Dynamical Evolution of Galaxies in Clusters

Tidal forces acting on galaxies in clusters lead to a strong dynamical evolution. In order to quantify the amount of evolution, I run self-consistent N-body simulations of disk galaxies for a variety of models in the hierarchically forming clusters. The tidal field along the galactic orbits is extracted from the simulations of cluster formation in the Ω₀ = 1, 0.4, and 0.4, Ω_Λ = 0.6 cosmological scenarios. For large spiral galaxies with a rotation speed of 250 km s^-1, tidal interactions truncate massive dark matter halos at 30 ± 6 kpc and thicken stellar disks by a factor of 2-3, increasing Toomre's parameter to Q ≳ 2 and halting star formation. Low-density galaxies, such as the dwarf spheroidals with a circular velocity of 20 km s^-1 and the extended low surface brightness galaxies with a scale length of 10-15 kpc, are completely disrupted by tidal shocks. Their debris contribute to the diffuse intracluster light. The tidal effects are significant not only in the core but throughout the cluster and can be parametrized by the critical tidal density. The tidally induced evolution results in the transformation of the infalling spirals into S0 galaxies and in the depletion of the low surface brightness galaxy population. In the low-Ω₀ cosmological models, clusters form earlier and produce stronger evolution of galaxies.