Researcher basic information

• PhD in Science, Hokkaido University

• https://researchmap.jp/read0152721?lang=en

• https://jglobal.jst.go.jp/detail?JGLOBAL_ID=201001086358550704
• http://astro3.sci.hokudai.ac.jp/~okamoto/
• http://www.ccs.tsukuba.ac.jp/Astro/Members/takashi/

• 50541893

• 201001086358550704

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

• Natural Science, Astronomy

• Bachelor's degree program, School of Science
• Master's degree program, Graduate School of Science
• Doctoral (PhD) degree program, Graduate School of Science

Research activity information

• Mar. 2022, Astronomical Society of Japan, PASJ Excellent Paper Award
  Big Three Dragons: A z = 7.15 Lyman-break galaxy detected in [O III] 88 μm, [C II] 158μm, and dust continuum with ALMA
  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

• Modeling supernova feedback in galaxy formation simulations with energy-conserving momentum injection
  Takashi Okamoto
  Publications of the Astronomical Society of Japan, 09 May 2026
  Scientific journal
• A warm ultraluminous infrared galaxy just 600 million years after the big bang
  T. J. L. C. Bakx; Laura Sommovigo; Yoichi Tamura; Renske Smit; Andrea Ferrara; Hiddo Algera; Susanne Aalto; Duncan Bossion; Stefano Carniani; Clarke Esmerian; Masato Hagimoto; Takuya Hashimoto; Bunyo Hatsukade; Edo Ibar; Hanae Inami; Akio K. Inoue; Kirsten Knudsen; Nicolas Laporte; Ken Mawatari; Juan Molina; Gunnar Nyman; Takashi Okamoto; Andrea Pallottini; W. M. C. Sameera; Hideki Umehata; Wouter Vlemmings; Naoki Yoshida
  MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, 544, 2, 1502, 1513, Dec. 2025, [Peer-reviewed]
  English, Scientific journal
• Comparison of simulations and semi-analytical model for warm dark matter subhalo mass functions
  Mizuki Ono; Takashi Okamoto; Shin'ichiro Ando; Tomoaki Ishiyama
  PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN, 77, 5, 1152, 1161, Oct. 2025, [Peer-reviewed], [Corresponding author]
  English, Scientific journal
• The origin of the metallicity difference between star-forming and passive galaxies: Insights from the ν²GC semi-analytic model
  Qiansheng Liu; Takashi Okamoto; Taira Oogi; Masahiro Nagashima
  PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN, 77, 5, 1016, 1024, 07 Oct. 2025, [Peer-reviewed], [Corresponding author]
  English, Scientific journal, 45252374;31948547
• The evolution of supermassive black hole mass–bulge mass relation by a semi-analytical model, ν2GC
  Tatsuki Shimizu; Taira Oogi; Takashi Okamoto; Masahiro Nagashima; Motohiro Enoki
  Monthly Notices of the Royal Astronomical Society, 531, 1, 851, 858, Oxford University Press (OUP), 13 May 2024, [Peer-reviewed], [Corresponding author]
  English, Scientific journal, ABSTRACT
  
