The MOSDEF Survey: Environmental Dependence of the Gas-phase Metallicity of Galaxies at 1.4 ≤ z ≤ 2.6*
Nima Chartab, Bahram Mobasher, Alice E. Shapley, Irene Shivaei, Ryan L. Sanders, Alison L. Coil, Mariska Kriek, Naveen A. Reddy, Brian Siana, William R. Freeman, Mojegan Azadi, Guillermo Barro, Tara Fetherolf, Gene Leung, Sedona H. Price, Tom Zick
Abstract
Abstract Using the near-IR spectroscopy of the MOSFIRE Deep Evolution Field survey, we investigate the role of the 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, [N ii ] λ 6584 and H α , we measure gas-phase oxygen abundances of 167 galaxies at 1.37 ≤ z ≤ 1.7 and 303 galaxies at 2.09 ≤ z ≤ 2.61, located in diverse environments. We find that at z ∼ 1.5, the average metallicity of galaxies in overdensities with M * ∼ 10 9.8 M ⊙ , 10 10.2 M ⊙, and 10 10.8 M ⊙ is higher relative to their field counterparts by 0.094 ± 0.051, 0.068 ± 0.028, and 0.052 ± 0.043 dex, respectively. However, this metallicity enhancement does not exist at higher redshift, z ∼ 2.3, where, compared to the field galaxies, we find 0.056 ± 0.043, 0.056 ± 0.028, and 0.096 ± 0.034 dex lower metallicity for galaxies in overdense environments with M * ∼ 10 9.8 M ⊙ , 10 10.2 M ⊙ and 10 10.7 M ⊙ , respectively. Our results suggest that, at 1.37 ≤ z ≤ 2.61, the variation of mass–metallicity relation with local environment is small (<0.1 dex), and reverses at z ∼ 2. 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 ≲ 2), the 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.