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Masashi Chiba

Section

Graduate School of Science

Job title

Professor

Degree

理学博士（東北大学）

researchmap

https://researchmap.jp/read0159427

J-GLOBAL ID

200901020654966124

Committee Memberships 11

国立天文台運営協議会　委員

2016/04 - 2020/03
日本天文学会研究奨励賞選考委員会　委員

2011/01 - 2015/12
日本天文学会研究奨励賞選考委員会　委員

2011/01 - 2015/12
すばるプログラム小委員会　委員

2013/04 - 2015/03
すばるプログラム小委員会　委員

2013/04 - 2015/03
すばるプログラム小委員会委員　委員長

2003/05 - 2007/05
すばるプログラム小委員会委員　委員長

2003/05 - 2007/05
すばる小委員会委員　委員

2005/04 - 2006/03
すばる小委員会委員　委員

2005/04 - 2006/03
国立天文台研究交流委員会委員　委員

2003/04 - 2006/03
国立天文台研究交流委員会委員　委員

2003/04 - 2006/03

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Professional Memberships 1

日本天文学会

Research Interests 2

Observational cosmology
Fomation and evolution of galaxies

Research Areas 1

Natural sciences / Astronomy /

Papers 108

Chemo-dynamical Evolution of Simulated Satellites for a Milky Way–like Galaxy

Yutaka Hirai, Evan N. Kirby, Masashi Chiba, Kohei Hayashi, Borja Anguiano, Takayuki R. Saitoh, Miho N. Ishigaki, Timothy C. Beers

The Astrophysical Journal　970　(2)　105-105　2024/07/23
Publisher: American Astronomical Society
DOI： 10.3847/1538-4357/ad500c 　

ISSN： 0004-637X

eISSN： 1538-4357

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Abstract The chemical abundances of Milky Way’s (MW's) satellites reflect their star formation histories (SFHs), yet, due to the difficulty of determining the ages of old stars, the SFHs of most satellites are poorly measured. Ongoing and upcoming surveys will obtain around 10 times more medium-resolution spectra for stars in satellites than are currently available. To correctly extract SFHs from large samples of chemical abundances, the relationship between chemical abundances and SFHs needs to be clarified. Here, we perform a high-resolution cosmological zoom-in simulation of a MW-like galaxy with detailed models of star formation, supernova (SN) feedback, and metal diffusion. We quantify SFHs, metallicity distribution functions, and the α-element (Mg, Ca, and Si) abundances in satellites of the host galaxy. We find that star formation in most simulated satellites is quenched before infalling to their host. Star formation episodes in simulated satellites are separated by a few hundred Myr owing to SN feedback; each star formation event produces groups of stars with similar [α/Fe] and [Fe/H]. We then perform a mock observation of the upcoming Subaru Prime Focus Spectrograph (PFS) observations. We find that Subaru PFS will be able to detect distinct groups of stars in [α/Fe] versus [Fe/H] space, produced by episodic star formation. This result means that episodic SFHs can be estimated from the chemical abundances of ≳1000 stars determined with medium-resolution spectroscopy.
The Milky Way tomography with Subaru Hyper Suprime-Cam. I. Halo substructures

Yoshihisa Suzuki, Masashi Chiba, Yutaka Komiyama, Kohei Hayashi, Masayuki Tanaka, Tetsuya Fukushima, Scott G Carlsten, Akira Tokiwa, Tian Qiu, Masahiro Takada

Publications of the Astronomical Society of Japan　2024/01/31
Publisher: Oxford University Press (OUP)
DOI： 10.1093/pasj/psae003 　

ISSN： 0004-6264

eISSN： 2053-051X

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Abstract We analyze the photometric data in the Wide layer of the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP) over ∼1200 deg2 to uncover new halo substructures beyond the distance, D⊙ ∼ 30 kpc, from the Sun. For this purpose, we develop an isochrone filter for an old, metal-poor stellar system to extract the faint main-sequence stars at a range of distances. With this method, we detect not only the previously discovered substructures such as the Orphan Stream, but also a new overdensity toward Boötes at about D⊙ ∼ 60 kpc and a new stream-like feature toward Pisces at around D⊙ ∼ 60 kpc. It has been suggested that a small-scale overdensity exists in this direction of Pisces (the so-called Pisces Overdensity), but our results show that the overdensity is widely spread with a tidally elongated feature. Combining our results with the ongoing Hyper Suprime-Cam narrow-band survey and the near-future spectroscopic survey with Prime Focus Spectrograph (PFS) will allow us to place strong constraints on the origin of these halo substructures.
Study of structural parameters and systemic proper motion of sextans dwarf spheroidal galaxy with subaru hyper suprime-cam data Peer-reviewed

Akira Tokiwa, Masahiro Takada, Tian Qiu, Naoki Yasuda, Yutaka Komiyama, Masashi Chiba, Kohei Hayashi

Monthly Notices of the Royal Astronomical Society　2023/08/18
Publisher: Oxford University Press (OUP)
DOI： 10.1093/mnras/stad2422 　

ISSN： 0035-8711

eISSN： 1365-2966

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Abstract We use the Subaru Hyper Suprime-Cam (HSC) data to study structural parameters and systemic proper motion of the Sextans dwarf spheroidal galaxy at the heliocentric distance of 86 kpc, which is one of the most important targets for studies of dark matter nature and galaxy formation physics. Thanks to the superb image quality and wide area coverage, the HSC data enables a secure selection of member star candidates based on the colour-magnitude cut, yielding about 10,000 member candidates at magnitudes down to i ∼ 24. We use a likelihood analysis of the two-dimensional distribution of stars to estimate the structural parameters of Sextans taking into account the contamination of foreground halo stars in the MW, and find that the member star distribution is well-fitted by an elliptical King profile with ellipticity ε ≃ 0.25 and the core and tidal radii of Rc = (368.4 ± 8.5) pc and Rt = (2.54 ± 0.046) kpc, respectively. Then using the two HSC datasets of 2.66 years time baseline on average, we find the systemic proper motions of Sextans to be (μα, μδ) = ( − 0.448 ± 0.075, 0.058 ± 0.078) mas yr−1 which is consistent with some of the previous works using the Gaia data of relatively bright member stars in Sextans. Thus, our results give a demonstration that a ground-based, large-aperture telescope data which covers a wide solid angle of the sky and has a long time baseline, such as the upcoming LSST data, can be used to study systemic proper motions of dwarf galaxies.
Origin of highly r-process-enhanced stars in a cosmological zoom-in simulation of a Milky Way-like galaxy Peer-reviewed

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　2022/11/14

DOI： 10.1093/mnras/stac2489 　
The Missing Satellite Problem outside of the Local Group. II. Statistical Properties of Satellites of Milky Way-like Galaxies Peer-reviewed

Nashimoto, Masashi, Tanaka, Masayuki, Chiba, Masashi, Hayashi, Kohei, Komiyama, Yutaka, Okamoto, Takashi

The Astrophysical Journal　2022/09

DOI： 10.3847/1538-4357/ac83a4 　

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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....
Dark matter halo properties of the Galactic dwarf satellites: implication for chemo-dynamical evolution of the satellites and a challenge to Λ CDM Peer-reviewed

Kohei Hayashi, Yutaka Hirai, Masashi Chiba, Tomoaki Ishiyama

The Astrophysical Journal　2022/06

DOI： 10.48550/arXiv.2206.02821 　
The diversity of core–halo structure in the fuzzy dark matter model Peer-reviewed

Hei Yin Jowett Chan, Elisa G M Ferreira, Simon May, Kohei Hayashi, Masashi Chiba

Monthly Notices of the Royal Astronomical Society　511　(1)　943-952　2022/02/03
Publisher: Oxford University Press (OUP)
DOI： 10.1093/mnras/stac063 　

ISSN： 0035-8711

eISSN： 1365-2966

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<title>ABSTRACT</title> In the fuzzy dark matter (FDM) model, gravitationally collapsed objects always consist of a solitonic core located within a virialized halo. Although various numerical simulations have confirmed that the collapsed structure can be described by a cored Navarro–Frenk–White-like density profile, there is still disagreement about the relation between the core mass and the halo mass. To fully understand this relation, we have assembled a large sample of cored haloes based on both idealized soliton mergers and cosmological simulations with various box sizes. We find that there exists a sizeable dispersion in the core–halo mass relation that increases with halo mass, indicating that the FDM model allows cores and haloes to coexist in diverse configurations. We provide a new empirical equation for a core–halo mass relation with uncertainties that can encompass all previously found relations in the dispersion, and emphasize that any observational constraints on the particle mass m using a tight one-to-one core–halo mass relation should suffer from an additional uncertainty of the order of 50 per cent for halo masses ${\gtrsim} 10^9 \, [8\times 10^{-23} \, \mathrm{eV}/(mc^2)]^{3/2} \, \mathrm{M}_\odot$. We suggest that tidal stripping may be one of the effects contributing to the scatter in the relation.
Proper motion measurements for stars up to 100 kpc with Subaru HSC and SDSS Stripe 82 Peer-reviewed

Tian Qiu, Wenting Wang, Masahiro Takada, Naoki Yasuda, Zeljko Ivezic, Robert H. Lupton, Masashi Chiba, Miho Ishigaki, Yutaka Komiyama

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY　501　(4)　5149-5175　2021/03

DOI： 10.1093/mnras/staa3975 　

ISSN： 0035-8711

eISSN： 1365-2966
The Nature of the Milky Way's Stellar Halo Revealed by the Three Integrals of Motion Peer-reviewed

Daniela Carollo, Masashi Chiba

ASTROPHYSICAL JOURNAL　908　(2)　2021/02

DOI： 10.3847/1538-4357/abd7a4 　

ISSN： 0004-637X

eISSN： 1538-4357
Long-term Orbital Evolution of Galactic Satellites and the Effects on Their Star Formation Histories Peer-reviewed

Takahiro Miyoshi, Masashi Chiba

ASTROPHYSICAL JOURNAL　905　(2)　2020/12

DOI： 10.3847/1538-4357/abc486 　

ISSN： 0004-637X

eISSN： 1538-4357
Diversity of Dark Matter Density Profiles in the Galactic Dwarf Spheroidal Satellites Peer-reviewed

Kohei Hayashi, Masashi Chiba, Tomoaki Ishiyama

The Astrophysical Journal　904　(1)　45-45　2020/11/20
Publisher: American Astronomical Society
DOI： 10.3847/1538-4357/abbe0a 　

eISSN： 1538-4357
Evidence for the Third Stellar Population in the Milky Way’s Disk Peer-reviewed

Daniela Carollo, Masashi Chiba, Miho Ishigaki, Ken Freeman, Timothy C. Beers, Young Sun Lee, Patricia Tissera, Chiara Battistini, Francesca Primas

The Astrophysical Journal　2019/12/06

DOI： 10.3847/1538-4357/ab517c 　
Void formation: does the void-in-cloud process matter? Peer-reviewed

Hei Yin Jowett Chan, Masashi Chiba, Tomoaki Ishiyama

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY　490　(2)　2405-2413　2019/12

DOI： 10.1093/mnras/stz2786 　

ISSN： 0035-8711

eISSN： 1365-2966
Bootes. IV. A new Milky Way satellite discovered in the Subaru Hyper Suprime-Cam Survey and implications for the missing satellite problem Peer-reviewed

Daisuke Homma, Masashi Chiba, Yutaka Komiyama, Masayuki Tanaka, Sakurako Okamoto, Mikito Tanaka, Miho N. Ishigaki, Kohei Hayashi, Nobuo Arimoto, Scott G. Carlsten, Robert H. Lupton, Michael A. Strauss, Satoshi Miyazaki, Gabriel Torrealba, Shiang-Yu Wang, Hitoshi Murayama

PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN　71　(5)　2019/10

DOI： 10.1093/pasj/psz076 　

ISSN： 0004-6264

eISSN： 2053-051X
Microlensing constraints on primordial black holes with Subaru/HSC Andromeda observations Peer-reviewed

Hiroko Niikura, Masahiro Takada, Naoki Yasuda, Robert H. Lupton, Takahiro Sumi, Surhud More, Toshiki Kurita, Sunao Sugiyama, Anupreeta More, Masamune Oguri, Masashi Chiba

NATURE ASTRONOMY　3　(6)　524-534　2019/06

DOI： 10.1038/s41550-019-0723-1 　

ISSN： 2397-3366
New structures of the Milky Way stellar and dark halos revealed from the Subaru/Hyper Suprime-Cam survey

Masashi Chiba

Proceedings of the International Astronomical Union　2019/06

DOI： 10.1017/S1743921319008640 　
Metallicity Distribution of Disk Stars and the Formation History of the Milky Way Peer-reviewed

Daisuke Toyouchi, Masashi Chiba

Astrophysical Journal　855　(2)　2018/03/10
Publisher: Institute of Physics Publishing
DOI： 10.3847/1538-4357/aab044 　

ISSN： 1538-4357 0004-637X
Stellar Stream and Halo Structure in the Andromeda Galaxy from a Subaru/Hyper Suprime-Cam Survey Peer-reviewed

Yutaka Komiyama, Masashi Chiba, Mikito Tanaka, Masayuki Tanaka, Takanobu Kirihara, Yohei Miki, Masao Mori, Robert H. Lupton, Puragra Guhathakurta, Jason S. Kalirai, Karoline Gilbert, Evan Kirby, Myun Gyoon Lee, In Sung Jang, Sanjib Sharma, Kohei Hayashi

Astrophysical Journal　853　(1)　2018/01/20

DOI： 10.3847/1538-4357/aaa129 　

ISSN： 1538-4357 0004-637X
Global Properties of M31's Stellar Halo from the SPLASH Survey. III. Measuring the Stellar Velocity Dispersion Profile Peer-reviewed

Karoline M. Gilbert, Erik Tollerud, Rachael L. Beaton, Puragra Guhathakurta, James S. Bullock, Masashi Chiba, Jason S. Kalirai, Evan N. Kirby, Steven R. Majewski, Mikito Tanaka

Astrophysical Journal　852　(2)　2018/01/10
Publisher: Institute of Physics Publishing
DOI： 10.3847/1538-4357/aa9f26 　

ISSN： 1538-4357 0004-637X
Hyper Suprime-Cam: System design and verification of image quality Peer-reviewed

Satoshi Miyazaki, Yutaka Komiyama, Satoshi Kawanomoto, Yoshiyuki Doi, Hisanori Furusawa, Takashi Hamana, Yusuke Hayashi, Hiroyuki Ikeda, Yukiko Kamata, Hiroshi Karoji, Michitaro Koike, Tomio Kurakami, Shoken Miyama, Tomoki Morokuma, Fumiaki Nakata, Kazuhito Namikawa, Hidehiko Nakaya, Kyoji Nariai, Yoshiyuki Obuchi, Yukie Oishi, Norio Okada, Yuki Okura, Philip Tait, Tadafumi Takata, Yoko Tanaka, Masayuki Tanaka, Tsuyoshi Terai, Daigo Tomono, Fumihiro Uraguchi, Tomonori Usuda, Yousuke Utsumi, Yoshihiko Yamada, Hitomi Yamanoi, Hiroaki Aihara, Hiroki Fujimori, Sogo Mineo, Hironao Miyatake, Masamune Oguri, Tomohisa Uchida, Manobu M. Tanaka, Naoki Yasuda, Masahiro Takada, Hitoshi Murayama, Atsushi J. Nishizawa, Naoshi Sugiyama, Masashi Chiba, Toshifumi Futamase, Shiang-Yu Wang, Hsin-Yo Chen, Paul T.P. Ho, Eric J.Y. Liaw, Chi-Fang Chiu, Cheng-Lin Ho, Tsang-Chih Lai, Yao-Cheng Lee, Dun-Zen Jeng, Satoru Iwamura, Robert Armstrong, Steve Bickerton, James Bosch, James E. Gunn, Robert H. Lupton, Craig Loomis, Paul Price, Steward Smith, Michael A. Strauss, Edwin L. Turner, Hisanori Suzuki, Yasuhito Miyazaki, Masaharu Muramatsu, Koei Yamamoto, Makoto Endo, Yutaka Ezaki, Noboru Ito, Noboru Kawaguchi, Satoshi Sofuku, Tomoaki Taniike, Kotaro Akutsu, Naoto Dojo, Kazuyuki Kasumi, Toru Matsuda, Kohei Imoto, Yoshinori Miwa, Masayuki Suzuki, Kunio Takeshi, Hideo Yokota

Publications of the Astronomical Society of Japan　70　(Special Issue 1)　2018/01/01

DOI： 10.1093/pasj/psx063 　

ISSN： 2053-051X 0004-6264

eISSN： 2053-051X
First data release of the Hyper Suprime-Cam Subaru Strategic Program Peer-reviewed

Hiroaki Aihara, Robert Armstrong, Steven Bickerton, James Bosch, Jean Coupon, Hisanori Furusawa, Yusuke Hayashi, Hiroyuki Ikeda, Yukiko Kamata, Hiroshi Karoji, Satoshi Kawanomoto, Michitaro Koike, Yutaka Komiyama, Dustin Lang, Robert H. Lupton, Sogo Mineo, Hironao Miyatake, Satoshi Miyazaki, Tomoki Morokuma, Yoshiyuki Obuchi, Yukie Oishi, Yuki Okura, Paul A. Price, Tadafumi Takata, Manobu M. Tanaka, Masayuki Tanaka, Yoko Tanaka, Tomohisa Uchida, Fumihiro Uraguchi, Yousuke Utsumi, Shiang-Yu Wang, Yoshihiko Yamada, Hitomi Yamanoi, Naoki Yasuda, Nobuo Arimoto, Masashi Chiba, Francois Finet, Hiroki Fujimori, Seiji Fujimoto, Junko Furusawa, Tomotsugu Goto, Andy Goulding, James E. Gunn, Yuichi Harikane, Takashi Hattori, Masao Hayashi, Krzysztof G. Helminiak, Ryo Higuchi, Chiaki Hikage, Paul T. P. Ho, Bau-Ching Hsieh, Kuiyun Huang, Song Huang, Masatoshi Imanishi, Ikuru Iwata, Anton T. Jaelani, Hung-Yu Jian, Nobunari Kashikawa, Nobuhiko Katayama, Takashi Kojima, Akira Konno, Shintaro Koshida, Haruka Kusakabe, Alexie Leauthaud, Chien-Hsiu Lee, Lihwai Lin, Yen-Ting Lin, Rachel Mandelbaum, Yoshiki Matsuoka, Elinor Medezinski, Shoken Miyama, Rieko Momose, Anupreeta More, Surhud More, Shiro Mukae, Ryoma Murata, Hitoshi Murayama, Tohru Nagao, Fumiaki Nakata, Mana Niida, Hiroko Niikura, Atsushi J. Nishizawa, Masamune Oguri, Nobuhiro Okabe, Yoshiaki Ono, Masato Onodera, Masafusa Onoue, Masami Ouchi, Tae-Soo Pyo, Takatoshi Shibuya, Kazuhiro Shimasaku, Melanie Simet, Joshua Speagle, David N. Spergel, Michael A. Strauss, Yuma Sugahara, Naoshi Sugiyama, Yasushi Suto, Nao Suzuki, Philip J. Tait, Masahiro Takada, Tsuyoshi Terai, Yoshiki Toba, Edwin L. Turner, Hisakazu Uchiyama, Keiichi Umetsu, Yuji Urata, Tomonori Usuda, Sherry Yeh, Suraphong Yuma

Publications of the Astronomical Society of Japan　70　(1)　2018/01/01

DOI： 10.1093/pasj/psx081 　

ISSN： 2053-051X 0004-6264

eISSN： 2053-051X
The Hyper Suprime-Cam SSP survey: Overview and survey design Peer-reviewed

Hiroaki Aihara, Nobuo Arimoto, Robert Armstrong, Stéphane Arnouts, Neta A. Bahcall, Steven Bickerton, James Bosch, Kevin Bundy, Peter L. Capak, James H. H. Chan, Masashi Chiba, Jean Coupon, Eiichi Egami, Motohiro Enoki, Francois Finet, Hiroki Fujimori, Seiji Fujimoto, Hisanori Furusawa, Junko Furusawa, Tomotsugu Goto, Andy Goulding, Johnny P. Greco, Jenny E. Greene, James E. Gunn, Takashi Hamana, Yuichi Harikane, Yasuhiro Hashimoto, Takashi Hattori, Masao Hayashi, Yusuke Hayashi, Krzysztof G. Hełminiak, Ryo Higuchi, Chiaki Hikage, Paul T. P. Ho, Bau-Ching Hsieh, Kuiyun Huang, Song Huang, Hiroyuki Ikeda, Masatoshi Imanishi, Akio K. Inoue, Kazushi Iwasawa, Ikuru Iwata, Anton T. Jaelani, Hung-Yu Jian, Yukiko Kamata, Hiroshi Karoji, Nobunari Kashikawa, Nobuhiko Katayama, Satoshi Kawanomoto, Issha Kayo, Jin Koda, Michitaro Koike, Takashi Kojima, Yutaka Komiyama, Akira Konno, Shintaro Koshida, Yusei Koyama, Haruka Kusakabe, Alexie Leauthaud, Chien-Hsiu Lee, Lihwai Lin, Yen-Ting Lin, Robert H. Lupton, Rachel Mandelbaum, Yoshiki Matsuoka, Elinor Medezinski, Sogo Mineo, Shoken Miyama, Hironao Miyatake, Satoshi Miyazaki, Rieko Momose, Anupreeta More, Surhud More, Yuki Moritani, Takashi J. M. Oriya, Tomoki Morokuma, Shiro Mukae, Ryoma Murata, Hitoshi Murayama, Tohru Nagao, Fumiaki Nakata, Mana Niida, Hiroko Niikura, Atsushi J. Nishizawa, Yoshiyuki Obuchi, Masamune Oguri, Yukie Oishi, Nobuhiro Okabe, Sakurako Okamoto, Yuki Okura, Yoshiaki Ono, Masato Onodera, Masafusa Onoue, Ken Osato, Masami Ouchi, Paul A. Price, Tae-Soo Pyo, Masao Sako, Marcin Sawicki, Takatoshi Shibuya, Kazuhiro Shimasaku, Atsushi Shimono, Masato Shirasaki, John D. Silverman, Melanie Simet, Joshua Speagle, David N. Spergel, Michael A. Strauss, Yuma Sugahara, Naoshi Sugiyama, Yasushi Suto, Sherry H. Suyu, Nao Suzuki, Philip J. Tait, Masahiro Takada, Tadafumi Takata, Naoyuki Tamura, Manobu M. Tanaka, Masaomi Tanaka, Masayuki Tanaka, Yoko Tanaka, Tsuyoshi Terai, Yuichi Terashima, Yoshiki Toba, Nozomu Tominaga, Jun Toshikawa, Edwin L. Turner, Tomohisa Uchida, Hisakazu Uchiyama, Keiichi Umetsu, Fumihiro Uraguchi, Yu Ji Urata, Tomonori Usuda, Yousuke Utsumi, Shiang-Yu Wang, Wei-Hao Wang, Kenneth C. Wong, Kiyoto Yabe, Yoshihiko Yamada, Hitomi Yamanoi, Naoki Yasuda, Sherry Yeh, Atsunori Yonehara, Suraphong Yuma

