The Prompt Inventory from Very Massive Stars and Elemental Abundances in Lyα Systems

Abstract

It has been proposed that very massive stars (VMSs) dominated heavy-element production until a "metallicity" threshold corresponding to [Fe/H] ≈ -3 was reached. This results in a prompt (P) inventory of elements, the abundances of which were determined from observations of Galactic halo stars with [Fe/H] ≈ -3. We calculate Ω_P(E) from the P inventory for a large number of elements in the intergalactic medium (IGM). Using the available data on Ω(E_(ion)) for C IV, O VI, and Si IV in Lyα systems, we find that the ionization fractions calculated from Ω(E_(ion))/Ω_P(E) are, within reasonable uncertainties, compatible with the values estimated from ionization models for Lyα systems. This agreement appears to hold from z ~ 0.09 to ~4.6, indicating that the bulk of the baryonic matter remains dispersed with a fixed chemical composition. We conclude that the P inventory was established in the epoch prior to z ~ 4.6. The dispersal of processed baryonic matter to the general IGM is considered to be the result of energetic VMS explosions that disrupted baryonic aggregates until the "metallicity" threshold was reached to permit normal astration. The formation of most galaxies is considered to have occurred subsequent to the achievement of this metallicity threshold in the IGM.