Weak lensing by high-redshift clusters of galaxies. I. Cluster mass reconstruction

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-ban d images of each cluster with the Keck Telescope and have measured a weak l ensing signal from each cluster. From the background galaxy ellipticities w e create two-dimensional maps of the surface mass density of each cluster. We find that the substructure seen in the mass reconstructions typically ag ree well with substructure in both the cluster galaxy distributions and X-r ay images of the clusters. We also measure the one-dimensional radial profi les of the lensing signals and fit these with both isothermal spheres and " universal" CDM profiles. We iind that the more massive clusters are less co mpact and not as well fitted by isothermal spheres as the less massive clus ters, possibly indicating that they are still in the process of collapse.