2009MNRAS.395..228S

We show that repeated sound waves in the intracluster medium (ICM) can be excited by a single inflation episode of an opposite bubble pair. To reproduce this behaviour in numerical simulations, the bubbles should be inflated by jets, rather than being injected artificially as already full-blown bubbles. The multiple sound waves are excited by the motion of the bubble-ICM boundary that is caused by vortices inside the inflated bubbles and the backflow (`cocoon') of the ICM around the bubble. These sound waves form a structure that can account for the ripples observed in the Perseus cooling flow cluster. We inflate the bubbles using slow massive jets either with a very wide opening angle or that are narrow and precessing. The wide jets (or collimated fast winds) are slow in the sense that they are highly subrelativistic, v_j∼ 0.01c- 0.1c, and they are massive in the sense that the pair of bubbles carries back to the ICM a large fraction of the cooling mass, i.e. ∼1-50M_☉/yr. We use a two-dimensional axisymmetric (referred to as 2.5D) hydrodynamical numerical code (vh-1).