The vertical growth and structure of galactic disks

The evolution of the vertical structure of galactic disks is investigated numerically, using the Spitzer and Schwarzschild (1951) scattering of stars out of the plane, due to giant molecular clouds (GMCs), as the physical mechanism of evolution. A population of GMCs is embedded in a thin, self-gravitating axisymmetric disk of stars, together with a fixed, nearly isothermal halo. The stars interact by way of a self-consistent axisymmetric potential determined from an expansion to twelfth order in spherical harmonics. A range of models with exponential disks is investigated. In an exponential disk with initially constant z-velocity disperion, the scale height becomes nearly constant with radius, over reasonable time scales, if the GMC distribution is more centrally concentrated than the stellar distribution. While the z-density distribution is fitted by an isothermal sech-squared distribution, z-velocity distribution is fitted by a Gaussian.