Substructure in lensing clusters and simulations

We present high-resolution mass reconstructions for five massive cluster-lenses spanning a redshift range from z = 0.18 to 0.57 utilizing archival Hubble Space Telescope data and applying galaxy-galaxy lensing techniques. These detailed mass models were obtained from the observations by combining constraints from the strong and weak lensing regimes. We ascribe local weak distortions in the shear maps to perturbations induced by the presence of galaxy haloes around individual bright early-type cluster member galaxies. This technique constrains the mass enclosed within an aperture for these subhaloes. We are sensitive to a specific mass range for these subhaloes, 10 11 -10 12. 5 M ⊙ , which we associate with galaxy-scale subhaloes. Adopting a parametric model for the subhaloes, we also derive their velocity dispersion function and the aperture radius function. The mass spectrum of substructure in the inner regions of the observed clusters is directly compared with that in simulated clusters extracted from the Millennium Simulation. The mass function, aperture radii and velocity dispersion function are compared in detail. Overall, we find good agreement between the distribution of substructure properties retrieved using the lensing analysis and those obtained from the simulation. We find that the fraction of total cluster mass associated with individual subhaloes within the inner 0.5-0.8 h -1 Mpc of our clusters ranges from 10-20 per cent, in broad agreement with simulations. Our work provides a powerful test of the Lambda cold dark matter model, which appears consistent with the amount of observed substructure in massive, lensing clusters based on the present data.