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An Investigation of the Mass-Metallicity Relation From a Spectroscopic Survey of Four Massive Galaxy Clusters at a Mean Redshift of 1.6

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We investigate the gas-phase versus stellar mass relation using a spectroscopic survey of four massive galaxy clusters and a sample of field galaxies using the Keck/MOSFIRE multi-object near-infrared spectrograph. We use a sample of 206 galaxies with spectroscopic coverage of \hbox{H$\alpha$} and \hbox{[N{\scriptsize II}]} optical rest-frame emission lines, and estimate gas-phase oxygen abundances using the N2 indicator. We find a positive correlation between metallicity and stellar mass for composite spectra in bins of stellar mass that is offset $\sim0.4{\rm dex}$ below the local MZR. We find qualitative agreement between the shape of the relation traced by our composite spectra sample and the local MZR. Using the adaptive kernel and shifting gapper techniques, we identify a subset of 49 galaxy cluster members with $\left=1.629$ and a subset of 156 field galaxies with $\left=1.538$. We do not find any statistically significant difference in the offset or shape of the MZR between the two subsets even when accounting for difference in redshift. There may be a hint of offset to enhanced metallicity at lower stellar mass for cluster galaxies compared to field galaxies but deeper observations will be required to confirm this. If a difference is substantiated, it would suggest a physical mechanism such as harassment or ram-pressure stripping related to local galaxy environment is acting to enhance metallicity for low mass galaxies. All data were reduced using a custom developed spectroscopic data reduction pipeline that utilizes a Markov Chain Monte Carlo to measure emission lines.

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