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

Abstract

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 wellcalibrated probability distributions. Based on rest-frame optical emission lines, [NII]λ6584 and Hα, we measure gas-phase oxygen abundance 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 (< 0.1dex), 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.

Evidence for gas-phase metal deficiency in massive protocluster galaxies at z~2.2

“…We resolve this by constructing the mass-matched samples. Similar to Chartab et al (2021), we match the stellar mass distributions of field and protocluster galaxies with the resolution of log(M * /M ) = 0.1 dex, which is the typical stellar mass uncertainties computed in section 2.3. As a result of mass-matched distributions, we have the same number of protocluster and field galaxies in each stellar mass bin of log(M * /M ) = 0.1 (green hatched region in the left panel of Figure 4).…”

“…Their results are in qualitative agreement with the results in this study; however, we find ∼ 0.1 dex metal deficiency for protocluster galaxies compared to the field sample in the massive end of the MZR at z ∼ 2.2. Moreover, Chartab et al (2021) recently studied the environmental dependence of the MZR for a sample of H-band selected galaxies in the MOSDEF survey at 1.37 ≤ z ≤ 2.61. For a mass-matched sample in the redshift range 2.09 ≤ z ≤ 2.61, they found ∼ 0.07 dex metal deficiency for galaxies in overdense regions compared to field galaxies.…”

“…However, there is observational evidence of metal deficiency in protocluster galaxies at z ∼ 2 compared to their field counterparts, according to Valentino et al (2015). Moreover, Chartab et al (2021) studied the relation between the local density of MOSFIRE Deep Evolution Field (MOSDEF; Kriek et al 2015) galaxies and their gas-phase metallicities and found that galaxies in overdensities have ∼ 0.07 dex lower metallicity than the field galaxies at z ∼ 2.3. On the other hand, Kacprzak et al (2015) and Alcorn et al (2019) found no significant environmental dependence on the MZR of galaxies at z ∼ 2.…”