Near-infrared evolution of brightest cluster galaxies in the most X-ray luminous clusters since z=1

We investigate the near infrared evolution of brightest cluster galaxies (BCGs) from a sample of rich galaxy clusters since z=1. By employing an X-ray selection of Lx>1e44 erg s-1 we limit environmental effects by selecting BCGs in comparably high density regions. We find a positive relationship between X-ray and near-infrared luminosity for BCGs in clusters with Lx>5e44 erg s-1. Applying a correction for this relation we reduce the scatter in the BCG absolute magnitude by a factor of 30%. The near-infrared J-K colour evolution demonstrates that the stellar population in BCGs has been in place since at least z=2 and that we expect a shorter period of star formation than that predicted by current hierarchical merger models. We also confirm that there is a relationship between `blue' J-K colour and the presence of BCG emission lines associated with star formation in cooling flows.