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Kazuyuki Omukai

Section

Graduate School of Science

Job title

Professor

Degree

博士（理学） (Kyoto University)

researchmap

https://researchmap.jp/7000014660

J-GLOBAL ID

201601000164682319

Research History 1

2013/04 - Present

Tohoku University　Graduate School of Science Department of Astronomy　Professor

Research Interests 2

宇宙物理学
天文学、宇宙物理学

Research Areas 1

Natural sciences / Astronomy /

Papers 120

Massive Black Hole Seed Formation in Strong X-Ray Environments at High Redshift

Kazutaka Kimura, Kohei Inayoshi, Kazuyuki Omukai

ASTROPHYSICAL JOURNAL　990　(2)　2025/09/10

DOI： 10.3847/1538-4357/adf2ad 　

ISSN： 0004-637X

eISSN： 1538-4357
Formation of supermassive stars and dense star clusters in metal-poor clouds exposed to strong FUV radiation

Sunmyon Chon, Kazuyuki Omukai

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY　539　(3)　2561-2582　2025/05

DOI： 10.1093/mnras/staf598 　

ISSN： 0035-8711

eISSN： 1365-2966
Impact of the Lyα radiation force on super-Eddington accretion on to a massive black hole

Takuya Mushano, Takumi Ogawa, Ken Ohsuga, Hidenobu Yajima, Kazuyuki Omukai

PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN　76　(6)　1260-1269　2024/10/23

DOI： 10.1093/pasj/psae086 　

ISSN： 0004-6264

eISSN： 2053-051X
Gravitational collapse at low to moderate Mach numbers: The relationship between star formation efficiency and the fraction of mass in the massive object

Jorge Saavedra-Bastidas, Dominik R. G. Schleicher, Ralf S. Klessen, Sunmyon Chon, Kazuyuki Omukai, Thomas Peters, Lewis R. Prole, Bastian Reinoso, Rafeel Riaz, Paulo Solar

ASTRONOMY & ASTROPHYSICS　690　2024/10/07

DOI： 10.1051/0004-6361/202450409 　

ISSN： 0004-6361

eISSN： 1432-0746
The Impact of Stellar Radiative Feedback on Formation of Young Massive Clusters via Fast H <sc>i</sc> Gas Collisions

Ryunosuke Maeda, Tsuyoshi Inoue, Kazuyuki Omukai, Yasuo Fukui, Kisetsu Tsuge

ASTROPHYSICAL JOURNAL　971　(1)　2024/08/01

DOI： 10.3847/1538-4357/ad5a05 　

ISSN： 0004-637X

eISSN： 1538-4357
First star formation in extremely early epochs

Mana Ito, Kazuyuki Omukai

PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN　76　(4)　850-862　2024/07/05

DOI： 10.1093/pasj/psae054 　

ISSN： 0004-6264

eISSN： 2053-051X
Impact of turbulent magnetic fields on disk formation and fragmentation in first star formation

Kenji Eric Sadanari, Kazuyuki Omukai, Kazuyuki Sugimura, Tomoaki Matsumoto, Kengo Tomida

PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN　76　(4)　823-840　2024/06/21

DOI： 10.1093/pasj/psae051 　

ISSN： 0004-6264

eISSN： 2053-051X
Impact of radiative feedback on the initial mass function of metal-poor stars

Sunmyon Chon, Takashi Hosokawa, Kazuyuki Omukai, Raffaella Schneider

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY　530　(3)　2453-2474　2024/04/25

DOI： 10.1093/mnras/stae1027 　

ISSN： 0035-8711

eISSN： 1365-2966
Exploring the nature of UV-bright z ≳ 10 galaxies detected by JWST: star formation, black hole accretion, or a non-universal IMF?

Alessandro Trinca, Raffaella Schneider, Rosa Valiante, Luca Graziani, Arianna Ferrotti, Kazuyuki Omukai, Sunmyon Chon

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY　529　(4)　3563-3581　2024/03/23

DOI： 10.1093/mnras/stae651 　

ISSN： 0035-8711

eISSN： 1365-2966
Formation of Massive and Wide First-star Binaries in Radiation Hydrodynamic Simulations

Kazuyuki Sugimura, Tomoaki Matsumoto, Takashi Hosokawa, Shingo Hirano, Kazuyuki Omukai

The Astrophysical Journal　959　(1)　17-17　2023/11/30
Publisher: American Astronomical Society
DOI： 10.3847/1538-4357/ad02fc 　

ISSN： 0004-637X

eISSN： 1538-4357

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Abstract We study the formation of Population III stars by performing radiation hydrodynamic simulations for three different initial clouds extracted from cosmological hydrodynamic simulations. Starting from the cloud collapse stage, we follow the growth of protostars by accretion for ∼10⁵ yr until the radiative feedback from the protostars suppresses the accretion and the stellar properties are nearly fixed. We find that Population III stars form in massive and wide binary/small-multiple stellar systems, with masses >30 M_⊙ and separations >2000 au. We also find that the properties of the final stellar system correlate with those of the initial clouds: the total mass increases with the cloud-scale accretion rate, and the angular momentum of the binary orbit matches that of the initial cloud. While the total mass of the system in our simulations is consistent with our previous single-star formation simulations, individual masses are lower due to mass sharing, suggesting potential modification in the extent of feedback from Population III stars in the subsequent evolution of the Universe. We also identify such systems as mini-binaries embedded in a wider outer multiple-star system, which could evolve into progenitors for observed gravitational wave events.
Metallicity Dependence of Molecular Cloud Hierarchical Structure at Early Evolutionary Stages

Masato I. N. Kobayashi, Kazunari Iwasaki, Kengo Tomida, Tsuyoshi Inoue, Kazuyuki Omukai, Kazuki Tokuda

The Astrophysical Journal　954　(1)　38-38　2023/08/22
Publisher: American Astronomical Society
DOI： 10.3847/1538-4357/ace34e 　

ISSN： 0004-637X

eISSN： 1538-4357

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Abstract The formation of molecular clouds out of H i gas is the first step toward star formation. Its metallicity dependence plays a key role in determining star formation throughout cosmic history. Previous theoretical studies with detailed chemical networks calculate thermal equilibrium states and/or thermal evolution under one-zone collapsing background. The molecular cloud formation in reality, however, involves supersonic flows, and thus resolving the cloud internal turbulence/density structure in three dimensions is still essential. We here perform magnetohydrodynamics simulations of 20 km s⁻¹ converging flows of warm neutral medium (WNM) with 1 μG mean magnetic field in the metallicity range from the solar (1.0 Z_⊙) to 0.2 Z_⊙ environment. The cold neutral medium (CNM) clumps form faster with higher metallicity due to more efficient cooling. Meanwhile, their mass functions commonly follow ${dn}/{dm}\propto {m}^{-1.7}$ at three cooling times regardless of the metallicity. Their total turbulence power also commonly shows the Kolmogorov spectrum with its 80% in the solenoidal mode, while the CNM volume alone indicates the transition toward Larson’s law. These similarities measured at the same time in units of the cooling time suggest that the molecular cloud formation directly from the WNM alone requires a longer physical time in a lower-metallicity environment in the 1.0–0.2 Z_⊙ range. To explain the rapid formation of molecular clouds and subsequent massive star formation possibly within ≲10 Myr as observed in the Large/Small Magellanic Clouds, the H i gas already contains CNM volume instead of pure WNM.
Vanishing Love numbers of black holes in general relativity: From spacetime conformal symmetry of a two-dimensional reduced geometry Peer-reviewed

Takuya Katagiri, Masashi Kimura, Hiroyuki Nakano, Kazuyuki Omukai

Physical Review D　107　(12)　2023/06/14
Publisher: American Physical Society (APS)
DOI： 10.1103/physrevd.107.124030 　

ISSN： 2470-0010

eISSN： 2470-0029
A needle in a haystack? Catching Population III stars in the epoch of reionization: I. Population III star-forming environments

Alessandra Venditti, Luca Graziani, Raffaella Schneider, Laura Pentericci, Claudia Di Cesare, Umberto Maio, Kazuyuki Omukai

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY　522　(3)　3809-3830　2023/05/02

DOI： 10.1093/mnras/stad1201 　

ISSN： 0035-8711

eISSN： 1365-2966
Direct-collapse black hole formation induced by internal radiation of host haloes Peer-reviewed

Gen Chiaki, Sunmyon Chon, Kazuyuki Omukai, Alessandro Trinca, Raffaella Schneider, Rosa Valiante

Monthly Notices of the Royal Astronomical Society　521　(2)　2845-2859　2023/03/06
Publisher: Oxford University Press (OUP)
DOI： 10.1093/mnras/stad689 　

ISSN： 0035-8711

eISSN： 1365-2966

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ABSTRACT We estimate the fraction of haloes that host supermassive black holes (SMBHs) forming through the direct-collapse (DC) scenario by using cosmological N-body simulations combined with a semi-analytic model for galaxy evolution. While in most of earlier studies, the occurrence of DC is limited only in chemically pristine haloes, we here suppose that DC can occur also in haloes with metallicity below a threshold value Zth = 0–10−3 Z⊙, considering the supercompetitive accretion pathway for DC black hole (DCBH) formation. In addition, we consider for the first time, the effect of Lyman–Werner (LW) radiation from stars within host haloes, i.e. internal radiation. We find that with low threshold metallicities of Zth ≤ 10−4 Z⊙, the inclusion of internal radiation rather reduces the number density of DCBHs from 0.2–0.3 to 0.03–0.06 Mpc−3. This is because star formation is suppressed due to self-regulation, and the LW flux emitted by neighbouring haloes is reduced. Only when Zth is as high as 10−3 Z⊙, internal radiation enhances the number density of DCBHs from 0.4 to 1 Mpc−3, thereby decreasing the threshold halo mass above which at least one DCBH forms from 2 × 109 to 9 × 108 M⊙. We also find that haloes with Mhalo ≳ 1011–1012 M⊙ can host more than one DCBH at z = 0. This indicates that the DC scenario alone can explain the observed number of SMBH-hosting galaxies.
Non-ideal magnetohydrodynamic simulations of the first star formation: the effect of ambipolar diffusion Peer-reviewed

Kenji Eric Sadanari, Kazuyuki Omukai, Kazuyuki Sugimura, Tomoaki Matsumoto, Kengo Tomida

Monthly Notices of the Royal Astronomical Society　2022/12/30

DOI： 10.1093/mnras/stac3724 　
Protostellar-disc fragmentation across all metallicities Peer-reviewed

Ryoki Matsukoba, Kei E. Tanaka, Kazuyuki Omukai, Eduard Vorobyov, Takashi Hosokawa

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY　515　(4)　5506-5522　2022/08

DOI： 10.1093/mnras/stac2161 　

ISSN： 0035-8711

eISSN： 1365-2966
Impact of the cosmic background radiation on the initial mass function of metal-poor stars Peer-reviewed

Sunmyon Chon, Haruka Ono, Kazuyuki Omukai, Raffaella Schneider

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY　514　(3)　4639-4654　2022/07

DOI： 10.1093/mnras/stac1549 　

ISSN： 0035-8711

eISSN： 1365-2966
Merger Rate Density of Binary Black Holes through Isolated Population I, II, III and Extremely Metal-poor Binary Star Evolution Peer-reviewed

