Keywords :
quasars absorption lines
Abstract:Using the Sloan Digital Sky Survey Data Release 5 (SDSS-DR5), we survey proximate damped Ly{alpha} systems (PDLAs): absorption-line systems with HI column density N_H_>=2x10^20^cm^-2^ at velocity separation {delta}v<2999km/s from their background quasar. Many of these absorbers may be physically associated with their background quasars, and their statistics allow us to study quasar environments out to z~5. However, the large ionizing flux emitted by a quasar can ionize the neutral gas in a nearby galaxy, possibly giving rise to a "proximity effect", analogous to the similar effect observed in the Ly{alpha} forest. From a sample of 108 PDLAs, we measure the HI frequency distribution f(N_H_,X) incidence, and gas mass density of
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