Researcher Database

Takashi Okamoto
Faculty of Science Physics Quantum Physics
Lecturer

Researcher Profile and Settings

Affiliation

  • Faculty of Science Physics Quantum Physics

Job Title

  • Lecturer

Degree

  • PhD in Science(Hokkaido University)

URL

Research funding number

  • 50541893

J-Global ID

Research Interests

  • 輻射流体力学   数値天文学   数値宇宙論   Computational Cosmology   

Research Areas

  • Natural sciences / Astronomy

Academic & Professional Experience

  • 2017/07 - Today Hokkaido University Faculty of Science Lecturer
  • 2013/03 - 2017/06 Hokkaido University Faculty of Science Assistant Professor
  • 2012/04 - 2013/03 University of Tsukuba Faculty of Pure and Applied Sciences Associate Professor
  • 2011/04 - 2012/03 - 筑波大学 数理物質科学研究科・准教授
  • 2010/12 - 2011/03 University of Tsukuba Center for Computational Sciences
  • 2010 - 2011 Senior Researcher at Center for Computational Sciences, University of Tsukuba
  • 2011 - Associate Professor at Graduate School of Pure and Applied Sciences, University of Tsukuba
  • 2008/12 - 2010/11 University of Tsukuba Graduate School of Pure and Applied Sciences
  • 2008 - 2010 Assistant Professor at Graduate School of Pure and Applied Sciences, University of Tsukuba
  • 2007 - 2008 英ダーラム大学物理学科・博士研究員
  • 2007 - 2008 Postdoctoral Research Associate at Department of Physics, University of Durham
  • 2004 - 2007 National Astronomical Observatory of Japan Division of Theoretical Astronomy
  • 2004 - 2007 JSPS Postdoctoral Research Fellow at Division of Theoretical Astronomy, National Astronomical Observatory Japan
  • 2001 - 2004 英ダーラム大学物理学科・博士研究員
  • 2001 - 2004 Postdoctoral Research Associate at Department of Physics, Durham University
  • 2001 京都大学理学研究科・研修員
  • 2001 Kyoto University Yukawa Institute for Theoretical Physics
  • 2001 Research Associate at Graduate School of Science, Kyoto University
  • 2001 Yukawa Memorial Fellow at Yukawa Institute for Theoretical Physics, Kyoto University

Education

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

Association Memberships

  • 国際天文学連合   日本天文学会   International Astronomical Union   Astronomical Society of Japan   

Research Activities

Published Papers

  • Bakx, Tom J. L. C., Tamura, Yoichi, Hashimoto, Takuya, Inoue, Akio K., Lee, Minju M., Mawatari, Ken, Ota, Kazuaki, Umehata, Hideki, Zackrisson, Erik, Hatsukade, Bunyo, Kohno, Kotaro, Matsuda, Yuichi, Matsuo, Hiroshi, Okamoto, Takashi, Shibuya, Takatoshi, Shimizu, Ikkoh, Taniguchi, Yoshiaki, Yoshida, Naoki
    2020/01 [Refereed][Not invited]
     
    We report on the detection of the [CII] 157.7 $\mu$m emission from the Lyman break galaxy (LBG) MACS0416_Y1 at z = 8.3113, by using the Atacama Large Millimeter/submillimeter Array (ALMA). The luminosity ratio of [OIII] 88 $\mu$m (from previous campaigns) to [CII] is 9.31 $\pm$ 2.6, indicative of hard interstellar radiation fields and/or a low covering fraction of photo-dissociation regions. The emission of [CII] is cospatial to the 850 $\mu$m dust emission (90 $\mu$m rest-frame, from previous campaigns), however the peak [CII] emission does not agree with the peak [OIII] emission, suggesting that the lines originate from different conditions in the interstellar medium. We fail to detect continuum emission at 1.5 mm (160 $\mu$m rest-frame) down to 18 $\mu$Jy (3$\sigma$). This nondetection places a strong limit on the dust spectrum, considering the 137 $\pm$ 26 $\mu$Jy continuum emission at 850 $\mu$m. This suggests an unusually warm dust component (T $>$ 80 K, 90% confidence limit), and/or a steep dust-emissivity index ($\beta_{\rm dust}$ $>$ 2), compared to galaxy-wide dust emission found at lower redshifts (typically T $\sim$ 30 - 50 K, $\beta_{\rm dust}$ $\sim$ 1 - 2). If such temperatures are common, this would reduce the required dust mass and relax the dust production problem at the highest redshifts. We therefore warn against the use of only single-wavelength information to derive physical properties, recommend a more thorough examination of dust temperatures in the early Universe, and stress the need for instrumentation that probes the peak of warm dust in the Epoch of Reionization....
  • 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]
     
