STATISTICAL-ANALYSIS OF PECULIAR VELOCITY-FIELDS IN COSMOLOGICAL N-BODY SIMULATIONS

Peculiar velocity fields of galaxies, computed by cosmological N-body simulations, are analyzed in detail. This Monte Carlo approach provides not only the expectation values of the bulk flow velocity and the cosmic Mach number, but their probability distributions. Since the presently available data are quite limited and thus poor in a statistical sense, the probability distributions are important in quantitatively testing various cosmological scenarios. The distribution of the cosmic Mach number is found to be almost Maxwellian in linear and mildly nonlinear regimes, independent of the shape of the density fluctuation spectrum. Applying the resulting probability distribution to the cold dark matter models based on the inflationary scenario, we found that the constraints derived by Ostriker and Suto hold at the 90% confidence level.