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Professor   OUCHI, Masami

Research Field

  • Galaxy Formation, Observational Cosmology, Early Universe, Optical Near-Infrared Astronomy


  • PhD (Astronomy), The University of Tokyo, 2003

Summary of Research

  •  My research group explores formation of galaxies and supermassive blackholes over the cosmic history with a strong focus on the early epoch of the universe. Having an emphasis on optical near-infrared observations such with Subaru Telescope, we are conducting multi-wavelength observational studies with various large facilities including the ALMA radio telescope. Here is the list of our research topics and the observational facilities to be used.
    1. Early galaxies and the supermassive blackholes
    (Hubble Space Telescope, ALMA, Spitzer Space Telescope etc.)
  • 2. Evolution of large scale structures and the cosmic reionization
    (Subaru Telescope, Hobby-Eberly Telescope Dark Energy Experiment HETDEX, Mileura Wide-Field Array MWA etc.)

    3. Explorations for the cosmic living fossils of nearby early galaxy/supermassive blackholes
    (Subaru Telescope, Keck Telescope, SDSS, Chandra X-ray Observatory etc.)

     Some of the studies above are empowered by the information technology of artificial intelligence including machine learning with and without a training data set. (For example, in the study of #3, we have successfully selected an early galaxy out of about one million objects detected in the Subaru Hyper Suprime-Cam data.) We also compare our observational results with our cosmology model calculations and the other groups’ numerical simulations, uncovering physical origins behind the observational results. (For examples, the observed cosmic star-formation history is explained by the combination of the cosmic expansion and the growth of cosmic structures by gravity. Our discovery of the 10-kpc scale giant carbon gas halos of early galaxies cannot be explained by the state-of-the-art numerical simulations, suggestive of strong outflows that have not been predicted by theoretical models.)
     In the coming 5 years, we will have exciting endeavors to witness the early stage of galaxy formation in the very distant universe with NASA’s James Webb Space Telescope (JWST) to be launched in a couple of years and to unveil the early large-scale structures of the universe under the process of the cosmic reionization with Subaru Prime-Focus Spectrograph (PFS). After the 5 years, we will further expand the scope of our studies with the forthcoming NASA’s WFIRST mission and Thirty Meter Telescope (TMT) program that is the on-going effort here at NAOJ.


  • Full Professor (National Astronomical Observatory of Japan/The University of Tokyo; Cross-Appointment) 2019-
    Associate Professor (The University of Tokyo) 2010-2019
    Carnegie Fellowship (Carnegie Institution of Washington) 2007-2010
    Hubble Fellowship (Space Telescope Science Institute) 2004-2007

Research Achievements or Papers

    * Three major papers
  • M. Ouchi et al. , “Systematic Identification of LAEs for Visible Exploration and Reionization Research Using Subaru HSC (SILVERRUSH). I. Program strategy and clustering properties of ~2000 Lyα emitters at z = 6-7 over the 0.3-0.5 Gpc^2 survey area”, Publications of the Astronomical Society of Japan, Volume 70, Issue SP1, 2018
  • M. Ouchi et al., “Statistics of 207 Lyα Emitters at a Redshift Near 7: Constraints on Reionization and Galaxy Formation Models”, The Astrophysical Journal, Volume 723, Issue 1, pp. 869-894, 2010
  • M. Ouchi et al., “Subaru Deep Survey. V. A Census of Lyman Break Galaxies at z~=4 and 5 in the Subaru Deep Fields: Photometric Properties”, The Astrophysical Journal, Volume 611, Issue 2, pp. 660-684, 2004

Academic Society

  • Astronomical Society of Japan
    American Astronomical Society
    International Astronomical Union

Academic Award

  • Japan Academy Medal Prize (2019)
  • Japan Society for the Promotion of Science (JSPS) Prize (2019)
  • The Young Scientists' Prize from Japan's Minister of Education MEXT (2014)
  • Beatrice M. Tinsley Research Scholar (2013)
  • The ASJ Young Astronomer Award (2008)

Other Activity

Web Page


  • masami.ouchi[at]
    (In the mailing address, replace [at] with @)