干旱区生态环境知识资源中心

Surveys undertaken in the 2nd quadrant of the Galaxy with the CfA 1.2 m telescope have been combined to produce a map covering about 620 deg2 in the 2.6 mm CO(J = 1 bar arrow pointing right 0) line at high galactic latitudes (16-degrees less-than-or-equal-to b less-than-or-equal-to 44-degrees, 117-degrees less-than-or-equal-to l less-than-or-equal-to 1600). There is CO emission from molecular ’’cirrus’’ clouds in about 13% of the region surveyed. The CO clouds are grouped together into three major cloud complexes with 29 individual members. All clouds are associated with infrared emission at 100 mum, although there is no one-to-one correlation between the corresponding intensities. CO emission is detected in all bright and dark Lynds’ nebulae cataloged in that region; however not all CO clouds are visible on optical photographs as reflection or absorption features. Velocities within v(LSR) less-than-or-equal-to 10 km s-1 indicate that the clouds are probably local. At an adopted distance of 240 pc cloud sizes range from 0.1 to 30 pc and cloud masses from 1 to 1600M.. The molecular cirrus clouds contribute between 0.4 and 0.8 M. pc-2 to the surface density of molecular gas in the galactic plane. Only 26% of the ’’infrared-excess clouds’’ in the area surveyed, predicted by Desert et al. to be molecular, actually show CO and about 2/3 of the clouds detected in CO do not show an infrared-excess. On the basis of this result we conclude that the catalog of Desert et al. is a relatively poor guide to most of the molecular material at high latitudes. Also, the assertion by Blitz et al. that a large fraction of these IR-excess clouds represents potential candidates for molecular clouds without detectable CO is not supported by the results of the present survey.