Comparison in the [S II] BPT diagram between MOSDEF galaxies, H II regions, and models with low DIG emission fraction. Left panel: [S II] BPT diagram for z ∼ 2.3 MOSDEF galaxies and stacks (green points, red stars), median sequence of local H II regions (magenta dotted line), and hiionly model from Sanders et al. (2017; black dashed line). z ∼ 2.3 MOSDEF galaxies are clearly offset toward larger [O III]λ 5007/Hβ and/or larger [S II]λλ6717,6731/Hα relative to local H II regions and the hiionly model. Right panel: the same plot, but for z ∼ 1.5 MOSDEF galaxies and stacks (blue points, gold stars), local H II regions (magenta dotted line), and a model from Sanders et al. (2017) representing the ensemble average emission from H II regions in star-forming galaxies plus a DIG fractional contribution to the Hα emission of f_DIG = 0.11. The offset between z ∼ 1.5 MOSDEF galaxies and the comparison curves is smaller than for the z ∼ 2.3 MOSDEF sample.