Program: GN-2021A-FT-107

This is a ”fourth” trial of our high-score telescope program which was lost by weather, water soaking and COVID-19 in S18A-S20A. Clusters of galaxies are statistical objects by nature, and investigating these systems over cosmic times will require a large sample at each epoch and that free from selection bias. With such motivations, we have been conducting a hybrid cluster search program with HSC on Subaru called “HSC2”, which can not only search for passively evolving red sequence galaxies with broad-band colours but also line emitting star-forming galaxies with narrow-band filters. During the course of this survey, we have identified the new class of objects, namely, ”blue-dominated young clusters” without developed red-sequence. As a pilot spectroscopic follow-up program, we aim to confirm 2 such new systems at z=0.84 with GMOS as well as 1 normal dual (blue+red) clusters for comparison, and investigate the properties of galaxies therein such as star formation rates, metallicities and ionization states. This study will unveil the intrinsic scatter of cluster/galaxy properties depending on the evolutionary phases of clusters even at the same cosmic times.