Publications of the Astronomical Society of Japan　70　(1)　2018/01/01

DOI： 10.1093/pasj/psx066 　

ISSN： 2053-051X 0004-6264

eISSN： 2053-051X
Universal Dark Halo Scaling Relation for the Dwarf Spheroidal Satellites Peer-reviewed

Kohei Hayashi, Tomoaki Ishiyama, Go Ogiya, Masashi Chiba, Shigeki Inoue, Masao Mori

ASTROPHYSICAL JOURNAL　843　(2)　2017/07

DOI： 10.3847/1538-4357/aa74d9 　

ISSN： 0004-637X

eISSN： 1538-4357
Resolved Stellar Streams around NGC 4631 from a Subaru/Hyper Suprime-Cam Survey Peer-reviewed

Mikito Tanaka, Masashi Chiba, Yutaka Komiyama

Astrophysical Journal　842　(2)　2017/06/20
Publisher: Institute of Physics Publishing
DOI： 10.3847/1538-4357/aa6d11 　

ISSN： 1538-4357 0004-637X
Structure and dynamics of the Milky Way disk as revealed from the radial velocity distributions of APOGEE red clump stars Peer-reviewed

Toyouchi, Daisuke, Chiba, Masashi

IAU Symp, Vol. 321　2017/03
The Missing Satellite Problem Outside of the Local Group Peer-reviewed

Tanaka, Masayuki, Chiba, Masashi, Komiyama, Yutaka, Tanaka, Mikito, Okamoto, Sakurako, Okamoto, Takashi

IAU Symp, Vol. 321　2017/03
Evidence for a Dusty Dark Dwarf Galaxy in the Quadruple Lens MG 0414+0534 Peer-reviewed

Kaiki Taro Inoue, Satoki Matsushita, Takeo Minezaki, Masashi Chiba

ASTROPHYSICAL JOURNAL LETTERS　835　(2)　2017/02

DOI： 10.3847/2041-8213/835/2/L23 　

ISSN： 2041-8205

eISSN： 2041-8213
BIMODIAL DISTRIBUTION OF GALACTIC DISK STARS ON THE [alpha/Fe]-[Fe/H] PLANE AS POSSIBLE EVIDENCE OF DISCONTINUOUS RADIAL MIGRATION HISTORY Peer-reviewed

Daisuke Toyouchi, Masashi Chiba

ASTROPHYSICAL JOURNAL　833　(2)　2016/12

DOI： 10.3847/1538-4357/833/2/239 　

ISSN： 0004-637X

eISSN： 1538-4357
A NEW MILKY WAY SATELLITE DISCOVERED IN THE SUBARU/HYPER SUPRIME-CAM SURVEY Peer-reviewed

Daisuke Homma, Masashi Chiba, Sakurako Okamoto, Yutaka Komiyama, Masayuki Tanaka, Mikito Tanaka, Miho N. Ishigaki, Masayuki Akiyama, Nobuo Arimoto, Jose A. Garmilla, Robert H. Lupton, Michael A. Strauss, Hisanori Furusawa, Satoshi Miyazaki, Hitoshi Murayama, Atsushi J. Nishizawa, Masahiro Takada, Tomonori Usuda, Shiang-Yu Wang

ASTROPHYSICAL JOURNAL　832　(1)　2016/11

DOI： 10.3847/0004-637X/832/1/21 　

ISSN： 0004-637X

eISSN： 1538-4357
EVOLUTION OF DWARF SPHEROIDAL SATELLITES IN THE COMMON SURFACE-DENSITY DARK HALOS Peer-reviewed

Yusuke Okayasu, Masashi Chiba

ASTROPHYSICAL JOURNAL　827　(2)　2016/08

DOI： 10.3847/0004-637X/827/2/105 　

ISSN： 0004-637X

eISSN： 1538-4357
Subaru Hyper Suprime Cam Survey of the Andromeda Halo Peer-reviewed

Chiba, Masashi, Tanaka, Mikito, Komiyama, Yutaka

IAU Symp, Vol. 317　2016/08
A universality of dark-halo surface density for the Milky Way and Andromeda dwarf satellites as a probe of the coldness of dark matter Peer-reviewed

Hayashi, Kohei, Chiba, Masashi

IAU Symp, Vol. 317　2016/08
Discovery of new dwarf galaxies around NGC4631 with Subaru/Hyper Suprime-Cam Peer-reviewed

Tanaka, Mikito, Chiba, Masashi, Komiyama, Yutaka

IAU Symp, Vol. 317　2016/08
LINE-OF-SIGHT VELOCITY AND METALLICITY MEASUREMENTS OF THE PALOMAR 5 TIDAL STREAM Peer-reviewed

M. N. Ishigaki, N. Hwang, M. Chiba, W. Aoki

ASTROPHYSICAL JOURNAL　823　(2)　2016/06

DOI： 10.3847/0004-637X/823/2/157 　

ISSN： 0004-637X

eISSN： 1538-4357
ALMA imprint of intergalactic dark structures in the gravitational lens SDP.81 Peer-reviewed

Kaiki Taro Inoue, Takeo Minezaki, Satoki Matsushita, Masashi Chiba

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY　457　(3)　2936-2950　2016/04

DOI： 10.1093/mnras/stw168 　

ISSN： 0035-8711

eISSN： 1365-2966
Prime Focus Spectrograph (PFS) for the Subaru Telescope: Overview, recent progress, and future perspectives Peer-reviewed

Naoyuki Tamura, Naruhisa Takato, Atsushi Shimono, Yuki Moritani, Kiyoto Yabe, Yuki Ishizuka, Akitoshi Ueda, Yukiko Kamata, Hrand Aghazarian, Stephane Arnouts, Gabriel Barban, Robert H. Barkhouser, Renato C. Borges, David F. Braun, Michael A. Carr, Pierre-Yves Chabaud, Yin-Chang Chang, Hsin-Yo Chen, Masashi Chiba, Richard C. Y. Chou, You-Hua Chu, Judith G. Cohen, Rodrigo P. de Almeida, Antonio C. de Oliveira, Ligia S. de Oliveira, Richard G. Dekany, Kjetil Dohlen, Jesulino B. dos Santos, Leandro H. dos Santos, Richard S. Ellis, Maximilian Fabricius, Didier Ferrand, Decio Ferreira, Mirek Golebiowski, Jenny E. Greene, Johannes Gross, James E. Gunn, Randolph Hammond, Albert Harding, Murdock Hart, Timothy M. Heckman, Christopher M. Hirata, Paul Ho, Stephen C. Hope, Larry Hovland, Shu-Fu Hsu, Yen-Shan Hui, Ping-Jie Huang, Marc Jaquet, Yipeng Jing, Jennifer Karr, Masahiko Kimura, Matthew E. King, Eiichiro Komatsu, Vincent Le Brun, Olivier Le Fevre, Arnaud Le Fur, David Le Mignant, Hung-Hsu Ling, Craig P. Loomis, Robert H. Lupton, Fabrice Madec, Peter Mao, Lucas S. Marrara, Claudia Mendes de Oliveira, Yosuke Minowa, Chaz N. Morantz, Hitoshi Murayama, Graham J. Murray, Youichi Ohyama, Joseph Orndorff, Sandrine Pascal, Jefferson M. Pereira, Daniel J. Reiley, Martin Reinecke, Andreas Ritter, Mitsuko Roberts, Mark A. Schwochertd, Michael D. Seiffert, Stephen A. Smee, Laerte Sodre, David N. Spergel, Aaron J. Steinkraus, Michael A. Strauss, Christian Surace, Yasushi Suto, Nao Suzuki, John Swinbank, Philip J. Tait, Masahiro Takada, Tomonori Tamura, Yoko Tanaka, Laurence Tresse, Orlando Verducci, Didier Viberte, Clement Vidale, Shiang-Yu Wang, Chih-Yi Wen, Chi-Hung Yan, Naoki Yasuda

GROUND-BASED AND AIRBORNE INSTRUMENTATION FOR ASTRONOMY VI　9908　2016

DOI： 10.1117/12.2232103 　

ISSN： 0277-786X

eISSN： 1996-756X
Thirty Meter Telescope Detailed Science Case: 2015

Warren Skidmore

RESEARCH IN ASTRONOMY AND ASTROPHYSICS　15　(12)　1945-2140　2015/12

DOI： 10.1088/1674-4527/15/12/001 　

ISSN： 1674-4527
STRUCTURAL PROPERTIES OF NON-SPHERICAL DARK HALOS IN MILKY WAY AND ANDROMEDA DWARF SPHEROIDAL GALAXIES Peer-reviewed

Kohei Hayashi, Masashi Chiba

ASTROPHYSICAL JOURNAL　810　(1)　2015/09

DOI： 10.1088/0004-637X/810/1/22 　

ISSN： 0004-637X

eISSN： 1538-4357
GAS INFLOW AND OUTFLOW HISTORIES IN DISK GALAXIES AS REVEALED FROM OBSERVATIONS OF DISTANT STAR-FORMING GALAXIES Peer-reviewed

Daisuke Toyouchi, Masashi Chiba

ASTROPHYSICAL JOURNAL　810　(1)　2015/09

DOI： 10.1088/0004-637X/810/1/18 　

ISSN： 0004-637X

eISSN： 1538-4357
Chemical abundances of giant stars in NGC 5053 and NGC 5634, two globular clusters associated with the Sagittarius dwarf spheroidal galaxy? Peer-reviewed

L. Sbordone, L. Monaco, C. Moni Bidin, P. Bonifacio, S. Villanova, M. Bellazzini, R. Ibata, M. Chiba, D. Geisler, E. Caffau, S. Duffau

ASTRONOMY & ASTROPHYSICS　579　2015/07

DOI： 10.1051/0004-6361/201425509 　

ISSN： 0004-6361

eISSN： 1432-0746
A COMMON SURFACE-DENSITY SCALE FOR THE MILKY WAY AND ANDROMEDA DWARF SATELLITES AS A CONSTRAINT ON DARK MATTER MODELS Peer-reviewed

Kohei Hayashi, Masashi Chiba

ASTROPHYSICAL JOURNAL LETTERS　803　(1)　11　2015/04

DOI： 10.1088/2041-8205/803/1/L11 　

ISSN： 2041-8205

eISSN： 2041-8213
GLOBAL PROPERTIES OF M31'S STELLAR HALO FROM THE SPLASH SURVEY. II. METALLICITY PROFILE Peer-reviewed

Karoline M. Gilbert, Jason S. Kalirai, Puragra Guhathakurta, Rachael L. Beaton, Marla C. Geha, Evan N. Kirby, Steven R. Majewski, Richard J. Patterson, Erik J. Tollerud, James S. Bullock, Mikito Tanaka, Masashi Chiba

ASTROPHYSICAL JOURNAL　796　(2)　76-95　2014/12

DOI： 10.1088/0004-637X/796/2/76 　

ISSN： 0004-637X

eISSN： 1538-4357
THE PROLATE DARK MATTER HALO OF THE ANDROMEDA GALAXY Peer-reviewed

Kohei Hayashi, Masashi Chiba

ASTROPHYSICAL JOURNAL　789　(1)　62-72　2014/07

DOI： 10.1088/0004-637X/789/1/62 　

ISSN： 0004-637X

eISSN： 1538-4357
ON THE CHEMICAL AND STRUCTURAL EVOLUTION OF THE GALACTIC DISK Peer-reviewed

Daisuke Toyouchi, Masashi Chiba

ASTROPHYSICAL JOURNAL　788　(1)　89-98　2014/06

DOI： 10.1088/0004-637X/788/1/89 　

ISSN： 0004-637X

eISSN： 1538-4357
Extragalactic science, cosmology, and Galactic archaeology with the Subaru Prime Focus Spectrograph Peer-reviewed

