Massive passive galaxies at z ~ 1.6

Abstract

We build a K-selected catalog of z ∼ 1.6 gzKs galaxies in the Deep and Wide fields of the Canada-France-Hawaii Legacy Survey, with a final effective area of 27.6 deg². This catalog allows us to recover a representative sample of rare massive passive galaxies (log (M_*/M_☉) > 11.14) and very rare ultra-massive passive galaxies (log (M_*/M_☉) > 11.49). The latter is an important population of galaxies, with significant build-up of stellar mass when the universe was only ∼ 4 Gyr old. This sample of ultra-massive passive galaxies (or UMPEGs) allows us to constrain the bright end of the stellar mass function. Once corrected for Eddington Bias, we find that passive galaxies at this redshift are well described by a Schechter function, as expected in a mass quenching scenario (Peng et al. 2010). Next, we find a lack of massive companions (star-forming or passive) to these UMPEGs and only a handful of lower mass (50% or less the mass of the UMPEG) companions. Using a simple dynamical friction estimate, we find that through merging these companions can at most contribute a ∼ 25% mass growth of these galaxies from z ∼ 1.6 to z ∼ 1. Finally, we recover regions with an over-density of massive passive galaxies as sample environments for proto-clusters with an evolved population. These proto-clusters have an under-density of bright star-forming galaxies, hinting at them being proto-clusters where quenching is largely done.