Dependences of O₃₂ = [O III] λ5007/[O II] λ3727 emission line ratios on (a) stellar masses M_⋆ and on (b) SFR^−0.9M_⋆ for samples of CSFGs and high-z SFGs. The black line in (b) is the maximum likelihood relation whereas the green line in (a) is the relation for z ∼ 1.7–3.6 galaxies (Sanders et al. 2020a). Black-filled circles represent high-z SFGs by Erb et al. (2016) (z ∼ 2.3), Onodera et al. (2016) (z ∼ 3–3.7), Troncoso et al. (2014) (z ∼ 3–5), and Cullen et al. (2014) (stacks of z > 2 galaxies). The meaning of symbols for our SDSS CSFGs are the same as in Fig. 1.