Relation between the observed Ne3O2 ratio (left y-axis), ξ_ion (right y-axis), and EW([O III]λ5007). The z ∼ 8 galaxies are marked with by black stars for our measurements and green stars using the line ratios and equivalent widths taken from Curti et al. (2022) and Trussler et al. (2022) respectively. The shaded stripe shows the mean Ne3O2–EW relation and scatter in the large low-z sample of Izotov et al. (2021a). The dotted lines show the relations between ξ_ion (right axis) and EW([O III]λ5007) found at z ∼ 0 − 1 (Chevallard et al. 2018; Izotov et al. 2021a).