Since the discovery of the first giant arcs and the weak shear signals, gravitational lensing has produced important progress in cosmology and the physics of galaxies. This effect allows us to measure the dark matter content of lensing systems acting as lenses free of assumptions regarding their dynamical state, and has also consistently provided record breaking high redshift galaxies. Massive galaxy clusters, in particular, are ideal `natural telescopes', as they generate high magnification factors over a large field-of view. The importance of lensing clusters appears clearly in recent ambitious programs implemented with the Hubble Space Telescope (in particular the CLASH multi-cycle Treasury project), and with the recent selection of the ~800 orbit "Hubble Frontier Fields'' Director's initiative: where 4 (and up to 6) massive clusters will be observed at UDF depth with Hubble. We expect to build from these new observations unrivalled datasets of highly-magnified objects, leading to many follow-up observations (multi-wavelength studies, IFU and high resolution spectroscopy). The future is even more promising for lensing clusters, as we expect to discover thousands of them with the EUCLID mission, and the high resolution from the future James Webb Space Telescope (JWST) will give us unique deep and multi-colour data.

In parallel, many developments have been made in the construction of accurate mass models reproducing the lensing effects. Both parametric and non-parametric approaches have been improved in detail and scope prompted by the increasing improvements in data quality. Modelings has also allowed for a better understanding of the accuracy of corrections for source magnification and reconstruction. Important effects, such as the amount and distribution of substructure, the magnification bias and the line-of-sight projection of the lensing mass, are also better understood via the use of numerical simulations, and can be taken into account.

Programme

• Galaxy Clusters and their mass distribution
• Lensing modelling techniques
• Lensed sources at high redshift
• Lensed sources at long wavelengths
• Analysis and follow-up studies of the Frontier Fields

Scientific organizers
Richard Ellis, Jens Hjorth, Jean-Paul Kneib, Marc Postman, Johan Richard, Ian Smail

Contact
Jean-Paul Kneib (jean-paul.kneib @ epfl.ch) and Johan Richard (johan.richard @ univ-lyon1.fr)