Researcher Database

OKAMOTO Takashi
Faculty of Science Physics Quantum Physics
Lecturer

Researcher Profile and Settings

Affiliation

  • Faculty of Science Physics Quantum Physics

Job Title

    Lecturer

URL

Research funding number

  • 50541893

Research Interests

  • Computational Cosmology   

Research Areas

  • Astronomy / Astronomy

Academic & Professional Experience

  • 2017/07 - Today    Hokkaido UniversityFaculty of ScienceLecturer
  • 2013/03 - 2017/06    Hokkaido UniversityFaculty of ScienceAssistant Professor
  • 2012/04 - 2013/03    University of Tsukuba Faculty of Pure and Applied SciencesAssociate Professor
  • 2011    - Associate Professor at Graduate School of Pure and Applied Sciences, University of Tsukuba
  • 2010 - 2011     Senior Researcher at Center for Computational Sciences, University of Tsukuba
  • 2008 - 2010     Assistant Professor at Graduate School of Pure and Applied Sciences, University of Tsukuba
  • 2007 - 2008     Postdoctoral Research Associate at Department of Physics, University of Durham
  • 2004 - 2007     JSPS Postdoctoral Research Fellow at Division of Theoretical Astronomy, National Astronomical Observatory Japan
  • 2001 - 2004     Postdoctoral Research Associate at Department of Physics, Durham University
  • 2001    Yukawa Memorial Fellow at Yukawa Institute for Theoretical Physics, Kyoto University
  • 2001    Research Associate at Graduate School of Science, Kyoto University

Education

  •        - 2001  Hokkaido University  Graduate School, Division of Natural Science  Department of Physics

Association Memberships

  • Astronomical Society of Japan   International Astronomical Union   

Research Activities

Published Papers

  • Hikari Shirakata, Toshihiro Kawaguchi, Taira Oogi, Takashi Okamoto, Masahiro Nagashima
    Monthly Notices of the Royal Astronomical Society 487 (1) 409 - 419 2019/06 [Refereed][Not invited]
     Research paper (scientific journal) 
    We show the Eddington ratio distributions of supermassive black holes at a wide redshift range (0 < z < 8) obtained with a semi-analytic model of galaxy formation. The distribution is broadly consistent with observational estimates at low redshift. We find that the growth rate of black holes at higher redshift is more likely to exceed the Eddington limit because the typical gas fraction of the host galaxies is higher at higher redshift. We also find that the super- Eddington growth is more common for less massive supermassive black holes, supporting an idea that supermassive black holes have been formed via super-Eddington accretion. These results indicate the "slowing down" of cosmic growth of supermassive black holes: the growth of supermassive black holes with a higher Eddington ratio peaks at higher redshift. We also show the effect of the sample selection on the shape of the Eddington ratio distribution functions and find that shallower observations will miss active galactic nuclei with not only the smaller but also higher Eddington ratios.
  • Tamura Yoichi, Mawatari Ken, Hashimoto Takuya, Inoue Akio K., Zackrisson Erik, Christensen Lise, Binggeli Christian, Matsuda Yuichi, Matsuo Hiroshi, Takeuchi Tsutomu T., Asano Ryosuke S., Sunaga Kaho, Shimizu Ikkoh, Okamoto Takashi, Yoshida Naoki, Lee Minju M., Shibuya Takatoshi, Taniguchi Yoshiaki, Umehata Hideki, Hatsukade Bunyo, Kohno Kotaro, Ota Kazuaki
    ASTROPHYSICAL JOURNAL 874 (1) 0004-637X 2019/03 [Refereed][Not invited]
