Upper panel: [N II]/Hα ratio normalized by the best-fit M_*–[N II]/Hα relation as a function of M_*. The FMOS objects are shown by gray circles and downward arrows (upper limits). Red error bars mark the estimated intrinsic scatter in overlapping M_* bins: the vertical bars indicate the central 68% confidence levels at the median M_* values, and the horizontal bars indicate the widths of the M_* bins. The black dashed lines indicate the central 68th percentiles of the individual SDSS galaxies in bins of M_*. Lower panel: same as upper panel but for Δlog [N II]/Hα as a function of N₂(M_*), i.e., the “best-fit” [N II]/Hα ratio at given M_*, which is taken from the best-fit relation at a given stellar mass for the FMOS and SDSS samples each. The solid curves indicate a second-order polynomial fit to the σ_int estimates of the FMOS sample.