Sharpening the Precision of the Sunyaev-Zel'dovich Power Spectrum
  Using both halo model calculations and a large sample of simulated SZ maps,
we demonstrate that high-mass clusters add significant non-Gaussian variance to
measurements of the SZ power spectrum amplitude. The difficulty in correctly
accounting theoretically for the contribution of these objects to the
uncertainty in C_l leads to a reduced sensitivity to \sigma_8. We show that a
simple solution is to mask out the brightest clusters in the map before
measuring the power spectrum. We demonstrate that fairly conservative masking
can reduce the variance and Gaussianize the statistics significantly, thus
increasing the sensitivity to cosmological parameters. Choosing which objects
to mask is non-trivial; we found that using a fixed sky density produced a
well-defined and well-behaved estimate that can easily be applied to real maps.
For example, masking the 10 (90) brightest clusters in a 100 deg^2 SZ map will
improve the sensitivity to C_l by a factor of two at l = 1000 (2000) and 1.5 at
l = 2000 (4000). We show that even in the presence of astrophysical foregrounds
(primary CMB and point sources) and instrument noise, one can increase the
precision on measurements of \sigma_8 by masking up to 0.9 clusters/deg^2.
