Optical selection bias and projection effects in stacked galaxy cluster
  weak lensing
  Cosmological constraints from current and upcoming galaxy cluster surveys are
limited by the accuracy of cluster mass calibration. In particular, optically
identified galaxy clusters are prone to selection effects that can bias the
weak lensing mass calibration. We investigate the selection bias of the stacked
cluster lensing signal associated with optically selected clusters, using as
case study clusters identified by the redMaPPer algorithm in the Buzzard
simulations. We find that at a given cluster halo mass, the residuals of
redMaPPer richness and weak lensing signal are positively correlated. As a
result, for a given richness selection, the stacked lensing signal is biased
high compared with what we would expect from the underlying halo mass
probability distribution. The cluster lensing selection bias can thus lead to
overestimated mean cluster mass and biased cosmology results. We show that this
selection bias largely originates from spurious member galaxies within +/-20 to
60 Mpc/h along the line of sight, highlighting the importance of quantifying
projection effects associated with the broad redshift distribution of member
galaxies in photometric cluster surveys. While our results qualitatively agree
with those in the literature, precise quantitative modelling of selection bias
is needed to achieve the goals of cluster lensing cosmology. An accurate
calibration of the cluster lensing selection bias will require synthetic
catalogues covering a wide range of galaxy-halo connection models.
