Large-Scale Mapping Observations of the C i (3P1–3P0) and CO (J = 3–2) Lines toward the Orion A Molecular Cloud

Large-scale mapping observations of the 3P1–3P0 fine-structure transition of atomic carbon (C i, 492 GHz) and the transition of CO (346 GHz) toward the Orion A molecular cloud have been carried out with the Mount Fuji submillimeter-wave telescope. The observations cover 9 deg2 and include the Orion Nebula M42 and the L1641 dark cloud complex. The C i emission extends over almost the entire region of the Orion A cloud and is surprisingly similar to that of 13CO (). The CO () emission shows a more featureless and extended distribution than C i. The C i/CO () integrated intensity ratio shows a spatial gradient running from the north (0.10) to the south (1.2) of the Orion A cloud, which we interpret as a consequence of the temperature gradient. On the other hand, the C i/13CO () intensity ratio shows no systematic gradient. We have found a good correlation between the C i and 13CO () intensities over the Orion A cloud. This result is discussed on the basis of photodissociation region models