%0 Generic %1 oppenheimer2017flickering %A Oppenheimer, Benjamin D. %A Segers, Marijke %A Schaye, Joop %A Richings, Alexander J. %A Crain, Robert A. %D 2017 %K OVI agn cgm %T Flickering AGN can explain the strong circumgalactic O VI observed by COS-Halos %U http://arxiv.org/abs/1705.07897 %X Proximity zone fossils (PZFs) are ionization signatures around recently active galactic nuclei (AGN) where metal species in the circumgalactic medium remain over-ionized after the AGN has shut-off due to their long recombination timescales. We explore cosmological zoom hydrodynamic simulations using the EAGLE model paired with a non-equilibrium ionization and cooling module including time-variable AGN radiation to model PZFs around star-forming, disk galaxies in the z~0.2 Universe. Previous simulations typically under-estimated the O VI content of galactic haloes, but we show that plausible PZF models increase O VI column densities by 2-3x to achieve the levels observed around COS-Halos star-forming galaxies out to 150 kpc. Models with AGN bolometric luminosities >~10^43.6 erg s^-1, duty cycle fractions <~10%, and AGN lifetimes <~10^6 yr are the most promising, because their super-massive black holes grow at the cosmologically expected rate and they mostly appear as inactive AGN, consistent with COS-Halos. The central requirement is that the typical star-forming galaxy hosted an active AGN within a timescale comparable to the recombination time of a high metal ion, which for circumgalactic O VI is 10^7 years. H I, by contrast, returns to equilibrium much more rapidly due to its low neutral fraction and does not show a significant PZF effect. O VI absorption features originating from PZFs appear narrow, indicating photo-ionization, and are often well-aligned with lower metal ions species. PZFs are highly likely to affect the physical interpretation of circumgalactic high ionization metal lines if, as expected, normal galaxies host flickering AGN.

@misc{oppenheimer2017flickering, abstract = {Proximity zone fossils (PZFs) are ionization signatures around recently active galactic nuclei (AGN) where metal species in the circumgalactic medium remain over-ionized after the AGN has shut-off due to their long recombination timescales. We explore cosmological zoom hydrodynamic simulations using the EAGLE model paired with a non-equilibrium ionization and cooling module including time-variable AGN radiation to model PZFs around star-forming, disk galaxies in the z~0.2 Universe. Previous simulations typically under-estimated the O VI content of galactic haloes, but we show that plausible PZF models increase O VI column densities by 2-3x to achieve the levels observed around COS-Halos star-forming galaxies out to 150 kpc. Models with AGN bolometric luminosities >~10^43.6 erg s^-1, duty cycle fractions <~10%, and AGN lifetimes <~10^6 yr are the most promising, because their super-massive black holes grow at the cosmologically expected rate and they mostly appear as inactive AGN, consistent with COS-Halos. The central requirement is that the typical star-forming galaxy hosted an active AGN within a timescale comparable to the recombination time of a high metal ion, which for circumgalactic O VI is 10^7 years. H I, by contrast, returns to equilibrium much more rapidly due to its low neutral fraction and does not show a significant PZF effect. O VI absorption features originating from PZFs appear narrow, indicating photo-ionization, and are often well-aligned with lower metal ions species. PZFs are highly likely to affect the physical interpretation of circumgalactic high ionization metal lines if, as expected, normal galaxies host flickering AGN.}, added-at = {2017-05-24T09:45:24.000+0200}, author = {Oppenheimer, Benjamin D. and Segers, Marijke and Schaye, Joop and Richings, Alexander J. and Crain, Robert A.}, biburl = {https://www.bibsonomy.org/bibtex/2ef22653d04dfce58bd02d8e39d4d61d3/miki}, description = {[1705.07897] Flickering AGN can explain the strong circumgalactic O VI observed by COS-Halos}, interhash = {21454452947c54ca5a9bc47dfb7e02e1}, intrahash = {ef22653d04dfce58bd02d8e39d4d61d3}, keywords = {OVI agn cgm}, note = {cite arxiv:1705.07897Comment: 15 pages, 10 figures, submitted to MNRAS, companion website: http://noneq.strw.leidenuniv.nl/PZF/}, timestamp = {2017-05-24T09:45:24.000+0200}, title = {Flickering AGN can explain the strong circumgalactic O VI observed by COS-Halos}, url = {http://arxiv.org/abs/1705.07897}, year = 2017 }