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

We examine the effects of supermassive black hole (SMBH) feedback on the circumgalactic medium (CGM) using a cosmological hydrodynamic simulation (ROMULUS25) 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 CGM, we show that O VI is a sensitive indicator of SMBH feedback. First, we calculate the column densities of O VI in simulated Milky-Way-mass galaxies and compare them with observations from the COS-Halos Survey. Our simulations show column densities of O VI 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 O VI. We determine that a galaxy’s star formation history and assembly record have little effect on the amount of O VI in its CGM. Instead, column densities of O VI 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 O VI in the CGM.