Redshift of reionization: are we there yet?

Comparison of the observed evolution of the Ly-alpha transmitted flux in the spectra of four highest redshift quasars discovered by SLOAN survey with the theoretical prediction for this evolution based on the state-of-the-art numerical simulations of cosmological reionization already allows one to constrain the redshift of reionization to z = 6.2 ± 0.1s ± 0.2r, where systematic and random errors are given respectively.