Ataru Tanikawa, Takashi Yoshida, Tomoya Kinugawa, Alessandro A. Trani, Takashi Hosokawa, Hajime Susa, Kazuyuki Omukai

The Astrophysical Journal　926　(1)　83-83　2022/02/01

DOI： 10.3847/1538-4357/ac4247 　

ISSN： 0004-637X

eISSN： 1538-4357
Transition of the initial mass function in the metal-poor environments Peer-reviewed

Sunmyon Chon, Kazuyuki Omukai, Raffaella Schneider

Monthly Notices of the Royal Astronomical Society　508　(3)　4175-4192　2021/09/07

DOI： 10.1093/mnras/stab2497 　

ISSN： 0035-8711

eISSN： 1365-2966
Light, medium-weight, or heavy? The nature of the first supermassive black hole seeds Peer-reviewed

Federica Sassano, Raffaella Schneider, Rosa Valiante, Kohei Inayoshi, Sunmyon Chon, Kazuyuki Omukai, Lucio Mayer, Pedro R. Capelo

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY　506　(1)　613-632　2021/09

DOI： 10.1093/mnras/stab1737 　

ISSN： 0035-8711

eISSN： 1365-2966
Radiation hydrodynamics simulations of line-driven AGN disc winds: metallicity dependence and black hole growth Peer-reviewed

Mariko Nomura, Kazuyuki Omukai, Ken Ohsuga

Monthly Notices of the Royal Astronomical Society　507　(1)　904-913　2021/08/19

DOI： 10.1093/mnras/stab2214 　

ISSN： 0035-8711

eISSN： 1365-2966
Magnetohydrodynamic effect on first star formation: prestellar core collapse and protostar formation Peer-reviewed

Kenji Eric Sadanari, Kazuyuki Omukai, Kazuyuki Sugimura, Tomoaki Matsumoto, Kengo Tomida

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY　505　(3)　4197-4214　2021/05/07

DOI： 10.1093/mnras/stab1330 　

ISSN： 0035-8711

eISSN： 1365-2966
Formation of the first galaxies in the aftermath of the first supernovae Peer-reviewed

Makito Abe, Hidenobu Yajima, Sadegh Khochfar, Claudio Dalla Vecchia, Kazuyuki Omukai

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY　508　(3)　3226-3238　2021/05/06

DOI： 10.1093/mnras/stab2637 　

ISSN： 0035-8711

eISSN： 1365-2966
Signatures of Hierarchical Mergers in Black Hole Spin and Mass distribution Peer-reviewed

Hiromichi Tagawa, Zoltán Haiman, Imre Bartos, Bence Kocsis, Kazuyuki Omukai

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY　507　(3)　3362-3380　2021/04/19

DOI： 10.1093/mnras/stab2315 　

ISSN： 0035-8711

eISSN： 1365-2966
Gravitational Wave Physics and Astronomy in the nascent era Peer-reviewed

Makoto Arimoto, Hideki Asada, Michael L. Cherry, Michiko S. Fujii, Yasushi Fukazawa, Akira Harada, Kazuhiro Hayama, Takashi Hosokawa, Kunihito Ioka, Yoichi Itoh, Nobuyuki Kanda, Koji S. Kawabata, Kyohei Kawaguchi, Nobuyuki Kawai, Tsutomu Kobayashi, Kazunori Kohri, Yusuke Koshio, Kei Kotake, Jun Kumamoto, Masahiro N. Machida, Hideo Matsufuru, Tatehiro Mihara, Masaki Mori, Tomoki Morokuma, Shinji Mukohyama, Hiroyuki Nakano, Tatsuya Narikawa, Hitoshi Negoro, Atsushi Nishizawa, Takayuki Ohgami, Kazuyuki Omukai, Takanori Sakamoto, Shigeyuki Sako, Mahito Sasada, Yuichiro Sekiguchi, Motoko Serino, Jiro Soda, Satoshi Sugita, Kohsuke Sumiyoshi, Hajime Susa, Teruaki Suyama, Hirotaka Takahashi, Kazuya Takahashi, Tomoya Takiwaki, Takahiro Tanaka, Masaomi Tanaka, Ataru Tanikawa, Nozomu Tominaga, Nami Uchikata, Yousuke Utsumi, Mark R. Vagins, Kei Yamada, Michitoshi Yoshida

PROGRESS OF THEORETICAL AND EXPERIMENTAL PHYSICS　2021/04/06

DOI： 10.1093/ptep/ptab042 　

ISSN： 2050-3911
Cosmological direct-collapse black hole formation sites hostile for their growth Peer-reviewed

Sunmyon Chon, Takashi Hosokawa, Kazuyuki Omukai

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY　502　(1)　700-713　2021/03

DOI： 10.1093/mnras/stab061 　

ISSN： 0035-8711

eISSN： 1365-2966
Ionization degree and magnetic diffusivity in star-forming clouds with different metallicities Peer-reviewed

Daisuke Nakauchi, Kazuyuki Omukai, Hajime Susa

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY　502　(3)　3394-3416　2021/01/26

DOI： 10.1093/mnras/stab248 　

ISSN： 0035-8711

eISSN： 1365-2966
Eccentric Black Hole Mergers in Active Galactic Nuclei Peer-reviewed

Hiromichi Tagawa, Bence Kocsis, Zoltán Haiman, Imre Bartos, Kazuyuki Omukai, Johan Samsing

The Astrophysical Journal　907　(1)　L20-L20　2021/01/21
Publisher: American Astronomical Society
DOI： 10.3847/2041-8213/abd4d3 　

eISSN： 2041-8213
Disc fragmentation and intermittent accretion on to supermassive stars Peer-reviewed

Ryoki Matsukoba, Eduard I Vorobyov, Kazuyuki Sugimura, Sunmyon Chon, Takashi Hosokawa, Kazuyuki Omukai

Monthly Notices of the Royal Astronomical Society　500　(3)　4126-4138　2020/12/04
Publisher: Oxford University Press (OUP)
DOI： 10.1093/mnras/staa3462 　

ISSN： 0035-8711

eISSN： 1365-2966

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<title>ABSTRACT</title> Supermassive stars (SMSs) with ∼104–105 M⊙ are candidate objects for the origin of supermassive black holes observed at redshift z &gt; 6. They are supposed to form in primordial-gas clouds that provide the central stars with gas at a high accretion rate, but their growth may be terminated in the middle due to the stellar ionizing radiation if the accretion is intermittent and its quiescent periods are longer than the Kelvin–Helmholtz (KH) time-scales at the stellar surfaces. In this paper, we examine the role of the ionizing radiation feedback based on the accretion history in two possible SMS-forming clouds extracted from cosmological simulations, following their evolution with vertically integrated two-dimensional hydrodynamic simulations with detailed thermal and chemical models. The consistent treatment of the gas thermal evolution is crucial for obtaining the realistic accretion history, as we demonstrate by performing an additional run with a barotropic equation of state, in which the fluctuation of the accretion rate is artificially suppressed. We find that although the accretion becomes intermittent due to the formation of spiral arms and clumps in gravitationally unstable discs, the quiescent periods are always shorter than the KH time-scales, implying that SMSs can form without affected by the ionizing radiation.
Mass-gap Mergers in Active Galactic Nuclei Peer-reviewed

Hiromichi Tagawa, Bence Kocsis, Zoltan Haiman, Imre Bartos, Kazuyuki Omukai, Johan Samsing

ASTROPHYSICAL JOURNAL　908　(2)　2020/11/30

DOI： 10.3847/1538-4357/abd555 　

ISSN： 0004-637X

eISSN： 1538-4357
Pulsation-driven Mass Loss from Massive Stars behind Stellar Mergers in Metal-poor Dense Clusters Peer-reviewed

Daisuke Nakauchi, Kohei Inayoshi, Kazuyuki Omukai

The Astrophysical Journal　902　(1)　81-81　2020/10/01
Publisher: American Astronomical Society
DOI： 10.3847/1538-4357/abb463 　

ISSN： 0004-637X

eISSN： 1538-4357
Star cluster formation and cloud dispersal by radiative feedback: dependence on metallicity and compactness Peer-reviewed

Hajime Fukushima, Hidenobu Yajima, Kazuyuki Sugimura, Takashi Hosokawa, Kazuyuki Omukai, Tomoaki Matsumoto

Monthly Notices of the Royal Astronomical Society　497　(3)　3830-3845　2020/09/21
Publisher: Oxford University Press (OUP)
DOI： 10.1093/mnras/staa2062 　

ISSN： 0035-8711

eISSN： 1365-2966

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<title>ABSTRACT</title> We study star cluster formation in various environments with different metallicities and column densities by performing a suite of 3D radiation hydrodynamics simulations. We find that the photoionization feedback from massive stars controls the star formation efficiency (SFE) in a star-forming cloud, and its impact sensitively depends on the gas metallicity Z and initial cloud surface density Σ. At Z = 1 Z⊙, SFE increases as a power law from 0.03 at Σ = 10 M⊙ pc−2 to 0.3 at $\Sigma = 300\,\mathrm{M}_{\odot }\, {\rm pc^{-2 } }$. In low-metallicity cases $10^{-2}\!-\!10^{-1}\, \mathrm{Z}_{\odot }$, star clusters form from atomic warm gases because the molecule formation time is not short enough with respect to the cooling or dynamical time. In addition, the whole cloud is disrupted more easily by expanding H ii bubbles that have higher temperature owing to less efficient cooling. With smaller dust attenuation, the ionizing radiation feedback from nearby massive stars is stronger and terminate star formation in dense clumps. These effects result in inefficient star formation in low-metallicity environments: the SFE drops by a factor of ∼3 at Z = 10−2 Z⊙ compared to the results for Z = 1 Z⊙, regardless of Σ. Newborn star clusters are also gravitationally less bound. We further develop a new semi-analytical model that can reproduce the simulation results well, particularly the observed dependencies of the SFEs on the cloud surface densities and metallicities.
Accretion bursts in low-metallicity protostellar disks

E. I. Vorobyov, V. G. Elbakyan, K. Omukai, T. Hosokawa, R. Matsukoba, M. Guedel

ASTRONOMY & ASTROPHYSICS　641　A72-A72　2020/06/30

DOI： 10.1051/0004-6361/202038354 　

ISSN： 0004-6361

eISSN： 1432-0746
Thermal evolution of protoplanetary disks: from β-cooling to decoupled gas and dust temperatures

Eduard I. Vorobyov, Ryoki Matsukoba, Kazuyuki Omukai, Manuel Guedel

Astronomy & Astrophysics　638　A102-A102　2020/06
Publisher: EDP Sciences
DOI： 10.1051/0004-6361/202037841 　

