Emergence of an Ultra-Red Ultra-Massive Galaxy Cluster Core at z=4
Abstract
Recent simulations and observations of massive galaxy cluster evolution predict that the majority of stellar mass build up happens within cluster members by z=2, before cluster virialization. Protoclusters rich with dusty, star-forming galaxies (DSFGs) at z>3 are the favored candidate progenitors for these massive galaxy clusters at z0. We present here the first study analyzing stellar emission along with cold dust and gas continuum emission in a spectroscopically confirmed z=4.002 protocluster core rich with DSFGs, the Distant Red Core (DRC). We combine new HST and Spitzer data with existing Gemini, Herschel, and ALMA observations to derive individual galaxy-level properties, and compare them to coeval field and other protocluster galaxies. All of the protocluster members are massive (>1010 M), but not significantly more so than their coeval field counterparts. Within uncertainty, all are nearly indistinguishable from galaxies on the star-forming vs. stellar mass main-sequence relationship, and on the star formation efficiency plane. Assuming no future major influx of fresh gas, we estimate that these gaseous DSFGs will deplete their gas reservoirs in 300 Myr, becoming the massive quiescent ellipticals dominating cluster cores by z3. Using various methodologies, we derive a total z=4 halo mass of 1014 M, and estimate that the DRC will evolve to become an ultra-massive cluster core of mass 1015 M by z=0.