On the gravitational stability of a galactic disc as a two-fluid system
  Gravitational stability of a disc consisting of the gaseous and the stellar
components are studied in the linear regime when the gaseous component is
turbulent. A phenomenological approach is adopted to describe the turbulence,
in which not only the effective surface density but the velocity dispersion of
the gaseous component are both scale-dependent as power-law functions of the
wavenumber of the perturbations. Also, the stellar component which has
gravitational interaction with the gas is considered as a fluid. We calculate
growth rate of the perturbations and in the most of the studied cases, the
stability of the disc highly depends on the existence of the stars and the
exponents of the functions for describing the turbulence. Our analysis suggests
that the conventional gas and star threshold is not adequate for analyzing
stability of the two-component discs when turbulence is considered.
