Proximate damped Ly{alpha} systems in SDSS-DR5

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 the PDLAs near luminous quasars over the redshift interval z=2.2-5. The incidence and mass density of PDLAs at z~3 is approximately twice that of intervening DLAs, while at z<2.5 and >3.5 the f(N_H_X) distribution is enhanced but statistically consistent with the intervening population. We interpret the observed enhancement of PDLAs around quasars in terms of quasar-galaxy clustering and compare the strength of the clustering signal to the expectation from independent measures of the respective clustering strengths of DLAs and quasars, as well as a complementary analysis of the clustering of absorbers around quasars in the transverse direction.