1. European Southern Observatory, Karl-Schwarzschild-Str 2, Garching bei München, D-85748 Bavaria, Germany
2. School of Physics and Astronomy, University of Birmingham, Edgbaston B15 2TT, UK
3. Cavendish Laboratory, University of Cambridge, 19 J. J. Thomson Avenue, Cambridge CB3 0HE, UK
4. Kavli Institute for Cosmology, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
5. Dipartimento di Fisica, Sezione di Astronomia, Università di Trieste, via G.B. Tiepolo 11, I-34100 Trieste, Italy
6. INAF, Osservatorio Astronomico di Trieste, via G.B. Tiepolo 11, I-34100 Trieste, Italy
7. INFN, Sezione di Trieste, Via Valerio 2, I-34100 Trieste, Italy