This work is based in part on observations obtained with MegaPrime/MegaCam, a joint project of CFHT and CEA/DAPNIA, at the Canada-France-Hawaii Telescope (CFHT), which is operated by the National Research Council (NRC) of Canada, the Institut National des Sciences de l’Univers of the Centre National de la Recherche Scientifique of France, and the University of Hawaii. This work is further based in part on observations obtained at the Gemini Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership: the National Science Foundation (United States), the National Research Council (Canada), CONICYT (Chile), the Ministerio de Ciencia, Tecnología e Innovación Productiva (Argentina), the Ministério da Ciência, Tecnologia e Inovação (Brazil) and the Korea Astronomy and Space Science Institute (Republic of Korea). Some of the data presented here were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. We wish to recognise and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. The William Herschel Telescope (WHT) is operated on the island of La Palma by the Isaac Newton Group of Telescopes in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias. This work is based in part on observations at Kitt Peak National Observatory, National Optical Astronomy Observatory, which is operated by the Association of Universities for Research in Astronomy (AURA) under cooperative agreement with the National Science Foundation. We are honoured to be permitted to conduct astronomical research on Iolkam Du’ag (Kitt Peak), a mountain with particular significance to the Tohono O’odham. D.M. is supported by an Australian Research Council (ARC) Future Fellowship (FT160100206). G.F.L. acknowledges support from a Partnership Collaboration Award between the University of Sydney and the University of Edinburgh. D.M. and G.F.L. appreciate the hospitality of the Royal Observatory, Edinburgh, where the final stages of the preparation of this paper were undertaken. B.J.B. thanks the Marsden Fund of the Royal Society of New Zealand. This work has been published under the framework of the IdEx Unistra and benefits from funding from the state managed by the French National Research Agency as part of the investments for the future program. Z.W. is supported by a Dean’s International Postgraduate Research Scholarship at the University of Sydney.