Self-reversed CO profiles in collapsing molecular clouds

Observations of self-reversed CO line profiles in four dense molecular clouds (Mon R2, W3, NGC 1333, and rho Oph) are compared to line profiles calculated for clouds undergoing nonhomologous gravitational collapse (Vcollapse proportional to r-1/2). While supersonic turbulent cloud models or collapse models with V proportional to r cannot easily account for either the observed line profiles or the line widths of CO and 13CO, the proposed V proportional r-1/2 collapse predicts line profiles with features similar to those observed. The best fit to the observed clouds is obtained, not with a pure collapse model, but with one in which a small amount of turbulence is added. The presence of a thermal gradient allows collapse and expansion motions to be distinguished. The four clouds known to possess CO line self-reversals are shown to be in a state of collapse, not expansion. The source-to-source variation of 13CO line intensity is shown to be a result of the magnitude of the collapse velocity. Predictions are made for the J=2-1 13CO line profile in nonhomologously collapsing clouds, and the presence of a self-reversal in these predicted lines provides an observational test for this model