Cooling Rates of Molecular Clouds Based on Numerical Magnetohydrodynamic Turbulence and Non‐LTE Radiative Transfer

We have computed line emission cooling rates for the main cooling species inmodels of interstellar molecular clouds. The models are based on numericalsimulations of super-sonic magneto-hydrodynamic (MHD) turbulence. Non-LTEradiative transfer calculations have been performed to properly account for thecomplex density and velocity structures in the MHD simulations. Three modelsare used. Two of the models are based on MHD simulations with differentmagnetic field strength and the third includes the computation of self-gravity(in the super-Alfvenic regime of turbulence). The density and velocity fieldsin the simulations are determined self-consistently by the dynamics ofsuper-sonic turbulence. The models are intended to represent molecular cloudswith linear size L~6 pc and mean density ~300 cm^-3, with the densityexceeding 10^4 cm^-3 in the densest cores. We present 12CO, 13CO, C18O, O2, OI,CI and H2O cooling rates in isothermal clouds with kinetic temperatures 10-80K.Analytical approximations are derived for the cooling rates. The inhomogeneityof the models reduces photon trapping and enhances the cooling in the densestparts of the clouds. Compared with earlier models the cooling rates are lessaffected by optical depth effects and are therefore higher. The main effectscomes, however, from the density variation since cooling efficiency increaseswith density. This is very important for the cooling of the clouds as a wholesince most cooling is provided by gas with density above the average.Comment: AASTeX, 19 pages, 15 figures; final, revised version; accepted to Ap