The Era of Massive Population III Stars: Cosmological Implications and Self‐Termination

The birth and death of the first generation of stars have importantimplications for the thermal state and chemical properties of the intergalacticmedium (IGM) in the early universe. Sometime after recombination, the neutral,chemically pristine gas was reionized by ultraviolet photons emitted from thefirst stars, but also enriched with heavy elements when these stars ended theirlives as energetic supernovae. Using the results from previous high-resolutioncosmological simulations of early structure formation that include radiativetransfer, we show that a significant volume fraction of the IGM can bemetal-polluted, as well as ionized, by massive Population III stars formed insmall-mass (10^6-10^7 Msun) halos early on. If most of the early generationstars die as pair-instability supernovae with energies up to 10^{53} ergs, thevolume-averaged mean metallicity will quickly reach Z ~ 10^{-4}Zsun by aredshift of 15-20, possibly causing a prompt transition to the formation of astellar population that is dominated by low-mass stars. In this scenario, theearly chemical enrichment history should closely trace the reionization historyof the IGM, and the end of the Population III era is marked by the completionof reionization and pre-enrichment by z=15. We conclude that, while thepre-enrichment may partially account for the ``metallicity-floor'' inhigh-redshift Lyman-alpha clouds, it does not significantly affect theelemental abundance in the intracluster medium.Comment: Version accepted by ApJ. Minor revisions and a few citations adde