Quasar spectral energy distribution in EUV restored from associated absorbers: indications to the He ii opacity of the quasar accretion disk wind⋆

Aims. To reconstruct the spectral shape of the quasar ionizing radiation in the extreme-UV range (1 Ryd ≤ E < 10 Ryd) from the analysis of narrow absorption lines (NAL) of the associated systems. Methods. Computational technique for inverse spectroscopic problems – Monte Carlo Inversion augmented by procedure of the spectral shape recovering and modified to account for the incomplete coverage of the light source. Results. The ionizing spectra responsible for the ionization structure of the NAL systems require an intensity depression at E > 4 Ryd which is attributed to the He ii Lyman continuum opacity (τ II c ∼1). A most likely source of this opacity is a quasar accretion disk wind. The corresponding column density of H i in the wind is estimated as a few times 10 cm . This amount of neutral hydrogen should cause a weak continuum depression at λ <∼ 912 Å (rest-frame), and a broad and shallow absorption in H i Ly-α. If metallicity of the wind is high enough, other resonance lines of Ovi, Nevi Neviii, etc. are expected. In the analyzed QSO spectra we do observe broad (stretching over 1000s km s ) and shallow (τ ≪ 1) absorption troughs of H i Ly-α and Ovi λλ1031, 1037 as well as continuum depressions at λ <∼ 912 Å which correspond to N(H i) ∼5× 10 cm . Observational data available in both the UV and X-ray ranges suggest that at least ∼50% of the quasar radiation passes through the gas opaque in the He ii Lyman continuum. This means that the outcoming ionizing spectrum should have a pronounced intensity break at E > 4 Ryd with a depth of this break depending on the angle to the rotational axis of the accretion disk (the larger the angle the deeper the break). The QSO spectra with a discontinuity at 4 Ryd can influence the rate of the He ii reionization in the intergalactic medium and partly explain inhomogeneous (patchy) ionization structure of the intergalactic He ii observed at z ∼ 3.