ISSN： 0004-6361

eISSN： 1432-0746

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<italic>Aims.</italic> We explore the long-term evolution of young protoplanetary disks with different approaches to computing the thermal structure determined by various cooling and heating processes in the disk and its surroundings. <italic>Methods.</italic> Numerical hydrodynamics simulations in the thin-disk limit were complemented with three thermal evolution schemes: a simplified <italic>β</italic>-cooling approach with and without irradiation, where the rate of disk cooling is proportional to the local dynamical time; a fiducial model with equal dust and gas temperatures calculated taking viscous heating, irradiation, and radiative cooling into account; and a more sophisticated approach allowing decoupled dust and gas temperatures. <italic>Results.</italic> We found that the gas temperature may significantly exceed that of dust in the outer regions of young disks thanks to additional compressional heating caused by the infalling envelope material in the early stages of disk evolution and slow collisional exchange of energy between gas and dust in low-density disk regions. However, the outer envelope shows an inverse trend, with the gas temperatures dropping below that of dust. The global disk evolution is only weakly sensitive to temperature decoupling. Nevertheless, separate dust and gas temperatures may affect the chemical composition, dust evolution, and disk mass estimates. Constant-<italic>β</italic> models without stellar and background irradiation fail to reproduce the disk evolution with more sophisticated thermal schemes because of the intrinsically variable nature of the <italic>β</italic>-parameter. Constant-<italic>β</italic> models with irradiation more closely match the dynamical and thermal evolution, but the agreement is still incomplete. <italic>Conclusions.</italic> Models allowing separate dust and gas temperatures are needed when emphasis is placed on the chemical or dust evolution in protoplanetary disks, particularly in subsolar metallicity environments.
Supermassive star formation via super competitive accretion in slightly metal-enriched clouds

Sunmyon Chon, Kazuyuki Omukai

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY　494　(2)　2851-2860　2020/05

DOI： 10.1093/mnras/staa863 　

ISSN： 0035-8711

eISSN： 1365-2966
The Birth of a Massive First-Star Binary Peer-reviewed

Kazuyuki Sugimura, Tomoaki Matsumoto, Takashi Hosokawa, Shingo Hirano, Kazuyuki Omukai

The Astrophysical Journal Letters　892　(1)　L14-L18　2020/01/31

DOI： 10.3847/2041-8213/ab7d37 　

ISSN： 2041-8205

eISSN： 2041-8213
First galaxy SED: Contribution from pre-main-sequence stars

Hiroto Mitani, Naoki Yoshida, Kazuyuki Omukai, Takashi Hosokawa

Proceedings of the International Astronomical Union　15　(S341)　287-288　2019/11
Publisher: Cambridge University Press (CUP)
DOI： 10.1017/s174392131900259x 　

ISSN： 1743-9213

eISSN： 1743-9221

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Abstract We calculate the spectral energy distribution of the first galaxies which contain pre-main-sequence stars by using the stellar evolution code Modules for Experiments in Stellar Astrophysics, the spectra model BT-Settl, and the stellar population synthesis code PEGASE. We calculate the galaxy spectral energy distribution for Salpeter Initial Mass Function. We find that very young first galaxies are bright also in mid-infrared, and the contribution of pre-main-sequence stars can be significant over 0.1 Myr after a star-formation episode.
Condition for low-mass star formation in shock-compressed metal-poor clouds

Daisuke Nakauchi, Kazuyuki Omukai, Raffaella Schneider

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY　480　(1)　1043-1056　2018/10

DOI： 10.1093/mnras/sty1911 　

ISSN： 0035-8711

eISSN： 1365-2966
Probing the High-Redshift Universe with SPICA: Toward the Epoch of Reionization and Beyond

E. Egami, S. Gallerani, R. Schneider, A. Pallottini, L. Vallini, E. Sobacchi, A. Ferrara, S. Bianchi, M. Bocchio, S. Marassi, L. Armus, L. Spinoglio, A. W. Blain, M. Bradford, D. L. Clements, H. Dannerbauer, J. A. Fernández-Ontiveros, E. González-Alfonso, M. J. Griffin, C. Gruppioni, H. Kaneda, K. Kohno, S. C. Madden, H. Matsuhara, P. Najarro, T. Nakagawa, S. Oliver, K. Omukai, T. Onaka, C. Pearson, I. Perez-Fournon, P. G. Pérez-González, D. Schaerer, D. Scott, S. Serjeant, J. D. Smith, F. F. S. van der Tak, T. Wada, H. Yajima

Publications of the Astronomical Society of Australia　35　2018/09/20

DOI： 10.1017/pasa.2018.41 　

ISSN： 1323-3580

eISSN： 1448-6083
Primordial protostars accreting beyond the $ΩΓ$-limit: radiation effect around the star-disk boundary Peer-reviewed

Sanemichi Z. Takahashi, Kazuyuki Omukai

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY　472　(1)　532-541　2017/08/02

DOI： 10.1093/mnras/stx1988 　

ISSN： 0035-8711

eISSN： 1365-2966
Fates of the dense cores formed by fragmentation of filaments: do they fragment again or not? Peer-reviewed

Kazuyuki Sugimura, Yurina Mizuno, Tomoaki Matsumoto, Kazuyuki Omukai

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY　469　(4)　4022-4033　2017/04/27

DOI： 10.1093/mnras/stx1129 　

ISSN： 0035-8711

eISSN： 1365-2966
Supermassive star formation with non-LTE primordial-gas chemistry

K. Sugimura, C. M. Coppola, K. Omukai, D. Galli, F. Palla

Memorie della Societa Astronomica Italiana - Journal of the Italian Astronomical Society　88　(4)　860-861　2017
Publisher: Societa Astronomica Italiana
ISSN： 1824-016X
Triggering the formation of direct collapse black holes by their congeners Peer-reviewed

Bin Yue, Andrea Ferrara, Fabio Pacucci, Kuzuyuki Omukai

ASTROPHYSICAL JOURNAL　838　(2)　article id. 111-17 pp.　2016/12/23

DOI： 10.3847/1538-4357/aa6627 　

ISSN： 0004-637X

eISSN： 1538-4357
Do Stellar Winds Prevent the Formation of Supermassive Stars by Accretion? Peer-reviewed

Daisuke Nakauchi, Takashi Hosokawa, Kazuyuki Omukai, Hideyuki Saio, Ken'ichi Nomoto

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY　465　(4)　5016-5025　2016/11/29

DOI： 10.1093/mnras/stw3114 　

ISSN： 0035-8711

eISSN： 1365-2966
Limits on Pop III star formation with the most iron-poor stars Peer-reviewed

M. de Bennassuti, S. Salvadori, R. Schneider, R. Valiante, K. Omukai

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY　465　(1)　926-940　2016/10/18

DOI： 10.1093/mnras/stw2687 　

ISSN： 0035-8711

eISSN： 1365-2966
Rapid Black Hole Growth under Anisotropic Radiation Feedback Peer-reviewed

Kazuyuki Sugimura, Takashi Hosokawa, Hidenobu Yajima, Kazuyuki Omukai

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY　469　(1)　62-79　2016/10/11

DOI： 10.1093/mnras/stx769 　

ISSN： 0035-8711

eISSN： 1365-2966
The Final Fates of Accreting Supermassive Stars Peer-reviewed

Hideyuki Umeda, Takashi Hosokawa, Kazuyuki Omukai, Naoki Yoshida

ASTROPHYSICAL JOURNAL LETTERS　830　(2)　L34　2016/09/14

DOI： 10.3847/2041-8205/830/2/L34 　

ISSN： 2041-8205

eISSN： 2041-8213
From the first stars to the first black holes Peer-reviewed

Rosa Valiante, Raffaella Schneider, Marta Volonteri, Kazuyuki Omukai

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY　457　(3)　3356-3371　2016/01/28

DOI： 10.1093/mnras/stw225 　

ISSN： 0035-8711

eISSN： 1365-2966
Supermassive star formation via episodic accretion: protostellar disc instability and radiative feedback efficiency Peer-reviewed

Yuya Sakurai, Eduard I. Vorobyov, Takashi Hosokawa, Naoki Yoshida, Kazuyuki Omukai, Harold W. Yorke

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY　459　(2)　1137-1145　2015/11/19

DOI： 10.1093/mnras/stw637 　

ISSN： 0035-8711

eISSN： 1365-2966
Formation of Massive Primordial Stars: Intermittent UV Feedback with Episodic Mass Accretion Peer-reviewed

Takashi Hosokawa, Shingo Hirano, Rolf Kuiper, Harold W. Yorke, Kazuyuki Omukai, Naoki Yoshida

ASTROPHYSICAL JOURNAL　824　(2)　id.119　2015/10/06

DOI： 10.3847/0004-637X/824/2/119 　

ISSN： 0004-637X

eISSN： 1538-4357
Impact of dust cooling on direct collapse black hole formation Peer-reviewed

M. A. Latif, K. Omukai, M. Habouzit, D. R. G. Schleicher, M. Volonteri

ASTROPHYSICAL JOURNAL　823　(1)　id.40　2015/09/23

DOI： 10.3847/0004-637X/823/1/40 　

ISSN： 0004-637X

eISSN： 1538-4357
Role of the H$_2^+$ channel in the primordial star formation under strong radiation field and the critical intensity for the supermassive star formation Peer-reviewed

Kazuyuki Sugimura, Carla M. Coppola, Kazuyuki Omukai, Daniele Galli, Francesco Palla

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY　456　(1)　270-277　2015/09/15

DOI： 10.1093/mnras/stv2655 　

ISSN： 0035-8711

eISSN： 1365-2966
Primordial Star Formation under the Influence of Far Ultraviolet Radiation: 1540 Cosmological Halos and the Stellar Mass Distribution Peer-reviewed

Shingo Hirano, Takashi Hosokawa, Naoki Yoshida, Kazuyuki Omukai, Harold W. Yorke

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY　448　(1)　568-587　2015/01/07

DOI： 10.1093/mnras/stv044 　

ISSN： 0035-8711

eISSN： 1365-2966
Dissipation of magnetic fields in star-forming clouds with different metallicities Peer-reviewed

Hajime Susa, Kentaro Doi, Kazuyuki Omukai

ASTROPHYSICAL JOURNAL　801　(1)　id.13　2014/12/31

DOI： 10.1088/0004-637X/801/1/13 　

ISSN： 0004-637X

eISSN： 1538-4357
Thermal instability and multi-phase interstellar medium in the first galaxies Peer-reviewed

Tsuyoshi Inoue, Kazuyuki Omukai

ASTROPHYSICAL JOURNAL　805　(1)　id.73　2014/12/18

DOI： 10.1088/0004-637X/805/1/73 　

ISSN： 0004-637X

eISSN： 1538-4357
Supernova dust formation and the grain growth in the early universe: The critical metallicity for low-mass star formation Peer-reviewed

Gen Chiaki, Stefania Marassi, Takaya Nozawa, Naoki Yoshida, Raffaella Schneider, Kazuyuki Omukai, Marco Limongi, Alessandro Chieffi

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY　446　(3)　2659-2672　2014/10/30

DOI： 10.1093/mnras/stu2298 　

ISSN： 0035-8711

eISSN： 1365-2966
The origin of the most iron-poor star Peer-reviewed

Stefania Marassi, Gen Chiaki, Raffaella Schneider, Marco Limongi, Kazuyuki Omukai, Takaya Nozawa, Alessandro Chieffi, Naoki Yoshida

ASTROPHYSICAL JOURNAL　794　(2)　id.100　2014/09/15

DOI： 10.1088/0004-637X/794/2/100 　

ISSN： 0004-637X

eISSN： 1538-4357
The critical radiation intensity for direct collapse black hole formation: dependence on the radiation spectral shape Peer-reviewed

