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Evolution of Clusters of Galaxies: Mass Stripping from Galaxies and Growth of Common Halos

We investigated the evolution of clusters of galaxies using self-consistent $N$-body simulations in which each galaxy was modeled by many particles. We carried out simulations for about 20 cases using different initial conditions. In all simulations, clusters were initially in virial equilibrium. We found that more than half of the total mass escaped from individual galaxies within a few crossing times of the cluster, and that a diffuse halo was formed. The growth rate of the common halo depended on the size of individual galaxies only weakly. The stripping of the mass from galaxies was mainly due to the interaction of galaxies, not due to the effect of the tidal field of the cluster potential. The amount of stripped mass was larger for galaxies in the central region than for those in the outer region, since the interactions were more frequent in the central region. As a result, a positive correlation between the distance from the center and the mass of the galaxy developed. The volume-density profile of the common halo is expressed as $ρ\propto r^{-1}$ in the central region. This mass distribution is consistent with the mass distribution in clusters estimated using X-ray observations.