Formation and Evolution of
Galaxy Clusters Across Cosmic Time

The study of very distant galaxy protoclusters (beyond z=4) has strongly developed in the past years. In particular, the range z=5-6 is considered as the epoch in which the progenitors of local galaxy clusters start to form. We present evidence of a rich protocluster at z=5.2 in the GOODS-N field containing an already known overdensity of galaxies around the well-studied submillimeter galaxy HDF850.1. We have selected candidate cluster members (Ly-alpha emitters and Lyman-break galaxies) from the optical 25 medium-band photometric catalog of the project SHARDS (Survey for High-z Absorption Red and Dead Sources). We have spectroscopically confirmed 10 new members via the Ly𝛼 line using OSIRIS at the GranTeCan (GTC), with a success rate of ~80%. Thus, we increased the number of confirmed members in this overdensity from 13 to 23 objects. Combining our dataset with the sample from the literature, we investigated the spatial distribution, the dynamical state and the clustering properties of this protocluster for the first time, revealing a complex structure in formation. Furthermore, by basing on cosmological simulations, we predict the fate of this overdensity at z=0. Considering that we observed only a part of this structure, we claim that it could be the richest protocluster beyond z=5.