Metal enrichment of galaxies in a massive node of the Cosmic Web at $z \sim 3$

TL;DR

This study investigates the metallicity of galaxies in a massive cosmic web node at z~3, revealing they are more metal-rich than field galaxies, likely due to more efficient mass assembly in overdense regions.

Contribution

First measurement of the mass-metallicity relation for galaxies in a high-redshift cosmic web node using JWST and HST data, highlighting environmental effects on galaxy evolution.

Findings

Galaxies in the overdense node have higher metallicity than field counterparts.

Metallicity differences decrease when considering the Fundamental Metallicity Relation.

Overdense region galaxies likely assemble mass more efficiently or earlier.

Abstract

We present the mass-metallicity relation for star-forming galaxies in the MUSE Quasar Nebula 01 (MQN01) field, a massive cosmic web node at $z \sim 3.245$, hosting one of the largest overdensities of galaxies and AGNs found so far at $z > 3$. Through James Webb Space Telescope (JWST) Near Infrared Spectrograph (NIRSpec) spectra and images from JWST and Hubble Space Telescope (HST), we identify a sample of 9 star-forming galaxies in the MQN01 field with detection of nebular emission lines ($\rm H\beta$, [OIII], $\rm H\alpha$, [NII]), covering the mass range of $\rm 10^{7.5}M_\odot - 10^{10.5}M_\odot$. We present the relations of the emission-line flux ratios versus stellar mass for the sample and derive the gas-phase metallicity based on the strong line diagnostics of [OIII]$\lambda5008$/$\rm H\beta$ and [NII]$\lambda6585$/$\rm H\alpha$. Compared to the typical, field galaxies at similar redshifts, MQN01 galaxies show relatively higher [NII]$\lambda6585$/$\rm H\alpha$ and lower [OIII]$\lambda5008$/$\rm H\beta$ at the same stellar mass, which implies a higher metallicity by about $0.25\pm 0.07$ dex with respect to the field mass-metallicity relation. These differences are decreased considering the ``Fundamental Metallicity Relation'', i.e. if the galaxies' Star Formation Rates (SFR) are also taken into account. We argue that these results are consistent with a scenario in which galaxies in overdense regions assemble their stellar mass more efficiently (or, equivalently, start forming at earlier epochs) compared to field galaxies at similar redshifts.