Luminosities of [0.1–2.4 keV] within R₅₀₀ of MCXC clusters (Piffaretti et al. 2011) as a function of redshift, up to z = 0.1. The colorbarshows the corresponding cluster velocity dispersion σ_V calculated from Eq. (7). Black plus signs indicate clusters from the current analysis. The black curve corresponds to the intrinsic dispersion of SNe Ia on the Hubble diagram found for the JLA sample (Betoule et al. 2014) projected onto cluster luminosities by combining the luminosity–mass and mass–velocity dispersion relations.