    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.
  • 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]
  • Masahiro Nagashima, Motohiro Enoki, Tomoaki Ishiyama, Masakazu A. R. Kobayashi, Ryu Makiya, Kazuyuki Ogura, Takashi Okamoto, Katsuya Okoshi, Taira Oogi, Hikari Shirakata
    Proceedings of the International Astronomical Union 14 (S344) 491 - 494 1743-9213 2018/08 [Refereed][Not invited]
     
    AbstractDwarf galaxies provide us many important clues to understanding of galaxy formation. By using the current version of our own semi-analytic model of galaxy formation, in which cosmic structure forms and evolves based on the cold dark matter model of cosmology, we analyze dwarf galaxies. We find that the model well reproduces many properties such as magnitudes, sizes, and velocity dispersions of, especially, dwarf elliptical galaxies. We also find that the dynamical response of the gravitational potential well of dwarf galaxies to the supernova-induced gas removal plays a very important role to obtain large sizes and small velocity dispersions as observed.
  • Yoichi Tamura, Ken Mawatari, Takuya Hashimoto, Akio K. Inoue, Erik Zackrisson, Lise Christensen, Christian Binggeli, Yuichi Matsuda, Hiroshi Matsuo, Tsutomu T. Takeuchi, Ryosuke S. Asano, Kaho Sunaga, Ikkoh Shimizu, Takashi Okamoto, Naoki Yoshida, Minju Lee, Takatoshi Shibuya, Yoshiaki Taniguchi, Hideki Umehata, Bunyo Hatsukade, Kotaro Kohno, Kazuaki Ota
    ASTROPHYSICAL JOURNAL 874 (1) 0004-637X 2018/06/11 [Refereed][Not invited]
     
    We present the Atacama Large Millimeter/submillimeter Array (ALMA) detection of the [O III] 88 $\mu$m line and rest-frame 90 $\mu$m dust continuum emission in a Y-dropout Lyman break galaxy (LBG), MACS0416_Y1, lying behind the Frontier Field cluster MACS J0416.1-2403. This [O III] detection confirms the LBG with a spectroscopic redshift of $z = 8.3118 \pm 0.0003$, making this object one of the furthest galaxies ever identified spectroscopically. The observed 850 $\mu$m flux density of $137 \pm 26$ $\mu$Jy corresponds to a de-lensed total infrared (IR) luminosity of $L_{\rm IR} = (1.7 \pm 0.3) \times 10^{11} L_{\odot}$ if assuming a dust temperature of $T_{\rm dust} = 50$ K and an emissivity index of $\beta = 1.5$, yielding a large dust mass of $4 \times 10^6 M_{\odot}$. The ultraviolet-to-far IR spectral energy distribution modeling where the [O III] emissivity model is incorporated suggests the presence of a young ($\tau_{\rm age} \approx 4$ Myr), star-forming (SFR $\approx 60 M_{\odot}$ yr$^{-1}$), moderately metal-polluted ($Z \approx 0.2 Z_{\odot}$) stellar component with a mass of $M_{\rm star} = 3 \times 10^8 M_{\odot}$. An analytic dust mass evolution model with a single episode of star-formation does not reproduce the metallicity and dust mass in $\tau_{\rm age} \approx 4$ Myr, suggesting a pre-existing evolved stellar component with $M_{\rm star} \sim 3 \times 10^9 M_{\odot}$ and $\tau_{\rm age} \sim 0.3$ Gyr as the origin of the dust mass.
  • Takuya Hashimoto, Akio K. Inoue, Ken Mawatari, Yoichi Tamura, Hiroshi Matsuo, Hisanori Furusawa, Yuichi Harikane, Takatoshi Shibuya, Kirsten K. Knudsen, Kotaro Kohno, Yoshiaki Ono, Erik Zackrisson, Takashi Okamoto, Nobunari Kashikawa, Pascal A. Oesch, Masami Ouchi, Kazuaki Ota, Ikkoh Shimizu, Yoshiaki Taniguchi, Hideki Umehata, Darach Watson
    PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 71 (4) 0004-6264 2018/06/01 [Refereed][Not invited]
     
