The Effect of the Cosmic Web on Cluster Weak Lensing Mass Estimates

In modern hierarchical theories of structure formation, rich clusters of galaxies form at the vertices of a weblike distribution of matter, with filaments emanating from them to large distances and with smaller objects forming and draining in along these filaments. The amount of mass contained in structure near the cluster can be comparable to the collapsed mass of the cluster itself. As the lensing kernel is quite broad along the line of sight around cluster lenses with typical redshifts z_l = 0.5, structures many megaparsecs away from the cluster are essentially at the same location as the cluster itself, when considering their effect on the cluster's weak lensing signal. We use large-scale numerical simulations of structure formation in a Λ-dominated cold dark matter model to quantify the effect that large-scale structure near clusters has upon the cluster masses deduced from weak lensing analysis. A correction for the scatter in possible observed lensing masses should be included when interpreting mass functions from weak lensing surveys.