1. Centre for Astrophysics and Supercomputing, Swinburne University of Technology , Hawthorn, VIC 3122 , Australia
2. Department of Astronomy, University of Cape Town , Rondebosch, Cape Town, 7700 , South Africa
3. Department of Physics and Astronomy, University of the Western Cape , Robert Sobukwe Road, Bellville 7535 , South Africa