Limits on Collisional Dark Matter from Elliptical Galaxies in Clusters

The dynamical evolution of galaxies in clusters is modified if dark matter is self-interacting. Heat conduction from the hot cluster halo leads to evaporation of the relatively cooler galactic halos. The stellar distribution would adiabatically readjust to the loss of dark matter, reducing the central velocity dispersion. This would change the fundamental plane relations beyond the observational scatter. The requirement that the galactic halos survive in clusters for a Hubble time appears to exclude just that range of the dark matter cross-section, 0. 1 < sigma/m < 10⁴ cm²/g, thought to be optimal for reducing central halo cusps.