The distribution of atomic carbon in the Orion giant molecular cloud 1

The large-scale distribution of the C I (³P₁- ³P₀, 492 GHz) emission line from Orion A and B giant molecular clouds has been imaged with the Mount Fuji submillimeter-wave telescope. The total area observed is about 15 deg². The overall spatial and velocity structure of the C I line is found to be similar to that of the ¹³CO (J = 1-0) line. The derived column density ratio N(C I)/N(CO) shows a large variation ranging from 0.2 to 2.9 toward the cloud edges, whereas it is relatively constant between 0.1 and 0.2 toward the interior region of the entire Orion clouds in both massive star-forming and dark cloud regions. This almost constant ratio suggests that C I can coexist with CO even in the deep inside of the molecular cloud.