The evolution of galaxies in different cosmological environment

According to the hierarchical scenario, galaxies form via merging and accretion of small objects. Within a series of high resolution simulations we have studied the formation and evolution of dark matter halos hosting galaxies. First halos have been formed at z > 10. We have studied the evolution of isolated halos (field galaxies) as well as of halos in dense regions (galaxies in groups or clusters and galaxies with satellites) and of small halos in voids. At z < 2 the merging rate of the overall halo population can be described by a simple power law $(1+z)^3$. Halos located at present inside clusters have formed earlier than isolated halos of the same mass. At low redshifts (z<1), their merger rate is 3 times lower than that of isolated halos and 2 times lower than the merger rate of halos that end up in groups by z=0. At higher redshifts (z>1), progenitors of cluster and group halos have 3--5 times higher merger rates than isolated halos. Subsamples of halos with different merging histories show different clustering properties.