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Accretion Shocks in Clusters of Galaxies and their SZ Signature from Cosmological Simulations

Cold dark matter (CDM) hierarchical structure formation models predict the existence of large-scale accretion shocks between the virial and turnaround radii of clusters of galaxies. Kocsis et al. (2005) suggest that the Sunyaev-Zel'dovich (SZ) signal associated with such shocks might be observable with the next generation radio interferometer, ALMA. We study the three--dimensional distribution of accretion shocks around individual clusters of galaxies drawn from adaptive mesh refinement (AMR) and smoothed particle hydrodynamics (SPH) simulations of LCDM (dark energy dominated CDM) models. In relaxed clusters, we find two distinct sets of shocks. One set ("virial shocks"), with Mach numbers of 2.5-4, is located at radii 0.9-1.3 Rvir, where Rvir is the spherical infall estimate of the virial radius, covering about 40-50% of the total surface area around clusters at these radii. Another set of stronger shocks ("external shocks") is located farther out, at about 3 Rvir, with large Mach numbers (~100), covering about 40-60% of the surface area. We simulate SZ surface brightness maps of relaxed massive galaxy clusters drawn from high resolution AMR runs, and conclude that ALMA should be capable of detecting the virial shocks in massive clusters of galaxies. More simulations are needed to improve estimates of astrophysical noise and to determine optimal observational strategies.