Vertical oscillation of the Galactic disk

Abstract

The possible oscillation modes of the local structure of the Galactic disk and their frequencies are derived for three families of one-dimensional disk models with and without external halos. Modes with horizontal as well as vertical structure are also considered. A series of simulations and interpretations based on the linearized solutions of the evolution equations is presented. The physics of oscillation modes, oscillations in models of the Galactic disk, and perturbations of the disk are examined. Linear analysis and n-body simulation demonstrated that a one-dimensional disk may have undamped oscillation modes. The higher order modes are not excited by passing satellites. In the presence of a harmonic halo, the disk undergoes a bulk oscillation; if the halo is anharmonic, this mode is still undamped. The long damping time that was found implies that ordered motion may persist for many vertical crossing times after a perturbation to the Galactic disk. The findings also suggest a general framework for studying oscillation modes. 28 refs.