The Mass-Metallicity Relation Of A Z~2 Protocluster With MOSFIRE

TL;DR

This study investigates how environment influences galaxy metallicity at z~2, revealing that protocluster galaxies show metallicity enhancements at low masses, contrasting with field galaxies, and providing insights into galaxy wind recycling processes.

Contribution

It presents the first detailed comparison of the mass-metallicity relation in a z~2 protocluster versus field galaxies using MOSFIRE spectroscopy, highlighting environmental effects on metallicity.

Findings

Protocluster galaxies show metallicity enhancement at low masses.

Field galaxies follow the established mass-metallicity trend.

Environmental effects can be explained by wind recycling timescales.

Abstract

We present Keck/MOSFIRE observations of the role of environment in the formation of galaxies at z~2. Using K-band spectroscopy of H-alpha and [N II] emission lines, we have analyzed the metallicities of galaxies within and around a z=2.3 protocluster discovered in the HS1700+643 field. Our main sample consists of 23 protocluster and 20 field galaxies with estimates of stellar masses and gas-phase metallicities based on the N2 strong-line metallicity indicator. With these data we have examined the mass-metallicity relation (MZR) with respect to environment at z~2. We find that field galaxies follow the well-established trend between stellar mass and metallicity, such that more massive galaxies have larger metallicities. The protocluster galaxies, however, do not exhibit a dependence of metallicity on mass, with the low-mass protocluster galaxies showing an enhancement in metallicity compared to field galaxies spanning the same mass range. A comparison with galaxy formation models suggests that the mass-dependent environmental trend we observed can be qualitatively explained in the context of the recycling of "momentum-driven" galaxy wind material. Accordingly, winds are recycled on a shorter timescale in denser environments, leading to an enhancement in metallicity at fixed mass for all but the most massive galaxies. Future hydrodynamical simulations of z~2 overdensities matching the one in the HS1700 field will be crucial for understanding the origin of the observed environmental trend in detail.