CODEX Weak Lensing: Concentration of Galaxy Clusters at z ~ 0.5

TL;DR

This study uses weak lensing to measure the mass and concentration of galaxy clusters at z ~ 0.5, finding no significant evolution in the concentration-mass relation and suggesting lower evolution than self-similar models predict.

Contribution

First weak lensing analysis of CODEX clusters at this redshift, constraining their mass and concentration, and comparing results with numerical predictions and other surveys.

Findings

Measured cluster mass $M_{200c} \,=\, 6.6^{+1.0}_{-0.8} \times 10^{14} h^{-1} M_{\odot}$

Derived concentration parameter $c_{200c} \,=\, 3.7^{+0.7}_{-0.6}$

No significant evolution observed in the concentration-mass relation

Abstract

We present a stacked weak lensing analysis of 27 richness selected galaxy clusters at $0.40 \leqslant z \leqslant 0.62$ in the CODEX survey. The fields were observed in 5 bands with the CFHT. We measure the stacked surface mass density profile with a $14\sigma$ significance in the radial range $0.1 < R\ Mpc\ h^{-1} < 2.5$. The profile is well described by the halo model, with the main halo term following an NFW profile and including the off-centring effect. We select the background sample using a conservative colour-magnitude method to reduce the potential systematic errors and contamination by cluster member galaxies. We perform a Bayesian analysis for the stacked profile and constrain the best-fit NFW parameters $M_{200c} = 6.6^{+1.0}_{-0.8} \times 10^{14} h^{-1} M_{\odot}$ and $c_{200c} = 3.7^{+0.7}_{-0.6}$. The off-centring effect was modelled based on previous observational results found for redMaPPer SDSS clusters. Our constraints on $M_{200c}$ and $c_{200c}$ allow us to investigate the consistency with numerical predictions and select a concentration-mass relation to describe the high richness CODEX sample. Comparing our best-fit values for $M_{200c}$ and $c_{200c}$ with other observational surveys at different redshifts, we find no evidence for evolution in the concentration-mass relation, though it could be mitigated by particular selection functions. Similar to previous studies investigating the X-ray luminosity-mass relation, our data suggests a lower evolution than expected from self-similarity.