Sound waves excitation by jet-inflated bubbles in clusters of galaxies

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∼ 0.01 c – 0.1 c   , 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.  ∼1–50 M_⊙ yr⁻¹  . We use a two-dimensional axisymmetric (referred to as 2.5D) hydrodynamical numerical code ( vh-1 ).