Photometric properties of Lyman-break galaxies at z= 3 in cosmological SPH simulations

We study the photometric properties of Lyman-break galaxies (LBGs) formed by redshift z= 3 in a set of large cosmological smoothed-particle hydrodynamics (SPH) simulations of the Λ cold dark matter (ΛCDM) model. Our numerical simulations include radiative cooling and heating with a uniform UV background, star formation, supernova feedback and a phenomenological model for galactic winds. Analysing a series of simulations of varying box size and particle number allows us to isolate the impact of numerical resolution on our results. We compute spectra of simulated galaxies using a population synthesis model, and derive colours and luminosity functions of galaxies at z= 3 after applying local dust extinction and absorption by the intergalactic medium (IGM). We find that the simulated galaxies have U_n−G and G−R colours consistent with observations, provided that intervening absorption by the IGM is applied. The observed properties of LBGs, including their number density, colours and luminosity functions, can be explained if LBGs are identified with the most massive galaxies at z= 3, having typical stellar mass of M_★∼ 10¹⁰h⁻¹ M_⊙, a conclusion broadly consistent with earlier studies based on hydrodynamic simulations of the ΛCDM model. We also find that most simulated LBGs were continuously forming stars at a high rate for more than 1 Gyr up until z= 3, but with numerous starbursts lying on top of the continuous component. Interestingly, our simulations suggest that more than 50 per cent of the total stellar mass and star formation rate in the Universe are accounted for by galaxies that are not detected in the current generation of LBG surveys.