Masahiro Takada, Richard S. Ellis, Masashi Chiba, Jenny E. Greene, Hiroaki Aihara, Nobuo Arimoto, Kevin Bundy, Judith Cohen, Olivier Dore, Genevieve Graves, James E. Gunn, Timothy Heckman, Christopher M. Hirata, Paul Ho, Jean-Paul Kneib, Olivier Le Fevre, Lihwai Lin, Surhud More, Hitoshi Murayama, Tohru Nagao, Masami Ouchi, Michael Seiffert, John D. Silverman, Laerte Sodre, David N. Spergel, Michael A. Strauss, Hajime Sugai, Yasushi Suto, Hideki Takami, Rosemary Wyse

PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN　66　(1)　1-51　2014/02

DOI： 10.1093/pasj/pst019 　

ISSN： 0004-6264

eISSN： 2053-051X
Extragalactic science, cosmology, and Galactic archaeology with the Subaru Prime Focus Spectrograph Peer-reviewed

Masahiro Takada, Richard S. Ellis, Masashi Chiba, Jenny E. Greene, Hiroaki Aihara, Nobuo Arimoto, Kevin Bundy, Judith Cohen, Olivier Doré, Genevieve Graves, James E. Gunn, Timothy Heckman, Christopher M. Hirata, Paul Ho, Jean-Paul Kneib, Olivier Le Fèvre, Lihwai Lin, Surhud More, Hitoshi Murayama, Tohru Nagao, Masami Ouchi, Michael Seiffert, John D. Silverman, Laerte Sodré, David N. Spergel, Michael A. Strauss, Hajime Sugai, Yasushi Suto, Hideki Takami, Rosemary Wyse

Publications of the Astronomical Society of Japan　66　(1)　2014
Publisher: Oxford University Press
DOI： 10.1093/pasj/pst019 　

ISSN： 2053-051X 0004-6264
The global dark halo structure of the Andromeda galaxy

Hayashi, K, Chiba, M

IAU Symp, Vol. 298　412-412　2014/01
Probing non-spherical dark halos in the Galactic dwarf satellites

Hayashi, K, Chiba, M

IAU Symp, Vol. 298　411-411　2014/01
Chemical differences and similarities among the kinematically

Ishigaki, M. N, Aoki, W, Chiba, M

IAU Symp, Vol. 298　71-76　2014/01
Elemental abundances in the Milky Way stellar disk(s), bulge, and halo Invited Peer-reviewed

Sofia Feltzing, Masashi Chiba

NEW ASTRONOMY REVIEWS　57　(3-4)　80-99　2013/09

DOI： 10.1016/j.newar.2013.06.001 　

ISSN： 1387-6473

eISSN： 1872-9630
CHEMICAL ABUNDANCES OF THE MILKY WAY THICK DISK AND STELLAR HALO. II. SODIUM, IRON-PEAK, AND NEUTRON-CAPTURE ELEMENTS Peer-reviewed

M. N. Ishigaki, W. Aoki, M. Chiba

ASTROPHYSICAL JOURNAL　771　(1)　67-92　2013/07

DOI： 10.1088/0004-637X/771/1/67 　

ISSN： 0004-637X

eISSN： 1538-4357
Global properties of M31's stellar halo from the SPLASH survey. I. Surface brightness profile Peer-reviewed

Karoline M. Gilbert, Puragra Guhathakurta, Rachael L. Beaton, James Bullock, Marla C. Geha, Jason S. Kalirai, Evan N. Kirby, Steven R. Majewski, James C. Ostheimer, Richard J. Patterson, Erik J. Tollerud, Mikito Tanaka, Masashi Chiba

Astrophysical Journal　760　(1)　2012/11/20
Publisher: Institute of Physics Publishing
DOI： 10.1088/0004-637X/760/1/76 　

ISSN： 1538-4357 0004-637X
PROBING NON-SPHERICAL DARK HALOS IN THE GALACTIC DWARF GALAXIES Peer-reviewed

Kohei Hayashi, Masashi Chiba

ASTROPHYSICAL JOURNAL　755　(2)　2012/08

DOI： 10.1088/0004-637X/755/2/145 　

ISSN： 0004-637X
A spectroscopic survey of Andromeda's Western Shelf Peer-reviewed

Mark A. Fardal, Puragra Guhathakurta, Karoline M. Gilbert, Erik J. Tollerud, Jason S. Kalirai, Mikito Tanaka, Rachael Beaton, Masashi Chiba, Yutaka Komiyama, Masanori Iye

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY　423　(4)　3134-3147　2012/07

DOI： 10.1111/j.1365-2966.2012.21094.x 　

ISSN： 0035-8711
CHEMICAL ABUNDANCES OF THE MILKY WAY THICK DISK AND STELLAR HALO. I. IMPLICATIONS OF [alpha/Fe] FOR STAR FORMATION HISTORIES IN THEIR PROGENITORS Peer-reviewed

Miho N. Ishigaki, Masashi Chiba, Wako Aoki

ASTROPHYSICAL JOURNAL　753　(1)　2012/07

DOI： 10.1088/0004-637X/753/1/64 　

ISSN： 0004-637X

eISSN： 1538-4357
THE CASE FOR THE DUAL HALO OF THE MILKY WAY Peer-reviewed

Timothy C. Beers, Daniela Carollo, Zeljko Ivezic, Deokkeun An, Masashi Chiba, John E. Norris, Ken C. Freeman, Young Sun Lee, Jeffrey A. Munn, Paola Re Fiorentin, Thirupathi Sivarani, Ronald Wilhelm, Brian Yanny, Donald G. York

ASTROPHYSICAL JOURNAL　746　(1)　2012/02

DOI： 10.1088/0004-637X/746/1/34 　

ISSN： 0004-637X

eISSN： 1538-4357
Key Science Drivers for MICHI, A Mid-IR Instrument Concept for the TMT

Chris Packham, M. Honda, M. Richter, Y. K. Okamoto, H. Kataza, T. Onaka, T. Fujiyoshi, Alan Tokunaga, M. Chun, A. Alonso-Herrero, J. Carr, M. Chiba, K. Enya, H. Fujiwara, P. Gandhi, M. Imanishi, K. Ichikawa, Y. Ita, N. Kawakatsu, T. Kotani, N. Levenson, T. Matsuo, M. Matsuura, T. Minezaki, J. Najita, N. Oi, T. Ootsubo, I. Sakon, M. Takami, C. Telesco, C. M. Wright, T. Yamashita

GROUND-BASED AND AIRBORNE INSTRUMENTATION FOR ASTRONOMY IV　8446　2012

DOI： 10.1117/12.924996 　

ISSN： 0277-786X

eISSN： 1996-756X
Chemical Abundances of the Milky Way Thick Disk and Stellar Halo Peer-reviewed

Miho N. Ishigaki, Wako Aoki, Masashi Chiba

FIRST STARS IV - FROM HAYASHI TO THE FUTURE　1480　379-381　2012

DOI： 10.1063/1.4754393 　

ISSN： 0094-243X
Chemical Abundances of the Kinematically Selected Thick Disk and Halo Stars Peer-reviewed

Miho Ishigaki, Masashi Chiba, Wako Aoki

GALACTIC ARCHAEOLOGY: NEAR-FIELD COSMOLOGY AND THE FORMATION OF THE MILKY WAY　458　157-+　2012
STRUCTURE AND POPULATION OF THE NGC 55 STELLAR HALO FROM A SUBARU/SUPRIME-CAM SURVEY Peer-reviewed

Mikito Tanaka, Masashi Chiba, Yutaka Komiyama, Puragra Guhathakurta, Jason S. Kalirai

ASTROPHYSICAL JOURNAL　738　(2)　2011/09

DOI： 10.1088/0004-637X/738/2/150 　

ISSN： 0004-637X

eISSN： 1538-4357
Erratum: Chemical abundances of the outer halo stars in the milky way (Publications of the Astronomical Society of Japan (2010) 62 (143-178)) Peer-reviewed

Miho Ishigaki, Masashi Chiba, Wako Aoki

Publications of the Astronomical Society of Japan　62　(5)　1369　2010/10/25
Publisher: Oxford University Press
DOI： 10.1093/pasj/62.5.1369 　

ISSN： 0004-6264
STRUCTURE AND KINEMATICS OF THE STELLAR HALOS AND THICK DISKS OF THE MILKY WAY BASED ON CALIBRATION STARS FROM SLOAN DIGITAL SKY SURVEY DR7 Peer-reviewed

Daniela Carollo, Timothy C. Beers, Masashi Chiba, John E. Norris, Ken C. Freeman, Young Sun Lee, Zeljko Ivezic, Constance M. Rockosi, Brian Yanny

ASTROPHYSICAL JOURNAL　712　(1)　692-727　2010/03

DOI： 10.1088/0004-637X/712/1/692 　

ISSN： 0004-637X
Chemical Abundances of Outer Halo Stars in the Milky Way Peer-reviewed

Miho Ishigaki, Masashi Chiba, Wako Aoki

PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN　62　(1)　143-178　2010/02

DOI： 10.1093/pasj/62.1.143 　

ISSN： 0004-6264

eISSN： 2053-051X
The science drivers for a mid-infrared instrument for the TMT

Y. K. Okamoto, C. Packham, A. Tokunaga, M. Honda, I. Sakon, J. Carr, M. Chiba, M. Chun, H. Fujiwara, T. Fujiyoshi, M. Imanishi, Y. Ita, H. Kataza, N. Levenson, M. Matsuura, T. Minezaki, J. Najita, T. Onaka, T. Ootsubo, M. Richter, M. Takami, C. M. Telesco, C. M. Wright, T. Yamashita

Proceedings of SPIE - The International Society for Optical Engineering　7735　(1)　2010

DOI： 10.1117/12.856670 　

ISSN： 0277-786X
The SPLASH Survey: Spectroscopy of Newly Discovered Tidal Streams in the Outer Halo of the Andromeda Galaxy

Guhathakurta, P, including Masashi Chiba

Bulletin of the American Astronomical Society　2010/01/01
STRUCTURE AND POPULATION OF THE ANDROMEDA STELLAR HALO FROM A SUBARU/SUPRIME-CAM SURVEY Peer-reviewed

Mikito Tanaka, Masashi Chiba, Yutaka Komiyama, Puragra Guhathakurta, Jason S. Kalirai, Masanori Iye

ASTROPHYSICAL JOURNAL　708　(2)　1168-1203　2010/01

DOI： 10.1088/0004-637X/708/2/1168 　

ISSN： 0004-637X

eISSN： 1538-4357
CHEMICAL COMPOSITIONS OF KINEMATICALLY SELECTED OUTER HALO STARS Peer-reviewed

Lan Zhang, Miho Ishigaki, Wako Aoki, Gang Zhao, Masashi Chiba

ASTROPHYSICAL JOURNAL　706　(2)　1095-1113　2009/12

DOI： 10.1088/0004-637X/706/2/1095 　

ISSN： 0004-637X
Li-6/Li-7 estimates for metal-poor stars Peer-reviewed

A. E. Garcia Perez, W. Aoki, S. Inoue, S. G. Ryan, T. K. Suzuki, M. Chiba

ASTRONOMY & ASTROPHYSICS　504　(1)　213-223　2009/09

DOI： 10.1051/0004-6361/200912289 　

ISSN： 0004-6361
ON THE SIZE EVOLUTION OF A GALACTIC DISK IN HIERARCHICAL MERGING OF COLD DARK MATTER HALOS Peer-reviewed

Hirohito Hayashi, Masashi Chiba

ASTROPHYSICAL JOURNAL　702　(2)　871-879　2009/09

DOI： 10.1088/0004-637X/702/2/871 　

ISSN： 0004-637X

eISSN： 1538-4357
SUBARU MID-INFRARED IMAGING OF THE QUADRUPLE LENSES. II. UNVEILING LENS STRUCTURE OF MG0414+0534 AND Q2237+030 Peer-reviewed

