The halo mass function into the dark ages

We use high-resolution N-body simulations to compute the mass function for haloes at redshifts 0-30. By using several runs of different mass resolution and box size, we are able to probe haloes down to a mass range of 10(5) M-circle dot. This allows us to model haloes containing the high redshift population III stars capable of cooling by molecular hydrogen emission as well as early galaxies capable of cooling by atomic hydrogen cooling at virial temperatures of 10(4)K. The mass and redshift range that we have modelled includes haloes favoured as hosts of the sources responsible for reionizing the universe. We account for the effects of finite simulation volume, which tends to suppress the mass function because mass fluctuations on scales larger than the box are not represented, and also adds run to run scatter (cosmic variance) due to finite sampling of the modes that are present. Code to generate our best-fit halo mass function may be downloaded from http://icc.dur.ac.uk/Research/PublicDownloads/genmf-readme.html.