SUBMILLIMETER DETECTION OF EXTRAGALACTIC C-1 EMISSION - IC-342

We report observations of the P-3(1) --> P-3(0) transition of atomic carbon at 492 GHz in IC 342, made at the Caltech Submillimeter Observatory, which represent the first extragalactic submillimeter detection of C I. The C I emission from IC 342 was found to have a main beam temperature of about 1 K, which is a factor of 2 greater than that for (CO(2 --> 1))-C-13 in the same size beam. Comparing our data with COBE observations of the Milky Way, we find that the ratio of C I to CO(2 --> 1) is approximately a factor of 2 lower in IC 342 than in our Galaxy. The result is interpreted in terms of photodissociation region models which require higher gas densities for IC 342 than for the Milky Way.