The M17 SW molecular cloud

The H II region M17 is one of the best known objects in the sky. The H II region abuts a dense, relatively hot molecular cloud known as M17 SW, which is itself embedded within the edge of one of the largest giant molecular cloud complexes in the Galaxy. Carbon monoxide observations (J = 1 to 0) were obtained during two observing runs at an 11 m telescope during the time of 1981 January 26-29 and 1981 September 22-27. New, moderate-resolution maps of the massive M17 SW molecular cloud are presented and discussed. It is found that the strongest molecular emission lies in a ridge parallel and adjacent to an apparent ionization and molecular dissociation front. M17 SW is a massive dense molecular condensation. The visual extinction through the center of the cloud is around 200 mag. The present data are consistent with the views that the M17 SW cloud is largely heated externally, by the ionizing stars of the H II region.