Neutral Atomic Carbon in Dense Molecular Clouds

The authors have detected the 370 μm ³P₂-³P₁ fine-structure line of neutral carbon (C I) in seven sources: OMC 1, NGC 2024, S140, W3, DR 21, M17, and W51. Simultaneous analysis of these J = 2-1 data and available observations of the J = 1-0 line is used to deduce optical depths and excitation temperatures for these lines. These data indicate that both C I lines are likely to be optically thin, and that the ratio of C I to CO column densities in these clouds is typically ≡0.1.