The Cold Interstellar Gas and the Stability of Thick Galactic Discs

摘要

The spiral structure theory relies on a number of working assumptions which allowto make the linearized system of the coupled fluid (or Vlasov) and Poisson equationsmore tractable. However, in some situations of astrophysical interest the validityof such assumptions may be questioned. For instance, we know that real galacticdiscs have finite, although small, thickness and the possibility of regarding them asinfinitesimally thin depends on the relevant wavelengths of the perturbations excited.In some cases, when the underlying spiral structure has a high winding degree, finite-thickness effects should be taken into account in the stability analysis. In view of theimportance that such effects may have in the self-regulation mechanisms which areexpected to operate in galactic discs and to be at the basis of their secular heating(Romeo 1987, 1990), we have tried to evaluate them. This can be done only afterthat their vertical structure at equilibrium has carefully been investigated.