Insights on metal enrichment and environmental effects at <i>z</i>  ≈ 5–7 with JWST ASPIRE/EIGER and the chemical evolution model

We present the mass–metallicity relation (MZR) for a parent sample of 604 galaxies at z = 5.34 − 6.94 with [O III ] doublets detected that was obtained from the deep JWST/NIRCam wide field slitless spectroscopic (WFSS) observations in 26 quasar fields. The sample incorporates the full observations of 25 quasar fields from the JWST Cycle 1 GO program ASPIRE and the quasar SDSS J0100+2802 from the JWST EIGER program. We identified 204 galaxies residing in overdense structures using the friends-of-friends (FoF) algorithm. We estimated the electron temperature of 2.0 +0.3 −0.4 × 10 4 K from the H γ and [O III ] 4363 lines in the stacked spectrum, indicating a metal-poor sample with a median gas phase metallicity of 12 + log(O/H) = 7.65 +0.26 −0.15 . With the most up-to-date strong line calibration based on NIRSpec observations, we find that the MZR shows a metal enhancement of ∼0.2 dex at the high mass end in overdense environments. However, compared to the local fundamental metallicity relation (FMR), our galaxy sample at z > 5 shows a metal deficiency of ∼0.2 dex relative to FMR predictions. We explain the observed trend of FMR with a simple analytical model, and we favor dilution from intense gas accretion over outflow to explain the metallicity properties at z > 5. The high-redshift galaxies are likely in a rapid gas accretion phase when their metal and gas contents are in a non-equilibrium state. According to model predictions, the protocluster members are closer to the gas equilibrium state than field galaxies and thus have a higher metallicity and are closer to the local FMR. Our results suggest that the accelerated star formation during protocluster assembly likely plays a key role in shaping the observed MZR and FMR, indicating a potentially earlier onset of metal enrichment in overdense environments at z ≈ 5 − 7.