Dark-ages reionization and galaxy formation simulation – IV. UV luminosity functions of high-redshift galaxies

In this paper, we present calculations of the UV luminosity function (LF) from the Dark-ages Reionization And Galaxy-formation Observables from Numerical Simulations project, which combines <it>N</it>-body, semi-analytic and seminumerical modelling designed to study galaxy formation during the Epoch of Reionization. Using galaxy formation physics including supernova feedback, the model naturally reproduces the UV LFs for high-redshift star-forming galaxies from <it>z</it> ∼ 5 through to <it>z</it> ∼ 10. We investigate the luminosity–star formation rate (SFR) relation, finding that variable SFR histories of galaxies result in a scatter around the median relation of 0.1–0.3 dex depending on UV luminosity. We find close agreement between the model and observationally derived SFR functions. We use our calculated luminosities to investigate the LF below current detection limits, and the ionizing photon budget for reionization. We predict that the slope of the UV LF remains steep below current detection limits and becomes flat at <it>M</it><inf>UV</inf> ≳ −14. We find that 48 (17) per cent of the total UV flux at <it>z</it> ∼ 6 (10) has been detected above an observational limit of <it>M</it><inf>UV</inf> ∼ −17, and that galaxies fainter than <it>M</it><inf>UV</inf> ∼ −17 are the main source of ionizing photons for reionization. We investigate the luminosity–stellar mass relation, and find a correlation for galaxies with <it>M</it><inf>UV</inf> < −14 that has the form <f>$M_{\\ast } \\propto 10^{-0.47M_\\mathrm{UV}}$</f>, in good agreement with observations, but which flattens for fainter galaxies. We determine the luminosity–halo mass relation to be <f>$M_\\mathrm{vir} \\propto 10^{-0.35M_\\mathrm{UV}}$</f>, finding that galaxies with <it>M</it><inf>UV</inf> = −20 reside in host dark matter haloes of 1011.0±0.1 M<inf>⊙</inf> at <it>z</it> ∼ 6, and that this mass decreases towards high redshift.