Is There a Missing Galaxy Problem at High Redshift ?

We study the evolution of the global stellar mass density in a Λ cold dark matter (ΛCDM) universe using two different types of hydrodynamical simulations (Eulerian TVD and SPH) and the analytical model of Hernquist & Springel (2003). We find that the theoretical calculations all predict both a higher stellar mass density at z ∼ 3 than indicated by current observations, and that the peak of the cosmic star formation rate history should lie at z & 5. Such a star formation history implies that as much as (70%, 30%) of the total stellar mass density today must already have formed by z = (1, 3). Our results suggest that current observations at z ∼ 3 are missing as much as 50% of the total stellar mass density in the Universe, perhaps owing to an inadequate allowance for dust obscuration in star-forming galaxies, limited sample sizes, or cosmic variance. We also compare our results with some of the updated semi-analytic models of galaxy formation. Subject headings: cosmology: theory — stars: formation — galaxies: formation — galaxies: evolution — methods: numerical