SPIRAL HEATING OF GALACTIC DISKS

We have investigated the combined effects of transient spiral waves and giant molecular clouds in heating stellar discs by solving the Fokker-Planck equation with a Monte Carlo simulation. By using observations of the velocities of local stellar populations we are able to estimate the product of the mean surface density and the mass-weighted mean mass of the clouds and the RMS potential fluctuations associated with the spiral waves. The estimates show good agreement with observations of giant molecular clouds in our galaxy and HI observations in other spiral galaxies. We make predictions of the vertical and radial velocity distributions of two disc populations.