First Stars, Very Massive Black Holes, and Metals

Recent studies suggest that the initial mass function (IMF) of the firststars 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 firstmassive stars have formed and derive constraints on the primordial IMF. Weestimate the mass fraction of pair-unstable supernovae, shown to be thedominant sources of the first heavy elements. These metals enrich the gas up toabout $10^{-5}$ solar metallicity, when a transition to efficientcooling-driven fragmentation occurs producing 1 solar mass clumps. We arguethat the remaining fraction of the first stars ends up in 100 solar mass VMBHs(Very Massive Black Holes). We obtain constraints on the fraction of firststars that contribute to the initial metal enrichment and the transitionredshift for primordial IMF away from a top-heavy one, by making variousassumptions about the fate of these VMBHs at late times. We conclude with adiscussion of several hitherto unexplored implications of a high-mass dominatedstar formation mode in the early Universe.