Correlation between the Lyman alpha absorption line density and the emission line redshift of QSOs

A statistical analysis of the absorption line density N(z_abs) in the Lαforest of 16 high-redshift quasars shows that the line density is clearly dependent on the emission redshift of the quasar, z_em. Not only is the mean density of all the Lα absorption lines larger for larger z_em, but more importantly, for each given absorption redshift interval, N(z_abs) is also positively correlated with z_em. A two-factor variance analysis, with ejection velocity as the second factor, shows that the line density in the Lα forest depends sensitively on z_em but not on the ejection velocity. These results are difficult to interpret by either the intervening or the ejecting hypothesis and are unlikely to be due to the selection effects suggested by Carswell et al. [13].