2025A&A...703A.106L

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}\times10^4 $ K from the Hγ and [O III]₄₃₆₃ lines in the stacked spectrum, indicating a metal-poor sample with a median gas phase metallicity of $ 12+\log(\mathrm{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.