Mass transport by buoyant bubbles in galaxy clusters

TL;DR

This paper examines how buoyant bubbles in galaxy clusters transport material through drift, wake, and entrainment, impacting cluster dynamics and cooling processes.

Contribution

It provides a detailed analysis of the roles of drift, wake, and entrainment in mass transport by AGN bubbles, highlighting their effects on cluster cooling and filament formation.

Findings

Drift can displace ~10^{7-9} solar masses of material.

Wake transport increases bubble density and influences filament formation.

Mass transport can prevent cool material buildup despite insufficient heating.

Abstract

We investigate the effect of three important processes by which AGN-blown bubbles transport material: drift, wake transport and entrainment. The first of these, drift, occurs because a buoyant bubble pushes aside the adjacent material, giving rise to a net upward displacement of the fluid behind the bubble. For a spherical bubble, the mass of upwardly displaced material is roughly equal to half the mass displaced by the bubble, and should be ~ 10^{7-9} solar masses depending on the local ICM and bubble parameters. We show that in classical cool core clusters, the upward displacement by drift may be a key process in explaining the presence of filaments behind bubbles. A bubble also carries a parcel of material in a region at its rear, known as the wake. The mass of the wake is comparable to the drift mass and increases the average density of the bubble, trapping it closer to the cluster centre and reducing the amount of heating it can do during its ascent. Moreover, material dropping out of the wake will also contribute to the trailing filaments. Mass transport by the bubble wake can effectively prevent the build-up of cool material in the central galaxy, even if AGN heating does not balance ICM cooling. Finally, we consider entrainment, the process by which ambient material is incorporated into the bubble. Abridged