BPT diagram for the galaxies in the sample with an error of 0.2 dex (0.5 dex) in the [O III]/Hβ and [N II]/Hα ratios in the left (right) panel. The errors are not plotted in the right panel for clarity. The color bar indicates the stellar mass of the galaxy. The solid (Ka03), dashed (Ke01), and dotted lines (S07) define the regions for the four main spectral classes. The relative percentage of each galaxy type in each subsample is indicated in the figure. In each panel, the number of galaxies is specified in the lower left corner. The parent sample contains 2154 galaxies.