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Astron. Astrophys. 345, 73-80 (1999)

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6. Conclusion

We have studied the associated absorption systems (zabs [FORMULA] zem) in QSO J 2233-606, seen over the redshift range 2.198-2.2215, corresponding to outflow velocities relative to the quasar emission redshift (zem = 2.252 from Mg II ) of 2800-5000 km s-1 which is modest compared to usual associated or BAL outflows.

We have shown that the Ly[FORMULA] line at zabs = 2.2215 is saturated but has non-zero residual intensity. The covering factor of the gas is of the order of 0.7. This absorption system is unusual in the sense that there is no detectable metal lines. This could reveal chemical inhomogeneities in the gas or, and more likely, this absorption could correspond to very highly ionized gas from which no absorption due to heavier element can be detected. If the latter is true, the ionization factor log HI/H could be smaller than -8 and the total column density in the cloud larger than log N(H) = 22. Such a cloud could be related to the warm absorbers.

Over the redshift range 2.198-2.21, conspicuous Ne VIII , O VI , C IV and N V absorptions are seen whereas the H I absorption is weak. From analysing these absorptions we conclude that (i) a two-phase medium of low and high-ionization respectively is required to explain the complete set of column densities; (ii) the abundances are close to the solar value but nitrogen is enhanced with respect to carbon; (iii) although difficult to ascertain there is a tendency for the absorption lines redshifted on top of the emission lines to have covering factors smaller than lines redshifted in parts of the spectrum free from emission-lines; this suggests that the gas covers the continuum emitting region but only part of the BLR. The component at zabs = 2.21 (+950 km s-1 on Fig. 1) is remarkable as, though conspicuous in Ne VIII and O VI , it is undetected in H I , C IV and N V . The column densities derived for this subcomponent by Voigt-profile fitting are log N(Ne VIII ) = 14.57[FORMULA]0.10; log N(O VI ) = 14.05[FORMULA]0.06 and log N(H I[FORMULA] 13.30, consistent with what is expected from a high-ionization zone.

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© European Southern Observatory (ESO) 1999

Online publication: April 12, 1999