Quasar Feedback: More Bang for Your Buck
Philip F. Hopkins (Berkeley), Martin Elvis (CfA)

TL;DR
This paper introduces a two-stage quasar feedback model where initial hot gas outflows indirectly enhance cold gas ionization and expulsion, significantly reducing the energy needed for galaxy feedback.
Contribution
It proposes a novel two-stage feedback mechanism that lowers the energy budget required for quasar-driven galaxy feedback by leveraging cloud expansion and ionization effects.
Findings
Moderate hot outflows can significantly increase cold gas susceptibility to ionization.
The energy requirement for effective feedback is reduced by an order of magnitude.
Hot gas outflows of only 5-10% of the black hole accretion rate can impact galaxy gas content.
Abstract
We propose a two-stage model for the effects of feedback from a bright quasar on the cold gas in a galaxy. It is difficult for feedback from near the accretion disk to directly impact dense molecular clouds at ~kpc. But if such feedback can drive a weak wind or outflow in the hot, diffuse ISM (a relatively 'easy' task), then in the wake of such an outflow passing over a cold cloud, a combination of instabilities will drive the cloud material to effectively expand in the direction perpendicular to the outflow. Such expansion dramatically increases the effective cross section of the cloud material and makes it more susceptible to ionization and momentum coupling from absorption of the incident quasar radiation field. Even a moderate effect of this nature can dramatically alter the ability of clouds at large radii to be fully ionized and driven into a secondary outflow by radiation…
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