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; Ω0 = 0.4; and Ω0 = 0.4, ΩΛ = 0.6 cosmological scenarios. For large spiral galaxies with the rotation speed of 250 km s , tidal interactions truncate massive dark matter halos at 30± 6 kpc, and thicken stellar disks by a factor 2 to 3, increasing Toomre’s parameter to Q & 2 and halting star formation. Low density galaxies, such as the dwarf spheroidals with the circular velocity of 20 km s and the extended low surface brightness galaxies with the 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 LSB population. In the low Ω0 cosmological models, clusters form earlier and produce stronger evolution of galaxies. Subject headings: stellar dynamics — galaxies: clusters: general — galaxies: evolution — galaxies: interactions — methods: N-body simulations