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

Abstract

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, vj∼ 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. ∼1–50 M⊙ yr−1. We use a two‐dimensional axisymmetric (referred to as 2.5D) hydrodynamical numerical code (vh‐1).

Hitomi observations of Perseus support heating by mixing

“…We note that heating by cosmic rays and mixing-heating are not excluded, as Pfrommer (2013) argued that mixing is essential for the heating by cosmic rays model to account for observations. Vortices that are formed in the interaction of the jets with the ICM excite both the sound waves (Sternberg & Soker 2009) and cause the mixing (Gilkis & Soker 2012;Hillel & Soker 2014, 2016.…”

“…1 and 2 demonstrate the complicated flow pattern with many vortices, that is induced by the jets and the bubbles, and the vigorous mixing that takes place. The vortices also induce sound waves (Sternberg & Soker 2009) and turbulence ). We now turn to examine the velocity dispersion of this complicated flow.…”

AGN Heating in Simulated Cool-core Clusters

“…Heating cool-core clusters with weak shock waves has been extensively discussed in the literature (e.g., Ruszkowski et al 2004;Voit & Donahue 2005;Fabian et al 2005;Mathews et al 2006;Sternberg & Soker 2009). All of these works generally agree that shock heating can be energetically sufficient to offset cooling.…”

A jet-driven dynamo (JEDD) from jets-inflated bubbles in cooling flows

“…The main process that is behind the JEDD is the turbulence that is formed by the many vortices formed in the inflation processes of bubbles. The same vortices also mix the hot shocked jet gas with the ICM (Hillel & Soker 2016;Gaspari et al 2017) and excite sound waves in the ICM (Sternberg & Soker 2009), both of which heat the ICM (see section 1).…”

“…Different processes have been proposed to channel energy from the jets and the bubbles they inflate to heat the ICM (e.g., Gaspari et al 2013;Li et al 2017), including cosmic rays and thermal conduction (e.g., Guo & Oh 2008), sound waves (Fabian 2012;Fabian et al 2017) that are excited by the inflation process of bubbles (Sternberg & Soker 2009), and mixing of hot post-shock gas from the bubble with the ICM (e.g., Brüggen & Kaiser 2002;Brüggen et al 2009;Gilkis & Soker 2012;Hillel & Soker 2014;Banerjee & Sharma 2014;Prasad et al 2015;Hillel & Soker 2016Gaspari et al 2017).…”