Kohei Ichikawa

Associate Professor, Faculty of Science and Engineering, Waseda University*Profile is at the time of the award.

2025Inamori Research GrantsScience & Engineering

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Research topics: Revealing most distant supermassive black holes from Subaru/HSC-dark radio sources

Keyword

Summary: There is at least one supermassive black hole (SMBH) at the center of galaxies, yet the detailed origins of their mass growth and formation mechanism remain unknown. I have conducted active galactic nucleus (AGN) surveys using GHz band radio observations, which are highly strong against gas absorption. Through this survey, I discovered "HSC dark" radio sources those are undetected even by the Hyper Suprime-Cam (HSC), an ultra-sensitive optical imaging instrument on the Subaru Telescope. These sources are prime candidates for extremely distant SMBHs in the early universe, where the Lyman-alpha emission line has shifted into the near-infrared wavelengths. In this study, I aim to obtain the first spectroscopic redshifts of these objects and achieve the first spectroscopic confirmation of radio-loud AGNs at redshift z > 8.

Comment

In observational astronomy, there are occasions when we discover very rarely happening or existing objects by surveying the vast volume of the Universe (covering extremely long times and large volumes). Personally, I find this process exciting and consider it as one of the interesting and enjoyable aspects of observational astronomy. In this study, I will investigate such extremely rare objects that have not discovered before, and hope to better understand the origins of the formation and/or growth mechanism of supermassive black holes in the early universe.

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