Spiral flows in cool-core galaxy clusters
  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.
