Synthetic molecular clouds from supersonic MHD and non-LTE radiative transfer calculations

The dynamics of molecular clouds is characterized by supersonic random moti ons in the presence of a magnetic held. We study this situation using numer ical solutions of the three-dimensional compressible magnetohydrodynamic (M HD) equations in a regime of highly supersonic random motions. The non-LTE radiative transfer calculations are performed through the complex density a nd velocity fields obtained as solutions of the MHD equations, and more tha n 5 x 10(5) spectra of (CO)-C-12, (CO)-C-13, and CS are obtained. In this w ay we build synthetic molecular clouds of 5 and 20 pc diameter, evolved for about one dynamical time from their initial cofiguration. We use a numeric al flow without gravity or external forcing. The flow is super-Alfvenic. Synthetic data consist of sets of 90 x 90 synthetic spectra with 60 velocit y channels, in five molecular transitions: J=1-->0 and J=2-->1 for (CO)-C-1 2 and (CO)-C-13 and J=1-->0 for CS. Although we do not consider the effects of stellar radiation, gravity, or mechanical energy input from discrete so urces, our models do contain the basic physics of magneto fluid dynamics an d non-LTE radiation transfer and are therefore more realistic than previous calculations. As a result, these synthetic maps and spectra bear a remarka ble resemblance to the corresponding observations of real clouds.