Quantifying AGN-Driven Metal-Enhanced Outflows in Chemodynamical Simulations

TL;DR

This study uses cosmological simulations to demonstrate how AGN-driven outflows eject metals from galaxies, enriching the circumgalactic and intergalactic media, and influence galaxy evolution and chemical enrichment.

Contribution

It provides the first detailed simulation-based quantification of AGN-driven metal-enriched outflows and their impact on large-scale chemical enrichment.

Findings

AGN outflows reach speeds over 8000 km/s near the AGN.

Approximately 2% of total metals are ejected by outflows.

18.4% of total metals are found in the CGM and IGM due to AGN feedback.

Abstract

We show the effects of AGN-driven outflows on the ejection of heavy elements using our cosmological simulations, where super-massive black holes originate from the first stars. In the most massive galaxy, we have identified two strong outflows unambiguously driven by AGN feedback. These outflows have a speed greater than $\sim 8000$ km\,s$^{-1}$ near the AGN, and travel out to a half Mpc with $\sim 3000$ km\,s$^{-1}$. These outflows remove the remaining gas ($\sim 3$ per cent of baryons) and significant amounts of metals ($\sim 2$ per cent of total produced metals) from the host galaxy, chemically enriching the circumgalactic medium (CGM) and the intergalactic medium (IGM). 17.6 per cent of metals from this galaxy, and 18.4 per cent of total produced metals in the simulation, end up in the CGM and IGM, respectively. The metallicities of the CGM and IGM are higher with AGN feedback, while the mass--metallicity relation of galaxies is not affected very much. We also find `selective' mass-loss where iron is more effectively ejected than oxygen because of the time-delay of Type Ia Supernovae. AGN-driven outflows play an essential role not only in quenching of star formation in massive galaxies to match with observed down-sizing phenomena, but also in a large-scale chemical enrichment in the Universe. Observational constraints of metallicities and elemental abundance ratios in outflows are important to test the modelling of AGN feedback in galaxy formation.