Extended [C I] and 13CO (5→4) emission in M17SW

We mapped a 13 x 22 pc region in emission from 492 GHz [C I] and, for the first time, 551 GHz (CO)-C-13 (5 --> 4) in the giant molecular cloud M17SW, The morphologies of the [C I] and (CO)-C-13 emission are strikingly similar The extent and intensity of the [C I] and (CO)-C-13 (5 --> 4) emission is explained as arising from photodissociation regions on the surfaces of embedded molecular clumps. Modeling of the (CO)-C-13 (5 --> 4) emission in comparison to (CO)-C-13 (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 EC: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 x 10(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.