CO(J = 1-0) line emission from giant molecular clouds

Numerical models of the (C-12)O (J = 1-0) line emission from giant molecular clouds (GMCs) have been constructed. Line profiles are presented for both microturbulent and macroturbulent clouds. The observed width of the CO (J = 1-0) line cannot be physically interpreted as a microturbulent gas velocity dispersion. Microturbulent models produce emission with a wide range of profile shapes and brightness temperatures at line center over a cloud mass range of 100 to 10 exp 6 solar masses. Macroturbulent models produce smooth, centrally peaked profiles. Clumpy GMC models can produce peak brightness temperatures over about 6 K provided that clump densities are larger than 1000/cu cm. If there are no significant velocity gradients, photoelectric heating dominates in the region where the CO line arises. The observed relation between cloud mass and CO luminosity can be constructed from theoretical models.