STRUCTURE AND HISTORY OF DARK MATTER HALOS PROBED WITH GRAVITATIONAL LENSING

Abstract

We test with gravitational lensing (GL) data the dark matter (DM) halos embedding the luminous baryonic component of galaxy clusters; our benchmark is provided by their two-stage cosmogonical development that we compute with its variance, and by the related "α-profiles" we derive. The latter solve the Jeans equation for the self-gravitating, anisotropic DM equilibria, and yield the radial runs of the density ρ(r) and the velocity dispersion σ2r(r) in terms of the DM "entropy" K ≡ σ2r/ρ2/3 ∝ rα highlighted by recent N-body simulations; the former constrains the slope to the narrow range α ≈ 1.25–1.3. These physically based α-profiles meet the overall requirements from GL observations, being intrinsically flatter at the center and steeper in the outskirts relative to the empirical Navarro, Frenk, & White formula. Specifically, we project them along the line of sight and compare with a recent extensive data set from strong and weak lensing observations in and around the cluster A1689. We find an optimal fit at both small and large scales in terms of a halo constituted by an early body with α ≈ 1.25 and by recent extensive outskirts, that make up an overall mass 1015 M☉ with a concentration parameter c ≈ 10 consistent with the variance we compute in the ΛCDM cosmogony. The resulting structure corresponds to a potential well shallow in the outskirts as that inferred from the X rays radiated from the hot electrons and baryons constituting the intracluster plasma.