Solving the angular momentum problem in the cold feedback mechanism of cooling flows

TL;DR

This paper demonstrates that cold clumps in galaxy clusters lose angular momentum efficiently, enabling them to feed the central black hole and sustain a feedback loop that prevents excessive cooling of the intra-cluster medium.

Contribution

It shows that angular momentum loss mechanisms make the cold feedback model a viable solution for regulating cooling flows in galaxy clusters.

Findings

Cold clumps lose angular momentum via drag and collisions.

Angular momentum loss allows rapid accretion onto the black hole.

Cold feedback model avoids problems of Bondi accretion models.

Abstract

We show that cold clumps in the intra--cluster medium (ICM) efficiently lose their angular momentum as they fall in, such that they can rapidly feed the central AGN and maintain a heating feedback process. Such cold clumps are predicted by the cold feedback model, a model for maintaining the ICM in cooling flows hot by a feedback process. The clumps very effectively lose their angular momentum in two channels: the drag force exerted by the ICM and the random collisions between clumps when they are close to the central black hole. We conclude that the angular momentum cannot prevent the accretion of the cold clumps, and the cold feedback mechanism is a viable model for a feedback mechanism in cooling flows. Cold feedback does not suffer from the severe problems of models that are based on the Bondi accretion.