Constraining the faint end of the luminosity function with the APOSTLE cosmological simulations

The LCDM cosmological framework predicts central galaxies of any mass should be surrounded by fainter satellites following the substructure of cold dark matter halos. However, the matching between halo mass and luminosity is not well known in the regime of dwarf galaxies, where the physics of stellar feedback, star formation and reionization play a vital role shaping the faint-end of the luminosity function. Deep surveys from upcoming facilities like the Rubin Observatory LSST and the Roman Space Telescope will provide exciting new constraints on the observed luminosity function of galaxies and, in particular, on the satellite luminosity function of L* as well as of isolated dwarf galaxies in the Local Universe. We use state of the art cosmological hydrodynamical simulations from the APOSTLE project to study the abundance of faint dwarf satellites predicted around central galaxies in the field spanning a wide range in stellar masses (M*=[1e7,1e11] Msun). We find that the combined data on satellite abundance for MW-like galaxies together with that of lower mass hosts can put strong constraints the M*-Mhalo relation, pushing the limits of current abundance matching models below M*=10^8 Msun. Our models promise to help constrain the physics of stellar feedback and reionization on small dark matter halos from observations of the population of faint satellites around dwarfs, data soon to become available from these upcoming observational surveys.