Radio Galaxies and the Magnetization of the IGM

Observed radio galaxies had a much higher comoving density during the `quasar era', at z ~ 2-3, but these sources are only detectable for small fractions of their active lifetimes at such high z due to expansion losses and increased inverse Compton losses against the cosmic microwave background. Using recent models for the evolution of the size and luminosity of powerful double radio sources, as well as LCDM simulations of the cosmic web of baryonic material, we argue that during the quasar era a high volume fraction of this web was occupied by the lobes of double radio sources. They could have seeded the IGM with an average magnetic field approaching 10^{-8} G. Further, these advancing overpressured lobes could compress the denser interstellar gas clouds of the galaxies engulfed by them and thus trigger starbursts. This can probably account for much of the intense star-formation activity witnessed beyond z ~ 1.5. Also, the sweeping up of the ISM of the gas-rich galaxies by the rapidly advancing radio lobes may well be responsible for the widespread metal pollution of the IGM and proto-galaxies at high redshifts.