The Least Action Principle And The Spin Of Galaxies In The Local Group

Abstract

Using Peebles' least action principle, we determine trajectories for the galaxies in the Local Group and the more massive galaxies in the Local Neighbourhood. We deduce the resulting angular momentum for the whole of the Local Group and study the tidal force acting on the Local Group and its galaxies. Although Andromeda and the Milky Way dominate the tidal force acting on each other during the present epoch, we show that there is a transition time at $z\approx 1$ before which the tidal force is dominated by galaxies outside the Local Group in each case. This shows that the Local Group can not be considered as an isolated system as far as the tidal forces are concerned. We integrate the tidal torques acting on the Milky Way and Andromeda and derive their spin angular momenta, obtaining results which are comparable with observation.