Millimeter and Submillimeter Studies on the Active Trinity of Gas, Stars, and Black Holes in Seyfert Galaxies

This thesis focuses on understanding the growth and formation mechanism of supermassive black holes (SMBHs), an issue it addresses by investigating the dense interstellar medium that is assumed to be a crucial component of the fuel for SMBHs. The thesis also offers unique guidance on using the Atacama Large Millimeter/submillimeter Array (ALMA) in active galactic nuclei (AGN) research.

The author presents the three major findings regarding SMBH formation and growth: (1) The development of a new diagnostic method for the energy sources in galaxies based on submillimeter spectroscopy, which allows identification of accreting SMBHs even in obscured environments, (2) the discovery that the circumnuclear dense gas disk (CND), with a typical size of a few tens of parsecs, which plays a crucial role in governing the growth of SMBHs, and (3) the discovery that the mass transfer budget from the CND to the central SMBHs can be quantitatively understood with a theoretical model incorporating the circumnuclear starburst as a driver of mass transfer. The thesis skillfully reviews these three findings, which have greatly improved our understanding of the growth mechanism of SMBHs.

Takuma Izumi is a National Astronomical Observatory of Japan (NAOJ) fellow engaged in millimeter/submillimeter investigations of actively mass accreting supermassive black holes (SMBHs). He has particularly studied mass fueling and obscuring mechanisms of those SMBHs in the nearby universe. He is currently also studying the star formation properties of galaxies hosting SMBHs at high redshift universe in order to understand their evolutionary links. He received his B.A. from the School of Science, M.A. in Astronomy and Ph.D. in Astronomy from The University of Tokyo in 2012, 2014 and 2016 respectively. During his M.A., he received a number of prize and awards: 1st prize in the AP-RASC 2013 Student Paper Competition in 2013, and Presidents' and Research Awards for AY 2014 from The University of Tokyo and the School of Science at The University of Tokyo, respectively. From 2014 to 2016, he was awarded a research fellowship for young scientists by the Japan Society for Promotion of Science (JSPS), and his research during his Ph.D. was supported by JSPS.