Scales of Stability and Turbulence in the Molecular ISM

From the archival data of the BU-FCRAO ^13 CO GRS, we measure the radial profiles of column density and turbulent velocity dispersion from the centers of molecular clouds outward into the surrounding diffuse molecular ISM. Averaged across spatial scales, the profiles are consistent with turbulence that is on average in hydrostatic equilibrium. We measure the turbulent kinetic energy (KE) and the gravitational potential energy (GE) within and the pressure energy (PE) outside the clouds. The distribution of the sum 2KE-|GE|-PE has a mean near zero indicating approximate virial equilibrium. The average pressure energy is consistent with estimates of the pressure of the multiphase ISM at the Galactic mid-plane. If the dynamical time scale of the turbulence scales with its crossing time, this apparent equilibrium may result from the rapid virialization of the KE and GE with respect to changes in PE. In a snapshot, the clouds appear to be in virial equilibrium within a confining pressure. However, the duration of the equilibrium is approximately the crossing time. An analysis of Larson's scaling relationships of line width and column density finds no correlation. Tthe inference of constant column density with cloud size is a misinterpretation of this lack of correlation.