Takeo Minezaki, Masashi Chiba, Nobunari Kashikawa, Kaiki Taro Inoue, Hirokazu Kataza

ASTROPHYSICAL JOURNAL　697　(1)　610-618　2009/05

DOI： 10.1088/0004-637X/697/1/610 　

ISSN： 0004-637X
ROLE OF GALACTIC GASEOUS HALOS IN RECYCLING ENRICHED WINDS FROM BULGES TO DISKS: A NEW BULGE-DISK CHEMICAL CONNECTION Peer-reviewed

Kenji Bekki, Takuji Tsujimoto, Masashi Chiba

ASTROPHYSICAL JOURNAL LETTERS　692　(1)　L24-L28　2009/02

DOI： 10.1088/0004-637X/692/1/L24 　
Lens Mapping of Dark Matter Substructure with VSOP-2

Shigenori Ohashi, Masashi Chiba, Kaiki Taro Inoue

APPROACHING MICRO-ARCSECOND RESOLUTION WITH VSOP-2: ASTROPHYSICS AND TECHNOLOGY　402　290-292　2009
Origin of Structural and Kinematic Properties of the Small Magellanic Cloud Peer-reviewed

Kenji Bekki, Masashi Chiba

PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF AUSTRALIA　26　(1)　37-57　2009

DOI： 10.1071/AS08020 　

ISSN： 1323-3580
Kinematics and chemical abundances of metal-poor stars in the Galactic outer halo Peer-reviewed

M. Ishigaki, M. Chiba, W. Aoki

ASTRONOMISCHE NACHRICHTEN　329　(9-10)　1073-1075　2008/12

DOI： 10.1002/asna.200811063 　

ISSN： 0004-6337
THE EXTENDED STAR FORMATION HISTORY OF THE ANDROMEDA SPHEROID AT 35 kpc ON THE MINOR AXIS Peer-reviewed

Thomas M. Brown, Rachael Beaton, Masashi Chiba, Henry C. Ferguson, Karoline M. Gilbert, Puragra Guhathakurta, Masanori Iye, Jasonjot S. Kalirai, Andreas Koch, Yutaka Komiyama, Steven R. Majewski, David B. Reitzel, Alvio Renzini, R. Michael Rich, Ed Smith, Allen V. Sweigart, Mikito Tanaka

ASTROPHYSICAL JOURNAL LETTERS　685　(2)　L121-L124　2008/10

DOI： 10.1086/592686 　
Formation of the Small Magellanic Cloud: An ancient major merger as a solution to the kinematical differences between old stars and HI gas Peer-reviewed

Kenji Bekki, Masashi Chiba

ASTROPHYSICAL JOURNAL LETTERS　679　(2)　L89-L92　2008/06

DOI： 10.1086/589441 　
The origin of the giant stellar stream of M 31 Peer-reviewed

Mikito Tanaka, M. Chiba, Y. Komiyama, M. Iye, P. Guhathakurta

Astrophysics and Space Science Proceedings　(208949)　335-336　2008
Publisher: Springer Netherlands
DOI： 10.1007/978-1-4020-6933-8_92 　

ISSN： 1570-6605 1570-6591
Structural and kinematic parameters of the two halo components of the Milky Way

Carollo, D, Beers, T. C, Chiba, M, Norris, J. E, Freeman, K

Proceedings of the 10th Symposium on Nuclei in the Cosmos　2008
Dark Matter Substructure in Lensing Galaxies

Masashi Chiba, Takeo Minezaki, Kaiki T. Inoue, Nobunari Kashikawa, Hirokazu Kataza, Hajime Sugai

PANORAMIC VIEWS OF GALAXY FORMATION AND EVOLUTION, PROCEEDINGS　399　98-101　2008
A Panoramic View of the Stellar Halo in My Neighbor Andromeda: A Metal Poor Halo Emerges in the North-West Fields

Mikito Tanaka, M. Chiba, Y. Komiyama, P. Guhathakurta, M. Iye

PANORAMIC VIEWS OF GALAXY FORMATION AND EVOLUTION, PROCEEDINGS　399　479-480　2008
Structure and dynamics of the old galactic components Invited

Masashi Chiba, Hirohito Hayashi, Motoko Yamada

MAPPING THE GALAXY AND NEARBY GALAXIES　55-+　2008

ISSN： 1570-6591
A Subaru/Suprime-Cam survey of the Andromeda giant stream: Constraints of the dwarf galaxy as the stream's progenitor

Mikito Tanaka, Masashi Chiba, Yutaka Komiyama, Masanori Iye, Puragra Guhathakurta

Mapping the Galaxy and Nearby Galaxies　381-381　2008

ISSN： 1570-6591
The magellanic impact: Collision between the outer Galactic HI disk and the leading arms of the magellanic stream Peer-reviewed

Kenji Bekki, Masashi Chiba, N. M. McClure-Griffiths

ASTROPHYSICAL JOURNAL LETTERS　672　(1)　L17-L20　2008/01

DOI： 10.1086/526456 　
Two stellar components in the halo of the Milky Way Peer-reviewed

Daniela Carollo, Timothy C. Beers, Young Sun Lee, Masashi Chiba, John E. Norris, Ronald Wilhelm, Thirupathi Sivarani, Brian Marsteller, Jeffrey A. Munn, Coryn A. L. Bailer-Jones, Paola Re Fiorentin, Donald G. York

NATURE　450　(7172)　1020-1025　2007/12

DOI： 10.1038/nature06460 　

ISSN： 0028-0836
The magellanic squall: Gas replenishment from the Small to the Large Magellanic Cloud Peer-reviewed

Kenji Bekki, Masashi Chiba

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY　381　(1)　L16-L20　2007/10

DOI： 10.1111/j.1745-3933.2007.00357.x 　

ISSN： 0035-8711
Massive stars and globular cluster formation Peer-reviewed

Kenji Bekki, Masashi Chiba

ASTROPHYSICAL JOURNAL　665　(2)　1164-1172　2007/08

DOI： 10.1086/519727 　

ISSN： 0004-637X
Integral field spectroscopy of the quadruply lensed quasar 1RXS J1131-1231: New light on lens substructures Peer-reviewed

H. Sugai, A. Kawai, A. Shimono, T. Hattori, G. Kosugi, N. Kashikawa, K. T. Inoue, M. Chiba

ASTROPHYSICAL JOURNAL　660　(2)　1016-1022　2007/05

DOI： 10.1086/513731 　

ISSN： 0004-637X

eISSN： 1538-4357
Dynamical influences of the last Magellanic interaction on the Magellanic Clouds Peer-reviewed

Kenji Bekki, Masashi Chiba

PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF AUSTRALIA　24　(1)　21-29　2007

DOI： 10.1071/AS06023 　

ISSN： 1323-3580
Dynamical effects of cold dark matter subhalos on a galactic disk Peer-reviewed

Hirohito Hayashi, Masashi Chiba

PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN　58　(5)　835-846　2006/10

DOI： 10.1093/pasj/58.5.835 　

ISSN： 0004-6264

eISSN： 2053-051X
Impact of dark matter subhalos on extended HI disks of galaxies: Possible formation of HI fine structures and stars Peer-reviewed

K Bekki, M Chiba

ASTROPHYSICAL JOURNAL　637　(2)　L97-L100　2006/02

DOI： 10.1086/500304 　

ISSN： 0004-637X

eISSN： 1538-4357
Direct Detection of Intermediate Mass Compact Objects via Submillilensing

Kaiki Taro Inoue, Masashi Chiba

Annual reports by Research Institute for Science and Technology, (2006) 18, p.11-14　2005/12/30

DOI： 10.1063/1.2204458 　

More details Close

A galaxy-sized halo may contain a large number of intermediate mass (10^{2-4} solar mass) compact objects (IMCOs), which can be intermediate mass black holes (IMBHs) or the CDM subhalos. We propose to directly detect the IMBHs by observing multiply imaged QSO-galaxy lens systems with a high angular resolution (~ 0.03mas), which would be achieved by the next-VLBI space missions. The silhouette of the IMBHs would appear as an either monopole-like or dipole-like variation at the scale of the Einstein radius against the QSO jets. As a byproduct, we can also directly detect the 10^{4-5} solar mass CDM subhalos. From a measurement of the local distortion in the surface brightness of the QSO jet, we can make a distinction between a point mass (corresponding to an IMBH) and an extended structure (corresponding to a CDM subhalo). It would be a unique probe of the IMCOs whose nature has been under the veil of mistery.
Three-dimensional mapping of CDM substructure at submillimeter wavelengths Peer-reviewed

KT Inoue, M Chiba

ASTROPHYSICAL JOURNAL　633　(1)　23-28　2005/11

DOI： 10.1086/452623 　

ISSN： 0004-637X

eISSN： 1538-4357
Extended source effects in substructure lensing Peer-reviewed

KT Inoue, M Chiba

ASTROPHYSICAL JOURNAL　634　(1)　77-89　2005/11

DOI： 10.1086/496870 　

ISSN： 0004-637X
Subaru mid-infrared imaging of the quadruple lenses PG 1115+080 and B1422+231: Limits on substructure lensing Peer-reviewed

M Chiba, T Minezaki, N Kashikawa, H Kataza, KT Inoue

ASTROPHYSICAL JOURNAL　627　(1)　53-61　2005/07

DOI： 10.1086/430403 　

ISSN： 0004-637X

eISSN： 1538-4357
Fossil records of cosmic reionization in galactic stellar halos Peer-reviewed

K Bekki, M Chiba

ASTROPHYSICAL JOURNAL　625　(2)　L107-L110　2005/06

DOI： 10.1086/431224 　

ISSN： 0004-637X
The surprisingly steep mass profile of A1689, from a lensing analysis of Subaru images Peer-reviewed

T Broadhurst, M Takada, K Umetsu, Kong, X, N Arimoto, M Chiba, T Futamase

ASTROPHYSICAL JOURNAL　619　(2)　L143-L146　2005/02

DOI： 10.1086/428122 　

ISSN： 0004-637X
Formation and evolution of the Magellanic Clouds - I. Origin of structural, kinematic and chemical properties of the Large Magellanic Cloud Peer-reviewed

K Bekki, M Chiba

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY　356　(2)　680-702　2005/01

DOI： 10.1111/j.1365-2966.2004.08510.x 　

ISSN： 0035-8711
Explaining the mysterious age gap of globular clusters in the Large Magellanic Cloud Peer-reviewed

K Bekki, WJ Couch, MA Beasley, DA Forbes, M Chiba, GS Da Costa

ASTROPHYSICAL JOURNAL　610　(2)　L93-L96　2004/08

DOI： 10.1086/423372 　

ISSN： 0004-637X
Formation of giant globular cluster G1 and the origin of the M31 stellar halo Peer-reviewed

K Bekki, M Chiba

ASTRONOMY & ASTROPHYSICS　417　(2)　437-442　2004/04

DOI： 10.1051/0004-6361:20034368 　

ISSN： 0004-6361

eISSN： 1432-0746
ERO R1 in the field of CL0939+4713 - Evidence for an SO-like galaxy at z similar to 1.5 Peer-reviewed

M Iye, N Kashikawa, M Imanishi, T Kodama, M Chiba, K Shimasaku, S Okamura, S Miyazaki, C Simpson, N Kobayashi, H Terada, M Goto, F Iwamuro

DARK MATTER IN GALAXIES　220　(220)　181-182　2004

ISSN： 0074-1809
On the kinematics of tidal debris from Omega Cen's progenitor galaxy Peer-reviewed

