1. Dipartimento di Fisica e Astronomia, Università di Bologna, via Gobetti 93/2, I-40129 Bologna, Italy
2. INAF – Osservatorio Astronomico di Bologna, via Gobetti 93/3, I-40129 Bologna, Italy
3. Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
4. Department of Physics, University of Surrey, Guildford GU2 7XH, UK
5. McWilliams Center for Cosmology, Department of Physics, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, PA 15213, USA
6. Kapteyn Astronomical Institute, University of Groningen, Landleven 12, NL-9747 AD Groningen, The Netherlands