A model for the chemical evolution of the intergalactic medium (IGM) is presented using theoretical yields of very massive stars (VMSs; MVMS > 100 M⊙) 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 (MVMS ≈ 140-260 M⊙) associated with pair-instability supernovae (PI-SNe) in low-mass (∼ 105 M⊙) 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 VVMS ≈ 260-2000 M⊙) producing massive black holes (MBHs) with an average mass (MMBH) ∼ 270-550 M⊙ is ≈0.72 times 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 constitutes a fraction ∼(4-8) × 10-5 of the total baryonic mass in the universe. This is comparable to the global mass budget of the central supermassive black holes (SMBHs) in present-day galaxies. The corresponding occurrence rates in each halo of ∼ 105 Modot; during the epoch of VMS formation at z ≳ 15 are ∼0.9 Gyr-1 for VMSs associated with PI-SNe and ∼0.6 Gyr-1 for the concomitant more massive stars producing MBHs. These rates may be of use to studies of H2 dissociation and reionization and to models of SMBH formation.
- Galaxies: formation
- Intergalactic medium
- Nuclear reactions, nucleosynthesis, abundances