Upper panel: local M − Z relation in the 0.07 <z< 0.1 redshift bin for galaxies classified as pure star-forming galaxies (gray dots) using the KK04 metallicity calibration. The red solid and red dashed line are the linear and second-order polynomial fit to the data, respectively, within the representativity limit of the sample log M_∗> 9.4. The blue symbols are galaxies without [O ii] detections (cross) and [O iii] (star). Their metallicities correspond to lower limits estimated from upper limits of the [O ii]λ3727 and [O iii]λ5007 line fluxes. Composite SF-Seyfert and SF-LINERs are represented as green triangles and green cross-squares, respectively. Lower panel: fraction of each spectral type for galaxies verifying the emission-line classification, i.e., EW(Hα) > 10 Å  (see Sect. 5.2) in the 0.07 <z< 0.1 sample as a function of the stellar mass. The pure star-forming galaxies shown in the upper panel are represented as a gray area. Composite SF-AGN and AGNs are represented as green and dashed red boxes. Weak-line galaxies, namely galaxies without [O ii]λ3727 and [O iii]λ5007 lines (see Sect. 5.2), are shown in blue. Unclassified galaxies are shown in gray.