Early enrichment of the intergalactic medium and its feedback on galaxy formation

Supernova-driven outflows from early galaxies may have had a large impact on the kinetic and chemical properties 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 by volume is enriched to values above 10^-3 Z⊙ in models that include only objects that cool by atomic transitions. The majority of enrichment occurs relatively early (5≤z≤12) and leads to a mass-averaged cosmological metallicity between 10^-3 and 10^-1.5 Z⊙. 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 z ≈ 14 at the earliest. Thus, enrichment by outflowing galaxies is likely to have been incomplete and inhomogeneous, biased to the areas near the starbursting galaxies themselves. Models with a 10% star formation efficiency can satisfactorily reproduce the nearly constant (2 ≤ z ≤ 5, Z ≈ 3.5 ± 10^-4 Z⊙) metallicity of the low column density Lyα forest derived by Songaila in 2001, an effect of the decreasing efficiency of metal loss from larger galaxies. Finally, we show that IGM enrichment is intimately tied to the ram-pressure stripping of baryons from neighboring perturbations. This results in the suppression of at least 20% of the dwarf galaxies in the mass range ∼3 × 10⁸-3 × 10⁹ M⊙ in all models with filling factors greater than 2% and an overall suppression of ∼50% of dwarf galaxies in the most observationally favored model.