  We have investigated the redshift evolution of the relationship between supermassive black hole (SMBH) mass and host bulge mass using a semi-analytical galaxy formation model ν2GC. Our model reproduces the relation in the local universe well. We find that, at high redshift (z ≳ 3), two sequences appear in the SMBH mass–bulge mass plane. The emergence of these two sequences can be attributed to the primary triggers of the growth of the SMBHs and bulges: galaxy mergers and disc instabilities. The growth of SMBHs and bulges as a result of galaxy mergers is responsible for giving rise to the high-mass sequence, in which SMBHs are more massive for a given host bulge mass than in the low-mas sequence. Conversely, disc instabilities are accountable for the emergence of the low-mass sequence. At lower redshifts, galaxy mergers tend to become increasingly deficient in gas, resulting in a preferential increase of bulge mass without a corresponding growth in SMBH mass. This has the effect of causing galaxies in the upper sequence to shift towards the lower one on the SMBH mass–bulge mass plane. The galaxies that undergo dry mergers serve to bridge the gap between the two sequences, eventually leading to convergence into a single relation known in the local universe. Our results suggest that the observations of the SMBH mass–bulge mass relation in high redshifts can provide insight into their growth mechanisms.
• Cloud-cloud collisions triggering star formation in galaxy simulations
  Horie, Shu; Okamoto, Takashi; Habe, Asao
  Monthly Notices of the Royal Astronomical Society, Feb. 2024, [Peer-reviewed]
  Scientific journal, Cloud-cloud collisions (CCCs) are expected to compress gas and trigger star formation. However, it is not well understood how the collisions and the induced star formation affect galactic-scale properties. By developing an on-the-fly algorithm to identify CCCs at each time-step in a galaxy simulation and a model that relates CCC-triggered star formation to collision speeds, we perform simulations of isolated galaxies to study the evolution of galaxies and giant molecular clouds (GMCs) with prescriptions of self-consistent CCC-driven star formation and stellar feedback. We find that the simulation with the CCC-triggered star formation produces slightly higher star formation rates and a steeper Kennicutt-Schmidt relation than that with a more standard star formation recipe, although collision speeds and frequencies are insensitive to the star formation models. In the simulation with the CCC model, about $70{ { \ \rm per\ cent } }$ of the stars are born via CCCs, and colliding GMCs with masses of $\approx 10^{5.5}\, \mbox{$\rm M_{\odot}$}$ are the main drivers of CCC-driven star formation. In the simulation with the standard star formation recipe, about 50 per cent of stars are born in colliding GMCs even without the CCC-triggered star formation model. These results suggest that CCCs may be one of the most important star formation processes in galaxy evolution. Furthermore, we find that a post-processing analysis of CCCs, as used in previous studies in galaxy simulations, may lead to slightly greater collision speeds and significantly lower collision frequencies than the on-the-fly analysis....
• The impact of bar origin and morphology on stellar migration
  Elizabeth J Iles; Alex R Pettitt; Takashi Okamoto; Daisuke Kawata
  Monthly Notices of the Royal Astronomical Society, 09 Nov. 2023, [Peer-reviewed]
  English, Scientific journal
• The 300 pc Resolution Imaging of a z = 8.31 Galaxy: Turbulent Ionized Gas and Potential Stellar Feedback 600 Million Years after the Big Bang
  Yoichi Tamura; Tom J. L. C. Bakx; Akio K. Inoue; Takuya Hashimoto; Tsuyoshi Tokuoka; Chihiro Imamura; Bunyo Hatsukade; Minju M. Lee; Kana Moriwaki; Takashi Okamoto; Kazuaki Ota; Hideki Umehata; Naoki Yoshida; Erik Zackrisson; Masato Hagimoto; Hiroshi Matsuo; Ikkoh Shimizu; Yuma Sugahara; Tsutomu T. Takeuchi
  The Astrophysical Journal, 952, 1, 01 Jul. 2023, [Peer-reviewed]
  English, Scientific journal
• Massive core/star formation triggered by cloud–cloud collision – II. High-speed collisions of magnetized clouds
  Nirmit Sakre; Asao Habe; Alex R Pettitt; Takashi Okamoto; Rei Enokiya; Yasuo Fukui; Takashi Hosokawa
  Monthly Notices of the Royal Astronomical Society, 11 May 2023, [Peer-reviewed]
  Scientific journal
• Updated Measurements of [O III] 88 μm, [C II] 158 μm, and Dust Continuum Emission from a z = 7.2 Galaxy
  Ren, Yi W.; Fudamoto, Yoshinobu; Inoue, Akio K.; Sugahara, Yuma; Tokuoka, Tsuyoshi; Tamura, Yoichi; Matsuo, Hiroshi; Kohno, Kotaro; Umehata, Hideki; Hashimoto, Takuya; Bouwens, Rychard J.; Smit, Renske; Kashikawa, Nobunari; Okamoto, Takashi; Shibuya, Takatoshi; Shimizu, Ikkoh
  The Astrophysical Journal, 945, 69, 01 Mar. 2023, [Peer-reviewed]
  Scientific journal, We present updated measurements of the [O III] 88 μm, [C II] 158 μm, and dust continuum emission from a star-forming galaxy at z = 7.212, SXDF-NB1006-2, by utilizing Atacama Large Millimeter/submillimeter Array (ALMA) archival data sets analysed in previous studies and data sets that have not been analysed before. The follow-up ALMA observations with higher angular resolution and sensitivity reveal a clumpy structure of the [O III] emission on a scale of 0.32-0.85 kpc. We also combined all the ALMA [O III] ([C II]) data sets and updated the [O III] ([C II]) detection to 5.9σ (3.6σ-4.5σ). The non-detection of [C II] with data from the REBELS large program implies the incompleteness of spectral-scan surveys using [C II] to detect galaxies with high star formation rates (SFRs) but marginal [C II] emission at high-z. The dust continuum at 90 and 160 μm remains undetected, indicating little dust content of <3.9 × 10⁶ M _⊙ (3σ), and we obtained a more stringent constraint on the total infrared luminosity. We updated the [O III]/[C II] luminosity ratios to 10.2 ± 4.7 (6.1 ± 3.5) and 20 ± 12 (9.6 ± 6.1) for the 4.5σ and 3.6σ [C II] detections, respectively, where the ratios in the parentheses are corrected for the surface brightness dimming effect on the extended [C II] emission. We also found a strong [C II] deficit (0.6-1.3 dex) between SXDF-NB1006-2 and the mean L _{[C II]}-SFR relation of galaxies at 0 < z < 9....
• CO(J = 1-0) Mapping Survey of 64 Galaxies in the Fornax Cluster with the ALMA Morita Array
  Morokuma-Matsui, Kana; Bekki, Kenji; Wang, Jing; Serra, Paolo; Koyama, Yusei; Morokuma, Tomoki; Egusa, Fumi; For, Bi-Qing; Nakanishi, Kouichiro; Koribalski, Bärbel S.; Okamoto, Takashi; Kodama, Tadayuki; Lee, Bumhyun; Maccagni, Filippo M.; Miura, Rie E.; Espada, Daniel; Takeuchi, Tsutomu T.; Yang, Dong; Lee, Minju M.; Ueda, Masaki; Matsushita, Kyoko
  The Astrophysical Journal Supplement Series, Dec. 2022, [Peer-reviewed]
  Scientific journal, We conduct a ¹²C¹⁶O(J = 1-0) (hereafter CO) mapping survey of 64 galaxies in the Fornax cluster using the Atacama Large Millimeter/submillimeter Array Morita array in cycle 5. CO emission is detected from 23 out of the 64 galaxies. Our sample includes dwarf, spiral, and elliptical galaxies with stellar masses of M _star ~ 10^6.3-11.6 M _⊙. The achieved beam size and sensitivity are 15″ × 8″ and ~12 mJy beam^-1 at the velocity resolution of ~10 km s^-1, respectively. We study the cold gas (molecular and atomic gas) properties of 38 subsamples with M _star > 10⁹ M _⊙ combined with literature H I data. We find that (1) the low star formation (SF) activity in the Fornax galaxies is caused by the decrease in the cold gas mass fraction with respect to stellar mass (hereafter, gas fraction) rather than the decrease of the SF efficiency from the cold gas; (2) the atomic gas fraction is more heavily reduced than the molecular gas fraction of such galaxies with low SF activity. A comparison between the cold gas properties of the Fornax galaxies and their environmental properties suggests that the atomic gas is stripped tidally and by the ram pressure, which leads to the molecular gas depletion with an aid of the strangulation and consequently SF quenching. Preprocesses in the group environment would also play a role in reducing cold gas reservoirs in some Fornax galaxies....
• Origin of highly r-process-enhanced stars in a cosmological zoom-in simulation of a Milky Way-like galaxy
  Yutaka Hirai; Timothy C Beers; Masashi Chiba; Wako Aoki; Derek Shank; Takayuki R Saitoh; Takashi Okamoto; Junichiro Makino
  Monthly Notices of the Royal Astronomical Society, 14 Nov. 2022, [Peer-reviewed]
  Scientific journal, The r-process-enhanced (RPE) stars provide fossil records of the assembly history of the Milky Way (MW) and the nucleosynthesis of the heaviest elements. Observations by the R-Process Alliance (RPA) and others have confirmed that many RPE stars are associated with chemo-dynamically tagged groups, which likely came from accreted dwarf galaxies of the MW. However, we do not know how RPE stars are formed. Here, we present the result of a cosmological zoom-in simulation of an MW-like galaxy with r-process enrichment, performed with the highest resolution in both time and mass. Thanks to this advancement, unlike previous simulations, we find that most highly RPE (r-II; [Eu/Fe] > +0.7) stars are formed in low-mass dwarf galaxies that have been enriched in r-process elements for [Fe/H] $\lt -2.5$, while those with higher metallicity are formed in situ, in locally enhanced gas clumps that were not necessarily members of dwarf galaxies. This result suggests that low-mass accreted dwarf galaxies are the main formation site of r-II stars with [Fe/H] $\, \lt -2.5$. We also find that most low-metallicity r-II stars exhibit halo-like kinematics. Some r-II stars formed in the same halo show low dispersions in [Fe/H] and somewhat larger dispersions of [Eu/Fe], similar to the observations. The fraction of simulated r-II stars is commensurate with observations from the RPA, and the distribution of the predicted [Eu/Fe] for halo r-II stars matches that observed. These results demonstrate that RPE stars can be valuable probes of the accretion of dwarf galaxies in the early stages of their formation....
• Modelling self-interacting dark matter substructures – I.  Calibration with N-body simulations of a Milky-Way-sized halo and its satellite
  Masato Shirasaki; Takashi Okamoto; Shin’ichiro Ando
  Monthly Notices of the Royal Astronomical Society, 23 Sep. 2022, [Peer-reviewed]
  Scientific journal, We study evolution of single subhaloes with their masses of ~10⁹ M_⊙ in a Milky Way-sized host halo for self-interacting dark matter (SIDM) models. We perform dark-matter-only N-body simulations of dynamical evolution of individual subhaloes orbiting its host by varying self-scattering cross-sections (including a velocity-dependent scenario), subhalo orbits, and internal properties of the subhalo. We calibrate a gravothermal fluid model to predict time evolution in spherical mass density profiles of isolated SIDM haloes with the simulations. We find that tidal effects of SIDM subhaloes can be described with a framework developed for the case of collision-less cold dark matter (CDM), but a shorter typical time-scale for the mass loss due to tidal stripping is required to explain our SIDM simulation results. As long as the cross-section is less than $\sim \! 10\, \mathrm{cm}^2\,\mathrm{g}^{ -1}$ and initial states of subhaloes are set within a 2σ-level scatter at redshifts of ~2 predicted by the standard ΛCDM cosmology, our simulations do not exhibit a prominent feature of gravothermal collapse in the subhalo central density for 10 Gyr. We develop a semi-analytic model of SIDM subhaloes in a time-evolving density core of the host with tidal stripping and self-scattering ram pressure effects. Our semi-analytic approach provides a simple, efficient, and physically intuitive prediction of SIDM subhaloes, but further improvements are needed to account for baryonic effects in the host and the gravothermal instability accelerated by tidal stripping effects....
• The Missing Satellite Problem outside of the Local Group. II. Statistical Properties of Satellites of Milky Way-like Galaxies
  Nashimoto, Masashi; Tanaka, Masayuki; Chiba, Masashi; Hayashi, Kohei; Komiyama, Yutaka; Okamoto, Takashi
  The Astrophysical Journal, Sep. 2022, [Peer-reviewed]
  Scientific journal, We present a new observation of satellite galaxies around seven Milky Way (MW)-like galaxies located outside of the Local Group (LG) using Subaru/Hyper Suprime-Cam imaging data to statistically address the missing satellite problem. We select satellite galaxy candidates using magnitude, surface brightness, Sérsic index, axial ratio, FWHM, and surface brightness fluctuation cuts, followed by visual screening of false positives such as optical ghosts of bright stars. We identify 51 secure dwarf satellite galaxies within the virial radius of nine host galaxies, two of which are drawn from the pilot observation presented in Paper I. We find that the average luminosity function of the satellite galaxies is consistent with that of the MW satellites, although the luminosity function of each host galaxy varies significantly. We observe an indication that more massive hosts tend to have a larger number of satellites. Physical properties of the satellites such as the size-luminosity relation are also consistent with the MW satellites. However, the spatial distribution is different; we find that the satellite galaxies outside of the LG show no sign of concentration or alignment, while that of the MW satellites is more concentrated around the host and exhibits a significant alignment. As we focus on relatively massive satellites with M _V < -10, we do not expect that the observational incompleteness can be responsible here. This trend might represent a peculiarity of the MW satellites, and further work is needed to understand its origin....
• Classification of cosmic structures for galaxies with deep learning: connecting cosmological simulations with observations
  Shigeki Inoue; Xiaotian Si; Takashi Okamoto; Moka Nishigaki
  Monthly Notices of the Royal Astronomical Society, 09 Aug. 2022, [Peer-reviewed]
  Scientific journal
• Differences in star formation activity between tidally triggered and isolated bars: a case study of NGC 4303 and NGC 3627
  Elizabeth J Iles; Alex R Pettitt; Takashi Okamoto
  Monthly Notices of the Royal Astronomical Society, Oxford University Press ({OUP}), 13 Jan. 2022, [Peer-reviewed]
  English, Scientific journal
• A Phase-space View of Cold-gas Properties of Virgo Cluster Galaxies: Multiple Quenching Processes at Work?
  Kana Morokuma-Matsui; Tadayuki Kodama; Tomoki Morokuma; Kouichiro Nakanishi; Yusei Koyama; Takuji Yamashita; Shuhei Koyama; Takashi Okamoto
  The Astrophysical Journal, 01 Jun. 2021, [Peer-reviewed]
  Scientific journal
• Testing the effect of resolution on gravitational fragmentation with Lagrangian hydrodynamic schemes
  Yasuyoshi Yamamoto; Takashi Okamoto; Takayuki R Saitoh
  Monthly Notices of the Royal Astronomical Society, 504, 3, 3986, 3995, Oxford University Press ({OUP}), 11 May 2021, [Peer-reviewed], [Corresponding author]
  Scientific journal,
  To study the resolution required for simulating gravitational fragmentation with newly developed Lagrangian hydrodynamic schemes, meshless finite-volume method (MFV) and meshless finite-mass method, we have performed a number of simulations of the Jeans test and compared the results with both the expected analytical solution and results from the more standard Lagrangian approach: smoothed particle hydrodynamics (SPH). We find that the different schemes converge to the analytical solution when the diameter of a fluid element is smaller than a quarter of the Jeans wavelength, λJ. Among the three schemes, SPH/MFV shows the fastest/slowest convergence to the analytical solution. Unlike the well-known behaviour of Eulerian schemes, none of the Lagrangian schemes investigated displays artificial fragmentation when the perturbation wavelength, λ, is shorter than λJ, even at low numerical resolution. For larger wavelengths (λ &gt; λJ), the growth of the perturbation is delayed when it is not well resolved. Furthermore, with poor resolution, the fragmentation seen with the MFV scheme proceeds very differently compared to the converged solution. All these results suggest that, when unresolved, the ratio of the magnitude of hydrodynamic force to that of self-gravity at the sub-resolution scale is the largest/smallest in MFV/SPH, the reasons for which we have discussed in detail. These tests are repeated to investigate the effect of kernels of higher order than the fiducial cubic spline. Our results indicate that the standard deviation of the kernel is a more appropriate definition of the ‘size’ of a fluid element than its compact support radius.
• A puzzling non-detection of [O III] and [C II] from a z ≈ 7.7 galaxy observed with ALMA
  C. Binggeli; A. K. Inoue; T. Hashimoto; M. C. Toribio; E. Zackrisson; S. Ramstedt; K. Mawatari; Y. Harikane; H. Matsuo; T. Okamoto; K. Ota; I. Shimizu; Y. Tamura; Y. Taniguchi; H. Umehata
  Astronomy & Astrophysics, 646, A26, A26, {EDP} Sciences, Feb. 2021, [Peer-reviewed]
  Scientific journal, Context. Characterizing the galaxy population in the early Universe holds the key to understanding the evolution of these objects and the role they played in cosmic reionization. However, there have been very few observations at the very highest redshifts to date.
  
