Formation and Evolution of Galactic Halos in Clusters of Galaxies

We investigate effects of time evolution of a rich cluster of galaxies on its member galactic halos in the standard cold dark matter (SCDM) universe using high resolution N-body simulations. We identify several hundred galactic halos within virial radius of our simulated cluster. We also find that a large number of halos have been tidally disrupted at z = 0. Therefore we improve a method of deriving merging history trees of galaxies taking account of tidally stripped galaxies. The main results are as follows: (1) At high redshift (z ≃ 2), the mass function of the galactic halos which are in the cluster at z = 0 is very similar to that obtained in the field region and well agrees with the Press-Schechter mass function. (2) The mass function of cluster galaxies which consist of both galactic halos and tidally stripped galaxies has hardly evolved since z ≃ 2. This mass function at z = 0 is well represented by the Press-Schechter mass function at z = 2. (3) At high redshift (z > 3), in the region which becomes the cluster the fraction of galaxies which have undergone recent merger is lager than that in the field. After z ∼ 3, however, it rapidly decreases and becomes smaller than that in the field. (4) The strongly stripped galaxy fraction of the cluster galaxies begins to increase from z ≃ 0.5. At z = 0, a clear correlation appears between this fraction and the distance from the center of the cluster. (5) Tidally truncated halos have steeper outer profiles than those of the model of Navarro, Frenk, & White (1996, 1997). Subject headings: galaxies: clusters: general — galaxies: halos — galaxies: interactions