Sources for Metals in the Intergalactic Medium

We present a discussion of possible sources of C, O, and Si in the IGM usingthe yields of VMSs and SNe II. The chemical evolution of the IGM is consideredbased on analytical phenomenological models of hierarchical structureformation. Two regimes are considered: one for gas expulsion by VMSs and SNe IIin low-mass halos prior to dissociation of H2 molecules and reionization, andthe other for later SN II-driven outflows from intermediate-mass halos. We userecent data on the abundances of C, O, and Si in the IGM inferred from two UVBmodels. We show that the results from a UVB model including quasars only cannotbe explained by existing stellar models. To account for the results, inparticular [Si/C], from a softer UVB model requires VMSs to provide more than15% of the C in the IGM. The preferred scenario is that VMSs in low-mass halosprovided between 15% and 60% of the C in the regime of very high redshift(z>15) and that galactic outflows provided the remainder during later epochs(4

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