MERGERS OF COLLISIONLESS SYSTEMS

The hierarchical clustering scenario is examined by merging haloes of collisionless particles under controlled conditions. Each simulation c ontains 16 000 particles, which gives a finer spatial resolution than in previous work. We find that dark matter haloes can grow homologousl y, obeying simple scaling laws. All the mergers tend towards a single density profile, which in our case closely resembles that given by de Vaucouleurs. The high resolution of our simulations also allows us to look at the resultant core structure of our haloes. We find that the c entral density is close to the maximum value allowed by phase-space co nstraints, indicating a smaller core radius in the dark matter than is generally assumed. The expected deviations from our results, given mo re realistic initial conditions, are discussed.