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Volume 415, Number 1, February III 2004
Page(s) 77 - 85
Section Extragalactic astronomy
DOI http://dx.doi.org/10.1051/0004-6361:20031688

A&A 415, 77-85 (2004)
DOI: 10.1051/0004-6361:20031688

VLT + UVES spectroscopy of the low-ionization intrinsic absorber in SDSS J001130.56+005550.7

D. Hutsemékers1, 2, P. B. Hall3, 4 and J. Brinkmann5

1  Institut d'Astrophysique, Université de Liège, Allée du 6 août 17, Bât. B5c, 4000 Liège, Belgium
2  European Southern Observatory, Casilla 19001, Santiago 19, Chile
3  Princeton University Observatory, Princeton, NJ 08544, USA
4  Departamento de Astronomía y Astrofísica, Pontificia Universidad Católica de Chile, Casilla 306, Santiago 22, Chile
5  Apache Point Observatory, PO Box 59, Sunspot, NM 88349-0059, USA

(Received 7 May 2003 / Accepted 31 October 2003)

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 -22 000 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 high- and low-ionization species, including in the excited $\ion{Si}{ii}$ $^{\star}$ and $\ion{C}{ii}$ $^{\star}$ 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 $\ion{Mg}{ii}$ than for $\ion{Si}{iv}$ and $\ion{N}{v}$, which demonstrates the intrinsic nature of absorber. From the analysis of the excited $\ion{Si}{ii}$ $^{\star}$ and $\ion{C}{ii}$ $^{\star}$ lines in the lowest velocity component, we find an electron density $\simeq$10 3 cm -3. Assuming photoionization equilibrium, we derive a distance $\simeq$20 kpc between the low-ionization region and the quasar core. The correspondence in velocity of the high- and 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.

Key words: quasars: general -- quasars: absorption lines

Offprint request: D. Hutsemékers, hutsemekers@astro.ulg.ac.be

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