Submillimeter Observations of Neutral Carbon in M51
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Session 19 -- Gas and Star Formation in Spiral Galaxies
Display presentation, Wednesday, January 12, 9:30-6:45, Salons I/II Room (Crystal Gateway)

## [19.02] Submillimeter Observations of Neutral Carbon in M51

D.J. Benford, T.R. Hunter, J.B. Keene, D.C. Lis, T.G. Phillips, E. Serabyn (Caltech)

We report observations of the $^3P_1\to^3P_0$ transition of atomic carbon at 492 GHz and the $J=(3\to2)$ transition of $^{12}$CO at 345 GHz in M51. The observations, made at the Caltech Submillimeter Observatory, cover seven points near the nucleus of the galaxy and three points in the spiral arms. Near the nucleus, the emission from C{\smc I} was found to have a main beam temperature of around 0.4 K, a factor of two lower than that of CO. In these regions, the C{\smc I}/CO column density ratio is up to a factor of 2 lower than in nearby regions in our Galaxy. This implies that the gas density is higher in photodissociation regions near the nucleus of M51. Away from the nucleus, emission is found to be absent at main beam temperatures of more than 0.1K, despite similarly strong CO emission. We conclude that this implies that there is substantially less mass in photodissocation regions away from the nucleus.