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

Abstract

Supernova--driven outflows from early galaxies may have had a large impact on the kinetic and chemical structure of the intergalactic medium (IGM). We use three--dimensional Monte Carlo cosmological realizations of a simple linear peaks model to track the time evolution of such metal--enriched outflows and their feedback on galaxy formation. We find that at most 30% of the IGM is enriched in models that only include objects that cool by atomic transitions, with the majority of enrichment occurring relatively early (5 < z < 12) and resulting in a mean IGM metallicity between 10^{-3} and 10^{-1.5} solar. The inclusion of Population III objects that cool through H2 line emission has only a minor impact on these results: increasing the mean metallicity and filling factor by at most a factor of 1.4, and moving the dawn of the enrichment epoch to a redshift of approximately 14 at the earliest. Choosing the model in which the mean IGM metallicity is most consistent with QSO absorption-line studies, on the other hand, leads to a filling factor of 15%. Thus enrichment by outflowing galaxies is likely to have been incomplete and inhomogeneous, biased to the areas near the starbursting galaxies themselves. Finally, we show that IGM enrichment is intimately tied to the ram-pressure stripping of baryons from neighboring perturbations, resulting in the suppression of at least 20% of galaxies in all models and redshifts with filling factors greater than 2%, and an overall suppression factor of approximately 50% in the most observationally-favored model.