Rescuing the intracluster medium of NGC 5813

TL;DR

This study uses X-ray observations of NGC 5813's intracluster medium to show that mixing of post-shock jet gas is the most effective heating mechanism, challenging shock-based models of ICM thermal regulation.

Contribution

It demonstrates that mixing heating is more efficient than shocks or turbulence in maintaining the ICM's thermal balance in NGC 5813.

Findings

Mixing heating dominates over shocks and turbulence.

Shocks overheat outer regions if they heat inner ICM.

Mixing rescues the outer ICM from cooling flow collapse.

Abstract

We use recent X-ray observations of the intracluster medium (ICM) of the galaxy group NGC 5813 to confront theoretical studies of ICM thermal evolution with the newly derived ICM properties. We argue that the ICM of the cooling flow galaxy group NGC 5813 is more likely to be heated by mixing of post-shock jets' gas residing in hot bubbles with the ICM, than by shocks or turbulent-heating. Shocks thermalize only a small fraction of their energy in the inner regions of the cooling flow; in order to adequately heat the inner part of the ICM, they would overheat the outer regions by a large factor, leading to its ejection from the group. Heating by mixing, that was found to be much more efficient than turbulent-heating and shocks-heating, hence, rescues the outer ICM of NGC 5813 from its predestined fate according to cooling flow feedback scenarios that are based on heating by shocks.