Comparison of Cluster Lensing Profiles with Lambda CDM Predictions

TL;DR

This study compares observed lensing profiles of four galaxy clusters with Lambda CDM predictions, revealing higher-than-expected concentration levels that suggest clusters formed earlier than current models predict.

Contribution

It provides the first detailed comparison of observed cluster lensing profiles with Lambda CDM predictions, highlighting a significant discrepancy in concentration parameters.

Findings

Observed concentrations are higher than Lambda CDM predictions.

Discrepancy suggests clusters formed earlier (z≥1) than models predict.

Results are consistent across independent distortion and magnification measurements.

Abstract

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}> = 10.4 \pm 0.9), compared to the relatively shallow profiles predicted by the Lambda CDM model, c_{vir}=5.1 \pm 1.1 (for <M_{vir}> =1.25\times 10^{15}M_{\odot}/h). This represents a 4sigma 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 clusters collapse earlier (z\geq 1) than predicted (z<0.5), when the Universe was correspondingly denser.