The kinematical structure of gravitationally lensed arcs

In this paper, the expected properties of the velocity fields of strongly lensed arcs behind galaxy clusters are investigated. The velocity profile along typical lensed arcs is determined by ray-tracing light rays from a model source galaxy through parametric cluster toy models consisting of individual galaxies embedded in a dark cluster halo. We find that strongly lensed arcs of high-redshift galaxies show complex velocity structures that are sensitive to the details of the mass distribution within the cluster, in particular at small scales. From fits to the simulated imaging and kinematic data, we demonstrate that reconstruction of the source velocity field is in principle feasible. Two-dimensional kinematic information obtained with integral field units on large ground-based telescopes in combination with adaptive optics will allow the reconstruction of rotation curves of lensed high redshift galaxies. This makes it possible to determine the mass-to-light ratios of galaxies at redshifts z > 1 out to about 2–3 scalelengths with better than ∼20 per cent accuracy. We also discuss the possibilities of using two-dimensional kinematic information along the arcs to give additional constraints on the cluster lens mass models.