Buoyant bubbles in a cooling intracluster medium

I. Hydrodynamic bubbles

¹ Department of Astronomy, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, USA e-mail: gardini@astro.uiuc.edu
² National Center for Supercomputing Applications, Urbana, IL, 61801, USA

Received: 21 September 2006
Accepted: 9 November 2006

Abstract

Aims.Over the past several years, numerous examples of X-ray cavities coincident with radio sources have been observed in so-called “cool core” clusters of galaxies. Motivated by these observations, we explore the evolution and the effect of cavities on a cooling intracluster medium (ICM) numerically, adding relevant physics step by step.

Methods.In this paper we present a first set of hydrodynamical, high resolution (1024³ effective grid elements), three-dimensional simulations, together with two-dimensional test cases. The simulations follow the evolution of radio cavities, modeled as bubbles filled by relativistic plasma, in the cluster atmosphere, while the ICM is subject to cooling.

Results.We find that the bubble rise retards the development of a cooling flow by inducing motions in the ICM, which repeatedly displace the material in the core. Even bubbles initially set significantly far from the cluster center affect the cooling flow, although much later than the beginning of the simulation. The effect is, however, modest: the cooling time is increased by at most only 25%. As expected, the overall evolution of pure hydrodynamic bubbles is at odds with observations, showing that some additional physics has to be considered to match the data.