Large-scale mapping observations of the CI (P-3(1)-P-3(0)) and CO (J=3-2) lines toward the Orion A molecular cloud

Large-scale mapping observations of the P-3(1)-P-3(0) fine-structure transi tion of atomic carbon (C I, 492 GHz) and the J = 3-2 transition of CO (346 GHz) toward the Orion A molecular cloud have been carried out with the Moun t Fuji submillimeter-wave telescope. The observations cover 9 deg(2) and in clude the Orion Nebula M42 and the L1641 dark cloud complex. The C I emissi on extends over almost the entire region of the Orion A cloud and is surpri singly similar to that of (CO)-C-13 (J = 1-0). The CO (J = 3-2) emission sh ows a more featureless and extended distribution than C I. The C I/CO (J = 3-2) integrated intensity ratio shows a spatial gradient running from the n orth (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/(CO)- C-13 (J = 1-0) intensity ratio shows no systematic gradient. We have found a good correlation between the C I and (CO)-C-13 (J = 1-0) intensities over the Orion A cloud. This result is discussed on the basis of photodissociat ion region models.