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

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 ($\mathrm{H}\beta$, [OIII], $\mathrm{H}\alpha$, [NII]), covering the mass range of ${10}^{7.5}{\mathrm{M}}_{\odot }-{10}^{10.5}{\mathrm{M}}_{\odot }$. 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]$\lambda 5008$/$\mathrm{H}\beta$ and [NII]$\lambda 6585$/$\mathrm{H}\alpha$. Compared to the typical, field galaxies at similar redshifts, MQN01 galaxies show relatively higher [NII]$\lambda 6585$/$\mathrm{H}\alpha$ and lower [OIII]$\lambda 5008$/$\mathrm{H}\beta$ 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.