Reconstructing the distribution of haloes and mock galaxies below the resolution limit in cosmological simulations

We present a method for populating dark matter simulations with haloes of mass below the resolution limit. It is based on stochastically sampling a field derived from the density field of the halo catalogue, using constraints from the conditional halo mass function n(m vertical bar delta). We test the accuracy of the method and show its application in the context of building mock galaxy samples. We find that this technique allows precise reproduction of the two-point statistics of galaxies in mock samples constructed with this method. Our results demonstrate that the main information content of a simulation can be communicated efficiently using only a catalogue of the more massive haloes.