Simulations of mergers between disc-halo galaxies

We have carried out a series of more than 30 simulations of the collision and merging of pairs of similar disc–halo ‘galaxies’. The initial systems in these experiments contain equal amounts of mass in a near exponential disc and in a centrally concentrated non-rotating spheroidal component. In addition we treat a fraction of the disc particles as ‘gas clouds’ which can undergo inelastic frictionless collisions and so simulate the dissipation of energy in the highly inhomogeneous interstellar media of real galaxies. We analyse in some detail aspects of the interaction process such as the formation of bridges and tails and the loss and transfer of mass, energy and angular momentum within the galaxy pair. We also analyse the shape and velocity structure of the resulting merger remnants and their dependence on the initial conditions of the galaxy encounter. We find that if most elliptical galaxies are remnants of single mergers between comparable systems, the initial orbits of these pairs must predominantly have had low angular momenta, and the observed galaxies must be prolate objects.