The average FIR SED of proto-clusters at z = 4

One of the key questions of the observational cosmology is how the environmental dependence of galaxies today formed. Proto-clusters, galaxy overdense regions at high redshift are important laboratory to study the formation history of clusters of galaxies. We perform the first statistic study of far-infrared spectral energy distribution(SED)s of proto-clusters at z ∼ 4 by the stacking analysis of Planck/ AKARI/ IRAS images of proto-clusters at z ∼ 4 selected from the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP) survey. By stacking ∼ 200 proto-clusters, we successfully constrain their average total SEDs in 60-850μm. Our results imply the excess of dusty starburst galaxies with star formation rate several 1000 M_⊙yr-1 in total and obscured AGNs in proto-clusters at z ∼ 4.