Constraining cosmic reionization with quasar, gamma ray burst, and Lya
  emitter observations
  We investigate the cosmic reionization history by comparing semi-analytical
models of the Lya 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 quasars spectra at 5.7<z<6.4 and in the
spectrum of the gamma ray burst 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
Lya emitters observations, finding that the ERM provide a good fit to the
evolution of the luminosity function of Lya 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.
