Establishing the impact of luminous AGN with multi-wavelength observations and simulations

TL;DR

This paper reviews observational evidence and simulations regarding the impact of luminous AGN on their host galaxies, emphasizing the complexity of feedback mechanisms and the challenges in linking observations with models.

Contribution

It provides a comprehensive review of multi-wavelength observations and simulations of AGN feedback, highlighting the multi-channel nature and cumulative effects of AGN on galaxy evolution.

Findings

Multi-phase AGN outflows are common and potentially impactful.

Multiple feedback channels can operate simultaneously in galaxies.

Simulations and observations show complex, cumulative AGN effects on host galaxies.

Abstract

Cosmological simulations fail to reproduce realistic galaxy populations without energy injection from active galactic nuclei (AGN) into the interstellar medium (ISM) and circumgalactic medium (CGM); a process called `AGN feedback'. Consequently, observational work searches for evidence that luminous AGN impact their host galaxies. Here, we review some of this work. Multi-phase AGN outflows are common, some with potential for significant impact. Additionally, multiple feedback channels can be observed simultaneously; e.g., radio jets from `radio quiet' quasars can inject turbulence on ISM scales, and displace CGM-scale molecular gas. However, caution must be taken comparing outflows to simulations (e.g., kinetic coupling efficiencies) to infer feedback potential, due to a lack of comparable predictions. Furthermore, some work claims limited evidence for feedback because AGN live in gas-rich, star-forming galaxies. However, simulations do not predict instantaneous, global impact on molecular gas or star formation. The impact is expected to be cumulative, over multiple episodes.