A LARGE-SCALE CO SURVEY TOWARD W3, W4, AND W5

摘要

A CO J = 1-0 survey of the outer Galaxy toward W3, W4, and W5 is described. The bright molecular emission in the W3 region in the Perseus arm is prominent, and little emission is seen at greater Galactocentric distances. The extensive local emission in the survey contains the large molecular cloud complex associated with Cam OB1. Between the local and Perseus arm emission, a nearly empty gap in velocity is seen across the entire longitude range. On the assumptions that the kinematically derived width of the gap is the true width and that the X ratio is constant, the arm-interarm contrast of CO is ≥25:1 in surface density. A few clouds are detected beyond the Perseus arm, and only one cloud, already known, is detected at extreme Galactocentric distances, beyond the Perseus and outer arms. The cumulative mass distribution of the clouds in the Perseus arm has power-law index 0.65 ± 0.15, and the clouds there are systematically less luminous in CO by a factor 3.5 ± 2 than clouds near the solar circle. The distribution of molecular gas with Galactocentric distance in the outer Galaxy is compared with that of luminous Infrared Astronomy Satellite point sources that trace massive star-forming regions. The agreement is generally good, with evidence for enhanced star formation relative to the surface density of molecular gas in the W3 region and perhaps also in the outer arm.