Bottom panel: comparison between our results (red diamonds, as in left-hand panel Fig. 4) and those obtained by Planck Collaboration (2011h) (green triangles), where MaxBCG clusters are investigated. X-ray luminosities and associated error bars for the MaxBCG clusters are based on the analysis of Rykoff et al. (2008). Vertical error bars are as in Fig. 4 and the X-ray prediction (i.e., Eq. (6)) is shown by the dashed blue line. Top panel: X-ray luminosity histograms of the MCXC (red) and MaxBCG (green) samples. For the MCXC the width of the bars is equal to the luminosity bin width, while for the MaxBCG we adopt the horizontal error bar shown in the bottom panel.