CONSTRAINING THE MASS-DISTRIBUTION OF CLUSTER GALAXIES BY WEAK LENSING

Analysing the weak lensing distortions of the images of faint backgrou nd galaxies provides a means to constrain the average mass distributio n of cluster galaxies and potentially to test the extent of their dark matter haloes as a function of the density of their environment. The observable image distortions are a consequence of the interplay betwee n the effects of a global cluster mass distribution and the perturbati ons resulting from individual cluster galaxies. Starting from a recons truction of the cluster mass distribution with conventional techniques , we apply a maximum likelihood method to infer the average properties of an ensemble of cluster galaxies. From simulations this approach is found to be reliable as long as the galaxies including their dark mat ter haloes only contribute a small fraction to the total mass of the s ystem. If their haloes are extended, the galaxies contain a substantia l mass fraction. In this case our method is still applicable in the ou ter regions of clusters, where the surface mass density is low, but yi elds biased estimates of the parameters describing the mass profiles o f the cluster galaxies in the central part of the cluster. In that cas e it will be necessary to resort to more sophisticated strategies by m odelling cluster galaxies and an underlying global mass distribution s imultaneously. We conclude that galaxy-galaxy lensing in clusters prov ides a unique means to probe the presence and extent of dark haloes of cluster galaxies.