Kazuyuki Sugimura, Kazuyuki Omukai, Akio K. Inoue

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY　445　(1)　544-553　2014/07/15

DOI： 10.1093/mnras/stu1778 　

ISSN： 0035-8711

eISSN： 1365-2966
Conditions for HD Cooling in the First Galaxies Revisited: Interplay between Far-Ultraviolet and Cosmic Ray Feedback in Population III Star Formation Peer-reviewed

Daisuke Nakauchi, Kohei Inayoshi, Kazuyuki Omukai

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY　442　(3)　2667-2679　2014/05/27

DOI： 10.1093/mnras/stu1042 　

ISSN： 0035-8711

eISSN： 1365-2966
Formation of an embryonic supermassive star in the first galaxy Peer-reviewed

Kohei Inayoshi, Kazuyuki Omukai, Elizabeth J. Tasker

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY　445　(1)　L109-L113　2014/04/17

DOI： 10.1093/mnrasl/slu151 　

ISSN： 0035-8711

eISSN： 1365-2966
Dust grain growth and the formation of the extremely primitive star SDSS J102915+172927 Peer-reviewed

Gen Chiaki, Raffaella Schneider, Takaya Nozawa, Kazuyuki Omukai, Marco Limongi, Naoki Yoshida, Alessandro Chieffi

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY　439　(3)　3121-3127　2014/01/20

DOI： 10.1093/mnras/stu178 　

ISSN： 0035-8711

eISSN： 1365-2966
Gravitational instability in protostellar disks at low metallicities Peer-reviewed

Kei E. I. Tanaka, Kazuyuki Omukai

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY　439　(2)　1884-1896　2014/01/13

DOI： 10.1093/mnras/stu069 　

ISSN： 0035-8711

eISSN： 1365-2966
Formation of Primordial Supermassive Stars by Rapid Mass Accretion Peer-reviewed

Takashi Hosokawa, Harold W. Yorke, Kohei Inayoshi, Kazuyuki Omukai, Naoki Yoshida

ASTROPHYSICAL JOURNAL　778　(2)　id.178　2013/08/21

DOI： 10.1088/0004-637X/778/2/178 　

ISSN： 0004-637X

eISSN： 1538-4357
One Hundred First Stars : Protostellar Evolution and the Final Masses Peer-reviewed

Shingo Hirano, Takashi Hosokawa, Naoki Yoshida, Hideyuki Umeda, Kazuyuki Omukai, Gen Chiaki, Harold W. Yorke

ASTROPHYSICAL JOURNAL　781　(2)　id.60　2013/08/21

DOI： 10.1088/0004-637X/781/2/60 　

ISSN： 0004-637X

eISSN： 1538-4357
Photoevaporation of Circumstellar Disks Revisited: The Dust-Free Case Peer-reviewed

Kei E. I. Tanaka, Taishi Nakamoto, Kazuyuki Omukai

ASTROPHYSICAL JOURNAL　773　(2)　155　2013/06/27

DOI： 10.1088/0004-637X/773/2/155 　

ISSN： 0004-637X
Pulsational instability of supergiant protostars: Do they grow supermassive by accretion? Peer-reviewed

Kohei Inayoshi, Takashi Hosokawa, Kazuyuki Omukai

Monthly Notices of the Royal Astronomical Society　431　(4)　3036-3044　2013/02/25

DOI： 10.1093/mnras/stt362 　

ISSN： 0035-8711 1365-2966
Protostellar Feedback and Final Mass of the Second-Generation Primordial Stars Peer-reviewed

Takashi Hosokawa, Naoki Yoshida, Kazuyuki Omukai, Harold W. Yorke

ASTROPHYSICAL JOURNAL LETTERS　760　(2)　2012/10/10

DOI： 10.1088/2041-8205/760/2/L37 　

ISSN： 2041-8205
Dissipation of magnetic fields in low-metallicity clouds Show affiliations

Doi, Kentaro, Susa, Hajime, Omukai, Kazuyuki

FIRST STARS IV - FROM HAYASHI TO THE FUTURE -. AIP Conference Proceedings　1480　349-351　2012/09/01

DOI： 10.1063/1.4754383 　

ISSN： 0094-243X
Do the environmental conditions affect the dust-induced fragmentation in low-metallicity clouds ?: Effect of pre-ionization and far-ultraviolet/cosmic-ray fields Peer-reviewed

Kazuyuki Omukai

PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN　64　(5)　2012/05/01

DOI： 10.1093/pasj/64.5.114 　

ISSN： 0004-6264

eISSN： 2053-051X
The formation of the extremely primitive star SDSS J102915+172927 relies on dust Peer-reviewed

Raffaella Schneider, Kazuyuki Omukai, Marco Limongi, Andrea Ferrara, Ruben Salvaterra, Alessandro Chieffi, Simone Bianchi

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY　423　(1)　L60-L64　2012/03/19

DOI： 10.1111/j.1745-3933.2012.01257.x 　

ISSN： 0035-8711

eISSN： 1365-2966
Rapidly Accreting Supergiant Protostars: Embryos of Supermassive Black Holes? Peer-reviewed

Takashi Hosokawa, Kazuyuki Omukai, Harold W. Yorke

ASTROPHYSICAL JOURNAL　756　(1)　2012/03/12

DOI： 10.1088/0004-637X/756/1/93 　

ISSN： 0004-637X

eISSN： 1538-4357
Supermassive black hole formation by the cold accretion shocks in the first galaxies Peer-reviewed

Kohei Inayoshi, Kazuyuki Omukai

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY　422　(3)　2539-2546　2012/02/24

DOI： 10.1111/j.1365-2966.2012.20812.x 　

ISSN： 0035-8711
Star Formation in the Early Universe

Kazuyuki Omukai

DEATH OF MASSIVE STARS: SUPERNOVAE AND GAMMA-RAY BURSTS　(279)　216-223　2012

DOI： 10.1017/S1743921312012951 　

ISSN： 1743-9213
The Role of Dust in the Early Universe: The Nature of Cosmological Reionization Sources

Daisuke Yamasawa, Asao Habe, Kazuyuki Omukai, Takashi Kozasa, Takaya Nozawa, Hiroyuki Hirashita

FIRST STARS IV - FROM HAYASHI TO THE FUTURE　1480　448-450　2012

DOI： 10.1063/1.4754416 　

ISSN： 0094-243X
Supermassive black hole formation by the cold accretion shocks in the first galaxies Peer-reviewed

K. Inayoshi, K. Omukai

FIRST STARS IV - FROM HAYASHI TO THE FUTURE　1480　309-312　2012

DOI： 10.1063/1.4754373 　

ISSN： 0094-243X
Radiative Feedback from Primordial Protostars and Final Mass of the First Stars Peer-reviewed

Takashi Hosokawa, Kazuyuki Omukai, Naoki Yoshida, Harold W. Yorke

FIRST STARS IV - FROM HAYASHI TO THE FUTURE　1480　91-96　2012

DOI： 10.1063/1.4754335 　

ISSN： 0094-243X
Formation of the first stars in the universe Peer-reviewed

Naoki Yoshida, Takashi Hosokawa, Kazuyuki Omukai

PROGRESS OF THEORETICAL AND EXPERIMENTAL PHYSICS　2012　(1)　2012

DOI： 10.1093/ptep/pts022 　

ISSN： 2050-3911
Variable Accretion Rates and Fluffy First Stars Peer-reviewed

Rowan J. Smith, Takashi Hosokawa, Kazuyuki Omukai, Simon C. O. Glover, Ralf S. Klessen

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY　424　(1)　457-463　2011/12/18

DOI： 10.1111/j.1365-2966.2012.21211.x 　

ISSN： 0035-8711
Protostellar Feedback Halts the Growth of the First Stars in the Universe International-journal Peer-reviewed

Takashi Hosokawa, Kazuyuki Omukai, Naoki Yoshida, Harold W. Yorke

SCIENCE　334　(6060)　1250-1253　2011/11/15

DOI： 10.1126/science.1207433 　

ISSN： 0036-8075
Effect of cosmic ray/X-ray ionization on supermassive black hole formation Peer-reviewed

Kohei Inayoshi, Kazuyuki Omukai

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY　416　(4)　2748-2759　2011/06/14

DOI： 10.1111/j.1365-2966.2011.19229.x 　

ISSN： 0035-8711

eISSN： 1365-2966
Low-Metallicity Star Formation : Prestellar Collapse and Protostellar Accretion in the Spherical Symmetry Peer-reviewed

Kazuyuki Omukai, Takashi Hosokawa, Naoki Yoshida

ASTROPHYSICAL JOURNAL　722　(2)　1793-1815　2010/08/25

DOI： 10.1088/0004-637X/722/2/1793 　

ISSN： 0004-637X
Evolution of Massive Protostars via Disk Accretion Peer-reviewed

Takashi Hosokawa, Harold W. Yorke, Kazuyuki Omukai

ASTROPHYSICAL JOURNAL　721　(1)　478-492　2010/05/17

DOI： 10.1088/0004-637X/721/1/478 　

ISSN： 0004-637X
Mass Accretion Process to the Forming First Star Peer-reviewed

Takashi Hosokawa, Kazuyuki Omukai, Harold W. Yorke

DECIPHERING THE ANCIENT UNIVERSE WITH GAMMA-RAY BURSTS　1279　327-+　2010

DOI： 10.1063/1.3509299 　

ISSN： 0094-243X
Low-metallicity Star Formation and Pop III-II Transition Peer-reviewed

Kazuyuki Omukai

DECIPHERING THE ANCIENT UNIVERSE WITH GAMMA-RAY BURSTS　1279　110-115　2010

DOI： 10.1063/1.3509245 　

ISSN： 0094-243X
The role of the Cosmic Microwave Background in high-z star formation Peer-reviewed

R. Schneider, Kazuyuki Omukai

TOURS SYMPOSIUM ON NUCLEAR PHYSICS AND ASTROPHYSICS - VII　1238　117-+　2010

DOI： 10.1063/1.3455912 　

ISSN： 0094-243X
Low-metallicity Star Formation Peer-reviewed

Kazuyuki Omukai

TOURS SYMPOSIUM ON NUCLEAR PHYSICS AND ASTROPHYSICS - VII　1238　111-116　2010

DOI： 10.1063/1.3455911 　

ISSN： 0094-243X
Magnetohydrodynamics of Population III Star Formation Peer-reviewed

Machida Masahiro N, Omukai Kazuyuki, Matsumoto Tomoaki

FIRST STARS AND GALAXIES: CHALLENGES FOR THE NEXT DECADE　1294　56-+　2010

ISSN： 0094-243X
Metals, dust and the cosmic microwave background: fragmentation of high-redshift star-forming clouds Peer-reviewed

Raffaella Schneider, Kazuyuki Omukai

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY　402　(1)　429-435　2009/10/19

DOI： 10.1111/j.1365-2966.2009.15891.x 　

ISSN： 0035-8711

eISSN： 1365-2966
Star Formation in Relic HII Regions of the First Stars: Binarity and Outflow Driving Peer-reviewed

Masahiro N. Machida, Kazuyuki Omukai, Tomoaki Matsumoto

ASTROPHYSICAL JOURNAL　705　(1)　64-67　2009/09/07

DOI： 10.1088/0004-637X/705/1/64 　

ISSN： 0004-637X
Star Formation Triggered by Supernova Explosions in Young Galaxies Peer-reviewed

