Left: Effective S/N for the brightest emission line using Eq. (3), as a function of the S/N of the total line flux from the integrated spectrum. Right: Ratio of the stellar half-light radius to the PSF radius as a function of the S/N in the brightest spaxel. The grey shaded area in the panels marks the exclusion region, i.e. all galaxies with S/N_eff < 10 and R_e/R_PSF < 0.5 are removed from the sample. The data points are colour-coded according to their half-light radii. The circles, stars, diamonds, and squares represent the [OII], Hα, Hβ, and [OIII] emitters, respectively.