M_⋆ − Z_g relation. The gas metallicity Z_g is given in terms of 12 + log₁₀⁽O / H⁾; we assume Z_⊙ = 8.94 (Karakas 2010). The four distinct panels are distributed as in Fig. 5 (see Table 3 for model references). Same colours and grey scale are used for the distribution of modelled galaxies (all sample, median trend). Our predictions are compared to observational measurements from i) Tremonti et al. (2004): yellow solid line; ii) Andrews & Martini (2013): solid red lines; and iii) Lee et al. (2006): orange points. The grey vertical dotted line represents the stellar mass resolution limit.