Accretion disk winds in active galactic nuclei: X-ray observations, models, and feedback

TL;DR

This paper reviews the role of accretion disk winds in active galactic nuclei, their observational evidence in X-ray spectra, theoretical models of their origin, and prospects for future high-resolution X-ray observations to better understand their physics and impact.

Contribution

It synthesizes current observational and theoretical understanding of AGN winds and highlights the importance of upcoming X-ray observatories for advancing this field.

Findings

X-ray observations support the ubiquity of accretion disk winds in AGN.

Models suggest radiation and MHD processes drive these winds.

Future observatories will significantly improve wind characterization.

Abstract

Powerful winds driven by active galactic nuclei (AGN) are often invoked to play a fundamental role in the evolution of both supermassive black holes (SMBHs) and their host galaxies, quenching star formation and explaining the tight SMBH-galaxy relations. A strong support of this "quasar mode" feedback came from the recent X-ray observation of a mildly relativistic accretion disk wind in a ultraluminous infrared galaxy (ULIRG) and its connection with a large-scale molecular outflow, providing a direct link between the SMBH and the gas out of which stars form. Spectroscopic observations, especially in the X-ray band, show that such accretion disk winds may be common in local AGN and quasars. However, their origin and characteristics are still not fully understood. Detailed theoretical models and simulations focused on radiation, magnetohydrodynamic (MHD) or a combination of these two processes to investigate the possible acceleration mechanisms and the dynamics of these winds. Some of these models have been directly compared to X-ray spectra, providing important insights into the wind physics. However, fundamental improvements on these studies will come only from the unprecedented energy resolution and sensitivity of the upcoming X-ray observatories, namely ASTRO-H (launch date early 2016) and Athena (2028).