Alcorn, Leo Y.Gupta, AnshuTran, Kim-VyKacprzak, GlennYuan, TiantianCohn, Jonathan H.Forrest, BenGlazebrook, KarlHarshan, AnishyaKewley, LisaLabbe, IvoNanayakkara, Themiya2022-03-300004-637Xhttp://hdl.handle.net/1885/262770The ZFIRE survey has spectroscopically confirmed two proto-clusters using the MOSFIRE instrument on Keck I: one at z = 2.095 in COSMOS and another at z = 1.62 in UKIRT Infrared Deep Sky Survey (UDS). Here, we use an updated ZFIRE data set to derive the properties of ionized gas regions of proto-cluster galaxies by extracting fluxes from emission lines Hβ 4861 Å, [O III] 5007 Å, Hα 6563 Å, [N II] 6585 Å, and [S II] 6716,6731 Å. We measure gas-phase metallicity of members in both proto-clusters using two indicators, including a strong-line indicator relatively independent of the ionization parameter and electron density. Proto-cluster and field galaxies in both UDS and COSMOS lie on the same Mass–Metallicity Relation with both metallicity indicators. We compare our results to recent IllustrisTNG results, which report no significant gas-phase metallicity offset between protocluster and field galaxies until z = 1.5. This is in agreement with our observed metallicities, where no offset is measured between proto-cluster and field populations. We measure tentative evidence from stacked spectra that indicate UDS high-mass proto-cluster and field galaxies have differing [O III]/Hβ ratios; however, these results are dependent on the sample size of the high-mass stacks.This work is supported by the National Science Foundation under grant #1410728. G.G.K. acknowledges the support of the Australian Research Council through the Discovery Project DP170103470. C.M.S.S. acknowledges funding through the H2020 ERC Consolidator grant 683184.application/pdfen-AU© 2019. The American Astronomical Societygalaxies: clusters: generalgalaxies: evolutiongalaxies: high-redshift201910.3847/1538-4357/ab3b0c2022-06-26