Ensemble Mass Distribution of Galaxy Clusters from the CLASH Survey: Concentration–Mass Relation, Stacked Mass Profile, and Splashback Radius

Clusters of galaxies, by virtue of their position at the high end of the cosmic mass function, play a fundamental role in testing models of structure formation. The ability of massive clusters, to significantly distort the images of background objects via gravitational lensing, can provide direct and unique constraints on the nature of the underlying matter distribution. I will present new results from a comprehensive strong-lensing, weak-lensing shear and magnification analysis of a sample of 20 high-mass clusters targeted in the CLASH survey. Our analysis combines high-quality data from 16-band Hubble Space Telescope observations and wide-field multi-color imaging taken primarily with Suprime-Cam on the Subaru Telescope. We reconstruct surface mass density profiles of individual clusters from a joint analysis of the full lensing constraints, and determine masses and concentrations for all clusters. For the X-ray-selected subsample, we examine the concentration–mass relation and its intrinsic scatter using a Bayesian regression approach. We show that the data are in excellent agreement with LCDM predictions when the CLASH selection function based on X-ray morphological regularity and the projection effects are taken into account. We also derive an ensemble-averaged surface mass density profile of this subsample by stacking their individual profiles. The stacked lensing signal is well described by a family of density profiles predicted for cuspy dark-matter-dominated halos in gravitational equilibrium, namely, the Navarro–Frenk–White, Einasto, and DARKexp models, whereas the single power-law, cored isothermal and Burkert density profiles are disfavored by the data. We show that cuspy halo models that include the large-scale two-halo term provide improved agreement with the data. Finally, we develop and apply a new non-parametric method for extracting the ensemble mass profile and its logarithmic gradient. We will discuss the detectability of the splashback radius, a physical halo boundary, using cluster lensing observations.