Extended [ C I ] and ( CO )-C13 ( 5-> 4 ) emission in M 17 SW

We mapped a 13 ×22 pc region in emission from 492 GHz [C I] and, for the first time, 551 GHz 13CO(5→4) in the giant molecular cloud M17SW. The morphologies of the [ C I] and 13CO emission are strikingly similar. The extent and intensity of the [CI] and 13CO(5→4) emission is explained as arising from photodissociation regions on the surfaces of embedded molecular clumps. Model ing of the13CO(5→4) emission in comparison to 13CO(1→0) indicates a temperature gradient across the cloud, peaki ng 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 1×1018 cm−2, and the mean column density ratioN(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. Subject headings: ISM: individual (M17SW) — ISM: molecules — ISM: structure — r adio lines: ISM — submillimeter