High spatial resolution observations of neutral atomic carbon in the molecular clouds M17 and W51

Abstract

The 370-micron 3P2-3P1 fine structure line of neutral atomic carbon in the molecular clouds M17 and W51 has been mapped with 25-arcmin resolution. In the H II region/molecular cloud interface in M17, bright C I forbidden line emission comes from a wide (about 1 pc) ridge at the edge of the molecular cloud. In W51, the C I forbidden line emission peaks on the compact IR source and H II region IRS 2, and at the interface between the extended H II region IRS 1 and the dense molecular condensation W51 Main. Spatial scales of the C I forbidden line emission, relative location of C I and C18O, and mean C I/CO ratio are similar in the two molecular clouds. The data are in good agreement with an origin of the atomic carbon in photodissociation regions created by UV radiation illuminating a clumpy molecular cloud.