The galaxy cluster concentration–mass scaling relation

Scaling relations of clusters have made them particularly important cosmological probes of structure formation. In this work, we present a comprehensive study of the relation between two profile observables, concentration (c vir) and mass (M vir). We have collected the largest known sample of measurements from the literature which make use of one or more of the following reconstruction techniques: weak gravitational lensing (WL), strong gravitational lensing (SL), weak+strong lensing (WL+SL), the caustic method (CM), line-of-sight velocity dispersion (LOSVD), and X-ray. We find that the concentration–mass (c–M) relation is highly variable depending upon the reconstruction technique used. We also find concentrations derived from dark matter-only simulations (at approximately M vir ∼ 1014 M⊙) to be inconsistent with the WL and WL+SL relations at the 1σ level, even after the projection of triaxial haloes is taken into account. However, to fully determine consistency between simulations and observations, a volume-limited sample of clusters is required, as selection effects become increasingly more important in answering this. Interestingly, we also find evidence for a steeper WL+SL relation as compared to WL alone, a result which could perhaps be caused by the varying shape of cluster isodensities, though most likely reflects differences in selection effects caused by these two techniques. Lastly, we compare concentration and mass measurements of individual clusters made using more than one technique, highlighting the magnitude of the potential bias which could exist in such observational samples.