GIANT MOLECULAR CLOUD COMPLEXES WITH OPTICAL H II REGIONS: ~(12)CO AND ~(13)CO OBSERVATIONS AND GLOBAL CLOUD PROPERTIES

摘要

Images of ~(12)CO and ~(13)CO J = 1-0 emission from the molecular clouds associated with the optical H II regions Sh 155, Sh 235, and Sh 140 are presented to better understand the interstellar gas conditions associated with regions of massive star formation. In the vicinity of the H II regions, there is evidence for the compression of ambient molecular material from shocks associated with the expansion of the ionized gas component and the near complete photoionization or photodissociation of molecular material within the H II region. However, the images also show that most of the molecular mass of the clouds resides within the extended, low column density regions well removed from the localized sites of star formation. Each cloud is characterized by a global line width which is dominated by the relative motions between resolved cloud substructures rather than motions along the line of sight inferred from individual profile line widths. We identify a relationship of the observed profile line widths with molecular gas column density which is consistent with opacity broadening of an intrinsic line width nearly independent with column density. Thus any tendency for neighboring emitting components to be at the same velocity (i.e., spatial coherence to the velocity field) must be weak or absent within CO-emitting regions of these clouds. In the context of a clumpy cloud medium, we use the variations of profile line width and antenna temperature with column density to derive the following limits for clump properties: clump masses less than 0.01 solar mass, clump sizes less than 4 x 10~(16) cm, and clump volume densities greater than 1 x 10~4 cm~(-3).