Influence of Population III stars on cosmic chemical evolution

TL;DR

This paper explores how Population III stars influenced early cosmic chemical evolution, showing their essential role in explaining observed metal-poor star abundances and cosmic reionization constraints.

Contribution

It demonstrates that Population III stars are crucial for understanding early chemical enrichment and matches observed metal-poor star abundance patterns.

Findings

PopIII nucleosynthetic yields match observed metal-poor star abundances.

PopIII stars are necessary for early cosmic chemical evolution.

Reionization constraints are marginally consistent with new star formation rates.

Abstract

New observations from the Hubble ultra deep field suggest that the star formation rate at z>7 drops off faster than previously thought. Using a newly determined star formation rate for the normal mode of Population II/I stars (PopII/I), including this new constraint, we compute the Thomson scattering optical depth and find a result that is marginally consistent with WMAP5 results. We also reconsider the role of Population III stars (PopIII) in light of cosmological and stellar evolution constraints. While this input may be needed for reionization, we show that it is essential in order to account for cosmic chemical evolution in the early Universe. We investigate the consequences of PopIII stars on the local metallicity distribution function of the Galactic halo (from the recent Hamburg/ESO survey of metal-poor stars) and on the evolution of abundances with metallicity (based on the ESO large program on very metal-poor stars), with special emphasis on carbon-enhanced metal-poor stars. Our most important results show that the nucleosynthetic yields of PopIII stars lead to abundance patterns in agreement with those observed in extremely metal-poor stars. In this chemical approach to cosmic evolution, PopIII stars prove to be a compulsory ingredient, and extremely metal-poor stars are inevitably born at high redshift. (Abridged)