Testing Models of Radio Galaxy Evolution and the Cosmological Impact of FR II Radio Galaxies

Abstract

We investigate aspects of the cosmological evolution of FR II radio galaxies, focusing first on the abilities of models to match data for linear-sizes, radio powers, redshifts and spectral indices. Here we consider modifications to the theoretical models we had treated earlier, primarily by accounting for the growth of the radius of hotspots with source size. Better fits to the distributions of most of the data in three low-frequency surveys can be found with sensible choices of model parameters but no model yet considered gives a good match to all of the survey data simultaneously, nor does any do a good job of producing the spectral index distributions. The observational datasets are too small to completely discriminate among the models. We calculate the volume fraction of the ``relevant universe'' cumulatively occupied by the expanding radio galaxy lobes over the quasar era, when these powerful radio galaxies were much more common, and when they have been argued to play an important role in triggering galaxy formation and spreading magnetic fields and metals. We found the cumulative relevant volume filling factor of radio galaxies to be $\sim 5 %$, so we conclude that these impacts are smaller than previously estimated but that they are still significant.