Photoionized O vi absorbers toward the bright QSO HE 0515 – 4414 ⋆

We report on detailed Monte Carlo inversion analysis of five Ovi systems from the spectrum of the bright quasar HE 0515–4414 (zem = 1.71). The associated system at zabs = 1.697 with the neutral hydrogen column density N(H i) = 4.4×10 cm shows pronounced absorption from highly ionized transitions of C iii, C iv, Nv, Ovi, Si iv, and probably Svi. We found that only a power law type ionizing spectrum (Jν ∝ ν ) 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 ∼ 16 pc. Two Ovi systems at zabs = 1.674 ([C/H] ≃ −1.6) and 1.602 ([O/H] ≃ −1.1), arising in intervening halos, have linear sizes of L ≃ 3–14 kpc and ≃ 17 kpc, respectively. Absorption systems at zabs = 1.385 ([C/H] ≃ −0.3, L ≃ 1.7–2.5 kpc) and zabs = 1.667 ([C/H] ≃ −0.5, L ≃ 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 (zabs = 1.667) and [C/H] < −3.7 (zabs = 1.385). We also found two additional extremely metal-poor Lyα systems at zabs = 1.500 and 1.681 with, respectively, N(H i) ≃ 1.7× 10 and 1.8× 10 cm 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 Ovi absorbers, ranging from z ≃ 1.4 to 1.7, can be maintained by photoionization only and that the fraction of the shock-heated hot gas with temperature Tkin > 10 5 K is negligible in these systems.