A model for the declining rotation curves of cluster spirals

Abstract

Numerical studies have shown that mean tidal field in clusters of galaxies can cause a significant increase in the planar velocity dispersions of stars, and gas clouds in disks of spiral galaxies. Since the perturbation caused by cluster tidal field are generally weak and fairly symmetric, the stellar distribution of galaxies would not necessary show obvious signs of tidal disturbance. In this paper it is shown that the increased non-circular velocities of stars can result in symmetric decline (at large radii) of the rotation curves of the perturbed spiral galaxies. This decline result from the well known phenomenon of the “asymmetric drift” a high velocity dispersion stellar population. This suggest that the observation of the declining rotation curves of spiral galaxies in clusters do not necessarily imply that their dark matter halos have been tidally truncated as is generally assumed.