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INEFFICIENT DRIVING of BULK TURBULENCE by ACTIVE GALACTIC NUCLEI in A HYDRODYNAMIC MODEL of the INTRACLUSTER MEDIUM

Accepted version
Peer-reviewed

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Type

Article

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Authors

Reynolds, CS 
Balbus, SA 
Schekochihin, AA 

Abstract

Central jetted active galactic nuclei (AGN) appear to heat the core regions of the intracluster medium (ICM) in cooling-core galaxy clusters and groups, thereby preventing a cooling catastrophe. However, the physical mechanism(s) by which the directed flow of kinetic energy is thermalized throughout the ICM core remains unclear. We examine one widely discussed mechanism whereby the AGN induces subsonic turbulence in the ambient medium, the dissipation of which provides the ICM heat source. Through controlled inviscid 3-d hydrodynamic simulations, we verify that explosive AGN-like events can launch gravity waves (g-modes) into the ambient ICM which in turn decay to volume-filling turbulence. In our model, however, this process is found to be inefficient, with less than 1% of the energy injected by the AGN activity actually ending up in the turbulence of the ambient ICM. This efficiency is an order of magnitude or more too small to explain the observations of AGN-feedback in galaxy clusters and groups with short central cooling times. Atmospheres in which the g-modes are strongly trapped/confined have an even lower efficiency since, in these models, excitation of turbulence relies on the g-modes' ability to escape from the center of the cluster into the bulk ICM. Our results suggest that, if AGN-induced turbulence is indeed the mechanism by which the AGN heats the ICM core, its driving may rely on physics beyond that captured in our ideal hydrodynamic model.

Description

Keywords

galaxies: clusters: intracluster medium, hydrodynamics, turbulence

Journal Title

Astrophysical Journal

Conference Name

Journal ISSN

0004-637X
1538-4357

Volume Title

815

Publisher

American Astronomical Society
Sponsorship
Directorate for Mathematical & Physical Sciences (1333514)