M Chiba, A Mizutani

PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF AUSTRALIA　21　(2)　237-241　2004

DOI： 10.1071/AS04002 　

ISSN： 1323-3580
Direct mapping of massive compact objects in extragalactic dark halos

Kaiki Taro Inoue, Masashi Chiba

Astrophysical Journal　591　(2)　L83-L86　2003/07/10
Publisher: Institute of Physics Publishing
DOI： 10.1086/377247 　

ISSN： 1538-4357 0004-637X
ERO R1 in the field of Cl 0939+4713: Evidence for an S0-like galaxy at z ∼ 1.5 Peer-reviewed

Masanori Iye, Kazuhiro Shimasaku, Satoshi Miyazaki, Chris Simpson, Masatoshi Imanishi, Nobunari Kashikawa, Tadayuki Kodama, Masashi Chiba, Yoshihiko Saito, Miwa Goto, Fumihide Iwamuro, Naoto Kobayashi, Sadanori Okamura, Hiroshi Terada

Astrophysical Journal　590　(2 I)　770-777　2003/06/20
Publisher: Institute of Physics Publishing
DOI： 10.1086/375146 　

ISSN： 1538-4357 0004-637X
Subaru spectroscopy of the gravitational lens HST 14176+5226: Implications for a large cosmological constant Peer-reviewed

Youichi Ohyama, Takashi Hamana, Nobunari Kashikawa, Masashi Chiba, Toshifumi Futamase, Masanori Iye, Koji S. Kawabata, Kentaro Aoki, Toshiyuki Sasaki, George Kosugi, Tadafumi Takata

Astronomical Journal　123　(6)　2903-2912　2002/06
Publisher: {IOP} Publishing
DOI： 10.1086/340565 　

ISSN： 0004-6256
Formation of galactic disk globular clusters in early dissipative minor merging Peer-reviewed

Kenji Bekki, Masashi Chiba

Astrophysical Journal　566　(1 I)　245-251　2002/02/10
Publisher: Institute of Physics Publishing
DOI： 10.1086/337984 　

ISSN： 1538-4357 0004-637X
Formation of the galactic stellar halo. I. Structure and kinematics Peer-reviewed

Kenji Bekki, Masashi Chiba

Astrophysical Journal　558　(2)　666-686　2001/09/10
Publisher: Institute of Physics Publishing
DOI： 10.1086/322300 　

ISSN： 1538-4357 0004-637X
Structure of the galactic stellar halo prior to disk formation Peer-reviewed

Masashi Chiba, Timothy C. Beers

Astrophysical Journal　549　(1)　325-336　2001/03/01
Publisher: Institute of Physics Publishing
DOI： 10.1086/319068 　

ISSN： 1538-4357 0004-637X
Kinematics of metal-poor stars in the galaxy. III. Formation of the stellar halo and thick disk as revealed from a large sample of nonkinematically selected stars Peer-reviewed

Masashi Chiba, Timothy C. Beers

Astronomical Journal　119　(6)　2843-2865　2000
Publisher: University of Chicago Press
DOI： 10.1086/301409 　

ISSN： 0004-6256

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Misc. 32

すばるHSC-SSPとPFSで迫る銀河系ハロー形成過程の探求

鈴木善久, 千葉柾司, 小宮山裕, 林航平, 田中賢幸, 福島徹也, 常盤晟, QIU Tian, 高田昌広

日本天文学会年会講演予稿集　2024　2024

ISSN： 1347-0639
HSC-SPPデータを用いた天の川銀河トモグラフィー 2

鈴木善久, 千葉柾司, 林航平, 小宮山裕, 田中賢幸, CARLSTEN Scott G., 高田昌広, 常盤晨, QIU Tian

日本天文学会年会講演予稿集　2023　2023

ISSN： 1347-0639
すばる望遠鏡/HSC深観測によるM33恒星ハローの探査

小上樹, 小上樹, 千葉柾司, 小宮山裕, GUHATHAKURTA Puragra, KIRBY Evan, 石垣美歩, 林航平, 桐原崇亘

日本天文学会年会講演予稿集　2023　2023

ISSN： 1347-0639
銀河系矮小銀河の化学動力学進化と星形成史

林航平, 林航平, 平居悠, 平居悠, 石山智明, 千葉柾司

日本天文学会年会講演予稿集　2022　2022

ISSN： 1347-0639
HSC-SSPデータを用いた天の川銀河トモグラフィー 1

鈴木善久, 千葉柾司, 林航平, 小宮山裕, 田中賢幸, CARLSTEN Scott G., 高田昌広, 常盤晟, QIU Tian

日本天文学会年会講演予稿集　2022　2022

ISSN： 1347-0639
局所銀河群外におけるミッシングサテライト問題への統計的検証

梨本真志, 田中賢幸, 千葉柾司, 林航平, 小宮山裕

日本天文学会年会講演予稿集　2021　2021

ISSN： 1347-0639
HSCとGaiaデータを用いた銀河系ハローサブ構造の恒星種族と運動

鈴木善久, 千葉柾司, 林航平, 小宮山裕, 田中賢幸, CARLSTEN Scott G.

日本天文学会年会講演予稿集　2021　2021

ISSN： 1347-0639
銀河形成シミュレーションで探るrプロセス元素に富んだ星の動力学的性質

平居悠, 青木和光, BEERS Timothy C., 千葉柾司, 斎藤貴之, 岡本崇, 牧野淳一郎, 牧野淳一郎

日本天文学会年会講演予稿集　2021　2021

ISSN： 1347-0639
銀河系矮小銀河ダークマター密度分布の多様性

林航平, 千葉柾司, 石山智明

日本天文学会年会講演予稿集　2021　2021

ISSN： 1347-0639
M31恒星ストリームと暗黒物質サブハローの相互作用:すばるPFSへの期待

三木洋平, 桐原崇亘, 森正夫, 小宮山裕, 千葉柾司, 田中幹人, 石垣美歩, 林航平

日本天文学会年会講演予稿集　2020　2020

ISSN： 1347-0639
The stellar halo of the Milky Way traced by blue horizontal-branch stars in the Subaru Hyper Suprime-Cam Survey International-journal International-coauthorship Peer-reviewed

Tetsuya Fukushima, Masashi Chiba, Mikito Tanaka, Kohei Hayashi, Daisuke Homma, Sakurako Okamoto, Yutaka Komiyama, Masayuki Tanaka, Nobuo Arimoto, Tadafumi Matsuno

PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN　71　(4)　2019/08

DOI： 10.1093/pasj/psz052 　

ISSN： 0004-6264

eISSN： 2053-051X
PFSによる銀河系外部ハローの元素組成分布の解明

石垣美歩, 林航平, 千葉柾司, 矢部清人, COHEN Judith G., WYSE Rosemary F. G., KIRBY Evan N.

日本天文学会年会講演予稿集　2018　2018

ISSN： 1347-0639
アンドロメダ銀河North-Westernストリームの形成過程

桐原崇亘, 三木洋平, 森正夫, 小宮山裕, 千葉柾司, 田中幹人, 田中賢幸, 林航平

日本天文学会年会講演予稿集　2018　2018

ISSN： 1347-0639
Hyper Suprime-Camで探るアンドロメダ銀河の恒星ストリームとハロー構造

小宮山裕, 千葉柾司, 田中幹人, 田中賢幸, 桐原崇亘, 三木洋平, 森正夫, LUPTON R. H., GUHATHAKURTA P., KALIRAI J. S., GILBERT K., KIRBY E., LEE M. G., JANG I. S., SHARMA S., 林航平

日本天文学会年会講演予稿集　2018　2018

ISSN： 1347-0639
すばるPFSによる銀河系矮小銀河観測を用いた暗黒物質ハロー構造の精密測定

林航平, 石垣美歩, 小宮山裕, 千葉柾司, COHEN Judith G., WYSE Rosemary F. G., KIRBY Evan N.

日本天文学会年会講演予稿集　2018　2018

ISSN： 1347-0639
Searches for new Milky Way satellites from the first two years of data of the Subaru/Hyper Suprime-Cam survey: Discovery of Cetus III

Daisuke Homma, Masashi Chiba, Sakurako Okamoto, Yutaka Komiyama, Masayuki Tanaka, Mikito Tanaka, Miho N. Ishigaki, Kohei Hayashi, Nobuo Arimoto, José A. Garmilla, Robert H. Lupton, Michael A. Strauss, Satoshi Miyazaki, Shiang-Yu Wang, Hitoshi Murayama

Publications of the Astronomical Society of Japan　70　2018/01/01
Publisher: Oxford University Press
DOI： 10.1093/pasj/psx050 　

ISSN： 2053-051X 0004-6264
すばる望遠鏡Hyper Suprime-Camを用いたDraco dSphの構造解析

佐々木花, 千葉柾司, 田中幹人, 小宮山裕, COHEN Judy, KIRBY Evan, 岡本桜子, 石垣美歩, 林航平, 林航平, WYSE Rosie

日本天文学会年会講演予稿集　2017　2017

ISSN： 1347-0639
矮小銀河ダークマターハローの普遍的性質

林航平, 林航平, 石山智明, 扇谷豪, 千葉柾司, 井上茂樹, 森正夫

日本天文学会年会講演予稿集　2017　2017

ISSN： 1347-0639
銀河系及びアンドロメダ銀河に付随する矮小銀河のダークハロー構造

林航平, 千葉柾司

日本天文学会年会講演予稿集　2015　2015

ISSN： 1347-0639
ダークハロー面密度の普遍性とダークマター理論への制限

林航平, 千葉柾司

日本天文学会年会講演予稿集　2015　2015

ISSN： 1347-0639
銀河系及びアンドロメダ矮小銀河の新たな化学動力学関係

林航平, 千葉柾司

日本天文学会年会講演予稿集　2014　2014

ISSN： 1347-0639
アンドロメダ銀河ダークハローの大局構造

林航平, 千葉柾司

日本天文学会年会講演予稿集　2013　2013

ISSN： 1347-0639
矮小銀河カスプ問題:非球対称モデルからの制限

林航平, 千葉柾司

日本天文学会年会講演予稿集　2013　2013

ISSN： 1347-0639
銀河系矮小銀河のダークハロー構造:ΛCDM理論の検証

林航平, 千葉柾司

日本天文学会年会講演予稿集　2012　2012

ISSN： 1347-0639
Dark Matter Profiles in Galactic Dwarf Satellites: Constraints from Non-Spherical Mass Models Peer-reviewed

Kohei Hayashi, Masashi Chiba

GALACTIC ARCHAEOLOGY: NEAR-FIELD COSMOLOGY AND THE FORMATION OF THE MILKY WAY　458　383-384　2012
矮小銀河の動力学解析に基づくダークハローの非球対称性

林航平, 千葉柾司

日本天文学会年会講演予稿集　2011　2011

ISSN： 1347-0639
Chemical Abundances of the Outer Halo Stars in the Milky Way (vol 62, pg 143, 2010)

Miho Ishigaki, Masashi Chiba, Wako Aoki

PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN　62　(5)　1369-1369　2010/10

DOI： 10.1093/pasj/62.5.1369 　

ISSN： 0004-6264

eISSN： 2053-051X
銀河系ハローの２重構造

千葉柾司

パリティ　2009/01
Publisher: 丸善
銀河考古学：古い星から銀河の成り立ちを読み解く

千葉柾司

天文月報　101　(11)　2008/11
Publisher: 日本天文学会
The Magellanic squall: Gas replenishment from the small to the large Magellanic Cloud

Kenji Bekki, Masashi Chiba

Monthly Notices of the Royal Astronomical Society: Letters　381　(1)　L15-L20　2007/10

