Circumgalactic Oxygen Absorption and Feedback

TL;DR

This paper investigates the origin, distribution, and maintenance of oxygen in the circumgalactic medium of galaxies, highlighting the role of black hole feedback in sustaining observed oxygen levels and explaining differences between galaxy types.

Contribution

It provides new insights into the oxygen content in the circumgalactic medium and proposes black hole feedback as a key mechanism for maintaining this gas in star-forming galaxies.

Findings

OVI absorption drops beyond 100 kpc from galaxies.

Over 10^9 solar masses of oxygen are concentrated near 100 kpc.

Black hole feedback may sustain oxygen-rich atmospheres in star-forming galaxies.

Abstract

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.