Comparison of cluster lensing profiles with ACDM predictions

We derive lens distortion and magnification profiles of four well-known clusters observed with Subaru. Each cluster is very well fitted by the general form predicted for cold dark matter (CDM) dominated halos, with good consistency found between the independent distortion and magnification measurements. The inferred level of mass concentration is surprisingly high, 8 < c _vir < 15 (〈c_vir〉=10.39 ± 0.91), compared to the relatively shallow profiles predicted by the ACDM model, c _vir=5.06 ± 1.10 (for 〈M_vir〉=1.25 × 10¹⁵ M_⊙ h^-1). This represents a 4 σ discrepancy, and includes the relatively modest effects of projection bias and profile evolution derived from N-body simulations, which oppose each other with little residual effect. In the context of CDM-based cosmologies, this discrepancy implies that clusters collapse earlier (z ≥ 1) than predicted (z < 0.5), when the universe was correspondingly denser.