2004A&A...418..857F

We present an analysis of the complex associated system of the high-redshift QSO HE 2347-4342. Absorption features of HI, CIII, CIV, NV, and OVI with up to 16 components occur in the optical spectral range located up to 1500km/s redwards from the emission line. Apparently, CIV and NV show the line locking effect. A quantivative analysis of the line distribution comparing simulated spectra with randomly distributed doublets reveals, however, no statistical evidence for its physical reality. Using photoionization calculations to emulate the observed ion column densities we constrain the quasar's spectral energy distribution. Absorbers in the velocity range of 200-600km/s can be modelled successfully with a spectral index of α~-3 at energies higher than 3-4Ryd, which is an energy distribution similar to the QSO continuum suggested by Mathews & Ferland (1988ApJ...323..456M). The analysis of a group of high velocity absorbers (v>1300km/s) leads to a harder energy distribution. The large amount of helium (logN_HeII>16.3) associated with these absorbers implies that they are responsible for the observed absence of the proximity effect (Reimers et al., 1997A&A...327..890R). Clouds located more distant from the quasar may be shielded from the high energy part of the quasar continuum due to optically thick absorption shortward of 228Å by the high velocity absorbers. A group of absorbers with 900<v<1200km/s, in particular a cloud at 1033km/s, which has the most reliable column density measurements, can be modelled neither with photoionzation nor under the assumption of collisionally ionized gas. Possible explanations are a multiphase medium with a mixture of photo and collisionally ionized gas and/or gas in non-equilibrium.