Dark Matter Halo Profiles Of Massive Clusters: Theory Versus Observations

Dark-matter-dominated cluster-scale halos act as an important cosmological probe and provide a key testing ground for structure formation theory. Focusing on their mass profiles, we have carried out (gravity-only) simulations of the concordance.CDM cosmology, covering a mass range of 2 x 10(12) to 2 x 10(15) h(-1) M-circle dot and a redshift range of z = 0-2, while satisfying the associated requirements of resolution and statistical control. When fitting to the Navarro-Frenk-White profile, our concentration-mass (c-M) relation differs in normalization and shape in comparison to previous studies that have limited statistics in the upper end of the mass range. We show that the flattening of the c-M relation with redshift is naturally expressed if c is viewed as a function of the peak height parameter, nu. Unlike the c-M relation, the slope of the c-nu relation is effectively constant over the redshift range z = 0-2, while the amplitude varies by similar to 30% for massive clusters. This relation is, however, not universal: using a simulation suite covering the allowed wCDM parameter space, we show that the c-nu relation varies by about +/- 20% as cosmological parameters are varied. At fixed mass, the c(M) distribution is well fit by a Gaussian with sigma(c)/< c > similar or equal to 1/3, independent of the radius at which the concentration is defined, the halo dynamical state, and the underlying cosmology. We compare the.CDM predictions with observations of halo concentrations from strong lensing, weak lensing, galaxy kinematics, and X-ray data, finding good agreement for massive clusters (M-vir > 4 x 10(14) h(-1) M-circle dot), but with some disagreements at lower masses. Because of uncertainty in observational systematics and modeling of baryonic physics, the significance of these discrepancies remains unclear.