Universal pressure profile for galaxy clusters

The utility of galaxy clusters for precision cosmology (in particular to constrain $\sigma_8$ and dark energy eq. of state) depends on our ability to determine their mass precisely from observations. Systematic scatter (and bias) in mass measurement needs to be reduced to better than 10%. This paper (http://arxiv.org/abs/0910.1234) uses the representative (a fair sample reflecting their real abundance) of  REXCESS clusters, and fits a generalized NFW profile to observational pressure profiles out to R_500. The scatter in pressure is much smaller at each radius than density, temperature, or entropy (something already emphasized by simulations). Pressure profile has smallest scatter at R_500 because inner parts are affected by cooling and outer by unvirialized clumps. Since SZ effect probes the pressure, this implies that Y_SZ can be more tightly correlated with M_500 than Y_X, and can improve cosmological constraints. Moreover, since SZ signal is not dimmed at high redshifts, SZ can be quite powerful in constraining dark energy and departures from non-gaussianities in the primordial power spectrum.