Gas-phase abundances estimated using the third order polynomial fitting functions for the Si3-O3C3 (top panel) and He2-03C3 (bottom panel) diagnostics from Byler et al. (2020) as a function of source redshift. The large symbols are MUSE sources from the UDF and small dots are from the literature collection described in Appendix C. The solid histograms show the subset of the objects from this work, whereas the dotted histograms also include the sources from the literature. All points are color coded according to EW₀(C III). The gray bands mark regions of super-solar gas-phase abundances at 12 + log₁₀(O/H) > 8.69.