Observed Scaling Relations for Strong Lensing Clusters: Consequences for Cosmology and Cluster Assembly

TL;DR

This paper demonstrates that incorporating the concentration-mass relation with the mass-temperature relation in galaxy clusters reduces uncertainties in cosmological parameter sigma8 estimates and suggests strong lensing clusters have more active merging histories.

Contribution

It introduces a method combining concentration-mass and mass-temperature relations to include unrelaxed clusters in sigma8 measurements, improving accuracy and sample size.

Findings

Concentration-mass relation reduces M-T scatter by a factor of 6.

Including unrelaxed clusters improves sigma8 measurement accuracy.

Preliminary evidence of a steeper BCG luminosity-mass relation in strong lensing clusters.

Abstract

Scaling relations of observed galaxy cluster properties are useful tools for constraining cosmological parameters as well as cluster formation histories. One of the key cosmological parameters, sigma8, is constrained using observed clusters of galaxies, although current estimates of sigma8 from the scaling relations of dynamically relaxed galaxy clusters are limited by the large scatter in the observed cluster mass-temperature (M-T) relation. With a sample of eight strong lensing clusters at 0.3 < z <0.8, we find that the observed cluster concentration-mass relation can be used to reduce the M-T scatter by a factor of 6. Typically only relaxed clusters are used to estimate sigma8, but combining the cluster concentration-mass relation with the M-T relation enables the inclusion of unrelaxed clusters as well. Thus, the resultant gains in the accuracy of sigma8 measurements from clusters are twofold: the errors on sigma8 are reduced and the cluster sample size is increased. Therefore, the statistics on sigma8 determination from clusters are greatly improved by the inclusion of unrelaxed clusters. Exploring cluster scaling relations further, we find that the correlation between brightest cluster galaxy (BCG) luminosity and cluster mass offers insight into the assembly histories of clusters. We find preliminary evidence for a steeper BCG luminosity - cluster mass relation for strong lensing clusters than the general cluster population, hinting that strong lensing clusters may have had more active merging histories.