Evolution of Cluster Galaxies in Hierarchical Clustering Universes
  Using cosmological N-body simulations of critical (SCDM) and open ($\Omega = 0.3$, OCDM) cold dark matter models, we investigate evolution of cluster galaxies. From our numerical simulation, we construct merging history trees of the galaxies. By following their merging history, we show major merger fractions of the galaxies in cluster forming regions is roughly proportional to (1+z)^{4.5} at low redshifts (z < 2) and has a steep peak at $z \simeq 2.5$ and $z \simeq 3$ in SCDM and OCDM, respectively. We also show that the cluster galaxies are affected by tidal interaction after the clusters formed. Because the formation redshift of the cluster in SCDM, z_{form} = 0.15, is much more recent than that of the cluster in OCDM, z_{form} = 1.6, the cluster galaxies in SCDM show more rapid evolution by tidal interactions from z = 0.5 than those in OCDM. 
Takashi Okamoto and Asao Habe