Weak- and strong-lensing analyses of the triaxial matter distribution of Abell 1689

Abstract

Haloes formed in the standard Λ cold dark matter framework should follow a universal mass density profile and fit a well-defined mass-concentration relation. Lensing analyses of clusters with a large Einstein radius seem to contradict this scenario, with the massive cluster Abell 1689 being often claimed as a notable example of a highly over-concentrated halo. Shape and orientation biases in lensing studies might be on the basis of this disagreement between theory and observations. We developed a method for a full three-dimensional analysis of strong- and weak-lensing data. Surface density maps estimated from lensing are deprojected to infer the actual triaxial structure of the cluster, whose mass distribution is approximated as an ellipsoidal Navarro-Frenk-White halo with arbitrary orientation. Inversion is performed under competing a priori assumptions, integrated in the method, thanks to Bayesian statistics. We applied the method to Abell 1689. Whatever the considered priors on shape and orientation, both weak- and strong-lensing analyses found the halo to be slightly over-concentrated but still consistent with theoretical predictions. We found some evidence for a mildly-triaxial lens (minor-to-major-axis ratio ∼ 0.5 ± 0.2) with the major-axis orientated along the line of sight. Exploiting priors from N-body simulations, we found mass M₂₀₀= (1.3 ± 0.4) × 10¹⁵ M_⊙ and concentration c₂₀₀= 10 ± 3 for the weak-lensing analysis of Subaru data, M₂₀₀= (1.7 ± 0.3) × 10¹⁵ M_⊙ and c₂₀₀= 6.1 ± 0.9 for the strong-lensing analysis of multiple-image systems, and M₂₀₀= (1.3 ± 0.2) × 10¹⁵ M_⊙ and c₂₀₀= 7.3 ± 0.8 for the combined weak- plus strong-lensing analysis. Based in part on data collected at the Subaru Telescope, which is operated by the National Astronomical Society of Japan.