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M. Ruszkowski (JILA, University of Colorado at Boulder), M. Bruggen (International University Bremen), M.C. Begelman (JILA, APS, University of Colorado at Boulder)
We present three-dimensional simulations of viscous dissipation of AGN induced gas motions and waves in clusters of galaxies. These simulations are motivated by recent detections of ripples in the Perseus and Virgo clusters. We show that, despite the fact that the sound waves generated by the buoyant bubbles decay with distance from the cluster center, these waves can substantially contribute to offsetting the radiative cooling at distances significantly exceeding the bubble size. The energy flux of the waves scales initially as an inverse-square powerlaw of the distance from the center, which is consistent with energy conservation. The slope of the energy flux gradually steepens as the waves propagate away from the center due to the effects of dissipation. We show that such dispersing sound waves/weak shocks are still detectable as ripples on unsharp-masked X-ray cluster maps. We point out that the interfaces between the intracluster medium and old bubbles are also clearly detectable in unsharp-masked X-ray maps. This opens up a possibility of detecting such fossil bubbles that are difficult to detect in radio emission. This mode of heating is consistent with other observational constraints, such as the presence of cool rims around the bubbles and the absence of strong shocks. Thus, the mechanism offers a way of heating clusters in a spatially distributed and gentle fashion as first suggested by Fabian et al. (2003). We also discuss the energy transfer between the central AGN and the surrounding medium. In our numerical experiments, we find that roughly 50 per cent of the energy injected by the AGN is transferred to the intra-cluster medium and approximately 10 percent of the injected energy is dissipated by viscous effects and contributes to heating of the gas. The overall transfer of heat from the AGN to the gas is comparable to the radiative cooling losses. The simulations were performed with the FLASH adaptive mesh refinement code.
The author(s) of this abstract have provided an email address for comments about the abstract: mr@quixote.colorado.edu
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Bulletin of the American Astronomical Society, 36 #2
© YEAR. The American Astronomical Soceity.