Cooling+Heating Flows in Galaxy clusters: Turbulent heating, spectral modelling, and cold mass budget

Mohammad H. Zhoolideh Haghighi, Niayesh Afshordi, Habib. G. Khosroshahi

Published 2018-06-22Version 1

The discrepancy between expected and observed cooling rates of X-ray emitting gas has led to the cooling flow problem at the cores of clusters of galaxies. A variety of models have been proposed to model the observed X-ray spectra and resolve the cooling flow problem, which involves heating the cold gas through different mechanisms. As a result, realistic models of X-ray spectra of galaxy clusters need to involve both heating and cooling mechanisms. In this paper, we argue that the heating time-scale is set by the magnetohydrodynamic (MHD) turbulent viscous heating for the Intracluster plasma, parametrised by the Shakura-Sunyaev viscosity parameter, $\alpha$. Using a cooling+heating flow model, we show that a value of $\alpha\simeq 0.08$ (with 20% scatter) provides improved fits to the X-ray spectra of cooling flow, while at the same time, predicting reasonable cold mass budgets accumulated in the cores of clusters over half the Hubble time. Our inferred values for $\alpha$ based on X-ray spectra are also in line with direct measurements of turbulent pressure in simulations and observations of galaxy clusters. This simple picture unifies astrophysical accretion, as a balance of MHD turbulent heating and cooling, across more than 16 orders of magnitudes in scale, from neutron stars to galaxy clusters.