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

TL;DR

This study uses quasar, gamma ray burst, and Lya emitter data to constrain the timeline of cosmic reionization, supporting an extended process ending around z=7 and starting before z=11.

Contribution

It introduces a semi-analytical model comparison with observations to constrain the epoch of reionization, favoring an early and extended reionization scenario.

Findings

Reionization likely completed by z>=7.

Current data do not require sudden ionization changes at z~6.

Lya emitter evolution supports an extended reionization process.

Abstract

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.