Stirring Up the Pot: Can Cooling Flows In Galaxy Clusters Be Quenched By Gas Sloshing?

TL;DR

This study uses high-resolution simulations to investigate whether gas sloshing caused by galaxy cluster mergers can heat the core and prevent cooling flows, highlighting the importance of disturbance strength and viscosity effects.

Contribution

It demonstrates through simulations that gas sloshing can significantly heat cluster cores and suppress cooling flows, considering effects of viscosity and repeated mergers.

Findings

Sloshing can raise core entropy by nearly an order of magnitude.

Viscosity reduces gas mixing and heat transfer to the core.

Repeated sloshing events can sustain core heating for several gigayears.

Abstract

X-ray observations of clusters of galaxies reveal the presence of edges in surface brightness and temperature, known as "cold fronts". In relaxed clusters with cool cores, these commonly observed edges have been interpreted as evidence for the "sloshing" of the core gas in the cluster's gravitational potential. Such sloshing may provide a source of heat to the cluster core by mixing hot gas from the cluster outskirts with the cool core gas. Using high-resolution $N$-body/Eulerian hydrodynamics simulations, we model gas sloshing in galaxy clusters initiated by mergers with subclusters. The simulations include merger scenarios with gas-filled and gasless subclusters. The effect of changing the viscosity of the intracluster medium is also explored. We find that sloshing can facilitate heat inflow to the cluster core, provided that there is a strong enough disturbance. In adiabatic simulations, we find that sloshing can raise the entropy floor of the cluster core by nearly an order of magnitude in the strongest cases. If the ICM is viscous, the mixing of gases with different entropies is decreased and consequently the heat flux to the core is diminished. In simulations where radiative cooling is included, we find that though eventually a cooling flow develops, sloshing can prevent the significant buildup of cool gas in the core for times on the order of a Gyr for small disturbances and a few Gyr for large ones. If repeated encounters with merging subclusters sustain the sloshing of the central core gas as is observed, this process can provide a relatively steady source of heat to the core, which can help to prevent a significant cooling flow.