The missing metals problem - III. How many metals are expelled from galaxies?

International audienceWe revisit the metal budget at z ~= 2, and include the contribution of the intergalactic medium (IGM). Past estimates of the metal budget have indicated that, at redshift z ~= 2.5, 90 per cent of the expected metals were missing. In the first two papers of this series, we have already shown that ~30 per cent of the metals are observed in all z ~ 2.5 galaxies detected in current surveys. This fraction could increase to 40 per cent of the metals missing. Here, we extend our analysis to the metals outside galaxies (i.e. in the IGM), using (i) observational data and (ii) analytical calculations. Our results for both are strikingly similar. (i) Observationally, we find that, besides the small (5 per cent) contribution of damped Lyalpha absorbers (DLAs), the forest and sub-DLAs contribute substantially to make ~2 to 65 per cent of the metals have been accounted for, and the `missing metals problem' is substantially eased. (ii) We perform analytical calculations based on the effective yield-mass (yeff-Vc) relation, whose deficit for small galaxies is considered as evidence for supernova-driven outflows. As a test of the method, we show that, at z = 0, the calculation self-consistently predicts the total amount of metals expelled from galaxies. At z = 2, we find that the method predicts that 25-50 per cent of the metals have been ejected from galaxies into the IGM, consistent with the observations