Spherical galaxy collisions: head-on encounters

A series of N-body simulations was performed in order to investigate head-on encounters between equal mass spherical galaxies of similar structure. Two different types of galaxy models were used in the experiments, differing mainly in the velocity distribution and central concentration: in the first kind of model, most of the particles moved predominantly along eccentric orbits, while in the second type most of the halo kinetic energy resided on the tangential velocity components of the particles and the core was rather isotropic. The fractional internal energy gain that a galaxy experiences after a head-on encounter was found to depend slightly on the type of orbits which predominate in the galaxy. The exchange of particles in a head-on collision is negligible. Tandem encounters are progressively more effective in producing escapers. The bounce induced by the overlapping at pericentric passage tends to erase the initial conditions of the galaxy models. 19 references.