Abstract We present an analysis of the gas-phase mass-metallicity relationship (MZR) and fundamental metallicity relationship (FMR) for 65 star-forming galaxies at 2 z 8 from the JWST/EXCELS survey. We calculate gas-phase metallicities (12 + log (O/H) ) using strong-line calibrations explicitly tested against the EXCELS sample, and report direct-method metallicities for 19 galaxies. Our sample spans 8. 1 (M_ /M_) 10. 3 and 0 (SFR/M_ \, yr^-1) 2, consistent with main-sequence star-forming galaxies at the same redshifts. We find a clear MZR at both 2 z 4 (〈z〉 = 3. 2) and 4 z 8 (〈z〉 = 5. 5), with consistent slopes and mild evolution in normalization of ≃ 0. 1 dex, matching trends from simulations and recent observations. Our results demonstrate rapid gas-phase enrichment in the early Universe; galaxies at z ≃ 3 (within the first ≃ 15 per cent of cosmic time) are enriched to ≃ 40 per cent of the metallicity of equivalent mass galaxies at z = 0. We find tentative evidence for SFR-dependence in the MZR scatter, though results remain inconclusive and highlight the need for larger high-redshift samples. Comparison with locally derived FMRs reveals a clear offset consistent with other z 3 studies. We discuss potential drivers of this offset, noting that high-redshift samples have significantly different physical properties compared to local samples used to define the z = 0 FMR. Our results confirm that low-mass, high specific star-formation rate galaxies common at high redshift are inconsistent with the equilibrium conditions underlying the local FMR, and highlight the rapid chemical enrichment at early cosmic epochs.
Stanton et al. (Thu,) studied this question.