http://arxiv.org/abs/1612.03802
Despite the substantial progress made recently in understanding the role of AGN feedback and associated non-thermal effects, the precise mechanism that prevents the core of some clusters of galaxies from collapsing catastrophically by radiative cooling remains unidentified. In this paper we demonstrate that the environment of a cluster’s core, in terms of its density, temperature, and magnetic field strength, enables the plasma electrons there to emit Cerenkov radiation at the radio frequency of $\lesssim$ 350 Hz, and with a rate considerably exceeding free-free continuum and line emission. However, the same does not apply to the plasmas at the cluster’s outskirts, which is void of such radiation. Owing to its low frequency, the radiation cannot escape, but because the reabsorption process is slower than stimulated emission the emitting gas cools before it reheats. This leaves behind the radiation itself, trapped by the overlying reflective plasma, yet providing enough pressure to maintain quasi-hydrostatic equilibrium. The mass condensation then happens by Rayleigh-Taylor instability, at a rate determined by the outermost (last) radius where Cerenkov radiation can occur. In this way, it is possible to estimate the rate at $\ap 2 M_\odot$~year$^{-1}$, consistent with observational inference. Thus the process appears to provide a natural solution to the long standing problem of `cooling flow’ in clusters.
R. Lieu
Tue, 13 Dec 16
39/77
Comments: 8 pages, 17 equations
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