Yq. Lou et Zh. Fan, COUPLED GALACTIC DENSITY-WAVE MODES IN A COMPOSITE SYSTEM OF THIN STELLAR AND GASEOUS DISCS, Monthly Notices of the Royal Astronomical Society, 297(1), 1998, pp. 84-100
A rotating disc galaxy is modelled as a composite system consisting of
thin stellar and gaseous discs, which are described by a two-fluid mo
dal formalism. The composite disc system is assumed to retain axisymme
try in the background equilibrium. General density-wave perturbations
in the two discs are coupled through the mutual gravitational interact
ion. We study the basic properties of open and tight spiral density-wa
ve modes in such a composite disc system. Within the Lindblad resonanc
es, perturbation enhancements of surface mass density in stellar and g
aseous discs are in phase; this is also true during the initial growth
phase of density-wave perturbations. Outside the Lindblad resonances,
there exists a possible spiral density-wave branch for which perturba
tion enhancements of surface mass density in stellar and gaseous discs
are out of phase. We discuss implications of these results on the cri
tical parameters for global star formation in barred and normal spiral
galaxies and on magnetohydrodynamic density waves within the Lindblad
resonances.