LARgE Survey. I. Dead Monsters: the Massive End of the Passive Galaxy Stellar Mass Function at Cosmic Noon

Abstract

We introduce the largest to date survey of massive quiescent galaxies at redshift z~1.6. With these data, which cover 27.6 deg^2, 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 adaptation of the BzK technique to select our z~1.6 galaxy catalog and then study the quiescent galaxy stellar mass function with good statistics over M_stars ~ 10^10.2 - 10^11.7 M_sun --- a factor of 30 in mass --- including 60 ultra-massive z~1.6 quiescent galaxies with M_stars > 10^11.5 M_sun. 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 affect 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), that could suggest that the efficiency of the quenching process evolves with time.