Mass-metallicity relation for the star-forming gas in the CIELO galaxies, coloured by the B/T. Observations by Tremonti et al. (2004) have been included for comparison rescaled to match the reported solar values by Asplund et al. (2009, black line). The shaded regions show the different percentiles as indicated by the labels. Lower panel: Mass-metallicity relation for the stellar populations of the CIELO galaxies, coloured by the B/T. Results from FIRE simulations Ma et al. (2015) and observations from Gallazzi et al. (2005) are included for comparison (the shaded regions represent the 25–75th percentiles).