Some aspects of cosmological n-body simulations

Various properties of the n-body models used in numerical studies of gravitational clustering in an expanding universe are considered. The characteristics of the five 4000-point models presented by Turner et al. (1979) are summarized, and the time evolution of groups with a mass density contrast with respect to the whole system equal to 10 is analyzed. It is shown that for model V, in which the particles are distributed inside a spherical region with equal spacing on randomly oriented rods with a cosmological density parameter of 0.1 and unit masses, a large number of groups is present at an early stage of expansion, and the number of members of such groups increases steadily. A substantial number of groups can also be identified at much higher density contrasts. Considerable clustering is observed in all groups, with differences in the initial fluctuation spectrum reflected in the population of the largest group of each model. Analysis of the dispersion of the velocities of the particles in the system with respect to the Hubble flow reveals that the peculiar velocities of systems in open cosmological models are significantly smaller than those of closed systems.