10 December 2009

Speaker: Mateusz Ruszkowski (U. of Michigan)

Title: Shaken and stirred: conduction and turbulence in clusters of galaxies

Abstract: Uninhibited radiative cooling in clusters of galaxies would lead to excessive mass accretion rates contrary to observations. Different mechanisms have been proposed to offset radiative losses. Leading contenders generally involve AGN heating, thermal conduction or (gas)dynamical friction. I will touch upon each of these processes but I will mostly focus on the role of thermal conduction and turbulence. In cool-core clusters the heat buoyancy instability (HBI) leads to B-fields ordered preferentially in the direction perpendicular to that of gravity, which significantly reduces the level of conduction below the classical Spitzer-Braginskii value. However, Chandra and XMM observations show that the cluster cool cores are rarely in perfect hydrostatic equilibrium. Sloshing motions due to minor mergers, galaxy motions or AGN can significantly perturb the gas which may affect the level of conduction. We perform 3D AMR MHD simulations of the effect of turbulence driven by galaxy motions on the properties of the anisotropic thermal conduction. We show that subsonic motions, well within observational constraints, can randomize the magnetic field and essentially restore the conductive heat flow to the cool core to the level comparable to the theoretical maximum. Remarkably, runs with radiative cooling show that the cooling catastrophe can be averted and the cluster core stabilized. Our results can be tested with future radio polarization measurements, and have implications for efficient metal dispersal in clusters. I will also briefly comment on the cosmological implications of these results.

Video of the Presentation (Talks can be viewed with RealPlayer. Free download is available from www.real.com )