4MOST Complete Calibration of the Colour-Redshift Relation (4C3R2)

Accurate knowledge of the redshift distributions of faint samples of galaxies selected by broad-band photometry is a prerequisite for future weak lensing experiments to deliver precision tests of our cosmological model. The most direct way to measure these redshift distributions is spectroscopic follow-up of representative galaxies. For this to be efficient and accurate, targets have to be selected such that they systematically cover a space defined by apparent colours in which there is little variation in redshift at any point. 4C3R2 will follow this strategy to observe over 100 000 galaxies selected by their KiDS-VIKING ugriZYJHKs photometry over a footprint identical to that of the WAVES survey, to constrain the colour-redshift relation with high multiplicity across two-thirds of the colour space of future Euclid and Rubin samples.