Two Strong-Lensing Clusters Confront Universal Dark Matter Profiles

In the galaxy clusters SSDS J1004+411 and ACO 1689, a large number ofmultiply-imaged background objects have recently been observed. We use thesedata to map the projected mass distribution in the inner regions of theseclusters. The source redshifts span a large range, which eliminates thedegeneracies that plague nearly all lensing work. As a result the mass maps arevery well-constrained, despite very weak prior assumptions. ACO 1689 lenses somany objects that we can afford to map it twice using disjoint sets of images,thus verifying our internal error estimates. We then deproject the mass maps(pretending for this purpose that they are spherical) and obtain inner profilesconsistent with rho propto r^{-1} and indistinguishable from recent cold darkmatter simulations. Assuming that baryons make only a small difference to theprofile outside sim 10 kpc, these results support the prediction of a universalinner profile for dark matter structures, independent of any parametrization ofthat profile.