Circumgalactic Oxygen Absorption and Feedback
  OVI absorption in quasar spectra caused by intervening circumgalactic
atmospheres suggests a downturn in the atmospheric column density in sightlines
passing beyond about 100 kpc from central star-forming galaxies. This turnover
supports the hypothesis that the oxygen originates in the central galaxies.
When converted into oxygen space density using an Abel integral inversion, the
OVI columns require greater than $\approx 10^9 M_\odot$ of oxygen concentrated
near 100 kpc. Circumgalactic gas within this radius cools in less than 1 Gyr
and radiates $\sim 10^{42.2}$ erg s$^{-1}$ overall. The feedback power
necessary to maintain such oxygen-rich atmospheres for many Gyrs cannot be
easily supplied by galactic supernovae. However, massive central black holes in
star-forming galaxies may generate sufficient accretion power and intermittent
shock waves at $r \sim 100$ kpc to balance circumgalactic radiation losses in
late-type $L^\star$ galaxies. The relative absence of OVI absorption observed
in early-type, passive $L^{\star}$ galaxies may arise from enhanced AGN
feedback from their more massive central black holes.
