The interplay between radio galaxies and cluster environment

By combining the REFLEX and NORAS cluster data sets with the NVSS radio catalogue, we obtain a sample of 145, z < 0.3, X-ray-selected clusters brighter than 3 x 10(-12) erg s(-1) cm(-2) that show a central radio emission above 3 mJy. For virial masses M-vir less than or similar to 10(14.5) M-circle dot, 11 clusters out of 12 (corresponding to 92 per cent of the systems) are inhabited by a central radio source. This fraction decreases with higher masses as alpha M-vir(-0.4). If this decrease is a selection effect, it suggests that the majority of X-ray-selected clusters host in their centre a radio source brighter than similar to 10(20) W Hz(-1) sr(-1). A division of the sample into clusters harbouring either point-like or an extended radio-loud active galactic nucleus (AGN) reveals that the steepening of the L-x-T relation for low-temperature clusters is strongly associated with the presence of central radio objects with extended jets and/or lobe structures. In the latter case, L-x proportional to T-4 while for point-like sources one recovers an approximately self-similar relation L-x proportional to T-2.3. Monte Carlo simulations show that the steepening of the L-x-T relation is not caused by clusters being underluminous in the X-ray band, but rather by overheating, most likely caused by the interplay between the extended radio structures and the intracluster medium. In the case of low-mass systems, we also find a tight correlation between radio luminosity and cluster temperature. The effects of the central radio source on the thermal state of a cluster become less important with increasing cluster mass. The presence of radio sources with extended structures (61, corresponding to similar to 42 per cent of the sample) is enhanced in X-ray luminous clusters with respect to 'field' radio-loud AGN. Furthermore, we find that the luminosity distribution of the cluster radio population differs from that of all radio sources, as there is a deficit of low-luminosity (L-R less than or similar to 10(22) W Hz(-1) sr(-1)) objects, while the number of high-luminosity ones is boosted. The net effect on the radio luminosity function of radio galaxies associated with cluster centres is of a flattening at all luminosities L-R less than or similar to 10(24) W Hz(-1) sr(-1).