DOI： 10.1111/j.1745-3933.2007.00357.x 　

ISSN： 1745-3933
Dark and stellar matter in strong lensing galaxies from a joint lensing and stellar dynamics

Takashi Hamana, Youichi Ohyama, Masashi Chiba, Nobunari Kashikawa

2005/07/04

More details Close

We present Subaru spectroscopy of the early-type lensing galaxies in the lens systems HST14113+5211 (z=0.464) and B2045+265 (z=0.868), being aimed at measuring the velocity dispersion of the lensing galaxies as an important component to their mass distributions and internal dynamics. For HST14113+5211 we have obtained 174+/-20km/s (1-sigma) inside an aperture of 0.9", and for B2045+265 we have obtained 213+/-23km/s inside an aperture of 1.2". To extract the significance of these information on the mass distributions and stellar dynamics of the lensing galaxies, we construct two alternative models for both the mass and velocity distributions. It is found that the mass-to-light ratios as derived from a joint lensing and stellar dynamics analysis are virtually consistent with those obtained from the use of the Fundamental Plane. Also, for HST14113+5211, we find that the total mass distribution is well reproduced by a power-law density profile with an index of 2, thereby suggesting that a singular isothermal model is a good fit to the lensing galaxy. In contrast, the corresponding slope for B2045+265 is flatter than isothermal, suggesting that additional contributions to lensing mass from surrounding structures (possibly the group of galaxies) provide the observed angular separations of multiple images.
Statitics of QSO Lensing and Cosmological Parameters

Masashi Chiba, Toshifumi Futamase

Progrese of Theroretical Physics, Supplement　133　115　1999

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Books and Other Publications 7

銀河考古学

千葉柾司

日本評論社　2015/07/20
天文学辞典

岡村定矩, 家正則, 犬塚修一郎, 小山勝二, 千葉柾司, 富阪幸治

日本評論社　2012/07/20
宇宙論ＩＩー宇宙の進化

二間瀬敏史, 池内了, 千葉柾司編

日本評論社　2007/09/15
天文学大辞典

山田卓他

地人書館　2007/06/01
銀河Ⅱ― 銀河系

祖父江義明他編

日本評論社　2007/04
天文の事典

磯部琇三他編

朝倉書店　2003/07/10
天文学への招待

岡村定矩他

朝倉書店　2001/11/10

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Presentations 62

すばる望遠鏡/HSC による深観測で探る NGC5466 広域分布

小上樹, 石垣美歩, 千葉柾司, 小宮山裕, 冨永望, Mohammad Mardini, Tilman Hartwig, 桐原崇亘, 岡田寛子

日本天文学会2023年春季年会　2023/03/15
HSC-SSP データを用いた天の川銀河トモグラフィー 2

鈴木善久, 千葉柾司, 林航平, 小宮山裕, 田中賢幸, Scott G. Carlsten, 高田昌広, 常盤晟, Tian Qiu

日本天文学会2023年春季年会　2023/03/13
すばる HSC データを用いた Sextans 矮小楕円体銀河の固有運動測定

常盤晟, Tian Qiu, 高田昌広, 安田直樹, 小宮山裕, 千葉柾司

日本天文学会2022年秋季年会　2022/09/15
HSC-SSP データを用いた天の川銀河トモグラフィー 1

鈴木善久, 千葉柾司, 林航平, 小宮山裕, 田中賢幸, Scott G. Carlsten, 高田昌広, 常盤晟, Tian Qiu

日本天文学会2022年秋季年会　2022/09/15
APOGEE red-clump star の解析から明らかになった銀河系円盤の化学動力学進化

豊内大輔, 千葉柾司

日本天文学会秋季年会　2016/09/14
４重像レンズQSOにおける暗黒矮小銀河のエビデンス

井上開輝, 松下聡樹, 峰崎岳夫, 千葉柾司

日本天文学会春季年会　2016/03/15
ダークハローの面密度の普遍性とダークマター理論への制限

林航平, 千葉柾司

日本天文学会秋季年会　2015/09/10
サブミリレンズ銀河SDP.81 におけるダークマター小構造の痕跡

井上開輝, 峰崎兵夫, 松下聡樹, 千葉柾司

日本天文学会秋季年会　2015/09/09
Discovery of new dwarf galaxies around NGC4631 with Subaru/Hyper Suprime-Cam International-presentation

Tanaka, M, Komiyama, Y, Chiba, M

IAU Symp 317　2015/08/03
A universality of dark-halo surface density for the Milky Way and Andromeda dwarf satellites as a probe of the coldness of dark matter International-presentation

Hayashi, K, Chiba, M

IAU Symp 317　2015/08/03
Baryonic inflow and outflow histories in disk galaxies as revealed from observations of distant star-forming galaxies International-presentation

Toyouchi, D, Chiba, M

IAU Symp 317　2015/08/03
Subaru Hyper Suprime Cam Survey of the Andromeda Halo International-presentation

Chiba, M, Tanaka, M, Komiyama, Y

IAU Symp 317　2015/08/03
Galactic Archaeology with the Subaru Prime Focus Spectrograph International-presentation

Chiba, M, Cohen, J, Wyse, R

IAU Symp 317　2015/08/03
銀河系及びアンドロメダ銀河に付随する矮小銀河のダークハロー構造

林航平

日本天文学会春季年会　2015/03/20
銀河系球状星団系の力学進化史と初期状態への制限

鈴木雄太

日本天文学会春季年会　2015/03/20
銀河系及びアンドロメダ矮小銀河の新たな化学動力学関係

林航平

日本天文学会秋季年会　2014/09/12
Subaru/Hyper Suprime-Camで探るNGC4631相互作用銀河群の構造I

田中幹人

日本天文学会秋季年会　2014/09/11
銀河系円盤の化学進化：金属量勾配進化に基づく円盤形成過程の解明

豊内大輔

日本天文学会春季年会　2014/03/21
矮小銀河カスプ問題：非球対称モデルからの制限

林航平

日本天文学会秋季年会　2013/09/11
Exploring the Local Universe with TMT International-presentation

TMT Science Forum　2013/07/22
PFS Galactic Archaeology International-presentation

Subaru PFS 4th collaboration meeting　2013/03/24
アンドロメダ銀河ダークハローの大局構造

林航平

日本天文学会春季年会　2013/03/21
HSCを用いたアンドロメダ銀河ハロー観測におけるNB515フィルターの有効性

田中幹人

日本天文学会春季年会　2013/03/21
銀河系の厚い恒星円盤成分の起源

豊内大輔

日本天文学会春季年会　2013/03/20
Too Big To Fail問題の解決に向けた暗黒物質サブハローの力学進化の研究

小室佑介

日本天文学会春季年会　2013/03/20
Near-field cosmology in the near future International-presentation

Korea-Japan Mini-Workshop on the Local Universe　2013/02/18
PFS Galactic Archaeology International-presentation

PFS 3rd collaboration meeting　2012/08/13
Dark matter structure in galactic and sub-galactic scales International-presentation

The 4th International Symposium on Neutrinos and Dark Matter in Nuclear Physics　2012/06/11
Probing kinematical substructures in the Milky Way halo International-presentation

Stellar Populations across Cosmic Times　2012/05/25
New views on the formation and evolution of the Milky Way International-presentation

Galaxies: Origin, Dynamics, Structure and Astrophysical DIsks　2012/05/14
Galactic Archaeology with Subaru/PFS International-presentation

PFS 2nd collaboration meeting　2012/01/09
銀河系・近傍銀河の形成史

第24回理論懇シンポジウム「理論天文学・宇宙物理学の革新」　2011/11/05
Galactic Archaeology with Subaru: Prospects for Wide-Field Surveys International-presentation

Galactic Archaeology　2011/10/27
New information from the kinematics and chemical abundances of stars in the Milky Way International-presentation

The Accelerating Universe　2011/10/24
銀河考古学の観点から

Subaru Next-Generation AO Workshop　2011/09/08
Michi: A MIR Instrument Concept for the TMT International-presentation

AAS Meeting　2011/01
すばる主焦点カメラで探るNGC55恒星ハローの構造と種族I

日本天文学会秋季年会　2010/09/24
The science drivers for a mid-infrared instrument for the TMT International-presentation

SPIE　2010/06
The SPLASH Survey: Spectroscopy of Newly Discovered Tidal Streams in the Outer Halo of the Andromeda Galaxy International-presentation

AAS Meeting　2010/01
広視野撮像・分光サーベイに基づく銀河考古学の展開

日本天文学会秋季年会　2009/09/16
Structure and Kinematics of the Stellar Halos and Thick Disks of the Milky Way Based on Calibration Stars from SDSS DR7 International-presentation

IAU Symposium　2009/08/12
すばる主焦点カメラで探るアンドロメダ恒星ハローの構造と種族

日本天文学会春季年会　2009/03/27
すばるHDS可視高分散分光データによる銀河系外部ハローの化学組成解析

日本天文学会春季年会　2009/03/26
銀河系外部ハローに属する金属欠乏星の軌道運動と化学組成

日本天文学会秋季年会　2008/09/12
Near-field cosmology: formation of the stellar halo International-presentation

Cosmology Near and Far: Science with WFMOS　2008/05
重力レンズで探る暗黒物質サブハロー

日本天文学会春季年会　2008/03
LENS MAPPING OF DARK MATTER SUBSTRUCTURE WITH VSOP-2 International-presentation

Approaching Micro-Arcsecond Resolution with VSOP-2: Astrophysics and Technology　2007/12
Dark matter substructure in lensing galaxies International-presentation

Panoramic Views of Galaxy Formation and Evolution　2007/12
Near-field cosmology: structure and dynamics of the old galactic components International-presentation

Decrypting the Universe – Large Surveys for Cosmology　2007/10
SDSSによる銀河系ハローの大局構造

日本天文学会秋季年会　2007/09
暗黒物質サブハローと銀河円盤形成の関係

日本天文学会秋季年会　2007/09
Subaru / Suprime-Cam photometric data International-presentation

Spectroscopic and Photometric Landscape of Andromeda's Stellar Halo　2007/09
厚い円盤と暗黒物質ハローの合体形成史の関係

日本天文学会春季年会　2007/03
Suprime-Camで探るアンドロメダストリームの起源

日本天文学会春季年会　2007/03
Keck/Deimos Spectroscopy of Distant M31 Fields with Deep HST Imaging International-presentation

AAS meeting　2007/01
A Search of Evidence of an Abundance Gradient in the Galactic Halo Based on Stars from SDSS-I DR-5 International-presentation

AAS meeting　2007/01
ダークハロー合体史に基づく銀河円盤の形成と進化

日本天文学会秋季年会　2006/10
多重像クエーサの中間赤外撮像に基づく冷たい暗黒物質の性質

日本天文学会秋季年会　2006/10
Suprime-Cam で探るアンドロメダ銀河ハローの構造

日本天文学会秋季年会　2006/10
Structure and Dynamics of the Old Galactic Components International-presentation

Mapping the Galaxy and Nearby Galaxies　2006/06
厚い円盤と暗黒物質ハローの合体形成史の関係

日本天文学会春季年会　2006/03
Suprime-Cam で探るアンドロメダストリームの起源

日本天文学会春季年会　2006/03

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Research Projects 17

銀河の恒星系動力学理論とその応用に基づく銀河暗黒物質の解明

千葉柾司

Offer Organization: 日本学術振興会

System: 科学研究費助成事業

Category: 基盤研究(B)

Institution: 東北大学

2024/04/01 - 2027/03/31
Exploring the nature of dark matter based on galactic dynamics and models of ultra-light dark matter particles

Offer Organization: Japan Society for the Promotion of Science

System: Grants-in-Aid for Scientific Research

Category: Grant-in-Aid for Transformative Research Areas (A)

