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

TL;DR

This study reconstructs the extreme-UV spectral shape of quasars using absorption lines, revealing a HeII opacity likely caused by a quasar accretion disk wind, with implications for understanding quasar environments.

Contribution

Introduces a Monte Carlo inversion method to recover quasar EUV spectra from absorption lines, highlighting the role of accretion disk winds in HeII opacity.

Findings

HeII Lyman continuum opacity (tau ~ 1) affects the ionizing spectrum.

Detected broad, shallow HI Ly-alpha and OVI absorption features.

Estimated neutral hydrogen column density in the wind as a few times 10^16 cm^-2.

Abstract

(abridged) Aims. To reconstruct the spectral shape of the quasar ionizing radiation in the extreme-UV range (1Ryd <= E < 10Ryd) 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 > 4Ryd which is attributed to the HeII Lyman continuum opacity (tau^HeII_c ~ 1). A most likely source of this opacity is a quasar accretion disk wind. The corresponding column density of HI in the wind is estimated as a few times 10^16 cm^-2. This amount of neutral hydrogen should cause a weak continuum depression at lamb <= 912A (rest-frame), and a broad and shallow absorption in HI Ly-alpha. 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 (tau << 1) absorption troughs of HI Ly-alpha and OVI 1031,1037A...