Stellar mass as a function of log O32 (black dots) and lower limits on O32 (orange triangles). The median per bin with 1-σ errors is shown by the red squares and error bars. We defined the bins by intervals of logO32 between −1.0 and 1.0 with a step size of 0.5. Three-σ lower limits on the O32 ratio for sources with a detection of [O II] below our S/N cut are shown by the orange triangles. The green stars indicate the positions of the confirmed Lyman continuum leakers from Izotov et al. (2016a,b, a) and the green square is a LyC emitter at z = 3.2 (de Barros et al. 2016; Vanzella et al. 2016). Galaxies above the grey dashed line have extreme O32 ratios (O32 > 4).