Massive Galaxy Protoclusters in the Early Universe uncovered by the South Pole Telescope

I will next describe an ambitious survey for early structures forming in the Universe, which represents a key science goal for WFIRST and JWST. The sub-millimeter galaxy (SMG) population represent the most intense stellar nurseries in the Universe, with star formation rates of 200-2000 Msun/yr (compared to the Milky Way’s 1 Msun/yr). They contribute significantly to the buildup of the Universe’s stars. SMGs are ubiquitous in distant, massive galaxy “protoclusters”, the precursors of rich galaxy clusters. As such they can elucidate the formation modes of cluster cores, the assembly of the “Brightest Cluster Galaxies”, and the collapse of the cosmic web over large scales. With the South Pole Telescope, we have uncovered a population of massive protoclusters of galaxies in the early (3<z<7) Universe. WFIRST will identify and characterize many such systems at this early formative assembly phase. I will discuss followup with ALMA, HST, Spitzer, and 8m optical telescopes, and what these structures teach us about galaxy growth and the collapse of large scale structure in an evolving Universe.