The warm-hot intergalactic medium at z~2.2: Metal enrichment and ionization source

Abstract

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 z_em and a third one should be of intrinsic origin. The seven remaining systems have HI column densities 10^13.7<N(HI)<10^15.6 cm^-2. At least ~1/3 of the individual OVI sub-systems have temperatures T<1x10^5 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 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 in 10-40.