First Stars, Very Massive Black Holes, and Metals

Recent studies suggest that the initial mass function (IMF) of the first stars was likely to be extremely top-heavy, unlike what is observed at present. We propose a scenario to generate fragmentation to lower masses once the first massive stars have formed and derive constraints on the primordial IMF. We estimate the mass fraction of pair-unstable supernovae, shown to be the dominant sources of the first heavy elements. These metals enrich the gas up to ≈ 10−5 Z⊙, when a transition to efficient cooling-driven fragmentation occurs producing < ∼ 1M ⊙ clumps. We argue that the remaining fraction of the first stars ends up in ≈ 100M ⊙ VMBHs (Very Massive Black Holes). If we further assume that all these VMBHs are likely to end up in the centers of galactic nuclei constituting the observed SMBHs, then ≈ 1 % of the first stars contributed to the initial metal enrichment and the IMF remained top-heavy down to a redshift z ≈ 10. Interestingly, this is the epoch at which the cool metals detected in the Lyα forest at z ≈ 3 must have been ejected from galaxies. At the other extreme