2. The dark cloud sample

Dame et al. (1987) have collected a comprehensive list of dark clouds in the Galaxy. Their survey was based on the detection of emission at 115 GHz, the frequency of the rotational transition of CO. This spectral line is a standard tracer of dense molecular gas. I used the coordinates provided by Dame et al. (1987). Table 1 (click here) lists all these clouds with the boundaries in Galactic coordinates.

Five cloud complexes have been excluded from the original list. The Lindblad Ring and the "-12 km/s'' clouds are irregular and poorly defined. The Aquila Rift, Per OB2 and  Oph were also excluded because they extend over a large area on the sky and appear to consist of smaller cloudlets. The area included in the survey covers approximately . The standard analysis of the ROSAT All-Sky survey finds 2270 source within this area above a maximum likelihood threshold of 10. This source list is based of the first processing of the survey at MPE (Voges 1993). All sources found inside the areas of Table 1 (click here) were included in the list of dark cloud sources.

 

Name b_max Size

Cloud A 44.0 49.5 -4.0 2.0

Cloud B 44.0 54.0 -4.0 5.0

Cloud C 50.0 55.0 -1.0 3.5

Vul Rift 54.0 63.0 -3.0 5.0

Cyg Rift 63.0 86.5 -4.0 4.0

Cyg OB7 87.0 99.0 -3.0 8.0

Cepheus 100.0 120.0 11.0 22.0

Taurus 163.0 178.0 -22.0 -9.5

Mon OB1 197.5 205.0 -1.0 4.0

Orion A 208.5 218.0 -21.0 -14.5

Orion B 202.5 208.0 -21.0 -6.0

Mon R2 210.0 218.0 -14.0 -10.0

Vela Sheet 272.0 279.0 -3.0 8.0

Cham 295.0 305.0 -20.0 -12.0

Coalsack 300.0 307.0 -4.0 3.0

G317-4 315.0 320.0 -6.0 -2.0

Lupus 333.0 346.0 4.0 22.0

R Cr A 357.0 4.0 -22.0 -14.0

Table 1: Areas in the Galactic plane that define the dark cloud sample (Dame et al. 1987): name of cloud, boundaries in Galactic longitude (l) and latitude (b), approximate size. The often complex shape of the clouds was approximated with a rectangle, thereby including an area larger than the actual cloud.