Detecting massive galaxies at high redshift using the Dark Energy Survey

The Dark Energy Survey (DES) will be unprecedented in its ability to probe exceptionally large cosmic volumes to relatively faint optical limits. Primarily designed for the study of comparatively low-redshift (z < 2) galaxies with the aim of constraining dark energy, an intriguing byproduct of the survey will be the identification of massive (>10^12.0M_^⊙) galaxies at z ≳ 4. This will greatly improve our understanding of how galaxies form and evolve. By both passively evolving the low-redshift mass function and extrapolating the observed high-redshift mass function, we find that such galaxies should be rare but nonetheless present at early times, with predicted number densities of ∼0.02 deg⁻². The unique combination of depth and coverage that DES provides will allow the identification of such galaxies should they exist – potentially identifying hundreds of such sources. We then model possible high-redshift galaxies and determine their detectability using the DES filter sets and depths. We model sources with a broad range stellar properties and find that for these galaxies to be detected they must be either sufficiently young, high mass and/or relatively dust free (E(B − V) < 0.45) – with these parameters jointly affecting each galaxy's detectability. We also propose colour–colour selection criteria for the identification of both pristine and dusty sources and find that, although contamination fractions will be high, the most reliable candidate massive high-redshift galaxies are likely to be identifiable in the DES data through prioritisation of colour-selected sources.