Annu. Rev. Astron. Astrophys. 2015. 53:115-154 Copyright © 2015 by Annual Reviews. All rights reserved

Reprinted with kind permission from Annual Reviews, 4139 El Camino Way, Palo Alto, California, USA

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Abstract: Active Galactic Nuclei (AGN) represent the growth phases of the supermassive black holes in the center of almost every galaxy. Powerful, highly ionized winds, with velocities ∼ 0.1− 0.2c are a common feature in X–ray spectra of luminous AGN, offering a plausible physical origin for the well known connections between the hole and properties of its host. Observability constraints suggest that the winds must be episodic, and detectable only for a few percent of their lifetimes. The most powerful wind feedback, establishing the M − σ relation, is probably not directly observable at all. The M − σ relation signals a global change in the nature of AGN feedback. At black hole masses below M − σ feedback is confined to the immediate vicinity of the hole. At the M − σ mass it becomes much more energetic and widespread, and can drive away much of the bulge gas as a fast molecular outflow.

Keywords Supermassive black holes, accretion, M − σ relation, X–ray winds, molecular outflows, quenching of star formation

Table of Contents

• INTRODUCTION
• SMBH Scaling relations
• Binding Energies
• Communicating the Energy: Feedback
• Powerful ionized winds
• THE OBSERVATIONAL EVIDENCE FOR ULTRA FAST OUTFLOWS
• The fast outflow in PG1211+143
• Mass rate and mechanical energy in the PG1211+143 outflow
• High speed winds are common
• Evidence for a shocked flow
• A self-consistent model for the shocked wind in NGC 4051
• Variability of UFOs
• BLACK HOLE WINDS
• The Eddington Accretion Ratio in AGN
• Eddington Winds
• Observability
• The Wind Ionization State, and BAL QSOs
• THE WIND SHOCK
• Momentum– and Energy–Driven Flows
• Shock Cooling
• THE M − σ RELATION
• Reaching M − σ: the Momentum–Driven Phase
• What Happens When M = M_σ?
• Clearing Out a Galaxy: the Energy–Driven Phase
• Effects of a Galaxy Disc: Stimulated Star Formation and Outflow Morphology
• The Three M − σ relations
• THE SMBH – BULGE MASS RELATION
• Feedback and the M − M_b relation
• The M − σ relation for Nucleated Galaxies
• Mergers and the M − M_b relation
• MOMENTUM, ENERGY OR RADIATION?
• Wind Momentum Driving
• Wind Energy Driving
• Cosmological Simulations
• Radiation Driving
• Electron scattering opacity
• Dust
• SMALL vs LARGE SCALE FEEDBACK
• REFERENCES