Stirring the intracluster medium : heat deposition from galaxy motions.




Ghazvini Zadeh, Aida

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Clusters of galaxies are the largest and most massive gravitationally bound objects in the universe. They contain several hundreds to thousands of galaxies orbiting in the gravitational potential well of the cluster. The space between galaxies is filled with a hot plasma that loses its thermal energy via X-ray emission. In the absence of heating sources in the ICM, the radiative cooling of the gas leads to a significant accumulation of cold gas in the cluster core which then should ultimately condense into stars or cold gas clouds (e.g.. Fabian 1994). However, high-resolution X-ray spectroscopy of the hot intracluster gas has revealed that there is little or no signature of significant cool gas in the cluster core. This strongly suggests that there must be other forms of heating mechanisms that offset radiative losses in the intracluster medium (ICM). In this dissertation, we focus on one of the potential heating sources in the ICM, and that involves the kinetic energy in the orbital motions of cluster galaxies. We examine in detail the effects of the heating due to dynamical friction of galaxies on the evolution of the ICM. We find that galaxy heating is immaterial in systems that are in cool core configurations with no other heating mechanisms operating in the ICM. Accordingly. dynamical friction-mediated heating can not be the only heating mechanism in galaxy clusters. The situation is, however, completely different if the systems have experienced sufficient amounts of energy input to warm or hot cores. We show that the role of dynamical friction heating in moderating radiative cooling cannot be neglected in these systems. We also address the results of the last generation of non-radiative cosmological simulations of galaxy clusters (Voit et al. 2005). According to these studies, the radial entropy distribution of the simulated clusters tends to follow a power law at large radii, with cores present in the entropy configurations of these systems at small radii. The origin of the entropy cores is presently unclear. We argue that the generation of entropy cores in non-radiative simulated clusters is the result of galaxy stirring.



Galaxies, Clusters