Distribution of the average stellar mass across the parent and the low + high flux sample. Top panel: SDSS-FIRST distribution of stellar masses in the optical BPT diagram for the whole parent sample. From the left to the right figures: galaxies with the average stellar mass in the range log(M_⋆[M_⊙]) <  11.25, 11.25 <  log(M_⋆[M_⊙]) <  11.5, log(M_⋆[M_⊙]) >  11.5, respectively, are represented with density contours. Bottom panel: distribution of the average stellar mass across the BPT diagram for the same mass bins as in the top panel, but for the combined low + high flux sample.