Extended [C I] and ^{13}CO(5-4) Emission in M17SW

摘要

We mapped a 13 by 22 pc region in emission from 492 GHz [C I] and, for thefirst time, 551 GHz ^{13}CO(5-4) in the giant molecular cloud M17SW, using theSubmillimeter 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 photodissociationregions on the surfaces of embedded molecular clumps. Modeling of the^{13}CO(5-4) emission in comparison to ^{13}CO(1-0) indicates a temperaturegradient across the cloud, peaking to at least 63 K near the M17 ionizationfront and decreasing to at least 20 K at the western edge of the cloud. We seeno correlation between gas density and column density. The beam-averaged columndensity of C I in the core is 1x10^{18} cm^-2, and the mean column densityratio N(C I)/N(CO) is about 0.4. The variations of N(C I)/N(CO) with positionin M17SW indicate a similar clump size distribution throughout the cloud.