Imanishi, Masatoshi - Astronomical Science Program, SOKENDAI

Assistant Professor Imanishi, Masatoshi

Infrared luminous merging galaxies, Active galactic nuclei, high-redshift quasars, Infrared astronomy, radio astronomy, Subaru telescope, ALMA

It is well known that supermassive black holes (SMBHs) are almost ubiquitously present at the center of galaxies in our universe. A mass-accreting SMBH emits strong radiation from the surrounding accretion disk and is observed as an active galactic nucleus (AGN). An AGN can be much brighter than whole galaxy stellar emission and so plays an important role in our universe in various aspects. I am studying AGNs through multi-wavelength observations.

Gas-rich galaxy mergers are common in our universe. It is predicted that during such mergers, a large amount of material accretes onto the existing SMBHs and luminous AGN activity occurs. However, it is deeply buried in a large amount of nuclear dust and gas, and so is undetectable with the widely conducted optical observations. I have been studying such optically elusive, but intrinsically luminous buried AGNs in gas-rich galaxy mergers at wavelengths of low dust extinction effects (infrared, radio, hard X-rays).

I have been conducting high-spatial-resolution multi-wavelength observations of nearby optically identified AGNs to scrutinize the spatial distribution, dynamics, and physical/chemical properties of dust and gas at the nuclear regions, in order to understand mass-accretion mechanisms onto central SMBHs in AGNs.

I have been investigating the properties and nature of optically identified unobscured AGNs in the distant universe (redshift > 4) discovered with the Subaru very wide field optical survey, through multi wavelength observations.

Imanishi et al. 2020, ApJ, 891, 140 “Subaru Infrared Adaptive Optics-assisted High-spatial-resolution Imaging Search for Luminous Dual Active Galactic Nuclei in Nearby Ultraluminous Infrared GalaxiesD”
Imanishi et al. 2019, ApJS, 241, 19 “ALMA Spatially-resolved Dense Molecular Gas Survey of Nearby Ultraluminous Infrared Galaxies”
Imanishi et al. 2018, ApJL, 853, L25 “ALMA Reveals an Inhomogeneous Compact Rotating Dense Molecular Torus at the NGC 1068 Nucleus”
Imanishi et al. 2016, AJ, 152, 218 “ALMA HCN and HCO+ J =3-2 Observations of Optical Seyfert and Luminous Infrared Galaxies: Confirmation of Elevated HCN-to-HCO+ Flux Ratios in AGNs”
Imanishi et al. 2006, ApJ, 637, 114 “Infrared 3-4 micron spectroscopic investigations of a large sample of nearby ultraluminous infrared galaxies”
Imanishi et al. 2007, AJ, 134, 2366, “Millimeter interferometric HCN(1-0) and HCO+(1-0) observations of luminous infrared galaxies”
Imanishi et al. 2007, ApJS, 171, 72 “A Spitzer IRS low-resolution spectroscopic search for buried AGNs in nearby ultraluminous infrared galaxies : A constraint on geometry between energy sources and dust”
Imanishi et al. 2010, ApJ, 721, 1233 “AKARI IRC infrared 2.5-5 micron spectroscopy of a large sample of luminous infrared galaxies”