  
  Aims. In order to shed light on the properties of galaxies in the high-redshift Universe and their interstellar media, we observe the Lyman-α emitting galaxy z7_GSD_3811 at z = 7.664 with bands 6 and 8 at the Atacama Large Millimeter/submillimeter Array (ALMA).
  
  
  Methods. We target the far-infrared [O III] 88 μm and [C II] 158 μm emission lines and dust continuum in the star-forming galaxy z7_GSD_3811 with ALMA. We combine these measurements with earlier observations in the rest-frame ultraviolet (UV) in order to characterize the object and compare the results to those of earlier studies that observed [O III] and [C II] emission in high-redshift galaxies.
  
  
  Results. The [O III] 88 μm and [C II] 158 μm emission lines are undetected at the position of z7_GSD_3811, with 3σ upper limits of 1.6  ×  10⁸ L_⊙ and 4.0  ×  10⁷ L_⊙, respectively. We do not detect any dust continuum in band 6 nor band 8. The measured rms in the band 8 and band 6 continua are 26 and 9.9 μJy beam⁻¹, respectively. Similar to several other high-redshift galaxies, z7_GSD_3811 exhibits low [C II] emission for its star formation rate compared to local galaxies. Furthermore, our upper limit on the [O III] line luminosity is lower than the previously observed [O III] lines in high-redshift galaxies with similar UV luminosities. Our ALMA band 6 and 8 dust continuum observations imply that z7_GSD_3811 likely has a low dust content, and our non-detections of the [O III] and [C II] lines could indicate that z7_GSD_3811 has a low metallicity (Z ≲ 0.1 Z_⊙).
• Semi-analytic modelling of AGNs: autocorrelation function and halo occupation
  Taira Oogi; Hikari Shirakata; Masahiro Nagashima; Takahiro Nishimichi; Toshihiro Kawaguchi; Takashi Okamoto; Tomoaki Ishiyama; Motohiro Enoki
  Monthly Notices of the Royal Astronomical Society, 497, 1, 1, 18, 01 Sep. 2020, [Peer-reviewed]
  English, Scientific journal
• Massive core/star formation triggered by cloud–cloud collision: Effect of magnetic field
  Nirmit Sakre; Asao Habe; Alex R Pettitt; Takashi Okamoto
  Publications of the Astronomical Society of Japan, 73, Supplement_1, S385, S404, Oxford University Press (OUP), 03 Jul. 2020, [Peer-reviewed]
  Scientific journal, Abstract
  
