Absorption lines and ion abundances in the QSO PKS 0528 - 250

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Abstract
Spectra of the QSO PKS 0528 – 250 (ze = 2.765) have been obtained with the AAT at 2 Å resolution from 3100 to 7180 Å. Absorption line systems have been identified at zA1 = 2.81322, zA2 = 2.81100, zB = 2.53758 and zc = 2.14077. The ionization ranges from H I, A1 II and Fe II to N V or O VI in system A, from H I and possibly Si II to C IV in B and from H I, A1 II and Si II to C IV in C. In system A the Si IV and higher stages are concentrated in A2. Broad Lα profiles in A and C correspond to 2 × 1021 and 5 × 1020 atom cm−2 respectively. Column densities also have been estimated for several heavier elements at each redshift. In system A depletions by factors of 8 to 160 relative to solar abundances appear to be present in S II, O I and N I as well as the typical factor 10 for Si II and Fe II similar to interstellar clouds in the plane of our galaxy. Longward of the Lα absorption in system A there are 44 lines of which only 27 have proposed identifications, whereas at the shorter wavelengths there are 112 lines of which 43 have plausible identifications due to one or more ions other than hydrogen. Thus caution is needed with the common assumption that most absorptions shortward of Lα emission in QSOs are due to Lα.

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