Extended [C I] and ^{13}CO(5-4) Emission in M17SW
  We mapped a 13 by 22 pc region in emission from 492 GHz [C I] and, for the first time, 551 GHz ^{13}CO(5-4) in the giant molecular cloud M17SW, using the Submillimeter Wave Astronomy Satellite. The morphologies of the [C I] and ^{13}CO emission are strikingly similar. The extent and intensity of the [C I] and ^{13}CO(5-4) emission is explained as arising from photodissociation regions on the surfaces of embedded molecular clumps. Modeling of the ^{13}CO(5-4) emission in comparison to ^{13}CO(1-0) indicates a temperature gradient across the cloud, peaking to at least 63 K near the M17 ionization front and decreasing to at least 20 K at the western edge of the cloud. We see no correlation between gas density and column density. The beam-averaged column density of C I in the core is 1x10^{18} cm^-2, and the mean column density ratio N(C I)/N(CO) is about 0.4. The variations of N(C I)/N(CO) with position in M17SW indicate a similar clump size distribution throughout the cloud. 
J. E. Howe, M. L. N. Ashby, E. A. Bergin, G. Chin, N. R. Erickson, P.   F. Goldsmith, M. Harwit, D. J. Hollenbach, M. J. Kau...