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Acknowledgements We acknowledge the builders of the XMM-LSS and XXL surveys, on
whose work this paper is based. This work is based on observations made with the NASA/ESA
Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is
operated by the Association of Universities for Research in Astronomy, Inc., under NASA
contract NAS5-26555. These observations are associated with programme number 15267.
J.P.W. and E.S.N. acknowledge support from NSERC. R.E.A.C., E.S.N., S.W.A., A.L.K., A.M. and
R.G.M. acknowledge support from NASA grant number HST-GO-15267.002-A. The Cosmic
Dawn Center is funded by the Danish National Research Foundation.
Author contributions J.P.W., R.E.A.C. and E.S.N. analysed the data and wrote the paper. S.W.A.,
A.L.K., A.M., R.G.M., S.A.S. and G.B. provided guidance on the analysis and commented on the
paper.
Competing interests The authors declare no competing interests.Additional information
Correspondence and requests for materials should be addressed to J.P.W.
Peer review information Nature thanks Florence Durret and the other, anonymous, reviewer(s)
for their contribution to the peer review of this work.
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