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From the Voigt profile fitting analysis of 183 intervening CIV systems at 1.7< z < 3.3 in 23 high-quality UVES/VLT and HIRES/Keck QSO spectra, we find thata majority of CIV systems (~75%) display a well-characterised scaling relationbetween integrated column densities of HI and CIV with a negligible redshiftevolution, when column densities of all the HI and CIV components areintegrated within a given (-150, +150) km/sec range centred at the CIV fluxminimum. The integrated CIV column density N(CIV, sys) increases with N(HI,sys) at log N(HI, sys) = 14.0--15.5 and log N(CIV, sys) = 11.8--14.0, thenbecomes almost independent of N(HI, sys) at log N(HI, sys) > 16, with a largescatter: at log N(HI, sys) = 14--22, log N(CIV, sys) = C1 / (log(NHI, sys) +C2) + C3, with C1 = -1.90+0.55, C2 = -14.11+0.19 and C3 = 14.76+0.17,respectively. The steep (flat) part is dominated by SiIV-free (SiIV-enriched)CIV systems. Extrapolating the N(HI, sys)-N(CIV, sys) relation implies thatmost absorbers with log N(HI) < 14 are virtually CIV-free. The N(HI,sys)-N(CIV, sys) relation does not hold for individual components, clumps orthe integration velocity range less than +-100 km/sec. It is expected if theline-of-sight extent of CIV is smaller than HI and N(CIV, sys) decreases morerapidly than N(HI, sys) at the larger impact parameter, regardless of thelocation of the HI+CIV gas in the IGM filaments or in the intervening galactichalos.

Triple-ionised carbon associated with the low-density neutral hydrogen gas at 1.7 < z < 3.3: the integrated N(HI)-N(CIV) relation