Early Enrichment of the Intergalactic Medium and Its Feedback on Galaxy Formation

Supernova-driven outflows from early galaxies may have had a large impact onthe kinetic and chemical structure of the intergalactic medium (IGM). We usethree-dimensional Monte Carlo cosmological realizations of a simple linearpeaks model to track the time evolution of such metal-enriched outflows andtheir feedback on galaxy formation. We find that at most 30% of the IGM byvolume is enriched to values above 10^-3 solar in models that only includeobjects that cool by atomic transitions. The majority of enrichment occursrelatively early (5 < z < 12) and resulting in a mass-averaged cosmologicalmetallicity between 10^-3 and 10^-1.5 solar. The inclusion of Population IIIobjects that cool through H2 line emission has only a minor impact on theseresults: increasing the mean metallicity and filling factor by at most a factorof 1.4, and moving the dawn of the enrichment epoch to a redshift ofapproximately 14 at the earliest. Thus enrichment by outflowing galaxies islikely to have been incomplete and inhomogeneous, biased to the areas near thestarbursting galaxies themselves. Models with a 10% star formation efficiencycan satisfactorily reproduce the nearly constant (2 < z < 5, Z approximately3.5 x 10^-4 solar) metallicity of the low column density Ly-alpha forestderived by Songaila (2001), an effect of the decreasing efficiency of metalloss from larger galaxies. Finally, we show that IGM enrichment is intimatelytied to the ram-pressure stripping of baryons from neighboring perturbations.This results in the suppression of at least 20% of the dwarf galaxies in themass range 10^8.5 to 10^9.5 solar, in all models with filling factors greaterthan 2%, and an overall suppression of approximately 50% of dwarf galaxies inthe most observationally-favored model.Comment: 8 pages, 5 figures, accepted to Ap