    We present new ALMA observations and physical properties of a Lyman Break Galaxy at z=7.15. Our target, B14-65666, has a bright ultra-violet (UV) absolute magnitude, $M_{\rm UV}\approx-22.4$, and has been spectroscopically identified in Ly$\alpha$ with a small rest-frame equivalent width of $\approx4$ \AA. Previous HST image has shown that the target is comprised of two spatially separated clumps in the rest-frame UV. With ALMA, we have newly detected spatially resolved [OIII] 88 $\mu$m, [CII] 158 $\mu$m, and their underlying dust continuum emission. In the whole system of B14-65666, the [OIII] and [CII] lines have consistent redshifts of $7.1520\pm0.0003$, and the [OIII] luminosity, $(34.4\pm4.1)\times10^{8}L_{\rm \odot}$, is about three times higher than the [CII] luminosity, $(11.0\pm1.4)\times10^{8}L_{\rm \odot}$. With our two continuum flux densities, the dust temperature is constrained to be $T_{\rm d}\approx50-60$ K under the assumption of the dust emissivity index of $\beta_{\rm d}=2.0-1.5$, leading to a large total infrared luminosity of $L_{\rm TIR}\approx1\times10^{12}L_{\rm \odot}$. Owing to our high spatial resolution data, we show that the [OIII] and [CII] emission can be spatially decomposed into two clumps associated with the two rest-frame UV clumps whose spectra are kinematically separated by $\approx200$ km s$^{-1}$. We also find these two clumps have comparable UV, infrared, [OIII], and [CII] luminosities. Based on these results, we argue that B14-65666 is a starburst galaxy induced by a major-merger. The merger interpretation is also supported by the large specific star-formation rate (defined as the star-formation rate per unit stellar mass), sSFR$=260^{+119}_{-57}$ Gyr$^{-1}$, inferred from our SED fitting. Probably, a strong UV radiation field caused by intense star formation contributes to its high dust temperature and the [OIII]-to-[CII] luminosity ratio.
  • Takuya Hashimoto, Nicolas Laporte, Ken Mawatari, Richard S. Ellis, Akio. K. Inoue, Erik Zackrisson, Guido Roberts-Borsani, Wei Zheng, Yoichi Tamura, Franz E. Bauer, Thomas Fletcher, Yuichi Harikane, Bunyo Hatsukade, Natsuki H. Hayatsu, Yuichi Matsuda, Hiroshi Matsuo, Takashi Okamoto, Masami Ouchi, Roser Pello, Claes-Erik Rydberg, Ikkoh Shimizu, Yoshiaki Taniguchi, Hideki Umehata, Naoki Yoshida
    NATURE 557 (7705) 392 - + 0028-0836 2018/05/15 [Refereed][Not invited]
     
    A fundamental quest of modern astronomy is to locate the earliest galaxies and study how they influenced the intergalactic medium a few hundred million years after the Big Bang. The abundance of star-forming galaxies is known to decline from redshifts of about 6 to 10, but a key question is the extent of star formation at even earlier times, corresponding to the period when the first galaxies might have emerged. Here we present spectroscopic observations of MACS1149-JD1, a gravitationally lensed galaxy observed when the Universe was less than four per cent of its present age. We detect an emission line of doubly ionized oxygen at a redshift of $9.1096\pm0.0006$, with an uncertainty of one standard deviation. This precisely determined redshift indicates that the red rest-frame optical colour arises from a dominant stellar component that formed about 250 million years after the Big Bang, corresponding to a redshift of about 15. Our results indicate the it may be possible to detect such early episodes of star formation in similar galaxies with future telescopes.
  • Ngan K. Nguyen, Alex R. Pettitt, Elizabeth J. Tasker, Takashi Okamoto
    Monthly Notices of the Royal Astronomical Society 475 (1) 27 - 42 1365-2966 2018/03/21 [Refereed][Not invited]
     
    We explore the effect of different galactic disc environments on the properties of star-forming clouds through variations in the background potential in a set of isolated galaxy simulations. Rising, falling, and flat rotation curves expected in halo-dominated, disc-dominated, and Milky Way-like galaxies were considered, with and without an additional two-arm spiral potential. The evolution of each disc displayed notable variations that are attributed to different regimes of stability, determined by shear and gravitational collapse. The properties of a typical cloud were largely unaffected by the changes in rotation curve, but the production of small and large cloud associations was strongly dependent on this environment. This suggests that while differing rotation curves can influence where clouds are initially formed, the average bulk properties are effectively independent of the global environment. The addition of a spiral perturbation made the greatest difference to cloud properties, successfully sweeping the gas into larger, seemingly unbound, extended structures and creating large arm-interarm contrasts.
  • 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]
     