  We study the effect of magnetic field on massive dense core formation in colliding unequal molecular clouds by performing magnetohydrodynamic simulations with sub-parsec resolution (0.015 pc) that can resolve the molecular cores. Initial clouds with the typical gas density of the molecular clouds are immersed in various uniform magnetic fields. The turbulent magnetic fields in the clouds consistent with the observation by Crutcher et al. (2010, ApJ, 725, 466) are generated by the internal turbulent gas motion before the collision, if the uniform magnetic field strength is 4.0 μG. The collision speed of 10 km s−1 is adopted, which is much larger than the sound speeds and the Alfvén speeds of the clouds. We identify gas clumps with gas densities greater than 5 × 10−20 g cm−3 as the dense cores and trace them throughout the simulations to investigate their mass evolution and gravitational boundness. We show that a greater number of massive, gravitationally bound cores are formed in the strong magnetic field (4.0 μG) models than the weak magnetic field (0.1 μG) models. This is partly because the strong magnetic field suppresses the spatial shifts of the shocked layer that should be caused by the nonlinear thin shell instability. The spatial shifts promote the formation of low-mass dense cores in the weak magnetic field models. The strong magnetic fields also support low-mass dense cores against gravitational collapse. We show that the numbers of massive, gravitationally bound cores formed in the strong magnetic field models are much larger than in the isolated, non-colliding cloud models, which are simulated for comparison. We discuss the implications of our numerical results on massive star formation.
• Revisiting the Sołtan Argument Based on a Semianalytical Model for Galaxy and Black Hole Evolution
  Shirakata, Hikari; Kawaguchi, Toshihiro; Okamoto, Takashi; Nagashima, Masahiro; Oogi, Taira
  The Astrophysical Journal, 898, 1, Jul. 2020, [Peer-reviewed]
  English, Scientific journal
• ALMA uncovers the [C ii] emission and warm dust continuum in a z = 8.31 Lyman break galaxy
  Tom J L C Bakx; Yoichi Tamura; Takuya Hashimoto; Akio K Inoue; Minju M Lee; Ken Mawatari; Kazuaki Ota; Hideki Umehata; Erik Zackrisson; Bunyo Hatsukade; Kotaro Kohno; Yuichi Matsuda; Hiroshi Matsuo; Takashi Okamoto; Takatoshi Shibuya; Ikkoh Shimizu; Yoshiaki Taniguchi; Naoki Yoshida
  Monthly Notices of the Royal Astronomical Society, 493, 3, 4294, 4307, 05 Mar. 2020, [Peer-reviewed]
  Scientific journal
• Detections of far-infrared [OIII] and dust emission in a galaxy at z = 8.312: Early metal enrichment in the heart of the reionization era
  Y. Tamura; K. Mawatari; T. Hashimoto; A. K. Inoue; E. Zackrissonm; L. Christensen; C. Binggeli; Y. Matsuda; H. Matsuo; T. T. Takeuchi; R. S. Asano; K. Sunaga; I. Shimizu; T. Okamoto; N. Yoshida; M. Lee; T. Shibuya; Y. Taniguchi; H. Umehata; B. Hatsukade; K. Kohno; K. Ota
  Proceedings of the International Astronomical Union, 15, S341, 211, 215, Cambridge University Press (CUP), Nov. 2019, [Peer-reviewed]
  Scientific journal, We present ALMA detection of the [O iii] 88 μm line and 850 μm dust continuum emission in a Y-dropout Lyman break galaxy, MACS0416_Y1. The [O iii] detection confirms the object with a spectroscopic redshift to be z = 8.3118±0.0003. The 850 μm continuum intensity (0.14 mJy) implies a large dust mass on the order of 4×10⁶M_⊙. The ultraviolet-to-far infrared spectral energy distribution modeling, where the [O iii] emissivity model is incorporated, suggests the presence of a young (τ_age ≍ 4 Myr), star-forming (SFR ≍ 60M_⊙yr⁻¹), and moderately metal-polluted (Z ≍ 0.2Z_⊙) stellar component with a stellar mass of 3 × 10⁸M_⊙. An analytic dust mass evolution model with a single episode of star formation does not reproduce the metallicity and dust mass in ≍ 4 Myr, suggesting an underlying evolved stellar component as the origin of the dust mass.
• Big Three Dragons: A z = 7.15 Lyman-break galaxy detected in [O III] 88 μm, [C II] 158 μm, and dust continuum with ALMA
  Hashimoto, Takuya; Inoue, Akio K.; Mawatari, Ken; Tamura, Yoichi; Matsuo, Hiroshi; Furusawa, Hisanori; Harikane, Yuichi; Shibuya, Takatoshi; Knudsen, Kirsten K.; Kohno, Kotaro; Ono, Yoshiaki; Zackrisson, Erik; Okamoto, Takashi; Kashikawa, Nobunari; Oesch, Pascal A.; Ouchi, Masami; Ota, Kazuaki; Shimizu, Ikkoh; Taniguchi, Yoshiaki; Umehata, Hideki; Watson, Darach
  Publications of the Astronomical Society of Japan, 71, 4, Aug. 2019, [Peer-reviewed]
  English, Scientific journal
• Slowing down of cosmic growth of supermassive black holes: theoretical prediction of the Eddington ratio distribution
  Shirakata, Hikari; Kawaguchi, Toshihiro; Oogi, Taira; Okamoto, Takashi; Nagashima, Masahiro
  Monthly Notices of the Royal Astronomical Society, 487, 1, 409, 419, Jul. 2019, [Peer-reviewed]
  English, Scientific journal
• Detection of the Far-infrared [O III] and Dust Emission in a Galaxy at Redshift 8.312: Early Metal Enrichment in the Heart of the Reionization Era
  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
  The Astrophysical Journal, 874, 1, Mar. 2019, [Peer-reviewed]
  English, Scientific journal
• The New Numerical Galaxy Catalogue (ν²GC): properties of active galactic nuclei and their host galaxies
  Shirakata, Hikari; Okamoto, Takashi; Kawaguchi, Toshihiro; Nagashima, Masahiro; Ishiyama, Tomoaki; Makiya, Ryu; Kobayashi, Masakazu A. R.; Enoki, Motohiro; Oogi, Taira; Okoshi, Katsuya
  Monthly Notices of the Royal Astronomical Society, 482, 4, 4846, 4873, Feb. 2019, [Peer-reviewed]
  English, Scientific journal
• The Missing Satellite Problem Outside of the Local Group. I. Pilot Observation
  Tanaka, Masayuki; Chiba, Masashi; Hayashi, Kohei; Komiyama, Yutaka; Okamoto, Takashi; Cooper, Andrew P.; Okamoto, Sakurako; Spitler, Lee
  The Astrophysical Journal, 865, 2, id125, 12, Oct. 2018, [Peer-reviewed]
  English, Scientific journal
• The onset of star formation 250 million years after the Big Bang
  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; Pelló, Roser; Rydberg, Claes-Erik; Shimizu, Ikkoh; Taniguchi, Yoshiaki; Umehata, Hideki; Yoshida, Naoki
  Nature, 557, 7705, 392, +, May 2018, [Peer-reviewed]
  English, Scientific journal
• The impact of galactic disc environment on star-forming clouds
  Nguyen, Ngan K.; Pettitt, Alex R.; Tasker, Elizabeth J.; Okamoto, Takashi
  Monthly Notices of the Royal Astronomical Society, 475, 1, 27, 42, Mar. 2018, [Peer-reviewed]
  English, Scientific journal
• The effect of radiation pressure on spatial distribution of dust inside H II regions
  Ishiki, Shohei; Okamoto, Takashi; Inoue, Akio K.
  Monthly Notices of the Royal Astronomical Society, 474, 2, 1935, 1943, Feb. 2018, [Peer-reviewed]
  English, Scientific journal
• Imprints of the super-Eddington accretion on the quasar clustering
  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, 471, 1, L21, L25, Oct. 2017, [Peer-reviewed]
  English, Scientific journal
• Theoretical Re-evaluations of Scaling Relations between SMBHs and Their Host Galaxies—1. Effect of Seed BH Mass
  Hikari Shirakata; Toshihiro Kawaguchi; Takashi Okamoto; Ryu Makiya; Tomoaki Ishiyama; Yoshiki Matsuoka; Masahiro Nagashima; Motohiro Enoki; Taira Oogi; Masakazu A. R. Kobayashi
  Frontiers in Astronomy and Space Sciences, 4, Frontiers Media SA, 21 Sep. 2017, [Peer-reviewed]
  Scientific journal
• Theoretical Re-evaluations of Scaling Relations between SMBHs and Their Host Galaxies - 2. Importance of AGN Feedback Suggested by Stellar Age - Velocity Dispersion Relation
  Shirakata, Hikari; Kawaguchi, Toshihiro; Okamoto, Takashi; Ishiyama, Tomoaki
  Frontiers in Astronomy and Space Sciences, Sep. 2017
