Peculiar Velocities of Rich Clusters in Hot and Cold Dark Matter Models

We examine the peculiar velocities of rich clusters of galaxies in numerical simulations of hot (HDM) and cold dark matter (CDM) universes. We have identified rich clusters in these simulations using a friends of friends algorithm and studied the amplitude and evolution of cluster peculiar velocities with time, The mean cluster peculiar velocity in a CDM universe is 313 km s^-1^ for a bias factor of 2.5, increasing to 614 km s^-1^ for a bias factor of 1.0. For an HDM universe these values are 289 km s^-1^ for b = 2.5 and 661 km s^-1^ for b = 1. The cluster peculiar motion amplitudes determined from the simulations are in conflict with recent observational claims of cluster peculiar motions as large as ~2000 km s^-1^. We find that the growth rate of cluster peculiar motions ν_p_ is proportional to a is larger than that predicted by linear theory ν_p_ is proportional to a^1/2^. We have examined the agreement between the force and peculiar velocity vectors in these simulations to see if one might derive the large-scale density field from cluster peculiar velocities. Our analysis indicates that this may be done for low bias parameters b < 1.5 in both the hot and cold dark matter galaxy formation scenarios.