The concentration-mass relation in galaxy clusters

The concentration of the dark matter haloes of galaxy clusters is relatedthrough their formation times to the power spectrum of perturbations fromwhich they formed. Measurements of the variation of concentration with masstherefore provide interesting constraints on cosmological models. Howeverpresently accepted observations of XMM will be able to accurately measureconcentrations over a limited mass range of about 10^1410^15 solar masses.We propose to supplement this with observations of galaxy groups in the range10^1310^14 solar masses in order to more precisely measure the slope andpossible curvature of the relation. Constraints on individual formation timescan be correlated with system properties to probe other physical processes. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]