Abstract
The birth and death of the first generation of stars have important implications for the thermal state and chemical properties of the intergalactic medium (IGM) in the early universe. Sometime after recombination, the neutral chemically pristine gas was reionized by ultraviolet photons emitted from the first stars but was also enriched with heavy elements when these stars ended their lives as energetic supernovae. Using the results from previous high-resolution cosmological simulations of early structure formation that include radiative transfer, we show that a significant volume fraction of the IGM can be metal polluted, as well as ionized, by massive Population III stars formed in small-mass (~106-107 M?) halos early on. If most of the early generation stars die as pair-instability supernovae with energies up to ~1053 ergs, the volume-averaged mean metallicity will quickly reach Z ~ 10-4 Z? by a redshift of ~15-20, possibly causing a transition to the formation of a stellar population that is dominated by low-mass stars. In this scenario, the early chemical enrichment history should closely trace the reionization history of the IGM, and the end of the Population III era is marked by the completion of reionization and preenrichment by z ~ 15. We conclude that, while the preenrichment may partially account for the metallicity floor in high-redshift Ly? clouds, it does not significantly affect the elemental abundance in the intracluster medium.
Highlights
Chemical elements heavier than lithium are thought to be produced exclusively through stellar nucleosynthesis
While early generation stars may be born with a broad range of masses (e.g., Bromm, Coppi, & Larson 1999; Nakamura & Umemura 2001, 2002; Omukai & Yoshii 2003), very massive stars are dominant in causing various feedback effects to the intergalactic medium (IGM) in the early universe such as ionization, heating, and chemical enrichment
We have revisited the cosmological consequences of an early generation of Population III stars
Summary
Chemical elements heavier than lithium are thought to be produced exclusively through stellar nucleosynthesis. If the first stars are as massive as ∼ 200M⊙, they end their lives as energetic SNe via the pair-instability mechanism (e.g., Barkat, Rakavy, & Sack 1967; Bond, Arnett, & Carr 1984; Fryer, Woosley, & Heger 2001; Heger & Woosley 2002; Woosley, Heger, & Weaver 2002), releasing a total energy of up to ∼ 1053 ergs Such energetic explosions in the early universe are violently destructive: they expel the ambient gas out of the gravitational potential well of small-mass dark matter halos, causing an almost complete evacuation (Bromm, Yoshida, & Hernquist 2003, hereafter Paper I; Wada & Venkatesan 2003). These parameters are consistent with those employed in the numerical simulations we refer to
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