A multiline study of a typical giant molecular cloud : S 147 / S 153.

The molecular cloud S 147/S 153, taken as an example of typical giant molecular cloud with a moderate star formation activity, has been mapped in several molecular lines [¹²CO(1-0), ¹³CO(1-0), HCO⁺(1-0), ¹²CO(2-1), ¹³CO(2-1), NH₃(1,1), and NH₃(2,2)] with different spatial resolutions (≡5arcmin, ≡1arcmin.4, and ≡0arcmin.7). The diffuse envelope shows a very smooth density structure and a velocity gradient strongly suggestive of an overall rotation of the cloud, even at the resolution of 1arcmin.4 towards the cloud core seen in ¹³CO. On the other hand, the NH₃ emission, although mapped with a resolution only twice better, presents at least 3 different condensations in the cloud core, with a velocity pattern unrelated to the large scale gradient in the cloud. A detailed analysis of this NH₃ emission suggests that the condensations are composed of many small turbulent clumps of mass ≡1 M_sun; and size ≡0.1 pc.