  • Masayuki Tanaka, Masashi Chiba, Kohei Hayashi, Yutaka Komiyama, Takashi Okamoto, Andrew Cooper, Sakurako Okamoto, Lee Spitler
    The Astrophysical Journal 865 (2) id125 - 12 2018/10 [Refereed][Not invited]
     Research paper (scientific journal)
  • Hashimoto Takuya, Laporte Nicolas, Mawatari Ken, Ellis Richard S., Inoue Akio K., Zackrisson Erik, Roberts-Borsani Guido, Zheng Wei, Tamura Yoichi, Bauer Franz E., Fletcher Thomas, Harikane Yuichi, Hatsukade Bunyo, Hayatsu Natsuki H., Matsuda Yuichi, Matsuo Hiroshi, Okamoto Takashi, Ouchi Masami, Pello Roser, Rydberg Claes-Erik, Shimizu Ikkoh, Taniguchi Yoshiaki, Umehata Hideki, Yoshida Naoki
    NATURE 557 (7705) 392 - + 0028-0836 2018/05 [Refereed][Not invited]
  • Nguyen Ngan K., Pettitt Alex R., Tasker Elizabeth J., Okamoto Takashi
    MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 475 (1) 27 - 42 0035-8711 2018/03 [Refereed][Not invited]
  • Hikari Shirakata, Takashi Okamoto, Toshihiro Kawaguchi, Masahiro Nagashima, Tomoaki Ishiyama, Ryu Makiya, Masakazu A. R. Kobayashi, Motohiro Enoki, Taira Oogi, Katsuya Okoshi
    MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 482 (4) 4846 - 4873 0035-8711 2018/02 [Refereed][Not invited]
     Research paper (scientific journal) 
    We present the latest results of a semi-analytic model of galaxy formation, "New Numerical Galaxy Catalogue", which is combined with large cosmological N-body simulations. This model can reproduce statistical properties of galaxies at z < 6.0. We focus on the properties of active galactic nuclei (AGNs) and supermassive black holes, especially on the accretion timescale onto black holes. We find that the number density of AGNs at z < 1.5 and at hard X-ray luminosity 10^{ 44 }< erg/s is underestimated compared with recent observational estimates when we assume the exponentially decreasing accretion rate and the accretion timescale which is proportional to the dynamical time of the host halo or the bulge, as is often assumed in semi-analytic models. We show that to solve this discrepancy, the accretion timescale of such less luminous AGNs instead should be a function of the black hole mass and the accreted gas mass. This timescale can be obtained from a phenomenological modelling of the gas angular momentum loss in the circumnuclear torus and/or the accretion disc. Such models predict a longer accretion timescale for less luminous AGNs at z < 1.0 than bright QSOs whose accretion timescale would be 10^{ 7-8 } yr. With this newly introduced accretion timescale, our model can explain the observed luminosity functions of AGNs at z < 6.0.
  • Ishiki Shohei, Okamoto Takashi, Inoue Akio K.
    MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 474 (2) 1935 - 1943 0035-8711 2018/02 [Refereed][Not invited]
  • Oogi Taira, Enoki Motohiro. Ishiyama Tomoaki, Kobayashi Masakazu A. R., Makiya Ryu, Nagashima Masahiro, Okamoto Takashi, Shirakata Hikari
    Monthly Notices of the Royal Astronomical Society: Letters 471 (1) L21 - L25 2017/10 [Refereed][Not invited]
     Research paper (scientific journal)
  • Ishiki Shohei, OKAMOTO Takashi
    Monthly Notices of the Royal Astronomical Society: Letters 466 (1) L123 - L127 2017/03 [Refereed][Not invited]
     Research paper (scientific journal)
  • Tanaka Satoshi, Yoshikawa Kohji, Okamoto Takashi, Hasegawa Kenji
    PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 67 (4) 0004-6264 2015/08 [Refereed][Not invited]

