Discovery of a Ringlike Dark Matter Structure in the Core of the Galaxy Cluster Cl 0024 17

Abstract

International audienceWe present a comprehensive mass reconstruction of the rich galaxy cluster Cl 0024 17 at z~=0.4 from ACS data, unifying both strong- and weak-lensing constraints. The weak-lensing signal from a dense distribution of background galaxies (~120 arcmin-2) across the cluster enables the derivation of a high-resolution parameter-free mass map. The strongly lensed objects tightly constrain the mass structure of the cluster inner region on an absolute scale, breaking the mass-sheet degeneracy. The mass reconstruction of Cl 0024 17 obtained in such a way is remarkable. It reveals a ringlike dark matter substructure at r~75'' surrounding a soft, dense core at