The role of large-scale environment in shaping the stellar mass-gas metallicity relation across time

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ABSTRACT We study the stellar mass-gas metallicity relation (MZR) which shows a significant scatter for a fixed stellar mass. By defining global environments, nodes, filaments, and voids within the Horizon Run 5 cosmological hydrodynamical simulation, we explore when and where the enrichment of galaxies occurs, analysing key evolution parameters such as star-formation rate and changes in gas-fraction and gas-metallicity per unit time. At high redshift ($z\gt 4.5$), there are minimal deviations from the MZR due to environment, however, larger deviations emerge as redshift decreases. Low stellar mass galaxies in nodes, $M_{\star } < 10^{9.8}\, \text{M}_{\odot }$, start showing deviations at $z = 3.5$, whilst other environments do not. For, $z < 2$, filaments and voids begin to show deviations above and below the MZR, respectively. By $z = 0.625$, the last epoch of HR5, deviations exist for all stellar masses and environments, with a maximum value of 0.13 dex at $M_{\star } \approx 10^{9.35}\, \text{M}_{\odot }$, between the median gas metallicities of node and void galaxies. To explain this environmental variance we discuss gas accretion, AGN, ram-pressure-stripping and strangulation as regulators of $Z_{\mathrm{ g}}$. Concurrently, at high metallicities, for $z < 2$, while massive galaxies in nodes show increasing $Z_{\mathrm{ g}}$ and decreasing [O/Fe], void galaxies show a turnover where $Z_{\mathrm{ g}}$ falls with decreasing [O/Fe]. This directly points to the importance of cold-gas accretion in retaining lower $Z_{\mathrm{ g}}$ in massive void galaxies for $z < 2$, whilst its absence in nodes allowed $Z_{\mathrm{ g}}$ to access higher values.

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