Weak lensing calibration of mass bias in the REFLEX+BCS X-ray galaxy
  cluster catalogue
  The use of large, X-ray selected galaxy cluster catalogues for cosmological
analyses requires a thorough understanding of the X-ray mass estimates. Weak
gravitational lensing is an ideal method to shed light on such issues, due to
its insensitivity to the cluster dynamical state. We perform a weak lensing
calibration of 166 galaxy clusters from the REFLEX and BCS cluster catalogue
and compare our results to the X-ray masses based on scaled luminosities from
that catalogue. To interpret the weak lensing signal in terms of cluster
masses, we compare the lensing signal to simple theoretical Navarro-Frenk-White
models and to simulated cluster lensing profiles, including complications such
as cluster substructure, projected large-scale structure, and Eddington bias.
We find evidence of underestimation in the X-ray masses, as expected, with
$\langle M_{\mathrm{X}}/M_{\mathrm{WL}}\rangle = 0.75 \pm 0.07$ stat. $\pm
0.05$ sys. for our best-fit model. The biases in cosmological parameters in a
typical cluster abundance measurement that ignores this mass bias will
typically exceed the statistical errors.
