The band-averaged X-ray cooling function, Λ_ee(r), for two different helium distributions in the ICM: a uniform helium abundance (blue dashed line) and a helium sedimentation distribution provided by Peng & Nagai (2009) (red line). The overdensity radius r₅₀₀ is the radius within which the mean cluster density is a factor of 500 times greater than the critical density of the universe at the cluster redshift.