The MOSDEF Survey: Environmental dependence of the gas-phase metallicity of galaxies at $1.4 \leq z \leq 2.6$.

Using the near-IR spectroscopy of the MOSFIRE Deep Evolution Field (MOSDEF) survey, we investigate the role of local environment in the gas-phase metallicity of galaxies. The local environment measurements are derived from accurate and uniformly calculated photometric redshifts with well-calibrated probability distributions. Based on rest-frame optical emission lines, [NII]$\lambda6584$ and H$\alpha$, we measure gas-phase oxygen abundance of 167 galaxies at $1.37\leq z\leq1.7$ and 303 galaxies at $2.09\leq z\leq2.61$, located in diverse environments. We find that at $z\sim1.5$, the average metallicity of galaxies in overdensities with $M_*\sim10^{9.8}M_\odot, 10^{10.2}M_\odot$ and $10^{10.8}M_\odot$ is higher relative to their field counterparts by $0.094\pm0.051$, $0.068\pm0.028$ and $0.052\pm0.043$ dex, respectively. However, this metallicity enhancement does not exist at higher redshift, $z\sim2.3$, where, compared to the field galaxies, we find $0.056\pm0.043$, $0.056\pm0.028$ and $0.096\pm 0.034$ dex lower metallicity for galaxies in overdense environments with $M_*\sim10^{9.8}M_\odot, 10^{10.2}M_\odot$ and $10^{10.7}M_\odot$, respectively. Our results suggest that, at $1.37\leq z\leq2.61$, the variation of mass-metallicity relation with local environment is small ($<0.1$dex), and reverses at $z\sim2$. Our results support the hypothesis that, at the early stages of cluster formation, owing to efficient gas cooling, galaxies residing in overdensities host a higher fraction of pristine gas with prominent primordial gas accretion, which lowers their gas-phase metallicity compared to their coeval field galaxies. However, as the Universe evolves to lower redshifts ($z\lesssim2$), shock-heated gas in overdensities cannot cool down efficiently, and galaxies become metal-rich rapidly due to the suppression of pristine gas inflow and re-accretion of metal-enriched outflows in overdensities.