Quasar feedback: accelerated star formation and chaotic accretion

TL;DR

This paper demonstrates that quasar feedback can sometimes accelerate star formation in host galaxies by compressing cold gas, challenging the traditional view that SMBHs only suppress galaxy growth.

Contribution

It presents advanced simulations showing that SMBH feedback can have positive effects, such as triggering star formation, and explores the resulting complex SMBH-galaxy relationship.

Findings

Quasars can trigger star formation by compressing cold gas.

Dense filaments resist feedback-driven ejection, complicating galaxy regulation.

Instabilities may promote chaotic accretion modes.

Abstract

Growing Supermassive Black Holes (SMBH) are believed to influence their parent galaxies in a negative way, terminating their growth by ejecting gas out before it could turn into stars. Here we present some of the most sophisticated SMBH feedback simulations to date showing that quasar's effects on galaxies are not always negative. We find that when the ambient shocked gas cools rapidly, the shocked gas is compressed into thin cold dense shells, filaments and clumps. Driving these high density features out is much more difficult than analytical models predict since dense filaments are resilient to the feedback. However, in this regime quasars have another way of affecting the host -- by triggering a massive star formation burst in the cold gas by over-pressurising it. Under these conditions SMBHs actually accelerate star formation in the host, having a positive rather than negative effect on their host galaxies. The relationship between SMBH and galaxies is thus even more complex and symbiotic than currently believed. We also suggest that the instabilities found here may encourage the chaotic AGN feeding mode.