Turbulent viscosity in clumpy accretion disks

The equilibrium state of a turbulent clumpy gas disk is analytically investigated. The disk consists of distinct self-gravitating clouds. Gravitational cloud–cloud interactions transfer energy over spatial scales and produce a viscosity, which allows mass accretion in the gas disk. Turbulence is assumed to be generated by instabilities involving self-gravitation and to be maintained by the energy input from differential rotation and mass transfer. Disk parameters, global filling factors, molecular fractions, and star formation rates are derived. The application of our model to the Galaxy shows good agreement with observations. They are consistent with the scenario where turbulence generated and maintained by gravitation can account for the viscosity in the gas disk of spiral galaxies. The rôle of the galaxy mass for the morphological classification of spiral galaxies is investigated