Takanori Nagakura, Takashi Hosokawa, Kazuyuki Omukai

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY　399　(4)　2183-2194　2009/07/21

DOI： 10.1111/j.1365-2966.2009.15423.x 　

ISSN： 0035-8711

eISSN： 1365-2966
Low-Metallicity Protostars and the Maximum Stellar Mass Resulting from Radiative Feedback Peer-reviewed

Takashi Hosokawa, Kazuyuki Omukai

ASTROPHYSICAL JOURNAL　703　(2)　1810-1818　2009/06/08

DOI： 10.1088/0004-637X/703/2/1810 　

ISSN： 0004-637X
The space infrared telescope for cosmology and astrophysics: SPICA A joint mission between JAXA and ESA

Bruce Swinyard, Takao Nakagawa, Patrick Merken, Pierre Royer, Tim Souverijns, Bart Vandenbussche, Christoffel Waelkens, Peter Davis, James Di Francesco, Mark Halpern, Martin Houde, Doug Johnstone, Gilles Joncas, David Naylor, Rene Plume, Douglas Scott, A. Abergel, S. Bensammar, J. Braine, V. Buat, D. Burgarella, Ph. Cais, H. Dole, L. Duband, D. Elbaz, M. Gerin, M. Giard, J. Goicoechea, C. Joblin, A. Jones, J. P. Kneib, G. Lagache, S. Madden, R. Pons, F. Pajot, D. Rambaud, L. Ravera, I. Ristorcelli, L. Rodriguez, S. Vives, A. Zavagno, Norbert Geis, Oliver Krause, Dieter Lutz, Albrecht Poglitsch, Walfried Raab, Jutta Stegmaier, Eckhard Sturm, Richard Tuffs, Hyung Mok Lee, Bon-Chul Koo, Myungshin Im, Soojong Pak, Wonyong Han, Jang-Hyun Park, Uk-Won Nam, Ho Jin, Dae-Hee Lee, In-Soo Yuk, Sungho Lee, Yuri Aikawa, Nobuo Arimoto, Yasuo Doi, Keigo Enya, Misato Fukagawa, Reiko Furusho, Sunao Hasegawa, Masahiko Hayashi, Mitsuhiko Honda, Shigeru Ida, Masatoshi Imanishi, Shu-ichiro Inutsuka, Hideyuki Izumiura, Hideyuki Kamaya, Hidehiro Kaneda, Toshihiro Kasuga, Hirokazu Kataza, Koji Kawabata, Mitsunobu Kawada, Hideyo Kawakita, Tsuneo Kii, Jin Koda, Tadayuki Kodama, Eiichiro Kokubo, Keiji Komatsu, Hideo Matsuhara, Toshio Matsumoto, Shuji Matsuura, Takashi Miyata, Hiroshi Murakam, Hirohisa Nagata, Tetsuya Nagata, Tadashi Nakajima, Kobayashi Naoto, Ryoichi Nishi, Atsushi Noda, Atsushi Okamoto, Yoshiko K. Okamoto, Kazuyuki Omukai, Takashi Onaka, Takafumi Ootsubo, Masami Ouchi, Hirobumi Saito, Yoichi Sato, Shigeyuki Sako, Tomohiko Sekiguchi, Hiroshi Shibai, Hiroyuki Sugita, Koji Sugitani, Hajime Susa, Pyo Tae-soo, Motohide Tamura, Yoshihiro Ueda, Munetaka Ueno, Takehiko Wada, Jun'ichi Watanabe, Toru Yamada, Issei Yamamura, Naoki Yoshida, Kitamura Yoshimi, Yukari Yui, Milena Benedettini, Riccardo Cerulli, Anna Di Giorgio, Sergio Molinari, Renato Orfei, Stefano Pezzuto, Lorenzo Piazzo, Paolo Saraceno, Luigi Spinoglio, Thijs de Graauw, Piet de Korte, Frank Helmich, Henk Hoevers, Robert Huisman, Russell Shipman, Floris van der Tak, Paul van der Werf, Wolfgang Wild, Jose Acosta-Pulido, Jose Cernicharo, Jose Herreros, Jesus Martin-Pintado, Francisco Najarro, Ismael Perez-Fourmon, Juan Ramon Pardo, Francisca Gomez, Nieves Castro Rodriguez, Peter Ade, Mike Barlow, David Clements, Marc Ferlet, Helen Fraser, Douglas Griffin, Matthew Griffin, Peter Hargrave, Kate Isaak, Robert Ivison, Malik Mansour, Jonathan Laniesse, Phillip Mauskopf, Dmitry Morozov, Seb Oliver, Angiola Orlando, Mathew Page, Cristina Popescu, Stephen Serjeant, Rashmi Sudiwala, Dimitra Rigopoulou, Ian Walker, Glenn White, Serena Viti, Berend Winter, Jamie Bock, Matt Bradford, Martin Harwit, Warren Holmes

EXPERIMENTAL ASTRONOMY　23　(1)　193-219　2009/03

DOI： 10.1007/s10686-008-9090-0 　

ISSN： 0922-6435

eISSN： 1572-9508
Evolution of Massive Protostars with High Accretion Rates Peer-reviewed

Takashi Hosokawa, Kazuyuki Omukai

ASTROPHYSICAL JOURNAL　691　(1)　823-846　2008/06/25

DOI： 10.1088/0004-637X/691/1/823 　

ISSN： 0004-637X
Can Supermassive Black Holes Form in Metal-Enriched High-Redshift Protogalaxies ?

K. Omukai, R. Schneider, Z. Haiman

2008/04/19

DOI： 10.1086/591636 　

More details Close

Primordial gas in protogalactic dark matter (DM) halos with virial temperatures Tvir > 10^4 K begins to cool and condense via atomic hydrogen. Provided this gas is irradiated by a strong ultraviolet (UV) flux and remains free of H2 and other molecules, it has been proposed that the halo with Tvir ~10^4 K may avoid fragmentation, and lead to the rapid formation of a supermassive black hole (SMBH) as massive as M=10^5-10^6 Msun. This ``head--start'' would help explain the presence of SMBHs with inferred masses of several x 10^9 Msun, powering the bright quasars discovered in the Sloan Digital Sky Survey at redshift z>~6. However, high-redshift DM halos with Tvir~10^4K are likely already enriched with at least trace amounts of metals and dust produced by prior star-formation in their progenitors. Here we study the thermal and chemical evolution of low-metallicity gas exposed to extremely strong UV radiation fields. Our results, obtained in one-zone models, suggest that gas fragmentation is inevitable above a critical metallicity, whose value is between Zcr~3x10^{-4} Zsun (in the absence of dust) and as low as Zcr~ 5 x 10^{-6} Zsun (with a dust-to-gas mass ratio of about 0.01 Z/Zsun). We propose that when the metallicity exceeds these critical values, dense clusters of low--mass stars may form at the halo nucleus. Relatively massive stars in such a cluster can then rapidly coalesce into a single more massive object, which may produce an intermediate-mass BH remnant with a mass up to M <~10^2-10^3 Msun.
Physical Mechanism for the Intermediate Characteristic Stellar Mass in the Extremely Metal-poor Environments Peer-reviewed

T. Tsuribe, K. Omukai

ASTROPHYSICAL JOURNAL LETTERS　676　(1)　L45-L48　2008/02/07

DOI： 10.1086/587035 　
Low-metallicity Star Formation: the characteristic mass and upper mass limit

Kazuyuki Omukai

LOW-METALLICITY STAR FORMATION: FROM THE FIRST STARS TO DWARF GALAXIES　(255)　49-55　2008

DOI： 10.1017/S1743921308024563 　

ISSN： 1743-9213
The evolution of supernova remnants in the early universe Peer-reviewed

Takanori Nagakura, Takashi Hosokawa, Kazuyuki Omukai

FIRST STARS III　990　423-425　2008

ISSN： 0094-243X
Formation of stars at very low metallicities Peer-reviewed

Kazuyuki Omukai

FIRST STARS III　990　63-+　2008

ISSN： 0094-243X
Formation of Massive Primordial Stars in a Reionized Gas Peer-reviewed

Naoki Yoshida, Kazuyuki Omukai, Lars Hernquist

ASTROPHYSICAL JOURNAL　667　(2)　L117-L120　2007/06/25

DOI： 10.1086/522202 　

ISSN： 0004-637X

eISSN： 1538-4357
Observational Characteristics of the First Protostellar Cores Peer-reviewed

K. Omukai

PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN　59　(3)　589-606　2007/05/23

DOI： 10.1093/pasj/59.3.589 　

ISSN： 0004-6264

eISSN： 2053-051X
The First Jet in the Universe: Protostellar Jets from the First Stars Peer-reviewed

Masahiro N. Machida, Kazuyuki Omukai, Tomoaki Matsumoto, Shu-ichiro Inutsuka

ASTROPHYSICAL JOURNAL　647　(1)　L1-L4　2006/05/05

DOI： 10.1086/507326 　

ISSN： 0004-637X
Fragmentation of star-forming clouds enriched with the first dust Peer-reviewed

Raffaella Schneider, Kazuyuki Omukai, Akio Inoue, Andrea Ferrara

Monthly Notices of the Royal Astronomical Society　369　(3)　1437-1444　2006/03/28

DOI： 10.1111/j.1365-2966.2006.10391.x 　

ISSN： 0035-8711

eISSN： 1365-2966
Formation of the first- and second-generation stars Peer-reviewed

Kazuyuki Omukai

STELLAR EVOLUTION AT LOW METALLICITY: MASS LOSS, EXPLOSIONS, COSMOLOGY　353　263-270　2006
Primordial Molecular Emission in Population III Galaxies Peer-reviewed

Hiromi Mizusawa, Kazuyuki Omukai, Ryoichi Nishi

Publications of the Astronomical Society of Japan　57　951-967　2005/09/24

DOI： 10.1093/pasj/57.6.951 　

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We study formation of molecules in primordial prestellar clumps and evaluate the line luminosities to assess detectability by next-generation facilities. If the initial H_2 fraction is sufficiently high, HD becomes an important coolant in the clumps. The luminosity from such HD cooling clumps is lower than that from H_2 cooling ones because of lower temperature (<100K). As for Li reactions, we include the three-body LiH formation approximately. The Li molecular fraction remains very low (<10^{-3}) throughout the evolution owing to the high dissociative reaction rate of LiH +H -> Li + H_2. LiH does not become an important coolant in any density range. The luminous emission lines from the prestellar cores include H_2 rovibrational lines: 1-0 Q(1), 1-0 O(3), 1-0 O(5), and pure rotational lines: 0-0 S(3), 0-0 S(4), 0-0 S(5). The next-generation facilities SPICA and JWST are able to detect H_2 emission in a large pre-galactic cloud that forms metal-free stars at a high rate of \sim 10^3 M_s/yr at redshift z<10. We also derive an analytical expression for the luminosity that reproduces the numerical results.
Thermal and Fragmentation Properties of Star-forming Clouds in Low-metallicity Environments

