Gravitational Stability of Molecular Clouds in the Galactic Center

The data from the Nobeyama Radio Observatory 45 m telescope Galactic Center CO survey have been analyzed to generate a compilation of molecular clouds with intense CO emission in this region. The measured parameters of identified clouds are analyzed and cross-correlated to compare with those of clouds in the Galactic disk. We diagnosed gravitational stability of identified clouds using their viral theorem mass and CO luminosity. If we assume that the disk clouds are nearly at the onset of gravitational instability, all the clouds and cloud complexes in the Galactic center must be gravitationally stable. This indicates that the GC clouds could be in equilibrium with high pressure in the Galactic center environment. The velocity dispersion of a cloud correlates inversely with the degree of gravitational instability. Gravitationally less stable clouds follow the main ridge of intense CO emission, part of which define two rigidly-rotating molecular arms. It is concluded that mechanisms such as orbit crowding at a resonant radius could promote dynamical evolution of clouds and thereby trigger subsequent star formation.