Metallicity gradients of the lensed galaxies. Left: [N ii]/Hα ratio as a function of radius. Right: gas-phase metallicity as a function of radius derived from the N2 index calibration of Pettini & Pagel (2004). The dashed lines show the best-fit linear metallicity gradient. [N ii]/Hα ratios are extracted along the kinematic major axis using the same slit as for the right panels of Figure 3.