Observed chemical abundances (N/O versus O/H in the top panel, C/O versus O/H in the bottom) of the six N-emitters (using the same symbols as in Fig. 6) and comparison with predictions for enrichment from massive stars (dotted and dash-dotted lines showing the “WR scenario” for non-rotating and rotating stars, respectively; see text) and supermassive stars (solid and dashed). Different colors indicate different metallicities. The predictions for the WR scenario are shown for a very low dilution (1%) with ISM matter. The solid lines show the predicted composition using SMS models with 10⁴ M_⊙ at different metallicities (12 + log(O/H) ≈ 7.0,7.8, 8.3) from Charbonnel et al. (2023) and for varying amounts of dilution with an ISM of standard composition. The dashed lines show an SMS model with 10⁵ M_⊙ from Nagele & Umeda (2023).