An Optimal and Model-Independent Measurement of the Intracluster
  Pressure Profile I: Methodology and First Applications
  We present a statistically-optimal and model-independent method to extract
the pressure profile of hot gas in the intracluster medium (ICM). Using the
thermal Sunyaev-Zeldovich effect, we constrain the mean pressure profile of the
ICM by appropriately considering all primary cosmic microwave background (CMB)
and instrumental noise correlations, while using the maximum resolution and
sensitivity of all frequency channels. As a first application, we analyze CMB
maps of WMAP 9-year data through a study of the Meta-Catalogue of X-ray
detected Clusters of galaxies (MCXC). We constrain the universal pressure
profile out to 4R_500 with 15-sigma confidence, though our measurements are
only significant out to R_200. Using a temperature profile constrained from
X-ray observations, we measure the mean gas mass fraction out to R_200. Within
statistical and systematic uncertainties, our constraints are compatible with
the cosmic baryon fraction and the expected gas fraction in halos. While Planck
multi-frequency CMB data are expected to reduce statistical uncertainties by a
factor of 20, we argue that systematic errors in determining mass of clusters
dominate the uncertainty in gas mass fraction measurements at the level of 20
percent.
