S21B0103

Radio galaxies are galaxies with powerful radio-jets, which can quench star formation in host galaxies. High-z RGs (HzRGs) provide us a key information on the formation and evolution of galaxies in the early universe, in particular, at z>3, where massive galaxies have been rapidly formed. However, only 14 HzRGs have been identified at z>4 so far due to their optical faintness. To build a statistical HzRG sample at z>4 and investigate their formation and evolution, we started searching for HzRGs using a new deep and wide optical imaging data of HSC-SSP and the VLA FIRST survey catalog. We found promising 14 RG candidates at z>4 by the Lyman-break technique. As a pilot study, we succeed in spectroscopically identifying a z=4.7 HzRG among the candidates. In this proposal, we propose a FOCAS spectroscopy to determine redshifts of all the z∼4−5 HzRG candidates observable in this semester (11 targets), to study the radio-AGN feedback on high-z massive galaxies, and characterize them. For the redshift-determined HzRGs, we derive their stellar mass and star formation activity. We will derive the space number densities of HzRGs at z>4 for the first time and constrain a role of HzRGs on the formation of massive galaxies in the early universe.

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