VLT + UVES Spectroscopy of the Low - Ionization Intrinsic Absorber in SDSS J 001130 . 56 + 005550 . 7 ⋆

We analyse high-resolution VLT+UVES spectra of the low-ionization intrinsic absorber observed in the BAL QSO SDSS J001130.56+005550.7. Two narrow absorption systems at velocities −600 km s−1 and −22000 km s−1 are detected. The low-velocity system is part of the broad absorption line (BAL), while the high-velocity one is well detached. While most narrow absorption components are only detected in the high-ionization species, the lowest velocity component is detected in both highand low-ionization species, including in the excited Si  and C  lines. From the analysis of doublet lines, we find that the narrow absorption lines at the low-velocity end of the BAL trough are completely saturated but do not reach zero flux, their profiles being dominated by a velocity-dependent covering factor. The covering factor is significantly smaller for Mg  than for Si  and N , which demonstrates the intrinsic nature of absorber. From the analysis of the excited Si  and C  lines in the lowest velocity component, we find an electron density ≃ 103 cm−3. Assuming photoionization equilibrium, we derive a distance ≃ 20 kpc between the low-ionization region and the quasar core. The correspondence in velocity of the highand low-ionization features suggests that all these species must be closely associated, hence formed at the same distance of ∼ 20 kpc, much higher than the distance usually assumed for BAL absorbers.