Pairwise velocity statistics of dark halos

We have accurately evaluated the halo pairwise velocity dispersion and the halo mean streaming velocity in the LCDM model (the flat omega(0) = 0.3 model) using a set of high-resolution N-body simulations. Based on the simulation results, we have developed a model for the pairwise velocity dispersion of halos. Our model agrees with the simulation results over all scales we studied. We have also tested the model of Sheth et al. for the mean streaming motion of halos derived from the pair-conservation equation. We found that their model reproduces the simulation data very well on large scale, but under-predicts the streaming motion on scales r < 10 h(-1) Mpc. We have introduced an empirical relation to improve their model. These improved models are useful for predicting the redshift correlation functions and the redshift power spectrum of galaxies if the halo occupation number model, e.g. the cluster weighted model, is given for the galaxies.