Central galaxy growth and feedback in the most massive nearby cool core cluster

We present multiwavelength observations of the centre of RXCJ1504.1 - 0248 - the galaxy cluster with the most luminous and relatively nearby cool core at z similar to 0.2. Although there are several galaxies within 100 kpc of the cluster core, only the brightest cluster galaxy (BCG), which lies at the peak of the X-ray emission, has blue colours and strong line-emission. Approximately 80 M-circle dot yr-1 of intracluster gas is cooling below X-ray-emitting temperatures, similar to the observed ultraviolet star formation rate of similar to 140 M-circle dot yr-1. Most star formation occurs in the core of the BCG and in a 42-kpc-long filament of blue continuum, line emission and X-ray emission, that extends south-west of the galaxy. The surrounding filamentary nebula is the most luminous around any observed BCG. The number of ionizing stars in the BCG is barely sufficient to ionize and heat the nebula, and the line ratios indicate that an additional heat source is needed. This heat source can contribute to the H alpha-deduced star formation rates (SFRs) in BCGs and therefore the derived SFRs should only be considered upper limits. AGN feedback can slow down the cooling flow to the observed mass deposition rate if the black hole accretion rate is of the order of 0.5 M-circle dot yr-1 at 10 per cent energy output efficiency. The average turbulent velocity of the nebula is v(turb) similar to 325 km s -1 which, if shared by the hot gas, limits the ratio of turbulent to thermal energy of the intracluster medium to less than 6 per cent.