Galaxy sizes and the galaxy–halo connection – I. The remarkable tightness of the size distributions

L.Z. acknowledges support from the Science and Technologies Facilities Council and from the Royal Astronomical Society. F.S. acknowledges partial support from a Leverhulme Trust Research Fellowship and from the European Union’s Horizon 2020 programme under the AHEAD project (grant agreement 654215). A.L. acknowledges PRIN MIUR 2017 prot. 20173ML3WW002, Opening the ALMA window on the cosmic evolution of gas, stars, and supermassive black holes.