Segers, M. C., Oppenheimer, B. D., Schaye, J., & Richings, A. J. (2017). Metals in the circumgalactic medium are out of ionization equilibrium due to fluctuating active galactic nuclei. Monthly Notices of the Royal Astronomical Society, 471(1), 1026-1044. https://doi.org/10.1093/MNRAS/STX1633