[1
] Department of Physics and Astronomy, University of Sheffield, Sheffield S3 7RH, UK
[2
] Instituto de Astrofìsica de Canarias, E-38205 La Laguna, Tenerife, Spain
[3
] Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn, Germany
[4
] Department of Physics, University of Warwick, Coventry CV4 7AL, UK
[5
] European Southern Observatory, Karl-Schwarzschild Str. 2, D-85748 Garching bei München,
Germany
[6
] National Astronomical Research Institute of Thailand, 191 Siriphanich Building, Huay
Kaew Road, Chiang Mai 50200, Thailand
[7
] Square Kilometre Array Organization, Jodrell Bank Observatory, Macclesfield SK11
9DL, UK
[8
] Jodrell Bank Centre for Astrophysics, School of Physics and Astronomy, University
of Manchester, Manchester M13 9PL, UK
[9
] Dark Cosmology Centre, Niels Bohr Institutet, University of Copenhagen, Juliane Maries
Vej 30, DK-2100 Copenhagen, Denmark
[10
] Instituto Nazionale di Astrofisica (INAF) Osservatorio Astronomico di Cagliari, Via
della Scienza 5, I-09047 Selargius (CA), Italy