Large-Scale Mapping Observations of the C [CSC]i[/CSC] ([TSUP]3[/TSUP][ITAL]P[/ITAL][TINF]1[/TINF]–[TSUP]3[/TSUP][ITAL]P[/ITAL][TINF]0[/TINF]) and CO ([ITAL]J[/ITAL] = 3–2) Lines toward the Orion A Molecular Cloud

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Abstract
Large-scale mapping observations of the 3P1-3P0 fine-structure transition 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 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 (J = 1-0). The CO (J = 3-2) emission shows 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 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 (J = 1-0) intensity ratio shows no systematic gradient. We have found a good correlation between the C I and 13CO (J = 1-0) intensities over the Orion A cloud. This result is discussed on the basis of photodissociation region models.
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