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

Abstract

We study the impact of supermassive black hole (SMBH) growth, $⟨{\dot{M}}_{\mathrm{SMBH}}⟩$, 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 $\log [Z_g/Z_{\odot }]$ where all environments display a maximum $0.22$ dex increase in the average $\log [Z_g/Z_{\odot }]$ compared to non-merging galaxies. The node population also displays a consistent $0.1$ dex negative offset in $\mathrm{d}\log [Z_g/Z_{\odot }]$, 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 $⟨{\dot{M}}_{\mathrm{SMBH}}⟩$ leads to a larger negative offset in $\mathrm{d}\log [Z_g/Z_{\odot }]$ 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 $\mathrm{d}\log [Z_g/Z_{\odot }]$ across all redshifts and environments, again a $0.25$ dex maximum for node galaxies. These galaxies also spike in $\mathrm{d}\log [Z_g/Z_{\odot }]$ at late times, below $z=1$. At this time, galaxies in the nodes show negative $⟨{\dot{M}}_{\mathrm{gas}}⟩$ whilst also showing the largest $\mathrm{d}\log [Z_g/Z_{\odot }]$ values we observe of $0.2$ dex.

This manuscript has been accepted for publication in MNRAS