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 similar to 1. By employing an X-ray selection of LX > 10(44) 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 L-X > 5 x 10(44) erg s(-1). Applying a correction for this relation, we reduce the scatter in the BCG absolute magnitude by a factor of 30 per cent. 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.