Weak Lensing by High-z Clusters of Galaxies

We present the results of our weak lensing survey by high-redshift, X-ray selected clusters of galaxies. We discuss the morphology of the mass distribution from weak lensing analysis and compare this to the X-ray and cluster galaxy distributions. Further, by combining the weak lensing analysis and the cluster galaxy and X-ray lumionosities we derive a median redshift of the faint background galaxy distribution and discuss the implications this has for ultra-high-redshift galaxies and for star formation rates in the early universe.