A Tale of Two Clusters: An Analysis of Gas-Phase Metallicity and Nebular Gas Conditions in Proto-cluster Galaxies at z~2

TL;DR

This study investigates the gas-phase metallicity and nebular conditions of proto-cluster galaxies at z~2, finding no significant metallicity differences from field galaxies and providing insights into galaxy evolution in dense environments.

Contribution

It provides the first detailed analysis of ionized gas properties in proto-cluster galaxies at z~2 using spectroscopic data, comparing them to field galaxies and simulations.

Findings

Proto-cluster and field galaxies follow the same Mass-Metallicity Relation.

No significant gas-phase metallicity offset between proto-cluster and field galaxies.

Tentative evidence of differing [OIII]/Hβ ratios in high-mass proto-cluster galaxies.

Abstract

The ZFIRE survey has spectroscopically confirmed two proto-clusters using the MOSFIRE instrument on Keck 1: one at z=2.095 in COSMOS and another at z=1.62 in UDS. Here we use an updated ZFIRE dataset to derive the properties of ionized gas regions of proto-cluster galaxies by extracting fluxes from emission lines H$\beta$ 4861\AA, [OIII] 5007\AA, H$\alpha$ 6563\AA, [NII] 6585\AA, and [SII] 6716,6731\AA. We measure gas-phase metallicity of members in both proto-clusters using two indicators, including a strong-line indicator relatively independent of ionization parameter and electron density. Proto-cluster and field galaxies in both UDS and COSMOS lie on the same Mass-Metallicity Relation with both metallicity indicators. We compare our results to recent IllustrisTNG results, which reports no significant gas-phase metallicity offset between proto-cluster and field galaxies until z=1.5. This is in agreement with our observed metallicities, where no offset is measured between proto-cluster and field populations. We measure tentative evidence from stacked spectra that UDS high mass proto-cluster and field galaxies have differing [OIII]/H$\beta$ ratios, however these results are dependent on the sample size of the high mass stacks.