Expansion of radio galaxies in a cosmologically evolving medium: possible implications for the cosmic star-formation history

Abstract

We compare earlier estimates of the volumes filed by lobes of radio galaxies during the quasar era based upon non-evolving ambient media with new ones assuming a strong cosmological evolution of the ambient medium. If the sources remain active for over 10⁸ years the volumes filed by them are found to be comparable for the two scenarios. This strengthens our earlier inference that much of the cosmic web of gaseous fiaments, the site of galaxy formation, was probably permeated by radio lobes during the quasar era and this could have triggered extensive star formation and made large contributions to the spread of magnetic filds and metals through the universe by z~2.