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We use an analytic model to investigate the theoretical uncertainty on the thermal Sunyaev-Zel'dovich (SZ) power spectrum due to astrophysical uncertainties in the thermal structure of the intracluster medium. Our model accounts for star formation and energy feedback (from supernovae and active galactic nuclei) as well as radially dependent non-thermal pressure support due to random gas motions, the latter calibrated by recent hydrodynamical simulations. We compare the model against X-ray observations of low-redshift clusters, finding excellent agreement with observed pressure profiles. Varying the levels of feedback and non-thermal pressure support can significantly change both the amplitude and shape of the thermal SZ power spectrum. Increasing the feedback suppresses power at small angular scales, shifting the peak of the power spectrum to lower . On the other hand, increasing the nonthermal pressure support has the opposite effect, significantly reducing power at large angular scales. In general, including non-thermal pressure at the level measured in simulations has a large effect on the power spectrum, reducing the amplitude by 50% at angular scales of a few arcminutes compared to a model without a non-thermal component. Our results demonstrate that measurements of the shape of the power spectrum can reveal useful information on important physical processes in groups and clusters, especially at high redshift where there exists little observational data. Comparing with the recent South Pole Telescope measurements of the small-scale cosmic microwave background power spectrum, we find our model reduces the tension between the values of σ 8 measured from the SZ power spectrum and from cluster abundances.

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We have identified over 2000 well resolved cluster halos, and also their associated bound subhalos, from the output of a 1024^3 particle cosmological N-body simulation (of box size 320 h^-1 Mpc and softening length 3.2 h^-1 kpc). This has allowed us to measure halo quantities in a statistically meaningful way, and for the first time analyse their distribution for a large and well resolved sample. We characterize each halo in terms of its morphology, concentration, spin, circular velocity and the fraction of their mass in substructure. We also identify those halos that have not yet reached a state of dynamical equilibrium using the virial theorem with an additional correction to account for the surface pressure at the boundary. These amount to 3.4% of our initial sample. For the virialized halos, we find a median of 5.6% of halo mass is contained within substructure, with the distribution ranging between no identified subhalos to 65%. The fraction of mass in substructure increases with halo mass with logarithmic slope of 0.44 +- 0.06. Halos tend to have a prolate morphology, becoming more so with increasing mass. Subhalos have a greater orbital angular momentum per unit mass than their host halo. Furthermore, their orbital angular momentum is typically well aligned with that of their host. Overall, we find that dimensionless properties of dark matter halos do depend on their mass, thereby demonstrating a lack of self-similarity.Comment: Updated to match version published in ApJ, includes longer discussion of the virialisation criterium, 4 figures from original version deemed not essential to the main results and conclusions removed, uses emulate ap