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 O VI systems of which two are within 5000 km s(-1) of z(em) and a third one should be of intrinsic origin. The seven remaining systems have H I column densities 10(13.7) less than or equal to N (H I) less than or equal to 10(15.6) cm(-2). At least similar to1/3 of the individual O VI sub-systems have temperatures T < 1 x 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 [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, [O/C] approximate to 0.0-1.3. For a hard(soft) U spectrum and [O/C] = 0(1), the O VI regions have overdensities rho root rho approximate to 10-40.