Stellar mass–stellar metallicity relation for star-forming galaxies at z ∼ 3 in different bins of virial mass of the host haloes, as predicted by the semi-analytic models of De Lucia & Blaizot (2007). The relations are drawn for the whole population (panel 3), for central galaxies only (panel 2), and for satellites (panel 3). The vertical error bars represent the median absolute deviation of the galaxy metallicities in each stellar mass bin. Panels 4–6: same as panels 1–3, but using the metallicity of the cold gas reservoir.