  Scientific journal, We present the galactic stellar age - velocity dispersion relation obtained from a semi-analytic model of galaxy formation. We divide galaxies into two populations: galaxies which have over-massive/under-massive black holes (BHs) against the best-fitting BH mass - velocity dispersion relation. We find that galaxies with larger velocity dispersion have older stellar ages. We also find that galaxies with over-massive BHs have older stellar ages. These results are consistent with observational results obtained from Martin-Navarro et al. (2016). We tested the model with weak AGN feedback and find that galaxies with larger velocity dispersion have a younger stellar age....
• Radiation feedback in dusty clouds
  Ishiki, Shohei; Okamoto, Takashi
  Monthly Notices of the Royal Astronomical Society, 466, 1, L123, L127, Mar. 2017, [Peer-reviewed]
  English, Scientific journal
• The metal enrichment of passive galaxies in cosmological simulations of galaxy formation
  Okamoto, Takashi; Nagashima, Masahiro; Lacey, Cedric G.; Frenk, Carlos S.
  Monthly Notices of the Royal Astronomical Society, 464, 4, 4866, 4874, Feb. 2017, [Peer-reviewed], [Lead author]
  English, Scientific journal
• Radiation feedback in dusty clouds
  Shohei Ishiki; Takashi Okamoto
  Monthly Notices of the Royal Astronomical Society: Letters, 466, 1, L123, L127, Oxford University Press, 2017, [Peer-reviewed]
  English, Scientific journal
• Theoretical re-evaluations of the black hole mass-bulge mass relation - I. Effect of seed black hole mass
  Shirakata, Hikari; Kawaguchi, Toshihiro; Okamoto, Takashi; Makiya, Ryu; Ishiyama, Tomoaki; Matsuoka, Yoshiki; Nagashima, Masahiro; Enoki, Motohiro; Oogi, Taira; Kobayashi, Masakazu A. R.
  Monthly Notices of the Royal Astronomical Society, 461, 4, 4389, 4394, Oct. 2016, [Peer-reviewed]
  English, Scientific journal
• Nebular line emission from z > 7 galaxies in a cosmological simulation: rest-frame UV to optical lines
  Shimizu, Ikkoh; Inoue, Akio K.; Okamoto, Takashi; Yoshida, Naoki
  Monthly Notices of the Royal Astronomical Society, 461, 4, 3563, 3575, Oct. 2016, [Peer-reviewed]
  English, Scientific journal
• Detection of an oxygen emission line from a high-redshift galaxy in the reionization epoch
  Inoue, Akio K.; Tamura, Yoichi; Matsuo, Hiroshi; Mawatari, Ken; Shimizu, Ikkoh; Shibuya, Takatoshi; Ota, Kazuaki; Yoshida, Naoki; Zackrisson, Erik; Kashikawa, Nobunari; Kohno, Kotaro; Umehata, Hideki; Hatsukade, Bunyo; Iye, Masanori; Matsuda, Yuichi; Okamoto, Takashi; Yamaguchi, Yuki
  Science, 352, 6293, 1559, 1562, Jun. 2016, [Peer-reviewed]
  English, Scientific journal
• The New Numerical Galaxy Catalog (ν²GC): An updated semi-analytic model of galaxy and active galactic nucleus formation with large cosmological N-body simulations
  Makiya, Ryu; Enoki, Motohiro; Ishiyama, Tomoaki; Kobayashi, Masakazu A. R.; Nagashima, Masahiro; Okamoto, Takashi; Okoshi, Katsuya; Oogi, Taira; Shirakata, Hikari
  Publications of the Astronomical Society of Japan, 68, 2, Apr. 2016, [Peer-reviewed]
  English, Scientific journal
• A new ray-tracing scheme for 3D diffuse radiation transfer on highly parallel architectures
  Tanaka, Satoshi; Yoshikawa, Kohji; Okamoto, Takashi; Hasegawa, Kenji
  Publications of the Astronomical Society of Japan, 67, 4, Aug. 2015, [Peer-reviewed]
  English, Scientific journal
• Cosmic evolution of bars in simulations of galaxy formation
  Okamoto, Takashi; Isoe, Mari; Habe, Asao
  Publications of the Astronomical Society of Japan, 67, 4, Aug. 2015, [Peer-reviewed], [Lead author]
  English, Scientific journal
• The impact of dust in host galaxies on quasar luminosity functions.
  Shirakata, H.; Okamoto, T.; Enoki, M.; Nagashima, M.; Kobayashi, M. A. R.; Ishiyama, T.; Makiya, R.
  Monthly Notices of the Royal Astronomical Society, 450, 1, L6, L10, Oxford University Press, Jun. 2015, [Peer-reviewed]
  English, Scientific journal
• The impact of dust in host galaxies on quasar luminosity functions
  Hikari Shirakata; Takashi Okamoto; Motohiro Enoki; Masahiro Nagashima; Masakazu A. R. Kobayashi; Tomoaki Ishiyama; Ryu Makiya
  MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, 450, 1, L6, L10, Jun. 2015, [Peer-reviewed]
  English, Scientific journal
• Reproducing cosmic evolution of galaxy population from z = 4 to 0
  Okamoto, Takashi; Shimizu, Ikkoh; Yoshida, Naoki
  Publications of the Astronomical Society of Japan, 66, 4, Jul. 2014, [Peer-reviewed], [Lead author]
  English, Scientific journal
• Physical properties of UDF12 galaxies in cosmological simulations
  Shimizu, Ikkoh; Inoue, Akio K.; Okamoto, Takashi; Yoshida, Naoki
  Monthly Notices of the Royal Astronomical Society, 440, 1, 731, 745, May 2014, [Peer-reviewed]
  English, Scientific journal
• ALMA Will Determine the Spectroscopic Redshift z > 8 with FIR [O III] Emission Lines
  Inoue, A. K.; Shimizu, I.; Tamura, Y.; Matsuo, H.; Okamoto, T.; Yoshida, N.
  The Astrophysical Journal, Jan. 2014, [Peer-reviewed]
  Scientific journal, 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....
• Phantom-GRAPE: Numerical software library to accelerate collisionless N-body simulation with SIMD instruction set on x86 architecture
  Tanikawa, Ataru; Yoshikawa, Kohji; Nitadori, Keigo; Okamoto, Takashi
  New Astronomy, 19, 74, 88, Feb. 2013, [Peer-reviewed]
  English, Scientific journal
• Calibrating an updated smoothed particle hydrodynamics scheme within gcd+
  Kawata, D.; Okamoto, T.; Gibson, B. K.; Barnes, D. J.; Cen, R.
  Monthly Notices of the Royal Astronomical Society, Jan. 2013, [Peer-reviewed]
  Scientific journal, We adapt a modern scheme of smoothed particle hydrodynamics (SPH) to our tree N-body/SPH galactic chemodynamics code gcd+. The applied scheme includes implementations of the artificial viscosity switch and artificial thermal conductivity proposed by Morris & Monaghan, Rosswog & Price and Price to model discontinuities and Kelvin-Helmholtz instabilities more accurately. We first present hydrodynamics test simulations and contrast the results to runs undertaken without artificial viscosity switch or thermal conduction. In addition, we also explore the different levels of smoothing by adopting larger or smaller smoothing lengths, i.e. a larger or smaller number of neighbour particles, N_nb. We demonstrate that the new version of gcd+ is capable of modelling Kelvin-Helmholtz instabilities to a similar level as the mesh code, athena. From the Gresho vortex, point-like explosion and self-similar collapse tests, we conclude that setting the smoothing length to keep N_nb as high as ∼58 is preferable to adopting smaller smoothing lengths. We present our optimized parameter sets from the hydrodynamics tests....
• The origin of pseudo-bulges in cosmological simulations of galaxy formation
  Takashi Okamoto
  Monthly Notices of the Royal Astronomical Society, 428, 1, 718, 728, Jan. 2013, [Peer-reviewed], [Lead author]
  English, Scientific journal
• Submillimetre galaxies in cosmological hydrodynamic simulations: source number counts and the spatial clustering
  Shimizu, Ikkoh; Yoshida, Naoki; Okamoto, Takashi
  Monthly Notices of the Royal Astronomical Society, 427, 4, 2866, 2875, Dec. 2012, [Peer-reviewed]
  English, Scientific journal
• The Aquila comparison project: the effects of feedback and numerical methods on simulations of galaxy formation
  Scannapieco, C.; Wadepuhl, M.; Parry, O. H.; Navarro, J. F.; Jenkins, A.; Springel, V.; Teyssier, R.; Carlson, E.; Couchman, H. M. P.; Crain, R. A.; Dalla Vecchia, C.; Frenk, C. S.; Kobayashi, C.; Monaco, P.; Murante, G.; Okamoto, T.; Quinn, T.; Schaye, J.; Stinson, G. S.; Theuns, T.; Wadsley, J.; White, S. D. M.; Woods, R.
  Monthly Notices of the Royal Astronomical Society, 423, 2, 1726, 1749, Jun. 2012, [Peer-reviewed]
  English, Scientific journal
• Origin of Multiple Nuclei in Ultraluminous Infrared Galaxies
  Matsui, Hidenori; Saitoh, Takayuki R.; Makino, Junichiro; Wada, Keiichi; Tomisaka, Kohji; Kokubo, Eiichiro; Daisaka, Hiroshi; Okamoto, Takashi; Yoshida, Naoki
  The Astrophysical Journal, 746, 1, 26, Feb. 2012, [Peer-reviewed]
  English, Scientific journal
• The baryons in the Milky Way satellites
  Parry, O. H.; Eke, V. R.; Frenk, C. S.; Okamoto, T.
