Wind from cold accretion flows

TL;DR

This paper reviews the physical mechanisms behind wind launching and acceleration in AGN accretion disks, focusing on radiation line force and magnetic driven models, and discusses their role in ultra-fast outflows and feedback.

Contribution

It provides a comprehensive review of the recent developments in understanding AGN disk winds, emphasizing the two main driving mechanisms and their connection to observed ultra-fast outflows.

Findings

Radiation line force and magnetic mechanisms can explain UFOs.

Wind propagation impacts AGN feedback processes.

Recent models improve understanding of wind acceleration.

Abstract

We describe the physical mechanisms of launching and acceleration of wind from an active galactic nucleus (AGN) accretion disk. We focus on the radiation line force driven and magnetic driven wind models, which operate on the accretion disk scale. We review the investigation histories of the two mechanisms and the most new results obtained recently. The ultra-fast outflows (UFOs) found in the hard X-ray bands are believed to directly originate from AGN accretion disks. We review the theoretical works applying the two mechanisms of wind to explain the UFOs. We briefly introduce the propagation of winds on a large scale which is important for AGN wind feedback study. Finally, the roles of wind in AGN feedback are briefly reviewed.