On the gravitational stability of a galactic disc as a two-fluid system

TL;DR

This paper investigates the gravitational stability of galactic discs composed of gas and stars, considering turbulence in the gaseous component and its impact on stability thresholds.

Contribution

It introduces a scale-dependent turbulence model for the gaseous component and analyzes its effects on the stability criteria of two-fluid galactic discs.

Findings

Stability depends heavily on star presence and turbulence exponents.

Conventional gas-star stability thresholds are inadequate with turbulence.

Turbulence significantly alters the growth rates of perturbations.

Abstract

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.