Program: GN-2008B-Q-79

We propose to obtain GMOS-N imaging and spectroscopic observations of six recently discovered strong lensing systems found in SDSS rich galaxy clusters at z=0.35-0.6. Five of these systems already have spectroscopically confirmed gravitationally lensed source galaxies with redshifts z=0.77-2.26, and we also propose to confirm the sixth system, which has a source galaxy with an estimated photo-z of 1.2. Our lensed galaxies range from single arcs to partial Einstein rings, and are among the brightest known lensed galaxy images to date, by virtue of their discovery in shallow SDSS imaging data. We propose to obtain high S/N spectra of our already confirmed arcs, new redshifts of other fainter arcs and arclets in our systems, as well as to measure the redshifts of the member galaxies of the lensing clusters to determine the cluster velocity dispersions. These data will allow us to carry out a comparison of cluster mass estimates from strong lensing, velocity dispersions and weak lensing, providing a valuable opportunity to cross-check the cluster mass-observable relationship using these multiple complementary techniques.