The edges of molecular clouds - Fractal boundaries and density structure

The spatial structure of the dense interstellar medium is examined on the basis of observations of clouds carried out at two different distances using several transitions of the carbon monoxide molecule. It is found that spatial structure exists on all scales down to the best angular resolution (0.02) and that the emission arises from structures that are small compared to the telescope beam. For all the fields, the maximum peak line intensities on the maps presented are comparable in spite of an anticipated variation of the beam dilution between the remote and nearby fields of (750/200)-squared = 14. The integrated intensity maps are self-similar. The maximum brightness contrast observed in a map scales with the size over which it is observed, and Taurus and Cygnus, although at different distances from the Sun, exhibit the same brightness contrast over comparable distances. The (J = 2-1) and (J = 3-2) integrated intensities stay proportional to each other over the entire range of values accessible to the observations.