1994A&A...291...29P

We present high spectral resolution (R∼15000) and high signal to noise ratio (20-50) of two z_em∼2 quasars PKS 0424-131 and Q 0450-131 in the wavelength range 370-510nm. We detect in total 16 CIV systems with CIVλ1548 rest equivalent width 0.03<w_r<1.06A. The number of such systems per unit redshift is N∼7.7 for z in the range 1.4-2, out of which 3.1 have w_r>0.15A. This suggests that the number of CIV systems is dominated by weak lines (w_r<0.15A) and is comparable to the number of Lyα clouds with N(HI)>10¹⁶cm^–2. Two intervening systems are of particular interest. The strong z_abs∼1.5615 CIV system in Q 0450-131 splits into components spread over 1030km/s. The system is a member of the distinct population of CIV systems exhibiting large velocity spread and small equivalent width, it is of high excitation with weak SiII absorption detected only in one component and no associated AlIII absorption. The z_abs=2.033 system in PKS 0424-131 has a strong SiIII and neither SiIV nor CIV absorption. We argue that the line of sight passes through a HII region of low carbon (0.04Z_☉) but enhanced oxygen (by a factor of five) abundances and ionized by a black body type spectrum with temperature 35000K. We are able to derive abundances in six z_abs∼z_ em_ systems since for each of them well detached and weak components are observed in which column densities of HI, OI, CII, CIV, NV, SiII, SiIII and SiIV can be evaluated. The systems are highly ionized and have N(HI)<10^15.4cm^–2. Using detailed photoionization models we find in all of these systems abundances close to or in excess of solar values. This is in sharp contrast with the abundances found in intervening Lyman limit (0.01-0.1Z_☉) or damped (∼0.1Z_☉ with large scatter) systems. The overabundances are found in systems with velocity separation relative to the emission redshift of the quasar as large as 13000km/s. Evidence for non solar elemental ratios is found in one system with overabundances of nitrogen and maybe silicon by a factor of eight compared to carbon.