Ian McCarthy


University of Cambridge


Thermodynamics of the Hot Gas in Galaxy Groups and Clusters

In the currently favoured cold dark matter cosmological model, structure formation proceeds hierarchically with the smallest systems collapsing first.  Progressively larger, more massive systems are formed through the mergers and accretion of smaller objects.  Galaxy groups and clusters (GGCs) sit atop this hierarchy as the largest objects that have had time to collapse under the influence of their own gravity.  While simulations can robustly predict the distribution of dark matter in these systems, much less is known about the formation and evolution of the dominant baryonic component - a hot plasma that fills GGCs known as the intracluster medium (ICM).  In this talk I will summarize our current theoretical understanding of the ICM with an emphasis on the dominant physical processes that set its thermodynamic properties, including gravitational collapse and shock heating, radiative cooling, and feedback from supernovae and active galactic nuclei (AGN).  I will show that comparisons of cosmological hydrodynamical simulations with a wide range of X-ray/optical/radio observations constrain the efficiencies of some of these processes relatively well but that many important questions remain unanswered.  Finally, I will present a discussion of the prospects for further refining our understanding of the ICM in the near future.