  Monthly Notices of the Royal Astronomical Society, 419, 4, 3304, 3318, Feb. 2012, [Peer-reviewed]
  English, Scientific journal
• ARGOT: accelerated radiative transfer on grids using oct-tree
  Okamoto, Takashi; Yoshikawa, Kohji; Umemura, Masayuki
  Monthly Notices of the Royal Astronomical Society, 419, 4, 2855, 2866, Feb. 2012, [Peer-reviewed], [Lead author]
  English, Scientific journal
• N-body simulation for self-gravitating collisional systems with a new SIMD instruction set extension to the x86 architecture, Advanced Vector eXtensions
  Tanikawa, Ataru; Yoshikawa, Kohji; Okamoto, Takashi; Nitadori, Keigo
  New Astronomy, 17, 2, 82, 92, Feb. 2012, [Peer-reviewed]
  English, Scientific journal
• Lyman α emitters in cosmological simulations - I. Lyman α escape fraction and statistical properties at z= 3.1
  Shimizu, Ikkoh; Yoshida, Naoki; Okamoto, Takashi
  Monthly Notices of the Royal Astronomical Society, 418, 4, 2273, 2282, Dec. 2011, [Peer-reviewed]
  English, Scientific journal
• The properties of satellite galaxies in simulations of galaxy formation
  Okamoto, Takashi; Frenk, Carlos S.; Jenkins, Adrian; Theuns, Tom
  Monthly Notices of the Royal Astronomical Society, 406, 1, 208, 222, Jul. 2010, [Peer-reviewed], [Lead author]
  English, Scientific journal
• The angular momentum of cold dark matter haloes with and without baryons
  Bett, Philip; Eke, Vincent; Frenk, Carlos S.; Jenkins, Adrian; Okamoto, Takashi
  Monthly Notices of the Royal Astronomical Society, 404, 3, 1137, 1156, May 2010, [Peer-reviewed]
  English, Scientific journal
• Shock-Induced Starburst and Star Cluster Formation in Colliding Galaxies
  Saitoh, Takayuki R.; Daisaka, Hiroshi; Kokubo, Eiichiro; Makino, Junichiro; Okamoto, Takashi; Tomisaka, Kohji; Wada, Keiichi; Yoshida, Naoki
  Galaxy Wars: Stellar Populations and Star Formation in Interacting Galaxies, 423, 185, +, 2010, [Peer-reviewed]
  Scientific journal
• The origin of failed subhaloes and the common mass scale of the Milky Way satellite galaxies
  Okamoto, Takashi; Frenk, Carlos S.
  Monthly Notices of the Royal Astronomical Society, 399, 1, L174, L178, Oct. 2009, [Peer-reviewed], [Lead author]
  English, Scientific journal
• Toward First-Principle Simulations of Galaxy Formation: II. Shock-Induced Starburst at a Collision Interface during the First Encounter of Interacting Galaxies
  Saitoh, Takayuki R.; Daisaka, Hiroshi; Kokubo, Eiichiro; Makino, Junichiro; Okamoto, Takashi; Tomisaka, Kohji; Wada, Keiichi; Yoshida, Naoki
  Publications of the Astronomical Society of Japan, 61, 3, 481, 486, Jun. 2009, [Peer-reviewed]
  English, Scientific journal
• Mass loss of galaxies due to an ultraviolet background
  Okamoto, Takashi; Gao, Liang; Theuns, Tom
  Monthly Notices of the Royal Astronomical Society, 390, 3, 920, 928, Nov. 2008, [Peer-reviewed], [Lead author]
  English, Scientific journal
• Toward First-Principle Simulations of Galaxy Formation: I. How Should We Choose Star-Formation Criteria in High-Resolution Simulations of Disk Galaxies?
  Saitoh, Takayuki R.; Daisaka, Hiroshi; Kokubo, Eiichiro; Makino, Junichiro; Okamoto, Takashi; Tomisaka, Kohji; Wada, Keiichi; Yoshida, Naoki
  Publications of the Astronomical Society of Japan, 60, 4, 667, 681, Aug. 2008, [Peer-reviewed]
  English, Scientific journal
• Bulges versus discs: the evolution of angular momentum in cosmological simulations of galaxy formation
  Zavala, Jesus; Okamoto, Takashi; Frenk, Carlos S.
  Monthly Notices of the Royal Astronomical Society, 387, 1, 364, 370, Jun. 2008, [Peer-reviewed]
  English, Scientific journal
• The impact of radio feedback from active galactic nuclei in cosmological simulations: formation of disc galaxies
  Okamoto, Takashi; Nemmen, Rodrigo S.; Bower, Richard G.
  Monthly Notices of the Royal Astronomical Society, 385, 1, 161, 180, Mar. 2008, [Peer-reviewed]
  English, Scientific journal
• Molecular cloud regulated star formation in galaxies
  Booth, C. M.; Theuns, Tom; Okamoto, Takashi
  Monthly Notices of the Royal Astronomical Society, 376, 4, 1588, 1610, Apr. 2007, [Peer-reviewed]
  English, Scientific journal
• Satellite systems around galaxies in hydrodynamic simulations
  Libeskind, Noam I.; Cole, Shaun; Frenk, Carlos S.; Okamoto, Takashi; Jenkins, Adrian
  Monthly Notices of the Royal Astronomical Society, 374, 1, 16, 28, Jan. 2007, [Peer-reviewed]
  English, Scientific journal
• Type Ia Supernovae in a Hierarchical Galaxy Formation Model: The Milky Way
  Nagashima, Masahiro; Okamoto, Takashi
  The Astrophysical Journal, 643, 2, 863, 880, Jun. 2006, [Peer-reviewed]
  English, Scientific journal
• Tidal Disruption of Dark Matter Halos around Proto-Globular Clusters
  Saitoh, Takayuki R.; Koda, Jin; Okamoto, Takashi; Wada, Keiichi; Habe, Asao
  The Astrophysical Journal, 640, 1, 22, 30, Mar. 2006, [Peer-reviewed]
  English, Scientific journal
• Effects of feedback on the morphology of galaxy discs
  Okamoto, Takashi; Eke, Vincent R.; Frenk, Carlos S.; Jenkins, Adrian
  Monthly Notices of the Royal Astronomical Society, 363, 4, 1299, 1314, Nov. 2005, [Peer-reviewed], [Lead author]
  English, Scientific journal
• The metal enrichment of elliptical galaxies in hierarchical galaxy formation models
  Nagashima, Masahiro; Lacey, Cedric G.; Okamoto, Takashi; Baugh, Carlton M.; Frenk, Carlos S.; Cole, Shaun
  Monthly Notices of the Royal Astronomical Society, 363, 1, L31, L35, Oct. 2005, [Peer-reviewed]
  English, Scientific journal
• Internal Alignment of the Halos of Disk Galaxies in Cosmological Hydrodynamic Simulations
  Bailin, Jeremy; Kawata, Daisuke; Gibson, Brad K.; Steinmetz, Matthias; Navarro, Julio F.; Brook, Chris B.; Gill, Stuart P. D.; Ibata, Rodrigo A.; Knebe, Alexander; Lewis, Geraint F.; Okamoto, Takashi
  The Astrophysical Journal, 627, 1, L17, L20, Jul. 2005, [Peer-reviewed]
  English, Scientific journal
• Panoramic Views of Cluster-Scale Assemblies Explored by Subaru Wide-Field Imaging
  Kodama, Tadayuki; Tanaka, Masayuki; Tamura, Takayuki; Yahagi, Hideki; Nagashima, Masahiro; Tanaka, Ichi; Arimoto, Nobuo; Futamase, Toshifumi; Iye, Masanori; Karasawa, Yoshikazu; Kashikawa, Nobunari; Kawasaki, Wataru; Kitayama, Tetsu; Matsuhara, Hideo; Nakata, Fumiaki; Ohashi, Takaya; Ohta, Kouji; Okamoto, Takashi; Okamura, Sadanori; Shimasaku, Kazuhiro; Suto, Yasushi; Tamura, Naoyuki; Umetsu, Keiichi; Yamada, Toru
  Publications of the Astronomical Society of Japan, 57, 2, 309, 323, Apr. 2005, [Peer-reviewed]
  English, Scientific journal
• Momentum transfer across shear flows in smoothed particle hydrodynamic simulations of galaxy formation
  Okamoto, Takashi; Jenkins, Adrian; Eke, Vincent R.; Quilis, Vincent; Frenk, Carlos S.
  Monthly Notices of the Royal Astronomical Society, 345, 2, 429, 446, Oct. 2003, [Peer-reviewed], [Lead author]
  English, Scientific journal
• Cluster Morphology as a Test of Different Cosmological Models
  Suwa, Tamon; Habe, Asao; Yoshikawa, Kohji; Okamoto, Takashi
  The Astrophysical Journal, 588, 1, 7, 17, May 2003, [Peer-reviewed]
  English, Scientific journal
• Environmental Effects on Evolution of Cluster Galaxies in a Λ-dominated Cold Dark Matter Universe
  Okamoto, Takashi; Nagashima, Masahiro
  The Astrophysical Journal, 587, 2, 500, 513, Apr. 2003, [Peer-reviewed], [Lead author]
  English, Scientific journal
• Morphology-Density Relation for Simulated Clusters of Galaxies in Cold Dark Matter-dominated Universes
  Okamoto, Takashi; Nagashima, Masahiro
  The Astrophysical Journal, 547, 1, 109, 116, Jan. 2001, [Peer-reviewed], [Lead author]
  English, Scientific journal
• Evolution of Cluster Galaxies in Hierarchical Clustering Universes
  Okamoto, Takashi; Habe, Asao
  Publications of the Astronomical Society of Japan, 52, 3, 457, 463, Jun. 2000, [Peer-reviewed], [Lead author]
  English, Scientific journal
• Formation and Evolution of Galactic Halos in Clusters of Galaxies
  Okamoto, Takashi; Habe, Asao
  The Astrophysical Journal, 240, 2, 57, 58, May 1999, [Peer-reviewed], [Lead author]
  English, Scientific journal

