The Density Profile of Cluster-Scale Dark Matter Halos

We measure the average gravitational shear profile of 6 massive clusters (M_vir ~ 10¹⁵ M_sun) at z=0.3 out to a radius ~2h⁻¹ Mpc. The measurements are fitted to a generalized NFW-like halo model rho(r) with an arbitrary r -> 0 slope alpha. The data are well fitted by such a model with a central cusp with alpha ~ 0.9 - 1.6 (68% confidence interval) for a SCDM cosmology and alpha ~ 1.3 - 1.6 for a LambdaCDM cosmology. For the standard-NFW case alpha = 1.0, we find a concentration parameter c_vir that is consistent with recent predictions from high-resolution CDM N-body simulations. Our results strongly disfavor constant density cores in clusters, as predicted by some recent dark matter models such as self-interacting dark matter.