Violence in the Dark Ages

A wide range of observational and theoretical arguments suggest that theuniverse experienced a period of heating and metal enrichment, most likely fromstarbursting dwarf galaxies. Using a hydrodynamic simulation we have conducteda uniquely detailed theoretical investigation of this epoch at the end of thecosmological ``dark ages''. Outflows strip baryons from pre-viralized haloswith total masses $\lesssim10{}^{10}$ M${}_\odot$, reducing their numberdensity and the overall star formation rate, while pushing these quantitiestoward their observed values. We show that the metallicity of$\lesssim10{}^{10}$ M${}_\odot$ objects increases with size, but with a largescatter, reproducing the metallicity-luminosity relation of dwarf galaxies.Galaxies $\gtrsim10{}^{10}$ M${}_\odot$ form with a roughly constant initialmetallicity of 10% solar, explaining the observed lack of metal-poor disk starsin these objects. Outflows enrich roughly 20% of the simulation volume,yielding a mean metallicity of 0.3% solar, in agreement with observations ofCIV in QSO absorption-line systems.Comment: 14 pages, 5 figures, condensed preprint version. Minor revisions included, accepted by Ap