Program: GN-2020B-Q-123

In LCDM models, galaxy clusters trace the highest density peaks of the large-scale structure. At these dense locations, galaxies are believed to have formed earlier, faster, and perhaps in a different manner compared to typical galaxies. However, nearly all of the empirical evidence for this comes from the fossil record in virialized clusters at z < 2, while most of the cluster galaxies formed at higher redshifts during the protocluster-phase of the collapse. Based on the first 107 sq. deg. of data from the Subaru HyperSuprimeCam Wide Survey, we have recently found an astonishing 179 good protocluster candidates at z~4. We have launched follow-up campaigns for spectroscopy (Subaru, Keck and Gemini), sub-mm data (JCMT and ALMA) and high resolution imaging (HST proposed, PI Overzier). Here, we ask for more GMOS multi-object spectroscopy to continue our spectroscopy started in 2017B/2019B to make a detailed study of these forming cluster environments and their galaxies.