Hα surface brightness of NGC 4361 (dots, left panel) derived from a cut along the semi-minor axis of the Hα image as indicated (right panel). We extracted this image from observations reported in Monreal-Ibero et al. (2005). The dark horizontal bars are artefacts of the VIMOS spectrograph. Also shown are the predicted Hα surface brightness distributions of models with different metal contents (see figure legend), taken from the α = 3 sequences. These models are chosen such that they match the observed size of NGC 4361, assuming a distance of 1 kpc. The model ages vary from about 6700 years (Z_GD/30, fast expansion) to 9100 years (Z_GD, slow expansion).