The effect of the cosmic web on cluster weak lensing mass estimates

In modern hierarchical theories of structure formation, rich clusters of ga laxies form at the vertices of a weblike distribution of matter, with filam ents emanating from them to large distances and with smaller objects formin g and draining in along these filaments. The amount of mass contained in st ructure near the cluster can be comparable to the collapsed mass of the clu ster itself. As the lensing kernel is quite broad along the line of sight a round cluster lenses with typical redshifts z(l) = 0.5, structures many meg aparsecs parsecs 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 form ation in a Lambda -dominated cold dark matter model to quantify the effect that large-scale structure near clusters has upon the cluster masses deduce d from weak lensing analysis. A correction for the scatter in possible obse rved lensing masses should be included when interpreting mass functions fro m weak lensing surveys.