A CO survey of giant molecular clouds near Cassiopeia A and NGC 7538.
UNGERECHTS H., UMBANHOWAR P. and THADDEUS P.
Abstract (from CDS):
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°.125 in latitude and longitude, covers 55 deg2 between l=107° and 116°. A smaller area of ~15 deg2 between l=108° and 113° was similarly surveyed in 13CO. In the region covered in both isotopic species we find at least seven GMCs with masses on the order of 105 M☉. 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 13CO, S12/S13, ranges from 6 to 10, with a mean of 8.5. The distribution of molecular gas is very similar in CO and 13CO, and the velocity-integrated intensities at each point are closely correlated. In the (l,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.