Stellar radial [Z] gradients, for disk stars in three different stellar populations: young (blue) is defined as stars formed in the last 100 Myr, intermediate (yellow) is defined as stars formed 6 to 7 Gyr ago, and old (red) is defined as stars older than 10 Gyr. Fits to the disk are overdrawn in black; the length of the black line corresponds to the region of the disk used in the fitting (see text for details). For clarity, only two galaxies are shown, one from MUGS (g15784, upper panel) and one from RaDES (Apollo, lower panel).