REEXAMINING THE UNIVERSALITY OF THE BURKERT PROFILE ON CLUSTER SCALES: DARK MATTER CORES

Abstract

The Burkert profile is a competing candidate for the analytic approximation of virialized dark halos especially when dark matter particles have a finite cross-section for elastic collisions. In this paper we reexamine its universality in massive systems, using an ensemble of 45 nearby X-ray clusters and 20 distant X-ray/lensing clusters. Despite the fact that this empirical profile turns out a great success on galactic scales and also reproduces approximately the X-ray observed surface brightness profiles of clusters, the dark matter cores of clusters predicted by the Burkert profile are too large to be reconciled with the strong gravitational lensing measurements. Specifically, the typical dark halo cores of clusters represented by the Burkert profile are about 0.2 Mpc, and only a small fraction (~1/4) of clusters can have compact cores smaller than 0.1 Mpc. This will constitute a critical challenge to the Burkert profile as a universal dark matter density law over entire mass ranges.