Intergalactic Magnetic Fields from Quasar Outflows

Outflows from quasars inevitably pollute the intergalactic medium (IGM) withmagnetic fields. The short-lived activity of a quasar leaves behind anexpanding magnetized bubble in the IGM. We model the expansion of the remnantquasar bubbles and calculate their distribution as a function of size andmagnetic field strength at different redshifts. We generically find that by aredshift z=3, about 5-20% of the IGM volume is filled by magnetic fields withan energy density >10% of the mean thermal energy density of a photo-ionizedIGM (at T=10^4 K). As massive galaxies and X-ray clusters condense out of themagnetized IGM, the adiabatic compression of the magnetic field could result inthe field strength observed in these systems without a need for further dynamoamplification. The intergalactic magnetic field could also provide a nonthermalcontribution to the pressure of the photo-ionized gas that may account for theclaimed discrepancy between the simulated and observed Doppler widthdistributions of the Ly-alpha forest.Comment: 40 pages, 8 figures, submitted to Ap