2020MNRAS.494..804C

We use a 27.6 deg² survey to measure the clustering of gzK_s-selected quiescent galaxies at z ∼ 1.6, focusing on ultramassive quiescent galaxies. We find that z ∼ 1.6 Ultra-Massive Passively Evolving Galaxies (UMPEGs), which have K_s(AB) < 19.75 (stellar masses of M_*≳10^11.4 M_☉ and mean <M_*> = 10^11.5 M_☉), cluster more strongly than any other known galaxy population at high redshift. Comparing their correlation length, r₀ = 29.77 ± 2.75h^–1Mpc, with the clustering of dark matter (DM) haloes in the Millennium XXL N-body simulation suggests that these z ∼ 1.6 UMPEGs reside in DM haloes of mass M_h ∼ 10^14.1h^–1M_☉. Such very massive z ∼ 1.6 haloes are associated with the ancestors of z ∼ 0 massive galaxy clusters such as the Virgo and Coma clusters. Given their extreme stellar masses and lack of companions with comparable mass, we surmise that these UMPEGs could be the already-quenched central massive galaxies of their (proto)clusters. We conclude that with only a modest amount of further growth in their stellar mass, z ∼ 1.6 UMPEGs could be the progenitors of some of the massive central galaxies of present-day massive galaxy clusters observed to be already very massive and quiescent near the peak epoch of the cosmic star formation.