Candidate massive galaxies at z similar to 4 in the Dark Energy Survey

Abstract

Using stellar population models, we predicted that the Dark Energy Survey (DES) - due to its special combination of area (5000 deg(2)) and depth (i = 24.3) - would be in the position to detect massive (greater than or similar to 10(11) M-circle dot) galaxies at z similar to 4. We confront those theoretical calculations with the first similar to 150 deg(2) of DES data reaching nominal depth. From a catalogue containing similar to 5 million sources, similar to 26 000 were found to have observed-frame g - r versus r - i colours within the locus predicted for z similar to 4 massive galaxies. We further removed contamination by stars and artefacts, obtaining 606 galaxies lining up by the model selection box. We obtained their photometric redshifts and physical properties by fitting model templates spanning a wide range of star formation histories, reddening and redshift. Key to constrain the models is the addition, to the optical DES bands g, r, i, z, and Y, of near-IR J, H, K-s data from the Vista Hemisphere Survey. We further applied several quality cuts to the fitting results, including goodness of fit and a unimodal redshift probability distribution. We finally select 233 candidates whose photometric redshift probability distribution function peaks around z similar to 4, have high stellar masses [log (M*/M-circle dot) similar to 11.7 for a Salpeter IMF] and ages around 0.1 Gyr, i.e. formation redshift around 5. These propertiesmatch those of the progenitors of the most massive galaxies in the local Universe. This is an ideal sample for spectroscopic follow-up to select the fraction of galaxies which are truly at high redshift. These initial results and those at the survey completion, which we shall push to higher redshifts, will set unprecedented constraints on galaxy formation, evolution, and the re-ionization epoch.