Early Metal Enrichment of the Intergalactic Medium by Pregalactic Outflows

We assess supernova (SN)-driven pregalactic outflows as a mechanism fordistributing the product of stellar nucleosynthesis over large cosmologicalvolumes prior to the reionization epoch. SN ejecta will escape the grasp ofhalos with virial temperatures T_vir>10^{4.3} K (corresponding to masses M>10^8h^{-1} M_sun at redshift z=9 when they collapse from 2-sigma fluctuations) ifrapid cooling can take place, and a significant fraction of their baryonic massis converted into stars over a dynamical timescale. We study the evolution ofSN-driven bubbles as they blow out from subgalactic halos and propagate intothe intergalactic medium (IGM), and show that to lift the halo gas out of thepotential well the energy injection must continue at least until blow-awayoccurs. The collective explosive output of about ten thousands SNe per halo atthese early epochs could pollute vast regions of intergalactic space to a meanmetallicity =Omega_Z/Omega_b>0.003 (comparable to the levels observed in theLyman-alpha forest at z=3) without much perturbing the IGM hydrodynamically,i.e. producing large variations of the baryons relative to the dark matter. Thevolume filling factor of the ejecta is higher than 20% if the star formationefficiency is of order 10%. When the filling factor of the ejecta becomessignificant, enriched material will typically be at a higher adiabat thanexpected from photoionization.Comment: 18 pages, 12 figures, emulateapj, revised version accepted for publication in the Ap