• Structure of dark matter haloes of Milky Way satellite galaxies in SIDM universes
  Takashi Okamoto, Proceedings of the International Astronomical Union, 14, S344, 498, 501, Aug. 2018
  Cambridge University Press ({CUP})
• ALMAによる赤方偏移z≒8.4のライマンブレイク銀河のダスト検出
  田村陽一; 竹内努; 井上昭雄; 橋本拓也; 馬渡健; 松尾宏; 松田有一; 清水一紘; 岡本崇; 吉田直紀; 澁谷隆俊; 河野孝太郎; 廿日出文洋; ZACKRISSON Erik; 谷口義明; 梅畑豪紀; 太田一陽, 日本天文学会年会講演予稿集, 2017, 2017
• VizieR Online Data Catalog: New Numerical Galaxy Catalog (ν^2GC)
  Ryu Makiya; Motohiro Enoki; Tomoaki Ishiyama; Masakazu A.R. Kobayashi; Masahiro Nagashima; Takashi Okamoto; Katsuya Okoshi; Taira Oogi; Hikari Shirakata, VizieR Online Data Catalog, Oct. 2016
  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)., English, Others
• 赤方偏移z=7.2ライマンα輝線銀河の遠赤外線[O III]88μm輝線の検出
  井上昭雄; 田村陽一; 松尾宏; 馬渡健; 清水一紘; 澁谷隆俊; 太田一陽; 吉田直紀; ZACKRISSON Erik; 柏川伸成; 河野孝太郎; 梅畑豪紀; 廿日出文洋; 家正則; 松田有一; 岡本崇; 山口裕貴, 日本天文学会年会講演予稿集, 2016, 2016
• ALMAによる赤方偏移8超銀河の遠赤外星雲輝線検出の可能性
  井上昭雄; 清水一紘; 松尾宏; 田村陽一; 吉田直紀; 岡本崇, 日本天文学会年会講演予稿集, 2013, 2013
• Cosmological pseudobulge formation
  Takashi Okamoto, FIRST STARS IV - FROM HAYASHI TO THE FUTURE, 1480, 403, 405, 2012, [Peer-reviewed]
  English
• Coevolution of galaxies and black-holes
  岡本 崇, Kagaku, 81, 4, 330, 334, 2011
  岩波書店, Japanese
• Shock-induced star cluster formation in colliding galaxies
  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
  English
• Shock-induced star cluster formation in colliding galaxies
  Cambridge University PressComputational Star Formation, Proceedings of the International Astronomical Union, IAU Symposium, 270, 483, 486, 2011
• Dark Satellites of the Milky Way
  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
• Dark satellites of the milky way
  Takashi Okamoto, AIP Conference Proceedings, 1240, 399, 402, 2010
  English
• Suppression of Galaxy Formation Due to an Ultraviolet-Background Radiation
  OKAMOTO Takashi, The astronomical herald, 102, 12, 759, 768, 20 Nov. 2009
  日本天文学会, Japanese
• 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
  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.
• Simulations of coevolving galaxies and supermassive black holes
  Takashi Okamoto, Astrophysics and Space Science Proceedings, 202419, 367, 2008
  Springer Netherlands, English
• Chemical Abundance Patterns in the Local Dwarf Galaxies in the CDM Universe
  Masahiro Nagashima; Takashi Okamoto, PANORAMIC VIEWS OF GALAXY FORMATION AND EVOLUTION, PROCEEDINGS, 399, 475, +, 2008
  English
• 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
  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
  Takayuki R. Saitoh; Jin Koda; Takashi Okamoto; Keiichi Wada; Asao Habe, MAPPING THE GALAXY AND NEARBY GALAXIES, 373, 373, 2008
  English
• Simulations of Coevolving Galaxies and Supermassive Black Holes
  SpringerMapping the Galaxy and Nearby Galaxies, Astrophysics and Space Science Proceedings, 367, 2008
• AM06-19-011 Origin of the Milkyway
  SAITOH Takayuki; DAISAKA Hiroshi; IDETA Makoto; OKAMOTO Takashi; KOKUBO Eiichiro; WADA Keiichi; TOMISAKA Kohji; MAKINO Junichiro; YOSHIDA Naoki, 日本流体力学会年会講演論文集, 2006, 286, 286, 2006
  In this paper, we introduce Project "Origin of the Milkyway". This project aims at reliable modeling of the formation history of our Galaxy (i.e., the Milkyway), as a typical spiral galaxy, with the mass resolution 2-3 orders of magnitude higher than what has been achieved so far. In order to achieve such state-of-the-art simulations, we construct two beowulf type PC-clusters with GRAPE-6A/7, and we develop a new N-body/SPH code for parallel computing., 日本流体力学会, Japanese
• The metal enrichment of galaxies and galaxy clusters in the cold dark matter universe
  M. Nagashima; C. G. Lacey; T. Okamoto; C. M. Baugh; C. S. Frenk; S. Cole, ORIGIN OF MATTER AND EVOLUTION OF GALAXIES, 847, 442, +, 2006
  English
• Cosmic cookery: Making a stereoscopic 3D animated movie
  Nick Holliman; Carlton Baugh; Carlos Frenk; Adrian Jenkins; Barbara Froner; Djamel Hassaine; John Helly; Nigel Metcalfe; Takashi Okamoto, STEREOSCOPIC DISPLAYS AND VIRTUAL REALITY SYSTEMS XIII, 6055, 34, 45, 2006
  English
• 超高分解能銀河形成シミュレーション
  斎藤貴之; 幸田仁; 幸田仁; 岡本崇; 岡本崇; 和田桂一; 羽部朝男, 日本天文学会年会講演予稿集, 2004, 2004
• 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
• 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
• 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
• 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
• 銀河形成期のガスの力学的進化
  斎藤貴之; 幸田仁; 岡本崇; 和田桂一; 羽部朝男, 日本天文学会年会講演予稿集, 2003, 2003
• Morphological evolution of cluster galaxies
  T Okamoto; M Nagashima, GALAXY EVOLUTION: THEORY AND OBSERVATIONS, 17, 98, 99, 2003
  English
• Environmental effects on evolution of cluster galaxies
  T Okamoto; M Nagashima, ASTROPHYSICAL SUPERCOMPUTING USING PARTICLE SIMULATIONS, 208, 435, 436, 2003
  English
• 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
• Substructure of galaxy clusters and cosmological constant
  T Suwa; A Habe; K Yoshikawa; T Okamoto, ASTROPHYSICAL SUPERCOMPUTING USING PARTICLE SIMULATIONS, 208, 447, 448, 2003
  English
• Cloud mass function in a gas rich dwarf galaxy
  T Saitou; A Habe, ASTROPHYSICAL SUPERCOMPUTING USING PARTICLE SIMULATIONS, 208, 441, 442, 2003
  English
• Environmental Effects on Evolution of Cluster Galaxies
  Astronomical Society of the PacificAstrophysical Supercomputing using Particle Simulations, IAU Symposium #208, 435, 2003
• 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
• 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
• Properties of galaxies in rich clusters
  T Okamoto; M Nagashima, PHYSICS OF GALAXY FORMATION, PROCEEDINGS, 222, 149, 154, 2001
  English
• Properties of Galaxies in Rich Clusters
  Astronomical Society of the Pacific,The Physics of Galaxy Formation, ASP Conference Proceedings, Vol. 222, 222, 149, 2001
• Formation and evolution of galactic halos in a cluster of galaxies
  Habe, A.; Okamoto, T., Nuclear Physics B Proceedings Supplements, 80, Jan. 2000
  ...
• 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
• 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
• Formation and Evolution of Galactic Halos in Clusters of Galaxies
  Okamoto, T.; Habe, A., Numerical Astrophysics, 80, 1999
  ...

