Metal abundances in the high-redshift intergalactic medium

Twenty years of high-resolution spectroscopy at the 8-10 m class telescopes have drastically expanded our view of the gas-phase metallicity in the zgtrsim 2 universe. This contribution briefly summarizes how these studies reveal a widespread metal pollution in the intergalactic medium with a median abundance [C/H]̃ -3.5 at z ̃ 3 that is increasing by a factor of ̃ 2-3 from z̃ 4.3 to z̃ 2.4. At the higher densities that are typical of galactic halos, observations uncover a metallicity spread of five orders of magnitude in Lyman limit systems, ranging from super-solar ([M/H] ̃ +0.7) to pristine ([M/H] ≲ -4) gas clouds. Finally, the neutral damped Lyalpha systems are enriched to a median metallicity of [M/H] ̃ -1.5 that slowly declines with redshift up to z̃ 4.5, at which point it appears to more rapidly evolve as one approaches the end of reionization.