Galactic cannibalism and cold dark matter density profiles

Using N-body simulations, we show that the process of formation of the brightest cluster galaxy through dissipationless galactic cannibalism can affect the inner cluster dark matter density profile. In particular, we use as a realistic test case the dynamical evolution of the galaxy cluster C0337-2522 at redshift z = 0.59, hosting in its centre a group of five elliptical galaxies which are likely to be the progenitor of a central giant elliptical. After the formation of the brightest cluster galaxy, the inner cluster dark matter density profile is significantly flatter (logarithmic slope 0.49 less than or similar to beta less than or similar to 0.90) than the original cusp (beta = 1), as a consequence of dynamical friction heating of the massive galaxies against the diffuse cluster dark matter. In our simulations we have assumed that the cluster galaxies are made of stars only. We also show that the presence of galactic dark matter haloes can steepen the cluster central density profile. We conclude that galactic cannibalism could be a viable physical mechanism to reconcile-at least at the cluster scale-the flat dark matter haloes inferred observationally in some galaxy clusters with the steep haloes predicted by cosmological simulations.