K. Omukai, T. Tsuribe, R. Schneider, A. Ferrara

2005/03/01

DOI： 10.1086/429955 　

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The thermal and chemical evolution of star-forming clouds is studied for different gas metallicities, Z, using the model of Omukai (2000), updated to include deuterium chemistry and the effects of cosmic microwave background (CMB) radiation. HD-line cooling dominates the thermal balance of clouds when Z \~ 10^{-5}-10^{-3} Z_sun and density ~10^{5} cm^{-3}. Early on, CMB radiation prevents the gas temperature to fall below T_CMB, although this hardly alters the cloud thermal evolution in low-metallicity gas. From the derived temperature evolution, we assess cloud/core fragmentation as a function of metallicity from linear perturbation theory, which requires that the core elongation E := (b-a)/a > E_NL ~ 1, where a (b) is the short (long) core axis length. The fragment mass is given by the thermal Jeans mass at E = E_NL. Given these assumptions and the initial (gaussian) distribution of E we compute the fragment mass distribution as a function of metallicity. We find that: (i) For Z=0, all fragments are very massive, > 10^{3}M_sun, consistently with previous studies; (ii) for Z>10^{-6} Z_sun a few clumps go through an additional high density (> 10^{10} cm^{-3}) fragmentation phase driven by dust-cooling, leading to low-mass fragments; (iii) The mass fraction in low-mass fragments is initially very small, but at Z ~ 10^{-5}Z_sun it becomes dominant and continues to grow as Z is increased; (iv) as a result of the two fragmentation modes, a bimodal mass distribution emerges in 0.01 < Z/Z_sun < 0.1. (v) For > 0.1Z_sun, the two peaks merge into a singly-peaked mass function which might be regarded as the precursor of the ordinary Salpeter-like IMF.
Thermal evolution of star forming clouds in low metallicity environment Peer-reviewed

K Omukai

Initial Mass Function 50 years Later　327　493-494　2005
H_2 Line Emission Associated with the Formation of the First Stars Peer-reviewed

Hiromi Mizusawa, Ryoichi Nishi, Kazuyuki Omukai

Publications of the Astronomical Society of Japan　56　(3)　487-495　2004/04/16
Publisher:
DOI： 10.1093/pasj/56.3.487 　

ISSN： 0004-6264

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Molecular hydrogen line radiation emitted in formation events of first-generation stars are evaluated in a discussion of its detectability by future observational facilities. H_2 luminosity evolution from the onset of prestellar collapse until the formation of a \sim 100 M_{\odot} protostar is followed. Calculations are extended not only to the early phase of the runaway collapse but also to the later phase of accretion, whose observational features have not been studied before. Contrary to the runaway collapse phase, where the pure-rotational lines are always dominant, in the accretion phase rovibrational line emission becomes prominent. The maximum luminosity is also attained in the accretion phase for strong emission lines. The peak intensity of the strongest rovibrational line reaches \sim 10^{-29} (W/m^2), corresponding to the flux density of 10^{-5} (\mu Jy), for a source at the typical redshift of first-generation star formation, 1+z=20. Although the redshifted rovibrational H_2 emission from such an epoch falls in the wavelength range of the next-generation infrared satellite, Space Infrared Telescope for Cosmology and Astrophysics, for exceeding the detection threshold 10^7 such protostars are required to reach the maximum luminosity simultaneously in a pregalactic cloud. It is improbable that this condition is satisfied in a realistic scenario of early structure formation.
The mass spectrum of metal-free Stars resulting from photodissociation feedback: A scenario for the formation of low-mass population III stars Peer-reviewed

K. Omukai, Y. Yoshii

ASTROPHYSICAL JOURNAL　599　(2)　746-758　2003/08/28

DOI： 10.1086/379319 　

ISSN： 0004-637X
Observing H2 Emission in Forming Galaxies Peer-reviewed

K. Omukai, T. Kitayama

ASTROPHYSICAL JOURNAL　599　(2)　738-745　2003/08/18

DOI： 10.1086/379282 　

ISSN： 0004-637X
Formation of the First Stars by Accretion Peer-reviewed

K. Omukai, F. Palla

ASTROPHYSICAL JOURNAL　589　(2)　677-687　2003/02/18

DOI： 10.1086/374810 　

ISSN： 0004-637X
First star formation - Protostellar evolution from prestellar cores to main-sequence stars Peer-reviewed

K Omukai

PROGRESS OF THEORETICAL PHYSICS SUPPLEMENT　(147)　129-153　2002

ISSN： 0375-9687
An Upper Limit on the Mass of a Primordial Star due to the Formation of an HII Region: The Effect of Ionizing Radiation Force Peer-reviewed

Kazuyuki Omukai, Shu-ichiro Inutsuka

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY　332　(1)　59-64　2001/12/14

DOI： 10.1046/j.1365-8711.2002.05276.x 　

ISSN： 0035-8711
First stars, very massive black holes and metals Peer-reviewed

R. Schneider, A. Ferrara, P. Natarajan, K. Omukai

ASTROPHYSICAL JOURNAL　571　(1)　30-39　2001/11/17

DOI： 10.1086/339917 　

ISSN： 0004-637X
Primordial Star Formation under Far-ultraviolet radiation Peer-reviewed

Kazuyuki Omukai

ASTROPHYSICAL JOURNAL　546　(2)　635-651　2000/11/23

DOI： 10.1086/318296 　

ISSN： 0004-637X
Protostellar collapse with various metallicities Peer-reviewed

K Omukai

ASTROPHYSICAL JOURNAL　534　(2)　809-824　2000/05

ISSN： 0004-637X
Protostellar Collapse with Various Metallicities Peer-reviewed

Kazuyuki Omukai

FIRST STARS　277-278　2000/03/15

DOI： 10.1086/308776 　
On the formation of primordial stars and Pop III luminous objects Peer-reviewed

R Nishi, H Susa, K Omukai

FIRST STARS　268-272　2000
Photodissociative Regulation of Star Formation in Metal-Free Pregalactic Clouds Peer-reviewed

Kazuyuki Omukai, Ryoichi Nishi

ASTROPHYSICAL JOURNAL　518　(1)　64-68　1999/04/22

DOI： 10.1086/307285 　

ISSN： 0004-637X
Thermal and Dynamical Evolution of Primordial Gas Clouds - On the Formation of First Luminous Objects - Peer-reviewed

Ryoichi Nishi, Hajime Susa, Hideya Uehara, Masako Yamada, Kazuyuki Omukai

Progress of Theoretical Physics　100　(5)　881-903　1998/12/08
Publisher: THE PHYSICAL SOCIETY OF JAPAN
DOI： 10.1143/PTP.100.881 　

ISSN： 0033-068x
Evolution of Primordial Protostellar Clouds --- Quasi-Static Analysis --- Peer-reviewed

Kazuyuki Omukai, Ryoichi Nishi, Hideya Uehara, Hajime Susa

Progress of Theoretical Physics　99　(5)　747-761　1998/09/18
Publisher:
DOI： 10.1143/PTP.99.747 　

ISSN： 0033-068x

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Misc. 30

Disc fragmentation and intermittent accretion on to supermassive stars

Ryoki Matsukoba, Eduard I Vorobyov, Kazuyuki Sugimura, Sunmyon Chon, Takashi Hosokawa, Kazuyuki Omukai

Monthly Notices of the Royal Astronomical Society　500　(3)　4126-4138　2020/12/04

DOI： 10.1093/mnras/staa3462 　

ISSN： 0035-8711

eISSN： 1365-2966
Eccentric Black Hole Mergers in Active Galactic Nuclei

Hiromichi Tagawa, Bence Kocsis, Zoltan Haiman, Imre Bartos, Kazuyuki Omukai, Johan Samsing

ASTROPHYSICAL JOURNAL LETTERS　907　(1)　2020/10/20

DOI： 10.3847/2041-8213/abd4d3 　

ISSN： 2041-8205

eISSN： 2041-8213
Pulsation-driven mass loss from massive stars behind stellar mergers in metal-poor dense clusters

Daisuke Nakauchi, Kohei Inayoshi, Kazuyuki Omukai

ASTROPHYSICAL JOURNAL　902　(1)　2020/08/31

DOI： 10.3847/1538-4357/abb463 　

ISSN： 0004-637X

eISSN： 1538-4357
Cosmological DCBH formation sites hostile for their growth

Sunmyon Chon, Takashi Hosokawa, Kazuyuki Omukai

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY　502　(1)　700-713　2020/08/20

DOI： 10.1093/mnras/stab061 　

ISSN： 0035-8711

eISSN： 1365-2966
Star cluster formation and cloud dispersal by radiative feedback: dependence on metallicity and compactness

Hajime Fukushima, Hidenobu Yajima, Kazuyuki Sugimura, Takashi Hosokawa, Kazuyuki Omukai, Tomoaki Matsumoto

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY　497　(3)　3830-3845　2020/05/27

DOI： 10.1093/mnras/staa2062 　

ISSN： 0035-8711

eISSN： 1365-2966
Supermassive star formation via super competitive accretion in slightly metal-enriched clouds

Sunmyon Chon, Kazuyuki Omukai

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY　494　(2)　2851-2860　2020/05

DOI： 10.1093/mnras/staa863 　

ISSN： 0035-8711

eISSN： 1365-2966
Thermal evolution of protoplanetary disks: from $β$-cooling to decoupled gas and dust temperatures

Eduard I. Vorobyov, Ryoki Matsukoba, Kazuyuki Omukai, Manuel Guedel

ASTRONOMY & ASTROPHYSICS　638　2020/04/28

DOI： 10.1051/0004-6361/202037841 　

ISSN： 0004-6361

eISSN： 1432-0746
Formation of massive stars under protostellar radiation feedback: Very metal-poor stars

Hajime Fukushima, Takashi Hosokawa, Gen Chiaki, Kazuyuki Omukai, Naoki Yoshida, Rolf Kuiper

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY　497　(1)　829-845　2020/04/06

DOI： 10.1093/mnras/staa1994 　

ISSN： 0035-8711

eISSN： 1365-2966
Ionization degree and magnetic diffusivity in the primordial star-forming clouds

Daisuke Nakauchi, Kazuyuki Omukai, Hajime Susa

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY　488　(2)　1846-1862　2019/04/17

DOI： 10.1093/mnras/stz1799 　

ISSN： 0035-8711

eISSN： 1365-2966
Spectral Energy Distribution of the First Galaxies: Contribution from Pre-Main-Sequence Stars

Hiroto Mitani, Naoki Yoshida, Kazuyuki Omukai, Takashi Hosokawa

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY　488　(1)　L64-L68　2019/04/16

DOI： 10.1093/mnrasl/slz100 　

ISSN： 0035-8711

eISSN： 1365-2966
Gravitational stability and fragmentation condition for discs around accreting supermassive stars

Ryoki Matsukoba, Sanemichi Z. Takahashi, Kazuyuki Sugimura, Kazuyuki Omukai

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY　484　(2)　2605-2619　2018/12/31

DOI： 10.1093/mnras/sty3522 　

ISSN： 0035-8711

eISSN： 1365-2966
Condition for low-mass star formation in shock-compressed metal-poor clouds

Daisuke Nakauchi, Kazuyuki Omukai, Raffaella Schneider

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY　483　(1)　1265-1265　2018/07/14

DOI： 10.1093/mnras/sty1911 　

ISSN： 0035-8711

eISSN： 1365-2966
Condition for dust evacuation from the first galaxies

Hajime Fukushima, Hidenobu Yajima, Kazuyuki Omukai

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY　477　(1)　1071-1085　2018/03/24

DOI： 10.1093/mnras/sty799 　

ISSN： 0035-8711

eISSN： 1365-2966
Stunted accretion growth of black holes by combined effect of the flow angular momentum and radiation feedback

Kazuyuki Sugimura, Takashi Hosokawa, Hidenobu Yajima, Kohei Inayoshi, Kazuyuki Omukai

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY　478　(3)　3961-3975　2018/02/20

DOI： 10.1093/mnras/sty1298 　

ISSN： 0035-8711

eISSN： 1365-2966
Upper stellar mass limit by radiative feedback at low-metallicities: metallicity and accretion rate dependence

Hajime Fukushima, Kazuyuki Omukai, Takashi Hosokawa

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY　473　(4)　4754-4772　2017/10/02

DOI： 10.1093/mnras/stx2620 　

ISSN： 0035-8711

eISSN： 1365-2966
The critical radiation intensity for direct collapse black hole formation: dependence on the radiation spectral shape (vol 445, pg 544, 2014)

Kazuyuki Sugimura, Kazuyuki Omukai, Akio K. Inoue

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY　452　(2)　1201-1201　2015/09

DOI： 10.1093/mnras/stv1347 　

ISSN： 0035-8711

eISSN： 1365-2966
The first low-mass stars: critical metallicity or dust-to-gas ratio?

