SIMBAD references

We present the results of a weak lensing survey of six high-redshift (z>0.5), X-ray-selected clusters of galaxies. We have obtained ultra-deep R-band images of each cluster with the Keck Telescope and have measured a weak lensing signal from each cluster. From the background galaxy ellipticities we create two-dimensional maps of the surface mass density of each cluster. We find that the substructure seen in the mass reconstructions typically agree well with substructure in both the cluster galaxy distributions and X-ray images of the clusters. We also measure the one-dimensional radial profiles of the lensing signals and fit these with both isothermal spheres and ``universal'' CDM profiles. We find that the more massive clusters are less compact and not as well fitted by isothermal spheres as the less massive clusters, possibly indicating that they are still in the process of collapse.