Violence in the Dark Ages

A wide range of observational and theoretical arguments suggest that the universe experienced a period of heating and metal enrichment, most likely from starbursting dwarf galaxies. Using a hydrodynamic simulation, we have conducted a detailed theoretical investigation of this epoch at the end of the cosmological "dark ages." Outflows strip baryons from previralized halos with total masses ≲1010 M☉, reducing their number density and the overall star formation rate, while pushing these quantities toward their observed values. We show that the metallicity of ≲1010 M☉ objects increases with size but with a large scatter, reproducing the metallicity-luminosity relation of dwarf galaxies. Galaxies ≳1010 M☉ form with a roughly constant initial metallicity of 10% solar, explaining the observed lack of metal-poor disk stars in these objects. Outflows enrich roughly 20% of the simulation volume, yielding a mean metallicity of 0.3% solar, in agreement with observations of C IV in quasi-stellar object absorption-line systems.