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 $z\sim 0$. 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 ($>10^{10}$ M${}_{\odot }$), 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 $\sim 300$ Myr, becoming the massive quiescent ellipticals dominating cluster cores by $z\sim 3$. Using various methodologies, we derive a total $z=4$ halo mass of $\sim 10^{14}$ M${}_{\odot }$, and estimate that the DRC will evolve to become an ultra-massive cluster core of mass $\gtrsim 10^{15}$ M${}_{\odot }$ by $z=0$.

16 pages, 7 figures, submitted to ApJ with first round of revisions incorporated