Spiral flows in cool-core galaxy clusters

TL;DR

This paper proposes that spiral flows are common in cool-core galaxy clusters, explaining observed features and providing a model that accounts for their thermal, chemical, and dynamic properties, with implications for cooling and feedback mechanisms.

Contribution

It introduces a new analytical model of spiral flows in cool-core clusters, linking observed features to a specific flow structure and dynamics, and suggests all such cores contain these flows.

Findings

Spiral features indicate fast cold flows beneath slow hot inflows.

The model reproduces observed density and temperature profiles of CCs.

Spiral flows can solve the cooling problem with feedback regulation.

Abstract

We argue that bulk spiral flows are ubiquitous in the cool cores (CCs) of clusters and groups of galaxies. Such flows are gauged by spiral features in the thermal and chemical properties of the intracluster medium, by the multi-phase properties of CCs, and by X-ray edges known as cold fronts. We analytically show that observations of piecewise-spiral fronts impose strong constraints on the CC, implying the presence of a cold, fast flow, which propagates below a hot, slow inflow, separated by a slowly rotating, trailing, quasi spiral, tangential discontinuity surface. This leads to the nearly logarithmic spiral pattern, two-phase plasma, \rho \sim r^{-1} density (or T \sim r^{0.4} temperature) radial profile, and ~100kpc size, characteristic of CCs. By advecting heat and mixing the gas, such flows can eliminate the cooling problem, provided that a feedback mechanism regulates the flow. In particular, we present a quasi-steady-state model for an accretion-quenched, composite flow, in which the fast phase is an outflow, regulated by active galactic nucleus bubbles, reproducing the observed low star formation rates and explaining some features of bubbles such as their R_b \propto r size. The simplest two-component model reproduces several key properties of CCs, so we propose that all such cores harbor a spiral flow. Our results can be tested directly in the next few years, for example by ASTRO-H.