1. Scuola Normale Superiore, Piazza dei Cavalieri 7, I-56126 Pisa, Italy
2. Leiden Observatory, P.O. Box 9513 NL-2300 RA, (NL)
3. Nordita, KTH Royal Institute of Technology and Stockholm University, Roslagstullsbacken 23, SE-10691 Stockholm, Sweden
4. Centro Fermi, Museo Storico della Fisica e Centro Studi e Ricerche ‘Enrico Fermi’, Piazza del Viminale 1, I-00184 Roma, Italy
5. Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
6. Kavli Institute for Cosmology, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
7. Cavendish Laboratory, University of Cambridge, 19 J. J. Thomson Ave., Cambridge CB3 0HE, UK
8. INAF - Osservatorio Astronomico di Brera, Via Brera 28, 20121 Milano, Italy
9. INAF Osservatorio Astronomico di Trieste, Via G. Tiepolo 11, Trieste, Italy
10. Institute de Radioastronomie Millimetrique, St. Martin d’Heres, F-38406, France
11. Kavli Institute of Astronomy and Astrophysics at Peking University, No.5 Yiheyuan Road, Haidian District, Beijing, 100871, China
12. Department of Astronomy, School of Physics, Peking University, Beijing 100871, China