    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.
  • Shohei Ishiki, Takashi Okamoto, Akio K. Inoue
    Monthly Notices of the Royal Astronomical Society 474 (2) 1935 - 1943 1365-2966 2018 [Refereed][Not invited]
     
    We investigate the impact of radiation pressure on spatial dust distribution inside HII regions using one-dimensional radiation hydrodynamic simulations, which include absorption and reemission of photons by dust. In order to investigate grain-size effects as well, we introduce two additional fluid components describing large and small dust grains in the simulations. Relative velocity between dust and gas strongly depends on the drag force. We include collisional drag force and coulomb drag force. We find that, in a compact HII region, a dust cavity region is formed by radiation pressure. Resulting dust cavity sizes (~0.2 pc) agree with observational estimates reasonably well. Since dust inside an HII region is strongly charged, relative velocity between dust and gas is mainly determined by the coulomb drag force. Strength of the coulomb drag force is about 2 order of magnitude larger than that of the collisional drag force. In addition, in a cloud of mass 105 M⊙, we find that the radiation pressure changes the grain-size distribution insideHII regions. Since large (0.1 μm) dust grains are accelerated more efficiently than small (0.01 μm) grains, the large-to-small grain mass ratio becomes smaller by an order of magnitude compared with the initial one. Resulting dust-size distributions depend on the luminosity of the radiation source. The large and small grain segregation becomes weaker when we assume stronger radiation source, since dust grain charges become larger under stronger radiation and hence coulomb drag force becomes stronger.
  • Taira Oogi, Motohiro Enoki, Tomoaki Ishiyama, Masakazu A. R. Kobayashi, Ryu Makiya, Masahiro Nagashima, Takashi Okamoto, Hikari Shirakata
    MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 471 (1) L21 - L25 0035-8711 2017/10 [Refereed][Not invited]
     
    Super-Eddington mass accretion has been suggested as an efficient mechanism to grow supermassive black holes. We investigate the imprint left by the radiative efficiency of the super-Eddington accretion process on the clustering of quasars using a new semi-analytic model of galaxy and quasar formation based on large-volume cosmological N-body simulations. Our model includes a simple model for the radiative efficiency of a quasar, which imitates the effect of photon trapping for a high mass accretion rate. We find that the model of radiative efficiency affects the relation between the quasar luminosity and the quasar host halo mass. The quasar host halo mass has only weak dependence on quasar luminosity when there is no upper limit for quasar luminosity. On the other hand, it has significant dependence on quasar luminosity when the quasar luminosity is limited by its Eddington luminosity. In the latter case, the quasar bias also depends on the quasar luminosity, and the quasar bias of bright quasars is in agreement with observations. Our results suggest that the quasar clustering studies can provide a constraint on the accretion disc model.
  • Shohei Ishiki, Takashi Okamoto
    MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 466 (1) L123 - L127 0035-8711 2017/03 [Refereed][Not invited]
     
    We have investigated the impact of photoionization and radiation pressure on a dusty starforming cloud using one-dimensional radiation hydrodynamic simulations, which include absorption and re-emission of photons by dust. We find that, in a cloud of mass 10(5)M circle dot and radius 17 pc, the effect of radiation pressure is negligible when star formation efficiency is 2 per cent. The importance of radiation pressure increases with increasing star formation efficiency or an increasing dust-to-gas mass ratio. The net effect of radiation feedback, however, becomes smaller with the increasing dust-to-gas mass ratio, since the absorption of ultraviolet photons by dust grains suppresses photoionization and hence photoheating.
  • Shohei Ishiki, Takashi Okamoto
    Monthly Notices of the Royal Astronomical Society: Letters 466 (1) L123 - L127 1745-3933 2017 [Refereed][Not invited]
     
