N-BODY SIMULATIONS OF DISC-HALO GALAXIES - ISOLATED SYSTEMS, TIDAL INTERACTIONS AND MERGING

Collisions of galaxies are studied through numerical simulations of 250-particle systems. Each model galaxy consists of a flat disc, an extended live halo and a core. The evolution of such systems and possible relaxation effects are investigated in detail.Slow hyperbolic encounters between exponential disc-type galaxies give rise to strong tidal effects. These lead to asymmetric mass exchange, energy change and angular momentum loss. Resonances between particles and the relative orbit depending on the orientation of the three spins involved determine the strength of the interaction. Only a few per cent of the particles escape, but they carry away a substantial fraction of the angular momentum. Generally, the galaxy spins decrease and the disc and halo angular momentum vectors are not aligned after an encounter. The response of a galaxy to a collision with another galaxy is considerably different from that caused by a single perturber.Merger cross-sections are spin-dependent. In the present experiments, the remnants have distinct visible cores and Hubble-type density profiles. They are triaxial, rotate slowly, and have anisotropic velocity structures. Some of them fit the observational data for elliptical galaxies reasonably well. © 1981 Oxford University Press. All rights reserved.