Metal Enrichment of the Intergalactic Medium and Production of Massive   Black Holes
  A model for the chemical evolution of the intergalactic medium (IGM) is presented using theoretical yields of very massive stars (VMSs) and Type II supernovae (SNe II). It is shown that if [Si/C] is indeed as high as ~0.7 in the IGM, then VMSs associated with pair-instability supernovae (PI-SNe) in low-mass halos at high redshift must produce at least 50% of the Si. The remainder is from later galactic outflows of SN II debris, which also provide most of the C and O. Both sources are required to account for the metal inventory in the IGM. The early VMS production must continue until redshift z~15 so that the efficiency of VMS formation per low-mass halo is significantly below unity. Contributions from the later galactic outflows mainly occur at z~4-6. Using a Salpeter initial mass function, we infer that the number of VMSs producing massive black holes (MBHs) is 0.72 times the the number of VMSs associated with PI-SNe. The amount of metals (particularly Si) in the IGM that is attributable to PI-SNe is thus closely coupled with the total mass of MBHs produced in epochs prior to galaxy formation. Production of ~50% of the Si in the IGM by PI-SNe corresponds to an early inventory of MBHs that is comparable to the global mass budget of the central supermassive black holes in present-day galaxies. (Abridged) 
Y.-Z. Qian (UMN), G. J. Wasserburg (Caltech)