    We have investigated the impact of photoionization and radiation pressure on a dusty starforming cloud using one-dimensional radiation hydrodynamic simulations, which include absorption and re-emission of photons by dust. We find that, in a cloud of mass 105M⊙ and radius 17 pc, the effect of radiation pressure is negligible when star formation efficiency is 2 per cent. The importance of radiation pressure increases with increasing star formation efficiency or an increasing dust-to-gas mass ratio. The net effect of radiation feedback, however, becomes smaller with the increasing dust-to-gas mass ratio, since the absorption of ultraviolet photons by dust grains suppresses photoionization and hence photoheating.
  • Masayuki Tanaka, Masashi Chiba, Yutaka Komiyama, Mikito Tanaka, Sakurako Okamoto, Takashi Okamoto
    Proceedings of the International Astronomical Union 11 (321) 196 - 198 1743-9221 2016/03/01 [Refereed][Not invited]
     
    We report on the first results from our pilot observation of nearby galaxies with Hyper Suprime-Cam. We have observed two galaxies with mass similar to that of the Milky Way Galaxy and measured the abundance of their satellite galaxies in order to address the missing satellite problem outside of the Local Group. We find that (1) the abundance of dwarf galaxies is smaller by a factor of two than the prediction from one of the current hydro-dynamical simulations and (2) there is a large halo to halo scatter. Our results highlight the importance of a statistical sample of nearby galaxies to address the missing satellite problem.
  • Satoshi Tanaka, Kohji Yoshikawa, Takashi Okamoto, Kenji Hasegawa
    PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 67 (4) 0004-6264 2015/08 [Refereed][Not invited]
     
    We present a new numerical scheme to solve the transfer of diffuse radiation on three-dimensional mesh grids which is efficient on processors with highly parallel architecture such as recently popular GPUs and CPUs with multi- and many-core architectures. The scheme is based on the ray-tracing method and the computational cost is proportional to N-m(5/3),where N-m is the number of mesh grids, and is devised to compute the radiation transfer along each light-ray completely in parallel, with appropriate grouping of the light-rays. We find that the performance of our scheme scales well with the number of adopted CPU cores and GPUs, and also that our scheme is nicely parallelized on a multi-node system by adopting the multiple wave front scheme, and the performance scales well with the amount of computational resources. As numerical tests to validate our scheme and to give a physical criterion for the angular resolution of our ray-tracing scheme, we perform several numerical simulations of the photoionization of neutral hydrogen gas by ionizing radiation sources without the "on-the-spot" approximation, in which the transfer of diffuse radiation by radiative recombination is incorporated in a self-consistent manner.
  • Hikari Shirakata, Takashi Okamoto, Motohiro Enoki, Masahiro Nagashima, Masakazu A.R. Kobayashi, Tomoaki Ishiyama, Ryu Makiya
    Monthly Notices of the Royal Astronomical Society: Letters 450 (1) L6 - L10 1745-3933 2015/04/07 [Refereed][Not invited]
     
    We have investigated effects of dust attenuation on quasar luminosity functions at z ~ 2 using a semi-analytic galaxy formation model combined with a large cosmological N-body simulation. We estimate the dust attenuation of quasars self-consistently with that of galaxies by considering the dust in their host bulges. We find that the luminosity of the bright quasars is strongly dimmed by the dust attenuation, ~2 mag in the B-band. Assuming the empirical bolometric corrections for active galactic nuclei (AGNs) by Marconi et al., we find that this dust attenuation is too strong to explain the B-band and X-ray quasar luminosity functions simultaneously. We consider two possible mechanisms that weaken the dust attenuation. As such a mechanism, we introduce a time delay for AGN activity, that is, gas fuelling to a central black hole starts sometime after the beginning of the starburst induced by a major merger. The other is the anisotropy in the dust distribution. We find that in order to make the dust attenuation of the quasars negligible, either the gas accretion into the black holes has to be delayed at least three times the dynamical time-scale of their host bulges or the dust covering factor is as small as ~0.1.
  • Inoue, A. K., Shimizu, I., Tamura, Y., Matsuo, H., Okamoto, T., Yoshida, N.
    The Astrophysical Journal 2014/01 [Refereed][Not invited]
     
    We investigate the potential use of nebular emission lines in the rest-frame far-infrared (FIR) for determining spectroscopic redshift of z > 8 galaxies with the Atacama Large Millimeter/submillimeter Array (ALMA). After making a line emissivity model as a function of metallicity, especially for the [O III] 88 μm line which is likely to be the strongest FIR line from H II regions, we predict the line fluxes from high-z galaxies based on a cosmological hydrodynamics simulation of galaxy formation. Since the metallicity of galaxies reaches at ~0.2 Z even at z > 8 in our simulation, we expect the [O III] 88 μm line as strong as 1.3 mJy for 27 AB objects, which is detectable at a high significance by <1 hr integration with ALMA. Therefore, the [O III] 88 μm line would be the best tool to confirm the spectroscopic redshifts beyond z = 8....

