EDP Sciences
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Volume 404, Number 2, June III 2003
Page(s) 449 - 463
Section Extragalactic astronomy
DOI http://dx.doi.org/10.1051/0004-6361:20030493

A&A 404, 449-463 (2003)
DOI: 10.1051/0004-6361:20030493

Photoionized $\ion{O}{vi}$ absorbers toward the bright QSO HE 0515-4414

S. A. Levshakov1, I. I. Agafonova1, D. Reimers2 and R. Baade2

1  Department of Theoretical Astrophysics, Ioffe Physico-Technical Institute, 194021 St. Petersburg, Russia
2  Hamburger Sternwarte, Universität Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany

(Received 20 December 2002 / Accepted 31 March 2003)

We report on detailed Monte Carlo inversion analysis of five $\ion{O}{vi}$ systems from the spectrum of the bright quasar HE 0515-4414 ( $z_{\rm em}\,$= 1.71). The associated system at $z_{\rm abs}\,$= 1.697 with the neutral hydrogen column density N( $\ion{H}{i}$) $= 4.4\times10^{13}$ cm -2 shows pronounced absorption from highly ionized transitions of $\ion{C}{iii}$, $\ion{C}{iv}$, $\ion{N}{v}$, $\ion{O}{vi}$, $\ion{Si}{iv}$, and probably $\ion{S}{vi}$. We found that only a power law type ionizing spectrum ( $J_\nu \propto \nu^{-1.5}$) is consistent with the observed sample of the line profiles, i.e. the system is definitely intrinsic. The relative metal abundances give almost the solar pattern and the metallicity of ~5 times solar. The system originates in a thin shell of the line-of-sight thickness $L \la 16$ pc. Two $\ion{O}{vi}$ systems at $z_{\rm abs}\,$= 1.674 ([C/H] $\simeq -1.6$) and 1.602 ([O/H] $\simeq -1.1$), arising in intervening halos, have linear sizes of $L \simeq$ 3-14 kpc and $\simeq$17 kpc, respectively. Absorption systems at $z_{\rm abs}\,$= 1.385 ([C/H] $\simeq -0.3$, $L \simeq$ 1.7-2.5 kpc) and $z_{\rm abs}\,$= 1.667 ([C/H] $ \simeq -0.5$, $L \simeq 1$ kpc) exhibit characteristics very similar to that observed in metal-enriched high velocity clouds in the Milky Way. These systems are probably embedded in extremely metal-poor halos with [C/H] < -2.4 ( $z_{\rm abs}\,$= 1.667) and [C/H] < -3.7 ( $z_{\rm abs}\,$= 1.385). We also found two additional extremely metal-poor Ly $\alpha$ systems at $z_{\rm abs}\,$= 1.500 and 1.681 with, respectively, N( $\ion{H}{i}$) $\simeq 1.7\times10^{15}$ and $1.8\times10^{15}$ cm -2 and [C/H] < -4.0 and <-3.0, - an indication that the distribution of metals in the metagalactic medium is utterly patchy. Our results show that the ionization states in the analyzed $\ion{O}{vi}$ absorbers, ranging from $z \simeq 1.4$ to 1.7, can be maintained by photoionization only and that the fraction of the shock-heated hot gas with temperature $T_{\rm kin} > 10^5$ K is negligible in these systems.

Key words: cosmology: observations -- line: formation -- line: profiles -- quasars: absorption lines -- quasars: individual: HE 0515-4414

Offprint request: S. A. Levshakov, lev@astro.ioffe.rssi.ru

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