Raffaella Schneider, Kazuyuki Omukai, Simone Bianchi, Rosa Valiante

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY　419　(2)　1566-1575　2011/09/13

DOI： 10.1111/j.1365-2966.2011.19818.x 　

ISSN： 0035-8711

eISSN： 1365-2966
Binary Formation with Different Metallicities: Dependence on Initial Conditions

Masahiro N. Machida, Kazuyuki Omukai, Tomoaki Matsumoto, Shu-ichiro Inutsuka

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY　399　(3)　1255-1263　2009/07/19

DOI： 10.1111/j.1365-2966.2009.15394.x 　

ISSN： 0035-8711
Dust coagulation in star formation with different metallicities

Hiroyuki Hirashita, Kazuyuki Omukai

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY　399　(4)　1795-1801　2009/07/17

DOI： 10.1111/j.1365-2966.2009.15410.x 　

ISSN： 0035-8711
Protostar Formation in the Early Universe International-journal

Naoki Yoshida, Kazuyuki Omukai, Lars Hernquist

Science (New York, N.Y.)　321　(5889)　669-71　2008/07/30

DOI： 10.1126/science.1160259 　

ISSN： 0036-8075
Conditions for the Formation of First-Star Binaries

Masahiro N. Machida, Kazuyuki Omukai, Tomoaki Matsumoto, Shu-ichiro Inutsuka

ASTROPHYSICAL JOURNAL　677　(2)　813-827　2007/11/01

DOI： 10.1086/533434 　

ISSN： 0004-637X
Synthetic Observations of Carbon Lines of Turbulent Flows in Diffuse Multiphase Interstellar Medium

M. Yamada, H. Koyama, K. Omukai, S. Inutsuka

2006/11/29

DOI： 10.1086/511257 　

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We examine observational characteristics of multi-phase turbulent flows in the diffuse interstellar medium (ISM) using a synthetic radiation field of atomic and molecular lines. We consider the multi-phase ISM which is formed by thermal instability under the irradiation of UV photons with moderate visual extinction $A_V\sim 1$. Radiation field maps of C$^{+}$, C$^0$, and CO line emissions were generated by calculating the non-local thermodynamic equilibrium (nonLTE) level populations from the results of high resolution hydrodynamic simulations of diffuse ISM models. By analyzing synthetic radiation field of carbon lines of [\ion{C}{2}] 158 $\mu$m, [\ion{C}{1}] $^3P_2-^3P_1$ (809 GHz), $^3P_1-^3P_0$ (492 GHz), and CO rotational transitions, we found a high ratio between the lines of high- and low-excitation energies in the diffuse multi-phase interstellar medium. This shows that simultaneous observations of the lines of warm- and cold-gas tracers will be useful in examining the thermal structure, and hence the origin of diffuse interstellar clouds.
Formation of Primordial Stars in a LCDM Universe

Naoki Yoshida, Kazuyuki Omukai, Lars Hernquist, Tom Abel

ASTROPHYSICAL JOURNAL　652　(1)　6-25　2006/06/06

DOI： 10.1086/507978 　

ISSN： 0004-637X

eISSN： 1538-4357
Dust-cooling--induced Fragmentation of Low-metallicity Clouds

T. Tsuribe, K. Omukai

2006/03/17

DOI： 10.1086/504290 　

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Dynamical collapse and fragmentation of low-metallicity cloud cores is studied using three-dimensional hydrodynamical calculations, with particular attention devoted whether the cores fragment in the dust-cooling phase or not. The cores become elongated in this phase, being unstable to non-spherical perturbation due to the sudden temperature decrease. In the metallicity range of 10^{-6}-10^{-5}Z_sun, cores with an initial axis ratio >2 reach a critical value of the axis ratio (>30) and fragment into multiple small clumps. This provides a possible mechanism to produce low-mass stars in ultra-metal-poor environments.
Formation of Population III Stars in Fossil HII Regions: Significance of HD

Takanori Nagakura, Kazuyuki Omukai

2005/05/30

DOI： 10.1111/j.1365-2966.2005.09685.x 　

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We study the evolution of gas in HII regions around the first stars after the death of the exciting stars. If the first star in a small halo dies without supernova (SN), subsequent star formation is possible in the same halo. We thus investigate the effect of ionization of the gas on subsequent star formation within small halos in the early universe using one-dimensional hydrodynamics with spherical symmetry along with non-equilibrium primordial gas chemistry. We find that the enhanced electron fraction facilitates the formation of molecular hydrogen at the cores of these halos. The low temperature circumstances produced by the H_2 cooling is suitable for HD formation and the resultant cooling further drops the temperature below 100 K. Consequently, low-mass stars with primordial abundances can form even in a small halo. After accreting the interstellar metals, these stars might resemble low-mass ultra metal-poor stars discovered in the present Galactic halo.
The Radio to Infrared Emission of Very High Redshift Gamma-Ray Bursts: Probing Early Star Formation through Molecular and Atomic Absorption Lines

Susumu Inoue, Kazuyuki Omukai, Benedetta Ciardi

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY　380　(4)　1715-1728　2005/02/10

DOI： 10.1111/j.1365-2966.2007.12234.x 　

ISSN： 0035-8711

eISSN： 1365-2966
Low-Mass Relics of Early Star Formation

R. Schneider, A. Ferrara, R. Salvaterra, K. Omukai, V. Bromm

2003/04/14

DOI： 10.1038/nature01579 　

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The earliest stars to form in the Universe were the first sources of light, heat and metals after the Big Bang. The products of their evolution will have had a profound impact on subsequent generations of stars. Recent studies of primordial star formation have shown that, in the absence of metals (elements heavier than helium), the formation of stars with masses 100 times that of the Sun would have been strongly favoured, and that low-mass stars could not have formed before a minimum level of metal enrichment had been reached. The value of this minimum level is very uncertain, but is likely to be between 10^{-6} and 10^{-4} that of the Sun. Here we show that the recent discovery of the most iron-poor star known indicates the presence of dust in extremely low-metallicity gas, and that this dust is crucial for the formation of lower-mass second-generation stars that could survive until today. The dust provides a pathway for cooling the gas that leads to fragmentation of the precursor molecular cloud into smaller clumps, which become the lower-mass stars.
First Star Formation--Protostellar Evolution from Prestellar Cores to Main-Sequence Stars (Star Formation in the Primordial Gas)

Progress of Theoretical Physics　109　129-153　2002
Publisher: Published for the Research Institute for Fundamental Physics by Physical Society of Japan
ISSN： 0033-068X
On the Formation of Massive Primordial Stars

K. Omukai, F. Palla

2001/09/21

DOI： 10.1023/A:1019503529129 　

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We investigate the formation by accretion of massive primordial protostars in the range 10 to 300 Msun. The high accretion rate used in the models (4.4 x 10^{-3} Msun/yr) causes the structure and evolution to differ significantly from those of both present-day protostars and primordial zero-age main sequence stars. After an initial expansion of the radius (for < 12 Msun), the protostar undergoes an extended phase of contraction (up to 60 Msun). The stellar surface is not visible throughout most of the main accretion phase, since a photosphere is formed in the infalling envelope. Also, significant nuclear burning does not take place until a protostellar mass of about 80 Msun. As the interior luminosity approaches the Eddington luminosity, the protostellar radius rapidly expands, reaching a maximum around 100 Msun. Changes in the ionization of the surface layers induce a secondary phase of contraction, followed by a final swelling due to radiation pressure when the stellar mass reaches about 300 Msun. This expansion is likely to signal the end of the main accretion phase, thus setting an upper limit to the protostellar mass formed in these conditions.
Formation of Primordial Protostars

Kazuyuki Omukai, Ryoichi Nishi

1998/11/19

DOI： 10.1086/306395 　

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The evolution of collapsing metal free protostellar clouds is investigated for various masses and initial conditions. We perform hydrodynamical calculations for spherically symmetric clouds taking account of radiative transfer of the molecular hydrogen lines and the continuum, as well as of chemistry of the molecular hydrogen. The collapse is found to proceed almost self-similarly like Larson-Penston similarity solution. In the course of the collapse, efficient three-body processes transform atomic hydrogen in an inner region of $\sim 1 M_{\sun}$ entirely into molecular form. However, hydrogen in the outer part remains totally atomic although there is an intervening transitional layer of several solar masses, where hydrogen is in partially molecular form. No opaque transient core is formed although clouds become optically thick to H$_{2}$ collision-induced absorption continuum, since H$_{2}$ dissociation follows successively. When the central part of the cloud reaches stellar densities ($\sim 10^{-2} {\rm g cm^{-3 } }$), a very small hydrostatic core ($\sim 5 \times 10^{-3} M_{\sun}$) is formed and subsequently grows in mass as the ambient gas accretes onto it. The mass accretion rate is estimated to be $3.7 \times 10^{-2} M_{\sun} {\rm yr^{-1 } } (M_{\ast}/M_{\sun})^{-0.37}$, where $M_{\ast}$ is instantaneous mass of the central core, by using a similarity solution which reproduces the evolution of the cloud before the core formation.

