Tidal generation of active spirals and S0 galaxies by rich clusters

Abstract

Activity in nuclei of Seyfert spiral galaxies is observationally related to the degree of tidal perturbation from nearby companions and is probably fueled by disk gas inflow to the nuclear regions. Using computer simulations, we previously showed that tides from companions could cause nuclear inflows from spiral galaxies' self-gravitating disks. The perturbation necessary to produce the levels of inflow required for activity matches Dahari's observed Seyfert tidal triggering level. Gavazzi and Jaffe found that late-type spiral galaxies in rich clusters are radio sources 10 times more powerful than spirals outside clusters. Gavazzi and Jaffe propose that ram pressure from the cluster medium causes collapse of dense molecular clouds, star formation, and other activity in the spirals' disks. Bothun and Dressler similarly explain blue H I poor disk galaxies found in the central regions of the Coma Cluster via ram pressure effects. With computer simulations, we show that the tidal field of the cluster as a whole is physically sufficient to trigger cluster spiral nuclear and disk activity. We show that tidally induced collisions of disk gas clouds should be much more effective than ram pressure in causing activity. Gisler and also Dressler find observationally that rich cluster S0 systems are not created by ram pressure stripping. We explain the observed tendency for disk galaxies in centers of rich clusters to be barred and S0 as due to the cluster tidal field. Metals in the cluster medium would be enhanced by the expulsion of spirals' enriched gas via tidally induced activity.