IGM metal enrichment with UVES deep spectrum

For each of our tests, we created a catalogue of 1000 mock spectra in which we shuffled the position of the absorption lines to derive an estimate for the TPCF noise level. The TPCF shows a clear peak at the characteristic velocity separation of the CIV doublet. However, when the CGM contribution is removed (i.e. when all metal lines and CIV lines associated with log N_HI_>14.0 are deabsorbed), the peak is no longer significant at 1{sigma}, even though seven weak CIV systems are still detectable by eye.

Even after including up to 135 additional weak mock CIV systems (logN_HI_<14.0) in the spectrum, we are not able to detect a significant CIV peak. Eventually, when we create a synthetic spectrum with gaussian distributed noise and the same S/N as the complete spectrum, we remove the signal caused by the spectral intrinsic features and thus find a peak compatible with a metallicity of -3.80<[C/H]<-3.50. We conclude that the TPCF method is not sensitive to the presence of the weakest systems in the real spectrum, despite the extremely high S/N and high resolution of the data.

However, the results of this statistical technique could change when combining more than one line of sight.