Offset between spiral arms and the ISM metallicity. Top: background maps are the residual ISM metallicity in model M1 (no radial gradient, left) and M3 (no ISM enrichment, right) where the location of the stellar spiral arms is shown with solid lines, while the mean location of the metallicity peaks is shown with dashed lines. Bottom: distribution of the radial offset between the mean location of the stellar spiral arms and the metallicity peaks for different models.