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Research Projects 14

The nature of the first galaxies and the origin of supermassive black holes as revealed by the star cluster formation process in the early universe

Offer Organization: Japan Society for the Promotion of Science

System: Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (A)

Category: Grant-in-Aid for Scientific Research (A)

Institution: Tohoku University

2022/04/01 - 2027/03/31
Gravitational wave physics and astronomy: Genesis

Offer Organization: Japan Society for the Promotion of Science

System: Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research on Innovative Areas (Research in a proposed research area)

Category: Grant-in-Aid for Scientific Research on Innovative Areas (Research in a proposed research area)

Institution: Kyoto University

2017/06/30 - 2022/03/31
Theoretical study on binary black hole formation

Offer Organization: Japan Society for the Promotion of Science

System: Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research on Innovative Areas (Research in a proposed research area)

Category: Grant-in-Aid for Scientific Research on Innovative Areas (Research in a proposed research area)

Institution: Tohoku University

2017/06/30 - 2022/03/31
Theoretical Study on Formation of Supermassive Black Holes

Offer Organization: Japan Society for the Promotion of Science

System: Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (A)

Category: Grant-in-Aid for Scientific Research (A)

Institution: Tohoku University

2017/04/01 - 2022/03/31
Star Formation in the verry Early Universe

Susa Hajime

Offer Organization: Japan Society for the Promotion of Science

System: Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B)

Category: Grant-in-Aid for Scientific Research (B)

Institution: Konan University

2017/04/01 - 2021/03/31

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The elucidation of the star formation process in the very early universe is one of the most important topics in modern cosmology. In this study, we investigated how stars are formed from the contraction of gas clouds in the early universe. In particular, we theoretically clarified the controversial question of whether multiple stars or a single star is born from a gas cloud, in a manner that encompasses many previous studies. We also succeeded in providing a clear theoretical explanation for the physical causes of the turbulent nature of such gas clouds, which had been known from previous numerical simulations.
Theoretical study on low-metallicity star formation in the early universe

Omukai Kazuyuki, Yoshida Naoki, Hosokawa Takashi, Machida Masahiro, Schneider Raffaella

Offer Organization: Japan Society for the Promotion of Science

System: Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B)

Category: Grant-in-Aid for Scientific Research (B)

Institution: Tohoku University

2013/04/01 - 2017/03/31

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We have studied formation of the first stars in the universe by combining cosmological simulations and radiation hydrodynamics for star formation. We have found that the first stars are typically massive in the range of a few tens to a few hundreds of the Sun. In exceptionally intense ultraviolet radiation fields, even supermassive stars with mass more than hundred thousand times the Sun can be formed. We have also studied the physical conditions in low-metallicity interstellar media by way of three-dimensional hydrodynamics. We have found that multi-phase media is realized in gases with relatively high-metallicity and strong ultraviolet irradiation. In such environment, turbulence can be maintained for long time and so the star formation would be less efficient.
Theoretical study on the formation of metal-poor stars

OMUKAI Kazuyuki

Offer Organization: Japan Society for the Promotion of Science

System: Grants-in-Aid for Scientific Research Grant-in-Aid for Young Scientists (A)

Category: Grant-in-Aid for Young Scientists (A)

2009/04/01 - 2013/03/31

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The first stars in the universe were formed from the primordial pristine gas, made only of hydrogen, helium and trace light elements.How massive were those stars is crucial for subsequent structure formation. Starting from the initial condition obtained by cosmological simulation, we carried out radiation hydrodynamical calculation for the first star formation. We found that when the protostar becomes 40 times more massive than the Sun, the emitted UV radiation becomes so intense that the ambient material is pushed outward, terminating accretion onto the star.The final stellar mass is set at this moment. Although this value of the first star's mass is lower than previously considered by theoretical arguments, it is in accordance with observation of the abundance ratio of low-metallicity stars in the Galactic halo.
Astronomy in ALMA-Era Driven by Radiation Transfer Simulation

TOMISAKA Kohji, MACHIDA Masahiro, WADA Keiichi, AIKAWA Yuri, OMUKAI Kazuyuki

Offer Organization: Japan Society for the Promotion of Science

System: Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (A)

Category: Grant-in-Aid for Scientific Research (A)

Institution: National Astronomical Observatory of Japan

2009 - 2012

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Observational visualization is a method to obtain expected observational features for the outcome from (magneto)hydrodynamical simulations. This enables us to compare directly simulation results and observations. Polarization of the thermal emissions from interstellar dusts is calculated for pre- and protostellar cores and molecular outflows. We are now able to estimate the 3-dimensional magnetic field configuration from the 2-dimensional polarization pattern. Using the non-local thermal equilibrium (NonLTE) radiation transfer calculation, we have found observational features characteristic to the early phase of protostar formation.
Theoretical Research on the Origin of Gamma Ray Bursts

NAKAMURA Takashi, NOMOTO Kennichi, NAGATAKI Shigehiro, OMUKAI Kazuyuki, IOKA Kunihito, YAMAZAKI Ryo

Offer Organization: Japan Society for the Promotion of Science

System: Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research on Priority Areas

Category: Grant-in-Aid for Scientific Research on Priority Areas

Institution: Kyoto University

2007 - 2010

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Adopting either (1)Gamma Ray Bursts (GRB) as a distance indicator, (2)Progenitor and host galaxy of GRB, (3) Supernova associated with GRB, (4)Emergence and propagation of jets, or (5)Radiation mechanism of prompt emission and afterglow of GRB etc as a research theme of each member, we performed the cooperative research program on GRB using TV conference system to communicate each other frequently. As a result, we succeeded in (1)simulating the formation of the first stars without metal and evolving them up to be seen as GRBs. (2)We also reanalyzed Yonetoku relation as a distance indicator to the first GRB and found that Yonetoku relation is a good distance indicator if we restrict only data within 10% errors and define the luminosity in the rest frame of GRBs. Besides these researches , big progress in (3)the origin of Yonetoku relation (4)the origin of the shallow decay phase of GRBs (5) relativistic MHD numerical simulations to clarify the origin of energy of GRBs etc. has been made.
Theory of Star Formation in Different Environments from the Solar Neighborhood

OMUKAI Kazuyuki

Offer Organization: Japan Society for the Promotion of Science

System: Grants-in-Aid for Scientific Research Grant-in-Aid for Young Scientists (B)

Category: Grant-in-Aid for Young Scientists (B)

Institution: National Astronomical Observatory of Japan

2006 - 2008
星間現象理論モデルの観測的可視化

大向一行, 西合一矢, 町田正博, 山田雅子

Offer Organization: 日本学術振興会

System: 科学研究費助成事業特定領域研究

Category: 特定領域研究

Institution: 国立天文台

2006 - 2007

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本研究課題による成果は以下の通りである。 1.太陽系と異なる環境下での星形成過程の解明マゼラン雲は銀河系よりも金属量が数倍低く、宇宙初期環境の金属量はほぼゼロである。本研究では低金属環境の星間ガス雲からの星形成を数値シミュレーションで追跡し、金属量が星形成に大きく影響することを定量的に示した。銀河系は太陽程度の星が形成されやすいが、太陽よりも1万分の1以下の金属量では大質量星が形成されやすい。しかし、金属量が太陽の10万分の1から100万分の1の時には例外的に太陽質量の星が形成される。これは観測的に謎とされている古い星の金属量分布を説明できる(大向)。金属量がほぼゼロである宇宙初期の星形成は、これまで考えられていたよりも複雑な分裂過程を含み多多重星や連星などを容易に形成しうる事も示した(町田)。 2.原始星ジェット・アウトフローの統一的理解星は形成過程で大きな分子流を放出し同時に細長く高速なジェットも放出することが観測的に知られている。本研究により、これが星形成過程における磁場による遠心力風で同時に説明できることが示された(町田)。観測的に困難な星形成の極初期段階の解明にとって非常に有効な成果である。 3.ファーストコア天体の観測的性質星形成の瞬間に近いと理論予想されている天体がファーストコアであり、これは現在世界的に観測競争が繰り広げられている。本研究では、これまで非現実的な球対称モデルに代わり、現実的な円盤構造を持つモデルを用いてその観測予測を行った(西合)。これによると、次期大型観測機ALMAで、十分に観測可能であり、中心集中した100K程度のコアと数十Kの円盤など、いくつかの観測的特徴を持つことも指摘した。
Numerical Astronomy using molecular and atomic line transfer calculations in the ALMA-era.

MIYAMA Shoken, TOMISAKA Kohji, WADA Keiichi, OMUKAI Kazuyuki, KOHNO Kotaro, TOMOHARU Oka

Offer Organization: Japan Society for the Promotion of Science

System: Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (A)

Category: Grant-in-Aid for Scientific Research (A)

Institution: National Astronomical Observatory of Japan

2004 - 2007

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We explore millimeter line diagnostics of an obscuring molecular torus modeled by a hydrodynamic simulation with three-dimensional non-local thermodynamic equilibrium radiative transfer calculations. Based on the results of a high-resolution hydrodynamic simulation of the molecular torus around an active galactic nucleus, we calculate the intensities of the HCN and HCO+ rotational lines as two representative high-density tracers. Three-dimensional radiative transfer calculations shed light on a complicated excitation state in the inhomogeneous torus, even though a spatially uniform chemical structure is assumed. We find that similar transition coefficients for the HCN and HCO+ rotational lines lead to a natural concordance of the level population distributions of these molecules and a line ratio RHCN/HC0+<〜1 for the same molecular abundance value over 2 orders of magnitude. Our results suggest that HCN must be much more abundant than HCO+ (yHCN>〜10yHCO+) in order to obtain the high ratio (RHCN/HCO+-2) observed in some nearby galaxies. There is a remarkable dispersion in the relation between integrated intensity and column density, indicative of possible shortcomings of the HCN (1-0) and HCO+ (1-0) lines as high-density tracers. The internal structures of inhomogeneous molecular tori down to subparsec scales in external galaxies will be revealed by the forthcoming Atacama Large Millimeter/submillimeter Array. Three-dimensional radiative transfer calculations of molecular lines with a high-resolution hydrodynamic simulation prove to be a powerful tool to provide a physical basis for molecular-line diagnostics of the central regions of external galaxies.
銀河形成期の星形成の理論

大向一行

Offer Organization: 日本学術振興会

System: 科学研究費助成事業特別研究員奨励費

Category: 特別研究員奨励費

Institution: 国立天文台

2001 - 2003

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宇宙で最初に形成された星は、その後の宇宙の進化において、たとえば重元素汚染や宇宙の再電離といったようにきわめて重要な影響を与える可能性がある。そこで、本研究では具体的にこの影響がどのようなものであるか明らかにする目的で、第一世代星の第二世代星形成過程への影響を考察し、第一世代星からの輻射場中での星形成過程を解析した。その結果、原始ガス中では周囲からの輻射が強くなればなるほど、形成される星の質量が小さくなることがわかった。これは原始ガス中でも低質量星が形成される新しい可能性を示すもので、非常に重要な結果である。また、宇宙初期の構造形成理論の観測による確認を目指して、宇宙初期天体形成過程の観測可能性に関しても考察した。宇宙で最初の星である第一世代星形成過程は、我々からの距離が遠すぎるため、さすがに次世代観測機器によっても不可能という結果になった。しかしながら、金属度が少ないガスから大中質量原始銀河が形成される過程は、赤方偏移が8程度までは、10年後あたりに計画されている次次世代観測機器で可能であることが分かった。上記の研究課題を遂行するため、オックスフォード大学物理学教室のJ.Silk教授のもとに平成15年4月から11月まで滞在して、研究うち合わせをおこなった。
銀河形成期の星形成の理論

大向一行

Offer Organization: 日本学術振興会

System: 科学研究費助成事業特別研究員奨励費

Category: 特別研究員奨励費

1999 - 2000

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Teaching Experience 4

相対論的天体物理学II
Selected topics in astronomy F　Tohoku University
恒星物理学I
天文学セミナー