• 宇宙物理学１, 2024年, 修士課程, 理学院
• 現代物理学入門, 2024年, 修士課程, 理学院
• 大学院共通授業科目（一般科目）：自然科学・応用科学, 2024年, 修士課程, 大学院共通科目
• プログラミング入門, 2024年, 学士課程, 総合教育部
• 物理学Ⅰ, 2024年, 学士課程, 全学教育
• 物理学Ⅱ, 2024年, 学士課程, 全学教育
• 物理学卒業研究Ⅰ, 2024年, 学士課程, 理学部
• 物理学卒業研究Ⅱ, 2024年, 学士課程, 理学部
• 物理数学Ⅱ, 2024年, 学士課程, 理学部

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

• 活動銀河核構造の全波長域新パラダイムの確立
  科学研究費助成事業
  05 Apr. 2021 - 31 Mar. 2025
  和田 桂一; 長尾 透; 岸本 真; 上田 佳宏; 中川 貴雄; 泉 拓磨; 岡本 崇
  日本学術振興会, 基盤研究(A), 鹿児島大学, 21H04496
• 宇宙構造形成理論から迫るダークマター
  科学研究費助成事業 学術変革領域研究(A)
  19 Nov. 2020 - 31 Mar. 2025
  安藤 真一郎; 樽家 篤史; 岡本 崇; 西道 啓博; 白崎 正人; Dalal Neal
  日本学術振興会, 学術変革領域研究(A), 東京大学, 20H05861
• 銀河団形成領域の高分解能計算と広視野・高分解能観測で解き明かす銀河と銀河団の進化
  科学研究費助成事業 基盤研究(B)
  01 Apr. 2019 - 31 Mar. 2022
  岡本 崇; 諸隈 佳菜; 児玉 忠恭
  銀河団内に形成される巨大楕円銀河は現在ほとんど星形成活動をしていない．このような大質量銀河の星形成を抑制するには銀河中心に存在する超大質量ブラックホール (SMBH) をエンジンとする活動銀河核からのエネルギー放出 (AGN フィードバック) が必要であると考えられている．2019 年度は，この SMBH の成長と AGN フィードバックを宇宙論的銀河形成シミュレーションで銀河形成と整合的に扱うためのシミュレーションコードを開発した．その際，シミュレーションの分解能に結果が強く依存しないように，SMBH へのガス降着は高分解能シミュレーションの結果にもとづいて実装した．
  まず，AGN フィードバックよりも超新星爆発が星形成の抑制を担っていると考えられている天の川銀河程度の質量の銀河のシミュレーションをそれぞれ AGN フィードバックをありとなしの 2 種類行った．AGN フィードバックとしては AGN 光度の 2% (降着質量エネルギーの 0.2%）をフィードバックの効率として仮定した．
  その結果，AGN フィードバックを入れても，母銀河の星形成史はそれがない場合と比較してほとんど変化しなかった．一方，SMBH の成長は AGN フィードバックにより強く抑制されて，最終的な SMBH の質量は AGN フィードバックを考慮したものの方がそうでもないものよりも1桁以上小さかった．
  このことは，バルジの星質量や速度分散と SMBH 質量の観測的関係を用いて AGN フィードバックの効率を決定できることを意味する．こうして決定した AGN フィードバックを用いて大質量銀河のシミュレーション（そこでは AGN フィードバックにより銀河の星形成が抑制されていると考えられている）を行うことにより，AGN フィードバックに今回考えたものと別のモードが必要かどうかを明らかにできる．
  日本学術振興会, 基盤研究(B), 北海道大学, 19H01931
• 銀河形成シミュレーションで探る衛星銀河サブハロー構造のダークマターモデル依存性
  科学研究費助成事業
  01 Apr. 2018 - 31 Mar. 2020
  岡本 崇
  高分解能の天の川質量銀河の形成シミュレーションを実行した．これは衛星銀河のダークマターハロー（サブハロー）の構造を十分に扱える高分解能シミュレーションである．そのさい，一般的に仮定されるコールドダークマター (CDM) だけでなく，ダークマター同士が弾性衝突をする self-interacting dark matter (SIDM) も考慮できるシミュレーションコードを開発した．また，サブハローの構造に大きな影響を与えると考えられている超新星爆発の影響を，超新星残骸の高分解能シミュレーションの結果を用いて物理的に正しい形で取り入れた．SIDM には観測的な制限の範囲内で矮小銀河スケールで CDM と大きく異なる振る舞いをするように，相対速度が小さいほど衝突断面積が大きくなるモデルを採用した．
  その結果，CDM と SIDM の両者で局所銀河群の衛星銀河の観測的性質は再現できた．一方，両者の違いは V-band で -10 等より暗いところで顕著であり，特徴的な半径内のダークマターの面密度や光度関数をそのような暗い衛星銀河にについて求めることで区別可能であることを示した．
  また，CDM と SIDM では衛星銀河の空間分布に大きな違いがあることが明らかになった．これは SIDM ではサブハローの中心密度が下がることにより，潮汐力によりホストダークマターハロー中心部の衛星銀河が破壊されてしまうためである．このため，天の川銀河近傍の衛星銀河の分布を調べることでもダークマターの性質に制限をつけられることがわかった．
  日本学術振興会, 新学術領域研究(研究領域提案型), 北海道大学, 18H04333
• 銀河形成シミュレーションで迫るダークマターの正体
  新学術領域研究(研究領域提案型)
  Apr. 2016 - Mar. 2018
  岡本 崇
  文部科学省, Principal investigator, Competitive research funding
• The role of radiation feedback in driving galactic outflows
  Grants-in-Aid for Scientific Research
  2012 - 2015
  Okamoto Takashi
  For studying roles of radiation from young massive stars in driving galactic outflows, we have developed a new radiation transfer code that can efficiently run on massively parallel computers including a cluster of GPGPUs. We have also implemented a phenomenological model of radiation pressure on dust grains in cosmological simulations of galaxy formation. We find that, without this process, evolution of a stellar mass-gas metallicity relation of star-forming galaxies cannot be explained.
  Japan Society for the Promotion of Science, Grant-in-Aid for Young Scientists (B), Hokkaido University, Principal investigator, Competitive research funding, 24740112
• 三次元輻射流体シミュレーションで探る銀河形成の物理
  科学研究費補助金(若手研究(スタートアップ), 研究活動スタート支援)
  2009 - 2010
  岡本 崇
  輻射輸送は,宇宙物理学において極めて基本的かつ重要な物理過程であり,例えばガスの冷却,大質量星や銀河中心超巨大ブラックホールからの輻射によるガスの光電離加熱や輻射圧による銀河風の駆動など,銀河形成においても無視できない役割を担っているはずである.しかしながら,空間3次元,角度2次元,波長1次元の計6次元を扱わねばならないという多次元性のために,現在までの研究ではその効果はほぼ無視されてきた.本研究では,輻射輸送計算の精度を落とさずに大幅に加速する新たなアルゴリズムを開発し,実際にその性能と精度を確認した.その結果既存のアルゴリズムでは実現不可能であった多数の光源を用いた輻射輸送計算を可能にした.この手法を用いることにより,銀河内の星による輻射性フィードバックの効果等を定量的に調べることが可能になり,銀河形成に対する理解が深まることが期待される.今後は流体計算,自己重力計算コードと統合し,上記の,大質量星や銀河中心超巨大ブラックホールからの輻射が銀河形成に果たす役割を明らかにしていく計画である.
  また,大規模な銀河形成シミュレーションを行い,銀河のハロー星の起源についても研究を行った.その結果,現在の標準的な宇宙モデルの元では,銀河系のハロー星を説明することが困難であることを明らかにした.
  文部科学省, 若手研究(スタートアップ), 研究活動スタート支援, 筑波大学, Principal investigator, Competitive research funding, 21840015
• 星間ガスの内部構造及びダストの分布を考慮した銀河の形成進化の研究
  科学研究費助成事業 特別研究員奨励費
  2004 - 2006
  岡本 崇
  自己重力・流体力学用シュミレーションコードに、銀河形成を調べる上で必要となる、ガス冷却、星形成、超新星爆発によるガスの過熱と重元素汚染等の効果を組み入れ、宇宙論的な銀河形成を研究できるようにした。さらに、銀河中心巨大ブラックホールの共進化を調べた。結果は、国際会議「Mapping the Galaxy and Nearby Galaxies]で報告した。現在Monthly Notice of Royal Astronomical Societyに論文を投稿中である。
  また、過去に行った宇宙論的な銀河形成シュミレーションを解析することにより、何故天の川銀河の衛星銀河はほぼ同一平面状に分布しているのか、またその平面はなぜ銀河円盤と直行しているのかを明らかにした(Libeskind et al. 2007).
  準解析的モデルを用いて、階層的構造形成の元で、銀河内の星の重元素量比と金属量の間の関係が自然に説明できることを示した。また、星形成のタイムスケールの違いにより、銀河円盤と銀河バルジでは、金属量の確率分布及び重元素量比と金属量の間の関係が異なる可能性を指摘した(Nagasima and Okamoto 2006).
  日本学術振興会, 特別研究員奨励費, 国立天文台, 04J01891
• Galaxy Formation
  Competitive research funding