The Many Routes to AGN Feedback

TL;DR

This review discusses recent observational advances in understanding how Active Galactic Nuclei (AGN) influence galaxy evolution through feedback mechanisms, highlighting new insights from cold gas observations and their implications for simulations.

Contribution

It summarizes recent multi-wavelength observational results on AGN feedback, emphasizing the role of cold molecular gas and providing constraints for galaxy formation models.

Findings

Deep cold gas observations reveal unexpected AGN feedback effects.

Cold molecular gas studies expand understanding of AGN impact.

Observational data constrain and inform galaxy evolution simulations.

Abstract

The energy released by Active Galactic Nuclei (AGN) in the form of radiation, winds, or radio plasma jets, is known to impact on the surrounding interstellar medium. The result of these processes, known as AGN (negative) feedback, is suggested to prevent gas, in and around galaxies, from cooling, and to remove, or at least redistribute, gas by driving massive and fast outflows, hence playing a key role in galaxy evolution. Given its importance, a large effort is devoted by the astronomical community to trace the effects of AGN on the surrounding gaseous medium and to quantify their impact for different types of AGN. This review briefly summarizes some of the recent observational results obtained in different wavebands, tracing different phases of the gas. I also summarize the new insights they have brought, and the constraints they provide to numerical simulations of galaxy formation and evolution. The recent addition of deep observations of cold gas and, in particular, of cold molecular gas, has brought some interesting surprises and has expanded our understanding of AGN and AGN feedback.