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Title:
Constraining the Nature of X-Ray Cavities in Clusters and Galaxies
Authors:
Diehl, Steven; Li, Hui; Fryer, Christopher L.; Rafferty, David
Affiliation:
AA(Theoretical Astrophysics Group (T-6), Los Alamos National Laboratory, Los Alamos, NM 87545; , ), AB(Theoretical Astrophysics Group (T-6), Los Alamos National Laboratory, Los Alamos, NM 87545; , ), AC(Computational Physics and Methods Group (CCS-2), Los Alamos National Laboratory, Los Alamos, NM 87545), AD(Astrophysical Institute, Department of Physics and Astronomy, Ohio University, Athens, OH 45701; and Department of Astronomy and Astrophysics, Pennsylvania State University, University Park, PA 16802)
Publication:
The Astrophysical Journal, Volume 687, Issue 1, pp. 173-192. (ApJ Homepage)
Publication Date:
11/2008
Origin:
UCP
ApJ Keywords:
Galaxies: Cooling Flows, Galaxies: Clusters: General, Instabilities, Magnetohydrodynamics: MHD, X-Rays: Galaxies: Clusters, X-Rays: ISM
DOI:
10.1086/591310
Bibliographic Code:
2008ApJ...687..173D

Abstract

We present results from an extensive survey of 64 cavities in the X-ray halos of clusters, groups, and normal elliptical galaxies. We show that the evolution of the size of the cavities as they rise in the X-ray atmosphere is inconsistent with the standard model of adiabatic expansion of purely hydrodynamic models. We also note that the majority of the observed bubbles should have already been shredded apart by Rayleigh-Taylor and Richtmyer-Meshkov instabilities if they were of purely hydrodynamic nature. Instead, we find that the data agree much better with a model where the cavities are magnetically dominated and inflated by a current-dominated MHD jet model, recently developed by Li and coworkers and Nakamura and coworkers. We conduct complex Monte Carlo simulations of the cavity detection process including incompleteness effects to reproduce the cavity sample's characteristics. We find that the current-dominated model agrees within 1 σ, whereas the other models can be excluded at >5 σ confidence. To bring hydrodynamic models into better agreement, cavities would have to be continuously inflated. However, these assessments are dependent on our correct understanding of the detectability of cavities in X-ray atmospheres and will await confirmation when automated cavity detection tools become available in the future. Our results have considerable impact on the energy budget associated with AGN feedback.
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