1998A&A...330...19M

We present spectroscopic observations of the damped Lyαabsorber at redshift z=1.9342 seen in the spectrum of the quasar Q 0151+048A. The redshift of the absorber is greater than the redshift of the quasar, so the system resembles the z_abs≃z_em damped absorber at z=2.81 towards the quasar PKS 0528-250. We have previously reported the detection of Lyαemission from the latter absorber, one of only two damped absorbers for which Lyαemission has unambiguously been detected. The resemblance between the PKS 0528-250 and Q 0151+048A systems is made closer by the detection of a weak emission feature in the trough of the Q 0151+048A absorber. This leads us to consider whether these z_abs≃z_em DLA absorbers are different objects to the intervening DLA absorbers. Two possibilities are examined and rejected. Firstly the Q 0151+048A and PKS 0528-250 z_abs≃z_em absorbers appear to be unrelated to the intrinsic absorbers (i.e. gas close to the quasar nucleus, ejected by the quasar), as intrinsic absorbers are of higher metallicity, have higher ionisation parameter, and show complex absorption profiles. Secondly these two DLA absorbers cannot be equated with the gaseous disks of the quasar host galaxies, as the absorber redshifts differ significantly from the quasar systemic redshifts. It is likely, then, that intrinsically the z_abs≃z_em DLA absorbers are the same as the intervening DLA absorbers, so that peculiarities in some of the z_abs≃z_em absorbers can be ascribed to their different environment i.e. proximity to the quasar, or membership of the same cluster as the quasar. We point out that the proximity effect may play some role, by reducing the Lyα-forest line blanketing of any Lyαemission line from z_abs≃z_em absorbers.