Evolution of isolated halos and halos inside of groups and clusters in a LCDM model

Abstract

A significant fraction of mass in the universe is believed to be in the form of dark matter (DM). Due to gravitational instability, the DM collapses hierarchically into DM halos. In this contribution we present a study of the formation and evolution of such DM halos in a COBE-normalized spatially flat LCDM model (Omega_0=1-Omega_L=0.3; h=0.7) using high-resolution N-body simulations. The novelty of this study is use of the newly developed halo-finding algorithms to study the evolution of both isolated and satellite (located inside virial radii of larger group- and cluster-size systems) halos. The force and mass resolution required for a simulated halo to survive in the high-density environments typical of groups and clusters is high: ~1-3 kpc and \~10^9 M_sun, respectively. We use the high-resolution Adaptive Refinement Tree (ART) N-body code to follow the evolution of 256^3 dark matter particles with dynamic range in spatial resolution of 32,000 in a box of 60/h Mpc. We show that the correlation function of these halos is anti-biased with respect to the dark matter correlation function and is high and steeper than the correlation function of the isolated virialized objects. The correlation function evolves only mildly between z=3 and z=1. The mass evolution of isolated virialized objects determined from the simulation is in good agreement with prediction of semi-analytical models. The differences exist, however, if we include satellite halos in the halo catalogs.