Henk Hoekstra

Groeningen

'Weak lensing: what one can do with HST mosaics'

We have obtained and analysed HST mosaics of two clusters of galaxies.
We studied the mass distribution using the technique of weak gravitational
lensing. The high number density and superb image quality of HST allow
us to make detailed mass maps. In the case of MS 1054 (z=0.83) we are
able to identify separate peaks in the mass distribution, indicating
we see a cluster forming.