On the Accuracy of Weak Lensing Cluster Mass Reconstructions
Abstract
We study the bias and scatter in mass measurements of galaxy clusters resulting from fitting spherically-symmetric Navarro, Frenk & White (NFW) model to the reduced tangential shear profile measured in weak lensing observations. The reduced shear profiles are generated for ~10^4 cluster-sized halos formed in LCDM cosmology using a cosmological N-body simulation of a 1 Gpc/h box. In agreement with previous studies, we find that the scatter in the weak lensing masses derived using such fitting method has irreducible contributions from the triaxial shapes of cluster-sized halos and uncorrelated large-scale matter projections along the line-of-sight. Additionally, we find that correlated large-scale structure within several virial radii of clusters contributes a smaller, but nevertheless significant, amount to the scatter. The intrinsic scatter due to these physical sources is ~25-30% depending on the cluster mass and redshift. For current, ground-based observations, however, the total scatter should be dominated by shape noise from the finite number of background galaxies used to measure the shear. Importantly, we find that weak lensing mass measurements can have a small, ~5-10%, but non-negligible amount of bias. Given that weak lensing measurements of cluster masses are a powerful way to calibrate cluster mass-observable relations for precision cosmological constraints in the near future, we strongly emphasize that a robust calibration of the mean amount of bias requires detailed simulations which include more observational effects than we consider here. Such a calibration exercise needs to be carried out for each specific weak lensing mass estimation method, as the details of the method determine in part the expected scatter and bias.Keywords
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