We present fully sampled \sim 3 \arcmin resolution images of the { { } ^ { 12 } CO } ( J = 2–1 ) , { { } ^ { 13 } CO } ( J = 2–1 ) , and { C ^ { 18 } O } ( J = 2–1 ) emission taken with the newly developed 1.85-m mm-submm telescope toward the entire area of the Orion A and B giant molecular clouds .
The data were compared with the J = 1–0 of the { { } ^ { 12 } CO } , { { } ^ { 13 } CO } , and { C ^ { 18 } O } data taken with the Nagoya 4-m telescope and the NANTEN telescope at the same angular resolution to derive the spatial distributions of the physical properties of the molecular gas .
We explore the large velocity gradient formalism to determine the gas density and temperature by using the line combinations of { { } ^ { 12 } CO } ( J = 2–1 ) , { { } ^ { 13 } CO } ( J = 2–1 ) , and { { } ^ { 13 } CO } ( J = 1–0 ) assuming uniform velocity gradient and abundance ratio of CO .
The derived gas density is in the range of 500 to 5000 cm ^ { -3 } , and the derived gas temperature is mostly in the range of 20 to 50 K along the cloud ridge with a temperature gradient depending on the distance from the star forming region .
We found the high-temperature region at the cloud edge facing to the H ii region , indicating that the molecular gas is interacting with the stellar wind and radiation from the massive stars .
In addition , we compared the derived gas properties with the Young Stellar Objects distribution obtained with the Spitzer telescope to investigate the relationship between the gas properties and the star formation activity therein .
We found that the gas density and star formation efficiency are well positively correlated , indicating that stars form effectively in the dense gas region .