Analysis of Ly α absorption lines in the vicinity of QSOs

Abstract

Recent evidence suggesting that at least some of the Lyman alpha forest absorbers are not primordial and are indeed associated with galaxies is disucussed. Proximity effect, which deals with the change in the distribution of Lyman alpha forest lines near the quasi-stellar objects (QSO) due to the radiation from the QSO is described. Results of calculations of the background UV intensity based on the proximity effect, for a large, homogeneous sample of lines, collected from the literature, are presented. It is shown that blending of lines in the intermediate resolution observations is responsible for an overestimation of the background UV flux in earlier calculations. Independent evidence is provided for the presence of dust in damped Lyman alpha absorbers. Causes for the occurence of the Lyman alpha forest lines with redshifts greater than the quasar redshift are investigated.