The absorption spectrum of the QSO PKS 2126 – 158 ( z em = 3 . 27 ) at high resolution ⋆

Spectra of the zem = 3.268 quasar PKS 2126– 158 have been obtained in the range λλ4300 − 6620 Å with a resolution R ≃ 27000 and an average signal-tonoise ratio s/n ≃ 25 per resolution element. The list of the identified absorption lines is given together with their fitted column densities and Doppler widths. The modal value of the Doppler parameter distribution for the Lyα lines is ≃ 25 km s. The column density distribution can be described by a power-law dn/dN ∝ N with β ≃ 1.5. 12 metal systems have been identified, two of which were previously unknown. In order to make the column densities of the intervening systems compatible with realistic assumptions about the cloud sizes and the silicon to carbon overabundance, it is necessary to assume a jump beyond the He II edge in the spectrum of the UV ionizing background at z ∼ 3 a factor 10 larger than the standard predictions for the integrated quasar contribution. An enlarged sample of C IV absorptions (71 doublets) has been used to analyze the statistical properties of this class of absorbers strictly related to galaxies. The column density distribution is well described by a single powerlaw, with β = 1.64 and the Doppler parameter distribution shows a modal value bCIV ≃ 14 km s. The two point correlation function has been computed in the velocity space for the individual components of C IV features. A significant signal is obtained for scales smaller than 200− 300 km s, ξ(30 < ∆v < 90km s) = 32.71 ± 2.89. A trend of decreasing clustering amplitude with decreasing column density is apparent, analogously to what has been observed for Lyα lines.