Intergalactic magnetic fields from quasar outflows

Outflows from quasars inevitably pollute the intergalactic medium (IGM) with magnetic fields. The short-lived activity of a quasar leaves behind an expanding magnetized bubble in the IGM. We model the expansion of the remnant quasar bubbles and calculate their distribution as a function of size and magnetic field strength at different redshifts. We generically find that by a redshift z similar to 3, about 5%-20% of the IGM volume is filled by magnetic fields with an energy density greater than or similar to 10% of the mean thermal energy density of a photoionized IGM (at similar to 10(4) K). As massive galaxies and X-ray clusters condense out of the magnetized IGM, the adiabatic compression of the magnetic field could result in the field strength observed in these systems without a need for further dynamo amplification. The intergalactic magnetic field could also provide a nonthermal contribution to the pressure of the photoionized gas that may account for the claimed discrepancy between the simulated and observed Doppler width distributions of the Ly alpha forest.