Buoyant radio plasma in clusters of galaxies

Radio galaxies are known to inflate lobes of hot relativistic plasmas into the intergalactic medium. Here we present hydrodynamical and magnetohydrody namical simulations of these hot plasma bubbles in FR II objects. We focus on the later stages of their evolution after the jet has died down and afte r the bow shock that surrounded the lobes at earlier stages has vanished. W e investigate the evolution of the plasma bubbles as they become subject to Rayleigh-Taylor instabilities. From our simulations we calculate the radio and X-ray emissivities of the bubbles and discuss their appearance in obse rvations. Finally, we investigate the influence of large-scale magnetic fie lds on the evolution of the bubbles. The issues of re-acceleration and diff usion of relativistic particles are briefly discussed.