Astronomy and Astrophysics – Astrophysics – Cosmology and Extragalactic Astrophysics
Scientific paper
2011-11-09
Astronomy and Astrophysics
Astrophysics
Cosmology and Extragalactic Astrophysics
16 pages, 10 figures, comments welcome; additional info and high resolution figures: http://physics.bgu.ac.il/~ukeshet/SpiralF
Scientific paper
We argue that spiral flows are ubiquitous in the cool cores 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 cores, and by X-ray edges known as cold fronts. We analytically show that observations of piecewise-spiral fronts impose strong constraints on the core, 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 cool cores. 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 AGN 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 cool cores, 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.
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