JADES z ∼ 5.5 − 9.5 galaxies compared to photoionisation models. Measured ratios are shown as purple points, as in Figs. 3–6 except that all galaxies are plotted in the same colour, regardless of redshift. SDSS galaxies are shown in the same manner as Figs. 3–6. Each line shows a set of models with constant metallicity with values of Z = [1, 2, 3, 4, 6, 8, 10, 14, 20, 30, 40] × 10⁻³ increasing from black to yellow. Assuming Z_⊙ = 0.0134 (Asplund et al. 2009), these correspond to Z/Z_⊙ = 0.07, 0.15, 0.22, 0.30, 0.45, 0.60, 0.75, 1.0, 1.5, 2.2, 3.0. Ionisation parameter varies along the grid line, increasing with marker size, with values of log U = −4.0, −3.5, −3.0, −2.5, −2.0, −1.5, −1.0, −0.5. Details of the photoionisation models are described in Sect. 4.1.