Constraining cosmic reionization with quasar, gamma ray burst, and Lyα emitter observations

We investigate the cosmic reionization history by comparing semi-analytical models of the Lyα forest with observations of high-z quasars and gamma ray bursts absorption spectra. In order to constrain the reionization epoch z_rei, we consider two physically motivated scenarios in which reionization ends either early (ERM, z_rei ≳ 7) or late (LRM, z_rei ≈ 6). We analyze the transmitted flux in a sample of 17 QSOs spectra at 5.7 ≲ z_em ≲ 6.4 and in the spectrum of the GRB 050904 at z = 6.3, studying the wide dark portions (gaps) in the observed absorption spectra. By comparing the statistics of these spectral features with our models, we conclude that current observational data do not require any sudden change in the ionization state of the IGM at z ≈ 6, favouring indeed a highly ionized Universe at these epochs, as predicted by the ERM. Moreover, we test the predictions of this model through Lyα emitters observations, finding that the ERM provide a good fit to the evolution of the luminosity function of Lyα emitting galaxies in the redshift range z = 5.7 - 6.5. The overall result points towards an extended reionization process which starts at z ≳ 11 and completes at z_rei ≳ 7, in agreement with the recent WMAP5 data.