Protocluster survey/characterization with NGRST

Protoclusters are interesting laboratories of galaxy evolution. To study their typical properties, first of all, deep and wide surveys are required since their surface density is quite small (a few in deg^2). Based on the deep and wide survey in optical by Hyper Suprime-Cam Subaru Strategic Program, the largest (N=179 in 121 deg^2) and uniform catalog of protoclusters at z~4 was obtained. We performed a stacking analysis of the low-resolution infrared archival data e.g., Planck of these protoclusters and showed the average total infrared (12-850 micron in observed frame) spectral energy distribution (SED) of one protocluster at z~4 for the first time (Kubo et al. 2019ApJ...887..214). Our results show that the total infrared luminosity of a protocluster is much larger than that expected from protocluster members selected in optical; There are significant dusty starburst/AGNs hidden in optical even at z~4. Thus multi-wavelength observations are necessary to characterize galaxies evolving in protoclusters. The deep and wide survey in near infrared by NGRST will show the detailed galaxy population in protoclusters and also discover protoclusters over cosmic time. Our infrared archival data stacking analysis method can be applied for protoclusters selected from NGRST and then the mid to far-infrared SEDs of them can be also discussed.