Halo evolution in a cosmological environment

We present results of a study of the formation and evolution of the dark matter (DM) halos in a COBE-normalized spatially flat ΛCDM model (Ω0 = 1 − ΩΛ = 0.3; h = 0.7). The dynamics of 256 3 DM particles is followed numerically in a box of 60h Mpc with the dynamic range of 32, 000 in spatial resolution. The high resolution of the simulation allows us to examine evolution of both isolated and satellite halos in a representative volume. We discuss the new halo finding algorithm designed to identify halos in high-density environments, present results on the evolution of velocity function of DM halos and compare it with the Press-Schechter function, discuss the evolution of power spectrum of matter and halo distributions, and mass evolution of halos. The velocity function of halos at z = 0 compares well with the prediction of the Press-Schechter approximation, but for circular velocities in the range 100 – 200 km/s simulations predict ∼ 1.3 time more halos (mostly in clusters or groups). In real space the power spectra of halos and DM are very different (halos are anti-biased). Both spectra do not have simple power-law shape. In redshift space the spectra are close to a power law with γ = −2.1 in the range of wave numbers k = 0.2 − 5hMpc. The power spectra of halo distribution evolves only mildly for z = 0− 3. The mass evolution of isolated virialized objects determined from the simulation is in good agreement with predictions of the extended PressSchechter models. However, satellite halos evolve very different: for some of them the mass decreases with time, which happens if the halos fall into clusters or groups. We discuss the dependence of the correlation function of halo populations on their environment and merging history. Also: Astronomy Department, NMSU, Dept.4500, Las Cruces, NM 88003-0001