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 longitude, 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 similarly surveyed in (CO)-C-13. I, the region covered in both isotopic species we find at least seven GMCs with masses on the order of 10(5) M-circle dot. An intensity-weighted radius gives a more meaningful measure of cloud size 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 gas is very similar in CO and (CO)-C-13, and the velocity-integrated intensities 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.