We compare earlier estimates of the volumes filled 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 10^8 years the volumes filled by them are found to be
comparable for the two scenarios. This strengthens our earlier inference that
much of the cosmic web of gaseous filaments, 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 fields and metals through the universe by z ~ 2.Comment: To appear in Bull. Astron. Soc. India; 10 pages, 3 Figures, basi.sty
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