The warm-hot intergalactic medium at : Metal enrichment and ionization source

Free access article

Issue		A&A Volume 396, Number 2, December III 2002


Page(s)		L11 - L15
Section		Letters
DOI		http://dx.doi.org/10.1051/0004-6361:20021611

A&A 396, L11-L15 (2002)
DOI: 10.1051/0004-6361:20021611

Letter

The warm-hot intergalactic medium at $\mathsf{\vec {z}\sim2.2}$ : Metal enrichment and ionization source

J. Bergeron¹, B. Aracil¹, P. Petitjean^{1, 2} and C. Pichon³

¹ Institut d'Astrophysique de Paris - CNRS, 98bis Boulevard Arago, 75014 Paris, France
² LERMA, Observatoire de Paris, 61 Avenue de l'Observatoire, 75014 Paris, France
³ Observatoire Astronomique de Strasbourg, 11 rue de l'Université, 67000 Strasbourg, France

(Received 10 October 2002 / Accepted 31 October 2002)

Abstract
Results are presented for our search for warm-hot gas towards the quasar Q 0329-385. We identify ten O VI systems of which two are within 5000 km s ^-1 of $z_{\rm em}$ and a third one should be of intrinsic origin. The seven remaining systems have H I column densities $10^{13.7}\le N (\mbox{H\,{\sc i}})\le 10^{15.6}$ cm ^-2. At least ~1/3 of the individual O VI sub-systems have temperatures $T < 1 \times 10^5$ K and cannot originate in collisionally ionized gas. Photoionization by a hard UV background field reproduces well the ionic ratios for metallicities in the range 10^-2.5-10^-0.5 solar, with possibly sub-solar N/C relative abundance. For $\rm [O/C]=0$ , the sizes inferred for the O VI clouds are in some cases larger than the maximum extent implied by the Hubble flow. This constraint is fulfilled assuming a moderate overabundance of oxygen relative to carbon. For a soft UV ionizing spectrum, an overabundance of O/C is required, $\rm [O/C]\approx 0.0{-}1.3$ . For a hard(soft) U spectrum and $\rm [O/C]=0(1)$ , the O VI regions have overdensities $\rho/\overline{\rho} \approx 10{-}40$ .

Key words: cosmology: observations -- intergalactic medium -- galaxies: halos -- quasars: absorption lines

Offprint request: J. Bergeron, bergeron@iap.fr

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