2019MNRAS.486.4880A

We introduce the largest to date survey of massive quiescent galaxies at redshift z ∼ 1.6. With these data, which cover 27.6 deg², we can find significant numbers of very rare objects such as ultra-massive quiescent galaxies that populate the extreme massive end of the galaxy mass function, or dense environments that are likely to become present-day massive galaxy clusters. In this paper, the first in a series, we apply our gzK_s adaptation of the BzK technique to select our z ∼ 1.6 galaxy catalogue and then study the quiescent galaxy stellar mass function with good statistics over M_* ∼ 10^10.2-10^11.7 M_☉ - a factor of 30 in mass - including 60 ultra-massive z ∼ 1.6 quiescent galaxies with M_* > 10^11.5 M_☉. We find that the stellar mass function of quiescent galaxies at z ∼ 1.6 is well represented by the Schechter function over this large mass range. This suggests that the mass-quenching mechanism observed at lower redshifts must have already been well established by this epoch, and that it is likely due to a single physical mechanism over a wide range of mass. This close adherence to the Schechter shape also suggests that neither merging nor gravitational lensing significantly affects the observed quenched population. Finally, comparing measurements of M^*parameters for quiescent and star-forming populations (ours and from the literature), we find hints of an offset (M^*_ SF_> M^*_ PE_), which could suggest that the efficiency of the quenching process evolves with time.