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 ΩP(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(Eion)/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.
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We would like to dedicate this Letter to the memory of Fritz Zwicky. We thank Antoinette Songaila, Todd Tripp, and David Tytler for generously answering many questions and for guiding us through their data. This work was supported in part by the Department of Energy under grants DE-FG02-87ER40328 and DE-FG02-00ER41149, by the NSF under grant AST 99-00733, and by NASA under grant NAG5-10293, Caltech division contribution 8780(1091).
- Early universe
- Intergalactic medium
- Quasars: absorption lines