Weighing the Giants – I. Weak-lensing masses for 51 massive galaxy clusters: project overview, data analysis methods and cluster images

This is the first in a series of papers in which we measure accurate weak-lensing masses for 51 of the most X-ray luminous galaxy clusters known at redshifts 0.15. zCl. 0.7, in order to calibrate X-ray and other mass proxies for cosmological cluster experiments. The primary aim is to improve the absolute mass calibration of cluster observables, currently the domi-nant systematic uncertainty for cluster count experiments. Key elements of this work are the rigorous quantification of systematic uncertainties, high quality data reduction and photomet-ric calibration, and the “blind ” nature of the analysis to avoid confirmation bias. Our target clusters are drawn from X-ray catalogs based on the ROSAT All-Sky Survey, and provide a versatile calibration sample for many aspects of cluster cosmology. We have acquired wide-field, high-quality imaging using the Subaru and CFHT telescopes for all 51 clusters, in at