Central density. Left: histogram of central densities for the SZE-selected systems, scaled according to the best-fitting model (Eq. (17)) derived in Sect. 3.2, measured at 0.05 R₅₀₀. The solid line is a kernel density plot with a smoothing width of 0.15. Middle: histogram of scaled central densities for the z < 0.3 SZE-selected systems compared to the X-ray-selected sample, measured at 0.015 R₅₀₀. The solid line is a kernel density plot with a smoothing width of 0.15. Right: histogram of central densities for the SZE-selected sample at 40 kpc.