The evolution of K_s-selected galaxies in the GOODS/CDFS deep ISAAC field

Abstract

We present estimated redshifts and derived properties of a sample of 1663 galaxies with K_s<= 22 (Vega), selected from 50.4 arcmin² of the Great Observatories Origins Deep Survey/Chandra Deep Field South (GOODS/CDFS) field with deep Infrared Spectrometer and Array Camera (ISAAC) imaging, and make an extensive comparison of their properties with those of the extremely red galaxies (ERGs) selected in the same field. We study in detail the evolution of K_s-selected galaxies up to redshifts z~ 4, and clarify the role of ERGs within the total K_s-band galaxy population. We compute the total K_s-band luminosity function (LF) and compare its evolution with the ERG LF. Up to <z_phot>= 2.5, the bright end of the K_s-band LF shows no sign of decline, and is progressively well reproduced by the ERGs with increasing redshift. We also explore the evolution of massive systems present in our sample: up to 20-25 per cent of the population of local galaxies with assembled stellar mass M > 1 × 10¹¹ M_solar has been formed before redshift z~ 4, and contains ~45-70 per cent of the stellar mass density of the Universe at that redshift. Within our sample, the comoving number density of these massive systems is then essentially constant down to redshift z~ 1.5, by which point most of them have apparently evolved into (I-K_s)-selected ERGs. The remaining massive systems observed in the local Universe are assembled later, at redshifts z<~ 1.5. Our results therefore suggest a twofold assembly history for massive galaxies, in which galaxy/star formation proceeds very efficiently in high mass haloes at very high redshift.