ATOMIC CARBON IN M82

We report observations of C I(P-3(1)-P-3(0)) emission at 492 GHz towar d the starburst galaxy M82. Both the C I/C II intensity ratio and the C/CO column density ratio are a factor of 2-5 higher than observed tow ard Galactic photodissociation regions (PDRs) or predicted by PDR mode ls. We argue that current PDR models are insufficient to explain the o bservations, and propose that some of the emission is due to atomic ca rbon existing within molecular clouds. Employing new chemical models, which use a fast H-3+ dissociative recombination rate, we find that en hanced cosmic-ray flux supplied by supernova remnants in the M82 starb urst lead to an enhanced atomic carbon abundance and elevated temperat ures deep within the molecular clouds, resulting in a higher C I emiss ivity than found in previous PDR models.