Galaxy-scale outflows driven by active galactic nuclei

Jackson Debuhr,Chung-Pei Ma,Eliot Quataert

doi:10.1111/j.1365-2966.2011.20187.x

Abstract

We present hydrodynamical simulations of major mergers of galaxies and study the effects of winds produced by active galactic nuclei (AGN) on interstellar gas in the AGN’s host galaxy. We consider winds with initial velocities ∼10 000 km s−1 and an initial momentum (energy) flux of ∼τw L/c (∼ 0.01 τw L), with ⁠. The AGN wind sweeps up and shock heats the surrounding interstellar gas, leading to a galaxy-scale outflow with velocities ∼1000 km s−1, peak mass outflow rates comparable to the star formation rate and a total ejected gas mass of ∼3 × 109 M⊙. Large momentum fluxes, τw≳ 3, are required for the AGN-driven galactic outflow to suppress star formation and accretion in the black hole’s host galaxy. Less powerful AGN winds (τw≲ 3) still produce a modest galaxy-scale outflow, but the outflow has little global effect on the ambient interstellar gas. We argue that this mechanism of AGN feedback can plausibly produce the high-velocity outflows observed in post-starburst galaxies and the massive molecular and atomic outflows observed in local ultraluminous infrared galaxies. Moreover, the outflows from local ultraluminous infrared galaxies are inferred to have τw∼ 10, comparable to what we find is required for AGN winds to regulate the growth of black holes and set the MBH - σ relation. We conclude by discussing theoretical mechanisms that can lead to AGN wind mass loading and momentum/energy fluxes large enough to have a significant impact on galaxy formation.

Highlights

Accretion onto a central massive black hole (BH) in a galactic nucleus produces energy in the form of radiation, relativistic jets, and wider angle nonrelativistic (v ∼ 104 km s−1) outflows (Krolik 1999)
In varying the active galactic nucleus (AGN) wind parameters, we are not guaranteed that the resulting BH mass will be consistent with the MBH − σ relation
We have carried out three-dimensional SPH simulations of the interaction between a high-speed outflow produced by an AGN and interstellar gas in the AGN’s host galaxy

Summary

Introduction

Accretion onto a central massive black hole (BH) in a galactic nucleus produces energy in the form of radiation, relativistic jets, and wider angle (less-collimated) nonrelativistic (v ∼ 104 km s−1) outflows (Krolik 1999) The coupling of this energy output to gas in galaxies and in the intergalactic medium is believed to play an important role in galaxy formation, potentially regulating the growth of massive galaxies and the thermal properties of the intracluster medium in galaxy groups and clusters (e.g., Silk & Rees 1998; Croton et al 2006). The physical processes most likely to produce such an effect are winds (King 2003; King et al 2011), radiation pressure (Murray et al 2005), and/or Compton heating (Sazonov et al 2004) from a central AGN. Understanding how this works in detail is one of the major challenges in our understanding of the connection between AGN physics and galaxy formation

Methods

Results

Conclusion