MISC

  • Ryu Makiya, Motohiro Enoki, Tomoaki Ishiyama, Masakazu A.R. Kobayashi, Masahiro Nagashima, Takashi Okamoto, Katsuya Okoshi, Taira Oogi, Hikari Shirakata  VizieR Online Data Catalog  2016/10  [Not refereed][Not invited]
     
    The mock galaxy catalog calculated by the nu2-GC model descri the paper.

    File light-cone_nu2gc-H2.dat contains the galaxies having B-band apparent magnitude brighter than 28 [AB mag] and located at the redshift range 0<z<20.0, with 1 deg2 aperture.

    We also provide "box-type" mock galaxy catalogs, catalognu2gc-Lz**.dat, that contain the simulated galaxies in the 1.123 (Gpc/h)3 size box at redshift z = 0.0, 0.48, 1.01, 1.97, 2.95, 6.97. For each simulated galaxy, redshift, comoving distance, stellar mass, gas mass, black hole mass, star formation rate, metallicity, and magnitude in B-, V-, SDSS-rp and 2MASS-Ks bands are given.

    Terms of Use : When you write papers using these catalogs, we would be very grateful if you could refer the following two papers: Ishiyama et al., 2015PASJ...67...61I, Makiya et al., 2016PASJ...68...25M.

    (7 data files).
  • 主役はどちら?銀河と共に育つ超巨大ブラックホール
    岩波書店科学  81-  (4)  330  -334  2011  [Not refereed][Not invited]
  • Takayuki R. Saitoh, Hiroshi Daisaka, Eiichiro Kokubo, Junichiro Makino, Takashi Okamoto, Kohji Tomisaka, Keiichi Wada, Naoki Yoshida  COMPUTATIONAL STAR FORMATION  270-  (270)  483  -486  2011  [Not refereed][Not invited]
     
    We studied the formation process of star clusters using high-resolution N-body/smoothed particle hydrodynamics simulations of colliding galaxies. The total number of particles is 1.2 x 10(8) for our high resolution run. The gravitational softening is 5 pc and we allow gas to cool clown to similar to 10 K. During the first encounter of the collision, a giant filament consists of cold and dense gas found between the progenitors by shock compression. A vigorous starburst took place in the filament, resulting in the formation of star clusters. The mass of these star clusters ranges from 10(5-8) M-circle dot. These star clusters formed hierarchically: at first small star clusters formed, and then they merged via gravity, resulting in larger star clusters.
  • Takayuki R. Saitoh, Hiroshi Daisaka, Eiichiro Kokubo, Junichiro Makino, Takashi Okamoto, Kohji Tomisaka, Keiichi Wada, Naoki Yoshida  COMPUTATIONAL STAR FORMATION  270-  (270)  483  -486  2011  [Not refereed][Not invited]
     
    We studied the formation process of star clusters using high-resolution N-body/smoothed particle hydrodynamics simulations of colliding galaxies. The total number of particles is 1.2 x 10(8) for our high resolution run. The gravitational softening is 5 pc and we allow gas to cool clown to similar to 10 K. During the first encounter of the collision, a giant filament consists of cold and dense gas found between the progenitors by shock compression. A vigorous starburst took place in the filament, resulting in the formation of star clusters. The mass of these star clusters ranges from 10(5-8) M-circle dot. These star clusters formed hierarchically: at first small star clusters formed, and then they merged via gravity, resulting in larger star clusters.
  • Takashi Okamoto  HUNTING FOR THE DARK: THE HIDDEN SIDE OF GALAXY FORMATION  1240-  399  -402  2010  [Not refereed][Not invited]
     
    We study the formation histories and present-day structure of galactic subsystems formed in a high resolution hydrodynamic simulation of a Milky Way-sized galaxy. The simulated satellites span nearly 4 orders of magnitude in luminosity but have a very similar mass within their inner 600 pc with very little scatter. This is in agreement with the recent measurements for dwarf spheroidal galaxies (dSphs). Interestingly, subhaloes with circular velocity around 20 km/s sometimes host satellites that are as bright as the classical satellites and sometimes they are found as completely dark objects. We find that there is a critical circular velocity at the epoch of reionization, below which haloes fail to host star formation and found as "dark satellites" today.
  • Takashi Okamoto  AIP Conference Proceedings  1240-  399  -402  2010  [Not refereed][Not invited]
     
