Not So Heavy Metals: Black Hole Feedback Enriches The Circumgalactic Medium

TL;DR

This study uses cosmological simulations to show that supermassive black hole feedback significantly enriches the circumgalactic medium with metals, especially oxygen VI, aligning well with observational data and highlighting the role of black hole growth in galaxy evolution.

Contribution

It demonstrates that SMBH feedback is a key factor in enriching the CGM with metals, resolving discrepancies between previous simulations and observations.

Findings

O VI column densities match COS-Halos observations.

SMBH feedback drives metal-enriched outflows into the CGM.

Galaxy star formation history has little effect on O VI levels.

Abstract

We examine the effects of SMBH feedback on the CGM using a cosmological hydrodynamic simulation \citep[{\sc Romulus25};][]{Tremmel2017} and a set of four zoom-in `genetically modified' Milky Way-mass galaxies sampling different evolutionary paths. By tracing the distribution of metals in the circumgalactic medium (CGM), we show that \ion{O}{6} is a sensitive indicator of supermassive black hole (SMBH) feedback. First, we calculate the column densities of \ion{O}{6} in simulated Milky Way-mass galaxies and compare them with observations from the COS-Halos Survey. Our simulations show column densities of \ion{O}{6} in the CGM consistent with those of COS-Halos star forming and quenched galaxies. These results contrast with those from previous simulation studies which typically underproduce CGM column densities of \ion{O}{6}. We determine that a galaxy's star formation history and assembly record have little effect on the amount of \ion{O}{6} in its CGM. Instead, column densities of \ion{O}{6} are closely tied to galaxy halo mass and BH growth history. The set of zoom-in, genetically modified Milky Way-mass galaxies indicates that the SMBH drives highly metal-enriched material out into its host galaxy's halo which in turn elevates the column densities of \ion{O}{6} in the CGM.