Population III generated cosmic rays and the production of ⁶Li

We calculate the evolution of ⁶Li generated from cosmic rays produced by an early population of massive stars. The computation is performed in the framework of hierarchical structure formation and is based on cosmic star formation histories constrained to reproduce the observed star formation rate at redshift z ≲ 6 and the observed chemical abundances both in damped Lyα absorbers and in the intergalactic medium, and to allow for an early reionization of the universe at z ∼ 11 by Population III stars as indicated by the third year results released by WMAP. We show that the pregalactic production of the ⁶Li isotope in the IGM via these Population III stars can account for the ⁶Li plateau observed in metal-poor halo stars without additional overproduction of ⁷Li. Our results depend on the efficiency of cosmic rays to propagate out of minihalos and the fraction of supernova energy deposited in cosmic rays. We also compute the cosmic-ray heating of the IGM gas. In general, we find somewhat high temperatures (of order 10⁵ K), implying that the cosmic rays production of ⁶Li may be required to be confined to the so-called warm-hot IGM.