Updating reionization scenarios after recent data
  The recent release of data on (i) high redshift source counts from NICMOS HUDF, and (ii) electron scattering optical depth from 3-year WMAP, require a re-examination of reionization scenarios. Using an improved self-consistent model, based on Choudhury & Ferrara (2005), we determine the range of reionization histories which can match a wide variety of data sets simultaneously. From this improved analysis we find that hydrogen reionization starts around z = 15, driven by the metal-free stars (with normal Salpeter-like IMF), and is 90% complete by z = 10. The photoionizing power of PopIII stars fades for z < 10 because of the concomitant action of radiative and chemical feedbacks, which causes the reionization process to stretch considerably and to end only by z = 6. The combination of different data sets still favours a non-zero contribution from metal-free stars, forming with efficiencies > 2%. 
T. Roy Choudhury and A. Ferrara