  The WMAP Q, V, and W band radial profiles of temperature deviation of the
cosmic microwave background (CMB) were constructed for a sample of 31 randomly
selected nearby clusters of galaxies in directions of Galactic latitude $|b| >$
30$^o$. The profiles were compared in detail with the expected CMB
Sunyaev-Zel'dovich effect (SZE) caused by these clusters, with the hot gas
properties of each cluster inferred observationally by applying gas
temperatures as measured by ASCA to isothermal $\beta$ models of the ROSAT
X-ray surface brightness profiles, and with the WMAP point spread function
fully taken into consideration. After co-adding the 31 cluster field, it
appears that WMAP detected the SZE in all three bands. Quantitatively, however,
the observed SZE only accounts for about 1/4 of the expected decrement. The
discrepancy represents too much unexplained extra flux: in the W band, the
detected SZE corresponds on average to 5.6 times less X-ray gas mass within a
10 arcmin radius than the mass value given by the ROSAT $\beta$ model. We
examined critically how the X-ray prediction of the SZE may depend on our
uncertainties in the density and temperature of the hot intracluster plasma,
and emission by cluster radio sources. Although our comparison between the
detected and expected SZE levels is subject to a margin of error, the fact
remains that the average observed SZE depth and profile are consistent with
those of the primary CMB anisotropy, i.e. in principle the average WMAP
temperature decrement among the 31 rich clusters is too shallow to accomodate
any extra effect like the SZE. A unique aspect of this SZE investigation is
that because all the data being analyzed are in the public domain, our work is
readily open to the scrutiny of others.
