The cosmological evolution of the properties of powerful extragalactic radio sources and their environments

Radio galaxies and radio-loud quasars produce powerful collimated gas flows or jets interacting with the gas in their environments. Here we seek to develop a model for the evolution of the jet pa rameters and the properties of their environments during cosmological timescales. Combining the evolutionary model for individual radio sources from Kaiser, Dennett-Thorpe & Alexander (1997) with the Radio Luminosity Function from Willott et al. (2000), we perform multi-dimensional Monte Carlo simulations in order to compile artificial samples. We then compare their statistical properties with those of sources contained in the observed low frequency radio surveys, 3CRR, 6CE and 7CRS. We compare them on the radio luminosity (P) - linear size (D) diagram and use the two-dimensional Kolmogorov-Smimov test to search for the best fitting parameters for each evolutionary model describing the source population as a whole. We find that the environments of radio sources evolve with cosmological time, in the sense that sources at high red shift are located in denser environments. However, we do not find a significant connection between the jet power and the density of the environment.