Comparing Dense Galaxy Cluster Redshift Surveys with Weak Lensing Maps
  We use dense redshift surveys of nine galaxy clusters at $z\sim0.2$ to
compare the galaxy distribution in each system with the projected matter
distribution from weak lensing. By combining 2087 new MMT/Hectospec redshifts
and the data in the literature, we construct spectroscopic samples within the
region of weak-lensing maps of high (70--89%) and uniform completeness. With
these dense redshift surveys, we construct galaxy number density maps using
several galaxy subsamples. The shape of the main cluster concentration in the
weak-lensing maps is similar to the global morphology of the number density
maps based on cluster members alone, mainly dominated by red members. We cross
correlate the galaxy number density maps with the weak-lensing maps. The cross
correlation signal when we include foreground and background galaxies at
0.5$z_{\rm cl}<z<2z_{\rm cl}$ is $10-23$% larger than for cluster members alone
at the cluster virial radius. The excess can be as high as 30% depending on the
cluster. Cross correlating the galaxy number density and weak-lensing maps
suggests that superimposed structures close to the cluster in redshift space
contribute more significantly to the excess cross correlation signal than
unrelated large-scale structure along the line of sight. Interestingly, the
weak-lensing mass profiles are not well constrained for the clusters with the
largest cross correlation signal excesses ($>$20% for A383, A689 and A750). The
fractional excess in the cross correlation signal including foreground and
background structures could be a useful proxy for assessing the reliability of
weak-lensing cluster mass estimates.
