D_n4000 vs. absolute magnitude in the r band. The values of D_n4000 are from the MaNGA DAP and the absolute magnitudes in the r band are from the NSA catalogue. The gray region shows the density distribution of all galaxies, while the orange contours are drawn at 10%, 30%, 68%, 95%, and 99% of all galaxies. Galaxies between the red dashed lines are selected as our quiescent galaxy sample. Galaxies with invalid M_r and D_n4000 are not plotted.