Stability of two-fluid galactic disc under the influence of an external tidal field.

We consider the dynamics of rotationally supported thin galactic disc composed of stars and gas under the influence of external tidal field and derive the coupled differential equations governing the evolution of instabilities. Further linearising the governing equation a modified dispersion relation and stability criterion for appraising the stability of the two fluid galactic disc under the influence of external tidal field is obtained. Possible applications and method for the same are discussed.