The evolution of the Si IV content in the Universe from the epoch of reionization to cosmic noon

We investigate the abundance and distribution of metals in the high-redshift intergalactic medium and circum-galactic medium through the analysis of a sample of almost 600 SiIV absorption lines detected in high and intermediate resolution spectra of 147 quasars. The evolution of the number density of SiIV lines, the column density distribution function and the cosmic mass density are studied in the redshift interval 1.7 <= z <= 6.2 and for log N(SiIV) >= 12.5. All quantities show a rapid increase between z~6 and z< 5 and then an almost constant behaviour to z~2 in very good agreement with what is already observed for CIV absorption lines. The present results are challenging for numerical simulations: when simulations reproduce our SiIV results, they tend to underpredict the properties of CIV, and when the properties of CIV are reproduced, the number of strong SiIV lines (log N(SiIV) > 14) is overpredicted.