The warm - hot intergalactic medium at z ∼ 2 . 2 : Metal enrichment and ionization source ⋆

Results are presented for our search for warm-hot gas towards the quasar Q 0329−385. We identify ten Ovi systems of which two are within 5000 km s of zem and a third one should be of intrinsic origin. The seven remaining systems have H i column densities 10≤N(H i)≤10 cm. At least ∼1/3 of the individual Ovi sub-systems have temperatures T<1×10 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 10-10 solar, with possibly sub-solar N/C relative abundance. For [O/C]=0, the sizes inferred for the Ovi 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, [O/C]≈0.0-1.3. For a hard(soft) UV spectrum and [O/C]=0(1), the Ovi regions have overdensities ρ/ρ≈10-40.