Abstract
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 ~ 3, about 5%-20% of the IGM volume is filled by magnetic fields with an energy density 10% of the mean thermal energy density of a photoionized IGM (at ~104 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? forest.
Highlights
The interstellar medium of galaxies is known to possess strong magnetic Ðelds that are dynamically important and reach near equipartition with the total kinetic energy (Zeldovich, Ruzmaikin, & Sokolo† 1983 ; Beck et al 1996)
The corresponding intergalactic magnetic Ðeld (IGMF) should have an energy density of B2/8n Z 4 ] 10~20 ergs cm~3, which amounts to Z5% of the thermal energy density of the intergalactic medium (IGM) at the mean cosmic density and the photoionization temperature of T D 104 K, typical of uncollapsed regions
In ° 2 we model the expansion of such a bubble into the surrounding IGM and add up the cumulative e†ects of many quasar sources
Summary
The interstellar medium of galaxies is known to possess strong magnetic Ðelds that are dynamically important and reach near equipartition with the total (turbulent plus thermal) kinetic energy (Zeldovich, Ruzmaikin, & Sokolo† 1983 ; Beck et al 1996). The corresponding intergalactic magnetic Ðeld (IGMF) should have an energy density of B2/8n Z 4 ] 10~20 ergs cm~3, which amounts to Z5% of the thermal energy density of the IGM at the mean cosmic density and the photoionization temperature of T D 104 K, typical of uncollapsed regions The existence of this nonthermal pressure component could have had a signiÐcant e†ect on the Lya forest and on the fragmentation of the IGM into dwarf galaxies. In this paper we explore the possibility that the observed galactic and intergalactic Ðelds originate from energetic quasar outÑows, an idea originally proposed by Rees & Setti (1968) for intergalactic Ðelds, by Hoyle (1969) for galactic Ðelds, and examined more recently by MedinaTanco & Enlin (2000) These outÑows can carry magnetic Ñux from the very compact accretion disk ([1015 cm) around a quasar black hole, where the growth time is very short, out to cosmological scales (D1024 cm), starting at high redshifts. Throughout the paper we assume a Ñat universe with a cosmological conkstmanst~h1aMvipncg~)1,0a\nd0p.38,\)0".09\. 0.7, )b h2 \ 0.019, H0 \ 70
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