Observational Tests of Intergalactic Enrichment Models
  We summarize recent results assessing the carbon and silicon abundances of the intergalactic medium (IGM) using the `pixel optical depth' technique. We briefly discuss the implications of these results for models of intergalactic enrichment, focusing on distinguishing `early' z >> 4 enrichment by the first generations of stars and objects from `late' enrichment by 2 < z < 5 Ly-break galaxies. We then discuss the comparison of observed QSO spectra to simulated spectra generated from cosmological simulations that self-consistently include enrichment, and draw qualitative implications for the general picture of intergalactic enrichment at z > 2. 
Anthony Aguirre, Joop Schaye