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R. Plume (CfA), J.E. Howe (UMass, Amherst), F. Bensch (U. Köln), M.J. Kaufman (SJSU), G.J Melnick, J.R. Stauffer, M.L.N. Ashby, E.A. Bergin, S.C. Kleiner, B.M. Patten, V. Tolls, Z. Wang, Y.F. Zhang (CfA), P.F. Goldsmith (Cornell U., NAIC), M. Harwit (Cornell U.), N.R. Erickson, R.L. Snell (UMass, Amherst), D.A. Neufeld (JHU), D.G. Koch (NASA ARC), R. Schieder, G. Winnewisser (U. Köln), G. Chin (NASA GSFC)
One of SWAS's mission goals is to map the emission from the 3P1arrow3P0 fine-structure transition of neutral carbon ([C~I]; \nu = 492 GHz) and 13CO J=5arrow4 (551 GHz) over large scales (> 1\circ) in molecular clouds. Owing to its low critical density (ncrit ~1000 cm-3) and the fact that it arises from a state that is only 24 K above ground, the [C~I] line is easily observable throughout the dense interstellar medium. In contrast, 13CO J=5arrow4 has a relatively high critical density (ncrit ~105 cm-3) and the J = 5 level lies at 79 K. We report here on the results of two large-scale mapping projects in Orion A and M17sw. In both sources, we find that the large-scale distribution of [C~I] emission is very extended and is very similar to that seen in low J transitions of 13CO. In Orion A the 13CO J=5arrow4 emission, is undetectable south of the BN/KL object. An LVG analysis of the data shows that the difference between the distribution of [C~I] and 13CO J=5arrow4 emission is most likely the result of temperature and density effects. In M17sw the 13CO J=5arrow4 emission is more confined to the cloud core than is the [C~I], but still extends over most of the cloud. Comparing the intensity ratios of the [C~I] and 13CO J=5arrow4 emission over the entire cloud to PDR models indicates a density range for the emitting gas of a few 104 to 105 cm-3. Even though the excitation requirements for the two transitions are quite different, there is a linear correlation between the intensity of the [C~I] and 13CO J=5arrow4 emission. In a clumpy or filamentary cloud, this could indicate that the distribution of clump densities, temperatures, and sizes is roughly the same over the region, and the line intensities depend on the number of clumps in the SWAS beam.
The SWAS team gratefully acknowledges NASA contract NAS5-30702.
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The author(s) of this abstract have provided an email address for comments about the abstract: rplume@cfa.harvard.edu