First page Back Continue Last page Overview Text
Notes:
Two models can account for the large optical depth at early times:
A moderately top heavy IMF (~5 Ms) with reionization by z~15. However, additional evidence suggests neutral gas was still present at z~6 and that the complete overlap of ionizing bubbles could not occur before z~9.
Partial ionization by very massive Population III at z~15 with more metal abundant population II causing complete reionization by z~6 could account for the high optical depth.