Comparison of the redshift evolution of the gradient with the chemical evolution models of Gibson et al. (2013); black (dashed and dot-dashed) lines are models with enhanced feedback from SNe, magenta (short-dashed and dotted) lines are models with normal feedback. Red circles and blue triangles show the slopes of the gradients from H ii regions and PNe with 1.2 M_⊙ progenitors, respectively. In this plot the slopes are expressed in dex/kpc for comparison with the models of Gibson et al. (2013).