The mutual interaction of powerful radio galaxies and their environments
  Using a self-similar model for the expansion of cocoons surrounding the jets in powerful extragalactic radio sources (type FRII), we investigate the influence of the properties of the gas surrounding these objects on their evolution. The variation of their radio luminosity as a function of linear size for individual sources is determined in dependence of the density distribution of the IGM the source is embedded in. Based on these results, the cosmological evolution of the FRII population and hence that of the environments of these sources can be constrained. The environments are found to be denser and/or more extended at high redshifts. The bow shock surrounding the cocoon of FRII sources compresses and heats the IGM. A numerical integration of the hydrodynamic equations governing the gas flow between the bow shock and the cocoon boundary is presented. From this we determine the appearance of the large scale structure of radio galaxies in X-rays and the cooling times for the IGM heated by the passage of the bow shock. This has important implications for the cosmological evolution of the IGM. 
Christian R. Kaiser (Oxford University) and Paul Alexander (MRAO,   Cambridge)