The influence of galaxy mergers, black-hole growth, and gas processes on the evolution of the stellar mass-gas metallicity relation of galaxies in different cosmic environments

We study the impact of supermassive black hole (SMBH) growth, SMBH, major and minor galaxy mergers, and gas processes, on the average gas metallicity of galaxies within the Horizon Run 5 simulation, with the aim to uncover which of these processes drive the scatter in the gas metallicity-stellar mass relation (MZR) at different redshifts in nodes, filaments and voids. At z=5, minor mergers produce the largest differential in [Z g/Z] where all environments display a maximum 0.22 dex increase in the average [Z g/Z] compared to non-merging galaxies. The node population also displays a consistent 0.1 dex negative offset in d [Z g/Z], the residual Z g from the total MZR of all galaxies, across all redshifts, whilst filament and void galaxies show a smaller offset. Major mergers show little influence on these same properties. This suggests minor mergers regulate metallicity and contribute to galaxy mass growth concurrently, accelerating chemical evolution post merger. Between z=1-3, a high SMBH leads to a larger negative offset in d [Z g/Z] for all environments. Here, node galaxies show the largest negative offset of approximately 0.25 dex, suggesting that AGN-driven gas removal may contribute to the MZR scatter at intermediate times. Finally, galaxies with low M gas/ M tot show increased d [Z g/Z] across all redshifts and environments, again a 0.25 dex maximum for node galaxies. These galaxies also spike in d [Z g/Z] at late times, below z=1. At this time, galaxies in the nodes show negative gas whilst also showing the largest d [Z g/Z] values we observe of 0.2 dex.