Bi-symmetric instabilities of the Kuz'min/Toomre disc

Abstract

This paper reports a numerical study of the effect of random motion on the unstable bar-forming modes of one type of stellar disc mass model. From measurements of the growth rates of the few most unstable bi-symmetric modes we evaluate the stabilizing influence of both random motion and halo mass. We find that the growth rate of bars is a simple function of these two variables. Our results suggest that the large degree of random motion recently observed near the centres of galactic discs substantially reduces the halo mass needed to understand their stability.