I, v)-diagram the Perseus arm is kinematically separated from the local arm by an interarm gap that is nearly free of CO; the contrast in molecular gas surface density between the Perseus arm and the interarm gap is apparently at least 20.