    We study the formation histories and present-day structure of galactic subsystems formed in a high resolution hydrodynamic simulation of a Milky Way-sized galaxy. The simulated satellites span nearly 4 orders of magnitude in luminosity but have a very similar mass within their inner 600 pc with very little scatter. This is in agreement with the recent measurements for dwarf spheroidal galaxies (dSphs). Interestingly, subhaloes with circular velocity around 20 km/s sometimes host satellites that are as bright as the classical satellites and sometimes they are found as completely dark objects. We find that there is a critical circular velocity at the epoch of reionization, below which haloes fail to host star formation and found as "dark satellites" today. © 2010 American Institute of Physics.
  • 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
  • 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.
  • 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]
  • 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]
  • 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
  • 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.
  • 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]
  • 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]
  • 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]
  • 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]
  • 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]
  • 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]
  • 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]
  • 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]
  • Morphological evolution of cluster galaxies
    T Okamoto, M Nagashima  GALAXY EVOLUTION: THEORY AND OBSERVATIONS  17-  98  -99  2003  [Not refereed][Not invited]
     
    We investigate environmental effects on morphology evolution of bright cluster galaxies (L > L.) in a Lambda-dominated cold dark matter universe using a combination of N-body simulations and semi-analytic (SA) model. We normalize our model parameters to reproduce the properties of local galaxies, and then we study how ram pressure stripping (RPS) and small starburst triggered by a minor merger (minor burst) affect the morphologies of cluster galaxies. We find that the morphological fraction of galaxies with intermediate bulge-to-total luminosity ratios (B/Ts) cannot be reproduced and the effect of the RPS is negligible unless we consider the minor burst.
  • 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]
  • 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]
  • 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]
  • 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]
  • 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]
  • 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]
  • 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]
  • 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]
  • 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]
  • 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]
  • 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]
  • Formation and evolution of galactic halos in a cluster of galaxies
    ElsevierNuclear Physics B Proceedings Supplements  80-  2000  [Not refereed][Not invited]
  • 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]
  • 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]

Research Grants & Projects

Educational Activities

Teaching Experience

  • Astrophysics 1
    開講年度 : 2018
    課程区分 : 修士課程
    開講学部 : 理学院
    キーワード : 宇宙物理学,宇宙論、宇宙の構造形成
  • Astrophysics 2
    開講年度 : 2018
    課程区分 : 修士課程
    開講学部 : 理学院
    キーワード : 宇宙物理学,銀河形成,銀河進化、星間物質、ガス運動、星形成
  • Special Lecture of Cosmosciences 1
    開講年度 : 2018
    課程区分 : 修士課程
    開講学部 : 理学院
    キーワード : Cosmology, structure formation, galaxies
  • Special Lecture of Cosmosciences 2
    開講年度 : 2018
    課程区分 : 修士課程
    開講学部 : 理学院
    キーワード : Cosmology, structure formation, galaxies
  • Introduction to Modern Physics
    開講年度 : 2018
    課程区分 : 修士課程
    開講学部 : 理学院
    キーワード : 現代物理学、ナノテクノロジー、デバイス物理、エントロピー、核力と原子核の構造、相転移、統計物理学、生命現象、宇宙論、低次元系
  • Inter-Graduate School Classes(General Subject):Natural and Applied Sciences
    開講年度 : 2018
    課程区分 : 修士課程
    開講学部 : 大学院共通科目
    キーワード : 現代物理学、ナノテクノロジー、デバイス物理、エントロピー、核力と原子核の構造、相転移、統計物理学、生命現象、宇宙論、低次元系
  • Seminar in Mechanics II
    開講年度 : 2018
    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 : 2018
    課程区分 : 学士課程
    開講学部 : 理学部
  • Reading of Original Articles in Physics II
    開講年度 : 2018
    課程区分 : 学士課程
    開講学部 : 理学部
    キーワード : 物理学、量子力学、統計力学、電磁気学
  • Arts and Science Courses in English 1
    開講年度 : 2018
    課程区分 : 学士課程
    開講学部 : 国際本部
    キーワード : 現代物理学、ナノテクノロジー、デバイス物理、エントロピー、核力と原子核の構造、相転移、統計物理学、生命現象、宇宙論、低次元系


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