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We have mapped the Orion-A Giant Molecular Cloud in the CO (J=4-3) line withthe Tsukuba 30-cm submillimeter telescope.The map covered a 7.125 deg^2 areawith a 9' resolution, including main components of the cloud such as OrionNebula, OMC-2/3, and L1641-N. The most intense emission was detected toward theOrion KL region. The integrated intensity ratio between CO (J=4-3) and CO(J=1-0) was derived using data from the Columbia-Univ. de Chile CO survey,which was carried out with a comparable angular resolution. The ratio wasr_{4-3/1-0} ~ 0.2 in the southern region of the cloud and 0.4-0.8 at starforming regions. We found a trend that the ratio shows higher value at edges ofthe cloud. In particular the ratio at the north-eastern edge of the cloud at(l, b) = (208.375 deg, -19.0 deg) shows the specific highest value of 1.1. Thephysical condition of the molecular gas in the cloud was estimated by non-LTEcalculation. The result indicates that the kinetic temperature has a gradientfrom north (Tkin=80 K) to south (20 K). The estimation shows that the gasassociated with the edge of the cloud is warm (Tkin~60 K), dense (n_{H_2}~10^4cm^{-3}), and optically thin, which may be explained by heating and sweeping ofinterstellar materials from OB clusters.

Large-scale CO (J=4-3) Mapping toward the Orion-A Giant Molecular Cloud