Average abundance of oxygen (coloured solid) in the cold gas as a function of stellar mass for different redshifts in NEWHORIZON as indicated in the panel. The error bars stand for the error around the mean. Several observational relations are also shown from Mannucci et al. (2009; M09; in dotted lines with four different colours corresponding to z = 0.07, 0.7, 2.2, and 3.5), Zahid et al. (2014; Z14; dot-dashed line), Sánchez et al. (2019; S19; dashed lines with different lines corresponding to various oxygen calibrators), and Curti et al. (2020; C20; black solid).