Spring 2009 Colloquia

Galaxy clusters, as the largest gravitationally-bound objects in the universe, are powerful cosmological probes of dark energy and dark matter. They are also great sites for studying plasma astrophysics. Galaxy clusters grows hierarchically via mergers and accretions, which shock-heated the intracluster medium (ICM) to very high temperature. The ICM contains rich plasma physics, such as particle diffusion, turbulence, magnetic fields, energy dissipation and shocks. The use of clusters as sensitive cosmological probes, therefore, requires solid understanding of these cluster gas physics. In this talk, I will focus on two pieces of plasma physics in the ICM: particle diffusion and electron-ion equilibration process. I will first discuss why we care about these two processes, then show how these processes introduced gas evolutions based on our models, and finally discuss the effect of these processes on measurements of the ICM and the cosmological parameters derived from these measurements.