1. Department of Astrophysics/IMAPP, Radboud University , PO Box 9010, 6500 GL Nijmegen , The Netherlands
2. Leiden Observatory, Leiden University , PO Box 9513, NL-2300 RA Leiden , the Netherlands
3. SRON, Netherlands Institute for Space Research , Nie ls Bohrweg 4, 2333 CA Leiden , the Netherlands
4. South African Astronomical Observatory , PO Box 9, Observatory, 7935 Cape Town , South Africa
5. Department of Astronomy, University of Cape Town , Private Bag X3, Rondebosch 7701 , South Africa
6. Institute of Astronomy, University of Cambridge , Madingley Road, Cambridge CB3 0HA , UK
7. Kavli Institute for Cosmology Cambridge, Institute of Astronomy , Madingley Road, Cambridge CB3 0HA , UK