In this talk I will present a comprehensive investigation of the ‘proximity effect’ in the spectra of high-redshift quasars. This phenomenon describes the reduced absorption by intergalactic hydrogen (and also helium) by the action of individual quasars. These provide additional ionizing photons in excess to those from the cosmic UV background, leading to a reduction of neutral gas column densities on Mpc-scales around the quasars. Typically found in medium/high resolution spectra and combining several lines of sight (LOS), this effect was never detected systematically on low or high resolution data and towards single objects. I will focus on the technique used to reveal the proximity effect along single LOS and the possibility to gain information from its strength, on cosmic variance and gravitational clustering around quasars. I will also show how a statistical analysis of the proximity effect strength is sensitive to overdensities around quasars and provides more accurate estimations of the UV background.
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