A plot showing the effect of AGN feedback on the X-ray luminosity–temperature relation in the OWLS simulation (as demonstrated in McCarthy et al. 2010). To help illustrate this point the temperatures here are cool-core corrected. Blue squares are the non-AGN feedback run, and red stars are with AGN feedback included. The connecting lines show where each individual cluster is moved to by the feedback process. The low-entropy gas, which would otherwise condense to form stars, is removed or heated at high redshift (z > 1) by energy input from AGN in typical L^★ galaxies. The ejection of low-entropy gas and the injection of energy by the AGN in the central galaxy stops the remaining gas from overcooling in the centre of the group and thus stops the gas from causing significant star formation in the central galaxy at late times.