Average ratios of [N II]/Hα (left panel), [N II][O II] (middle panel), and [N II][S II] (right panel) versus BHAR/SFR in different redshift intervals (same key as in Fig. 12, with an additional redshift 0–0.4 line in indigo). Overplotted are the best linear fits between −4 ≤ log₁₀(BHAR/SFR)≤ − 1 (dotted lines). Respectively shown for N2, N2O2, and N2S2 are the 2, 1.5, and 1σ scatter of the entire 0–2.5 redshift range, which each encompass the 12 + log₁₀(O/H) = 8 − 9 range (grey shaded area).