MISC

  • Formation and evolution of galactic halos in a cluster of galaxies
    ElsevierNuclear Physics B Proceedings Supplements  80-  2000   [Not refereed] [Not invited]
  • Galaxy Distribution in Clusters of Galaxies
    Kluwer AcademicProceedings of the 183rd symposium of the International Astronomical Union held in Kyoto, Japan, August 18-22, 1997  262  1999   [Not refereed] [Not invited]
  • Properties of Galaxies in Rich Clusters
    Astronomical Society of the Pacific,The Physics of Galaxy Formation, ASP Conference Proceedings, Vol. 222  222-  149  2001   [Not refereed] [Not invited]
  • Study of Multiphase Interstellar Matter in a Gas Rich Dwarf Galaxy
    The Astronomical Society of JapanThe Proceedings of the IAU 8th Asian-Pacific Regional Meeting  2-  289  -290  2002   [Not refereed] [Not invited]
  • Environmental Effects on Evolution of Cluster Galaxies
    Astronomical Society of the PacificAstrophysical Supercomputing using Particle Simulations, IAU Symposium #208  435  2003   [Not refereed] [Not invited]
  • Cloud mass function in a gas rich dwarf galaxy
    Astronomical Society of the PacificAstrophysical Supercomputing using Particle Simulations, IAU Symposium #208  441  2003   [Not refereed] [Not invited]
  • Substructure of Galaxy Clusters and Cosmological Constant
    Astronomical Society of the PacificAstrophysical Supercomputing using Particle Simulations, IAU Symposium #208  447  2003   [Not refereed] [Not invited]
  • Morphological Evolution of Cluster Galaxies
    Galaxy Evolution: Theory & Observations (Eds. Vladimir Avila-Reese, Claudio Firmani, Carlos S. Frenk & Christine Allen) Revista Mexicana de Astronomía y Astrofísica (Serie de Conferencias)  17-  98  -99  2003   [Not refereed] [Not invited]
  • Structure of Clusters of Galaxies and Open CDM and rHΛ CDM
    Studies of Galaxies in the Young Universe with New Generation Telescope, Proceedings of Japan-German Seminar  99  -106  2004   [Not refereed] [Not invited]
  • The roles of ram-pressure stripping and minor mergers in the evolution of galaxies
    Outskirts of Galaxy Clusters: Intense Life in the Suburbs. Edited by Antonaldo Diaferio, IAU Colloquium #195  534  -538  2004   [Not refereed] [Not invited]
  • Cosmic cookery: making a stereoscopic 3D animated movie
    Stereoscopic Displays and Virtual Reality Systems XIII. Edited by Woods, Andrew J.; Dodgson, Neil A.; Merritt, John O.; Bolas, Mark T.; McDowall, Ian E. Proceedings of the SPIE  6055-  34  -45  2006   [Not refereed] [Not invited]
  • American Institute of PhysicsORIGIN OF MATTER AND EVOLUTION OF GALAXIES: International Symposium on Origin of Matter and Evolution of Galaxies 2005: New Horizon of Nuclear Astrophysics and Cosmology. AIP Conference Proceedings  847-  442  -444  2006   [Not refereed] [Not invited]
  • Simulations of Coevolving Galaxies and Supermassive Black Holes
    SpringerMapping the Galaxy and Nearby Galaxies, Astrophysics and Space Science Proceedings  367  2008   [Not refereed] [Not invited]
  • Tidal Disruption of Dark Matter Halos Around Proto-globular Cluster
    SpringerMapping the Galaxy and Nearby Galaxies, Astrophysics and Space Science Proceedings  373  2008   [Not refereed] [Not invited]
  • Galaxy Formation
    Astronomical Society of the PacificNew Horizons in Astronomy: Frank N. Bash Symposium 2007 ASP Conference Series, Vol. 393, proceedings of the conference held 14-16 October 2007 at the University of Texas, Austin, Texas, USA. Edited by Anna Frebel, Jus・・・  111  -125  2008   [Not refereed] [Not invited]  
    Astronomical Society of the PacificNew Horizons in Astronomy: Frank N. Bash Symposium 2007 ASP Conference Series, Vol. 393, proceedings of the conference held 14-16 October 2007 at the University of Texas, Austin, Texas, USA. Edited by Anna Frebel, Justyn R. Maund, Juntai Shen, and Michael H. Siegel.
  • Chemical Abundance Patterns in the Local Dwarf Galaxies in the CDM Universe
    Astronomical Society of the PacificPanoramic Views of Galaxy Formation and Evolution ASP Conference Series, Vol. 399, proceedings of the conference held 11-16 December, 2007, at Shonan Village Center, Hayama, Japan. Edited by Tadayuki Kodama, Toru Yama・・・  475  2008   [Not refereed] [Not invited]  
    Astronomical Society of the PacificPanoramic Views of Galaxy Formation and Evolution ASP Conference Series, Vol. 399, proceedings of the conference held 11-16 December, 2007, at Shonan Village Center, Hayama, Japan. Edited by Tadayuki Kodama, Toru Yamada, and Kentaro Aoki
  • American Institute of PhysicsHUNTING FOR THE DARK: THE HIDDEN SIDE OF GALAXY FORMATION. Edited by Victor P. Debattista and Cristina C. Popescu AIP Conference Proceedings, Volume 1240  1240-  399  -402  2010   [Not refereed] [Not invited]
  • Cambridge University PressComputational Star Formation, Proceedings of the International Astronomical Union, IAU Symposium  270-  483  -486  2011   [Not refereed] [Not invited]

Research Grants & Projects

  • Galaxy Formation

Educational Activities

Teaching Experience

  • Special Lecture of Cosmosciences 1
    開講年度 : 2017
    課程区分 : 修士課程
    開講学部 : 理学院
    キーワード : 英文シラバス参照
  • Special Lecture of Cosmosciences 2
    開講年度 : 2017
    課程区分 : 修士課程
    開講学部 : 理学院
    キーワード : 英文シラバス参照
  • Physics I
    開講年度 : 2017
    課程区分 : 学士課程
    開講学部 : 全学教育
    キーワード : 運動、力、運動の法則、仕事、エネルギー、運動量、保存則、剛体、流体、単振動、音と光、干渉、回折
  • Seminar in Classical Mechanics
    開講年度 : 2017
    課程区分 : 学士課程
    開講学部 : 理学部
    キーワード : 古典力学、解析力学、拘束系、一般化座標、ラグランジアン、変分原理、 ハミルトニアン、正準形式、正準変換、ハミルトン・ヤコビ方程式
  • Seminar in Mechanics II
    開講年度 : 2017
    課程区分 : 学士課程
    開講学部 : 理学部
    キーワード : 古典力学、解析力学、拘束系、一般化座標、ラグランジアン、変分原理、 ハミルトニアン、正準形式、正準変換、ハミルトン・ヤコビ方程式
  • Special Lectures for Modern Physics
    開講年度 : 2017
    課程区分 : 学士課程
    開講学部 : 理学部


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