Left: Classical emission-line diagnostic diagram showing the galaxies from the LyC22 sample (blue and red symbols). LyC22 objects with significant [O III] λ4363 detections are surrounded by a black square. LyC22 galaxies with log(N/O) >  − 1.2 are shown in red. We only show objects where the involved emission lines are detected at ≥3σ. Typical uncertainties are comparable to the size of the symbols and are hence not plotted. The maximum starburst line from Kewley et al. (2001) (dotted) and the empirical AGN/star-formation threshold from Kauffmann et al. (2003) established for z ∼ 0 (dash-dotted) are also shown. Average relations for z ∼ 2.3 galaxies from Steidel et al. (2014), Shapley et al. (2015) are shown by orange and magenta lines; the average relation of SDSS galaxies from Kewley et al. (2013a) is shown by the red line. Observations from the LzLCS at z ∼ 0.3 are shown by small gray squares. Right: Zoomed-in view of part of the BPT diagram showing all LyC22 sources with color-coded N/O abundances (in log(N/O)); computed from [N II]/[O II].