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© 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society

Abstract or Description

We investigate the evolution of the galaxy stellar mass function at high redshift (z ≥ 5) using a pair of large cosmological hydrodynamical simulations: MassiveBlack and MassiveBlack-II. By combining these simulations, we can study the properties of galaxies with stellar masses greater than 108 Mh−1 and (comoving) number densities of log10(ϕ [Mpc−3 dex−1h3]) > −8. Observational determinations of the galaxy stellar mass function at very high redshift typically assume a relation between the observed ultraviolet (UV) luminosity and stellar mass-to-light ratio which is applied to high-redshift samples in order to estimate stellar masses. This relation can also be measured from the simulations. We do this, finding two significant differences with the usual observational assumption: it evolves strongly with redshift and has a different shape. Using this relation to make a consistent comparison between galaxy stellar mass functions, we find that at z = 6 and above the simulation predictions are in good agreement with observed data over the whole mass range. Without using the correct UV luminosity and stellar mass-to-light ratio, the discrepancy would be up to two orders of magnitude for large galaxies (>1010 Mh−1). At z = 5, however, the stellar mass function for low-mass galaxies (<109 Mh−1) is overpredicted by factors of a few, consistent with the behaviour of the UV luminosity function, and perhaps a sign that feedback in the simulation is not efficient enough for these galaxies.



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Published In

Monthly Notices of the Royal Astronomical Society, 429, 3, 2098-2103.