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, $\langle \dot{M}_\mathrm{SMBH}\rangle$, major and minor galaxy mergers, and gas processes, on the average gas metallicity of galaxies, 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 $\log[Z_g/Z_\odot]$ for all environments, where the node population displays a maximum $0.38$ 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 reduction in $δ\log[Z_g/Z_{\odot}]$ across all redshifts, whilst filament and void galaxies show a lower magnitude of reduction. Major mergers show little influence on these same properties. This suggests minor mergers regulate metallicity and contribute to over galaxy mass growth concurrently, accelerating chemical evolution post merger. Between $z=1-3$, a high $\langle \dot{M}_\mathrm{SMBH}\rangle$ leads to a reduction in $δ\log[Z_g/Z_{\odot}]$ for all environments. Here, node galaxies show the largest reduction of approximately $0.25$ dex, suggesting that metal-rich outflows strongly drive the MZR at intermediate times. Finally, galaxies with low $M_{gas}/{M_{tot}}$ show increased $δ\log[Z_g/Z_{\odot}]$ across all redshifts and environments, again a $0.25$ dex maximum for node galaxies. These galaxies also spike in $δ\log[Z_g/Z_{\odot}]$ at late times, below $z=1$. At this time, galaxies in the nodes show negative $\langle \dot{M}_\mathrm{gas} \rangle$ whilst also showing the largest $δ\log[Z_g/Z_{\odot}]$ values we observe of $0.2$ dex, suggesting the importance of the balance between gas accretion and starvation in driving MZR scatter at low redshifts.

Figures (16)

• Figure 1: The median MZR residual, $\delta \log[Z_g/Z_{\odot}]$, against redshift for the 3 environments. Nodes in orange, filaments in blue and voids in purple. $\delta \log[Z_g/Z_{\odot}]$ increases rapidly, from negative to postive, for galaxies that end up in nodes at $z=0.625.$, over the same range, galaxies that end up in voids see a drop in $\delta \log[Z_g/Z_{\odot}]$.
• Figure 2: The median evolution of $M_\mathrm{tot}$ (left), $\frac{M_\star}{M_{tot}}$ (right) and gas mass, $\frac{M_{gas}}{M_{tot}}$. (right) across time for each environment. Nodes in orange, filaments in blue, voids in purple. Below $z\approx1$, galaxies that end up in nodes show a turnover in $M_\mathrm{tot}$, with filament galaxies showing signs of following after. This same drop is seen on the right panel as a fall in $\frac{M_{gas}}{M_{tot}}$.
• Figure 3: The $\langle \dot{M}_\mathrm{gas} \rangle$ of galaxies in the three environments. Nodes in orange, filaments in blue and voids in purple. Galaxies that end up in nodes show a rapidly falling $M_\mathrm{gas}$ below $z\approx 2$, whilst filament galaxies show a lesser drop, and void galaxies show a flat trend over the same range.
• Figure 4: The evolution of $\delta \log[Z_g/Z_{\odot}]$ for galaxies in the three environments with high and low fractional gas mass. Node galaxies in orange, filaments in blue and voids in purple. Generally, galaxies with higher gas fraction show reduced $\delta \log[Z_g/Z_{\odot}]$, whilst those with low gas fraction show increased $\delta \log[Z_g/Z_{\odot}]$, particularly for galaxies that end up in nodes at $z=1$.
• Figure 5: The evolution of $\delta \log[Z_g/Z_{\odot}]$ for galaxies with high and low fractional $M_{star}$ in the three environments. Nodes in orange, filaments in blue, and voids in purple. Galaxies with high $M_\mathrm{\star}/M_\mathrm{tot}$ show dramatically increased $\delta \log[Z_g/Z_{\odot}]$ values, particularly below $z=1.5$ for galaxies that end up in nodes. This node population also has the largest range of $\delta \log[Z_g/Z_{\odot}]$ values across all redshifts, increasing to the lower redshifts, whilst the filament and void population are more flat.