Institution: Tohoku University

2021/09/10 - 2023/03/31
Theory for the Formation of Star Clusters and the Evolution of Our Galaxy

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: Nagoya University

2018/06/29 - 2023/03/31
Origin of Galactic First Generation Stars Based on Both Obserbations and Simulations of Very Metal-Poor Stars

CHIBA MASASHI

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 - 2021/03/31

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How the first stars in the Universe formed? Where and to what extent their survivors are remaining in the Milky Way? This research group has established the photometric search for such ancient stars and also explored the detailed theoretical investigations on the formation of the first stars and the related galaxy formation histories. In order to search for extremely metal-poor stars as the remnants of the first stars using the Hyper-Suprime Camera (HSC) attached on Subaru telescope, we have made a set of specially designed narrow-band filters. Also, high-resolution cosmological simulations have been carried out on the formation of the first stars, which have enabled us to establish the theoretical framework for the survival rate of such ancient stars in the present time.
Probing the nature of dark matter based on the theoretical analyses for observed dynamical structures of old stellar components in the Milky Way

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

2018/04/01 - 2020/03/31
Probing dark matter structure based on dynamics of old stellar population in galaxies

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

2016/04/01 - 2018/03/31
Probing the origin of primordial minihalos with gravitational lensing

INOUE Kaiki, CHIBA Masashi, MINEZAKI Takeo, TAKAHASHI Ryuichi, MATSUSHITA Satoki

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: Kinki University

2013/04/01 - 2016/03/31

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We estimated the lensing effect caused by subhalos in a lensing galaxy and dark matter structures in the line-of-sight using quadruple gravitational lenses. We found that: 1) The observed data are consistent with the cold dark matter (CDM) based cosmological model. 2) The observed data are not consistent with the warm dark matter (WDM) model if the WDM mass is smaller than 1/400 of the electron mass. These results imply that the origin of primordial minihalos, which are considered to be the progenitors of primordial galaxies is CDM rather tan WDM. On the other hand, we found that observational data of the Milky Way and the Andromeda galaxies suggest that some associated dwarf galaxies have a core rather than a cusp. This relult is not consistent with the CDM prediction.
Exploring precision cosmology with wide-field Subaru galaxy surveys

Takada Masahiro, AIHARA Hiroaki, CHIBA Masashi, HAMANA Takashi, TARUYA Atsushi, ICHIKI Kiyotomo

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: The University of Tokyo

2011/04/01 - 2015/03/31

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This research program carried out preparation studies for the wide-area Subaru Hyper Suprime-Cam galaxy survey that enables us to explore precision cosmology. The main achievements are: (1) We established the concrete foundation and platform needed for the international HSC collaboration that consists of researchers from Japan, Princeton University and Taiwan. (2) Under a strong leadership of this research program PI (M. Takada), we built up the survey design of HSC galaxy survey based on the discussion and preparation studies we had in the collaboration. The proposed HSC survey was approved by the Subaru community and the Subaru 300 nights are granted for the HSC survey. (3) We developed a novel cosmological method of combining imaging and spectroscopic galaxy surveys for the same region of the sky to constrain cosmological parameters.
investigation on the history of structure formation in the universe and distribution of the dark matter by gravitational lensing

FUTAMASE Toshifumi, CHIBA Masashi

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: Tohoku University

2006 - 2011

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We have studied the distribution of Dark Matter and the formation history of galaxy and galaxy cluster. In particular we have developed a new method to measure the shape of background galaxies which gives more accurate measurement of lensing signal and applied real date to detect detailed distribution of Dark Matter in some clusters. We have performed deep observation using Subaru for Halo component of nearby galaxies and obtained their detailed structure and components. This give us an important suggestion for the formation of galaxy. We have examined a new possible survey project to observe on the oldest components in nearby galaxies using HSC.
Resolving structure of cosmic dark matter based on extremely high-resolution radio observations

CHIBA Masashi, INOUE Kaiki, MINEZAKI Takeo, SAITO Masao, KAMENO Seiji, SUGAI Hajime, SUMI Takahiro

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

2008 - 2010

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Hierarchical clustering models of cold dark matter (CDM)predict that a galaxy-sized dark halo with total mass being comparable to the Milky Way contains thousands of substructures (so-called CDM subhalos)having each mass of million to billion solar masses. To directly identify such substructures and set limits on standard model of dark matter, we have developed the new method based on radio observation of gravitationally lensed objects using ALMA, TMT and other large-aperture telescopes with extremely high angular resolution.
Dark Matter Structure in Galaxies

CHIBA Masashi, TAKADA Masahiro, MINEZAKI Takeo, KASHIKAWA Nobunari, INOUE Kaiki

Offer Organization: Japan Society for the Promotion of Science

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

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

Institution: Tohoku University

2005 - 2006

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We investigate the extended source size effects on gravitational lensing in which a lens consists of a smooth potential and small mass clumps ("substructure lensing"). We first consider a lens model that consists of a clump modeled as a singular isothermal sphere (SIS) and a primary lens modeled as an external background shear and convergence. For this simple model, we derive analytic formulae for (de)magnification of circularly symmetric top-hat sources with three types of parity for their lensed images, namely, positive, negative and doubly negative parities. Provided that the source size is sufficiently larger than the Einstein radius of an SIS, we find that in the positive (doubly-negative) parity case, an extended source is always magnified (demagnified) in comparison with an unperturbed macrolens system, whereas in the negative parity case, (de)magnification effect which depends on a sign of convergence minus unity is weaker than those in other parities. It is shown that a measurement of distortion pattern in a multiply lensed image enables us to break the degeneracy between the lensing effects of a clump mass and those of a clump distance if lensing parameters of the relevant macrolens model are determined from the position and flux of multiple images. We also show that an actual density profile of a clump can be directly measured by analyzing a "fine structure" in a multiply lensed image within the Einstein radius of a clump.
Formation and Evolution of the Milky Way

CHIBA Masashi, TOSA Makoto, AOKI Wako, KODAMA Tadayuki

Offer Organization: Japan Society for the Promotion of Science

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

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

Institution: Tohoku University

2003 - 2004

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Structural, kinematical, and chemical properties of old, metal-poor stellar haloes of galaxies have long provided valuable information on early formation histories of galaxies, in particular; galaxies in the Local Group. For example, the observed correlation between chemical and dynamical properties of Galactic halo stars or lack thereof have enabled authors to discuss whether the Galaxy was formed by a monolithic collapse within a few dynamical timescales. Numerical simulations of Galaxy formation based on the cold dark matter model have demonstrated that basic physical processes involved in the formation of the metal-poor, old stellar halo in a disk galaxy are described by both dissipative and dissipationless merging of subgalactic clumps and their resultant tidal disruption in the course of gravitational contraction of the galaxy at high redshift : Thus, understanding of star formation and chemical evolution histories in subgalactic clumps (i.e., progenitors of low-mass dwarfs) are key for better understanding of the origin of galactic stellar halos. Also, although many observational and theoretical studies in the young universe have already provided important constraints on the cosmic reionization history, it remains yet to be explored in the present-day universe as to (1)whether old stellar halos of galaxies contain the fossil records of reionization history and (2)what observations of stellar halos can provide what clues to the possible influences of reionization on galaxy formation processes. Physical properties of metal-poor, old stellar halos in galaxies beyond the Local Group have been recently investigated by the Hubble Space Telescope and large ground--based telescopes. Furthermore, recent numerical studies provided some specific predictions on star formation histories of dwarf galaxies under the influence of reionization. Thus it is quite timely to discuss the above questions based on the comparison between observations and numerical simulations addressing the possible influence of reionization on the properties of galactic stellar halos. Taking advantage of this grant awarded, we have made a lot of progresses about the above issue as well as other relevant issues on the formation and evolution of the Milky Way and Local Group galaxies. Furthermore, we have studied the structure of dark matter surrounding the visible parts of galaxies, which is supposed to play an important role in the formation process of galaxies through hierarchical clustering. For this purpose, we have focused on gravitational lensing phenomena on background sources (such as QSOs), to set limits on mass substructure in lensing galaxies. Both observational and theoretical analyses have been made on this issue.
Nucleosynthesis of Radioactive Nuclei in Explosive Stellar Objects and Cosmic and Galactic Ages

KAJINO Toshitaka, MOTOBAYASHI Tohru, CHIBA Masashi, ANDO Hiroyasu, SUMIYOSHI Kohsuke, TANIHATA Isao

Offer Organization: Japan Society for the Promotion of Science

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

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

Institution: National Astronomical Observatory of Japan

2001 - 2003

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We tried model construction on of n tern with high precision, summing the progress in theoretical studies of explosive nucleosynthesis, observational anal astronomy, and nuclear experiment in this project Comparing our theoretical model calculations with observed elemental abundances of long-lived radioactive nuclei in metal-deficient halo stars, we found that the U-Th chronometer has better precision than the UT-Eu chronometer. Long-lived radioactive nuclei are produced d either in rapid-neutron capture process (r-process) in supernova explosion and in slow-neutron capture process (s-process) in War stage of small-to-intermediate mass AGB stars. Physical conditions of astrophysical nucleosynthesis environments were dared theoretically in numerical simulation of explosive nude synthesis It was found that neutron and alpha induced reactions on light mass neutron-rich unstable nuclei and neutron capture reactions on intermediate-to-heavy mass neutron-rich unstable nuckei play the important roles in the r-process. These cross section data were taken from nuclear experiments which were carried outin experimental facilities of nuclear and particle physics in the world including RIKEN and CNS, University of Tokyo. Unmeasured nuclear data and cuss sections for neutrino-nucleus interactions, which are very important for gravitational collapse of supernovae, were theoretically calculated by the use of the quantum theory for particles and nuclei. Using these experimental and theoretical inputs hum particle and nuclear physics we can carry out nucleosynthesis calculations with better precision and provide reliable initial abundance distribution of the r-process elements. We then applied these products to Galactic chemical evolution in order to theoretically predict time variation of elemental abundances at long-lived radioactive heavy elements such as Th and U. Combining the theoretical prediction with observed data which were taken by using High Dispersion Spectrograph equipped with SUBARU Telescope, we tried to estimate the age of the early generation, metal-deficient halo stars in our constructed cosmochrometers of the r-process elements. We compared the results with the constraints on the cosmic age which was determined from observational cosmology which include several cosmological parameters, and dish consistency between both ages We also studied big-hang nucleosynthesis, cosmic microwave background anisotropy, and luminosity-redshift relation of type Ia supernovae in order to construct cosmological model that is consistent with the cosmic and Galacticages determined in our project
ニュートリノ放射をともなう星内原子核・素粒子反応率の精密決定と天体現象への応用

安藤裕康, 梶野敏貴, 上村正康, 千葉柾司, 梶野敏貴, 山田章一, 本林透, 大坪久夫, 戸谷友則, 安藤裕康

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

2000 - 2003

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太陽中心部で起こっている核融合反応^3He+^4He->^7Be+γと^7Be+p->^8B*+γ、CNPサイクルの核反応率を、理論・実験・観測から総合的に研究し、太陽ニュートリノ放射率が持つ不定性を除く研究を展開した。多核子系の量子力学的波動関数を構築することによって、^7Be+p->^8B*+γ -> 2^4He+e^++νの核反応率を理論的に高精度で計算するとともに、核融合反応直接測定法、光分解反応間接測定法、クーロン散乱ANC法という複数の異なる実験方法を用いて測定し、これらの原子核構造・反応理論による詳細な計算と比較して理論計算の妥当性を詳細に検証した。その結果、理論的には5%の精度で、実験的には15%の精度で天体核反応率パラメータS17を決定した。同様に、^3He+^4He->^7Be+γおよび^3H+^4He->^7Li+γ反応率の理論計算を高精度で実行し、高エネルギー電子散乱による電磁気形状因子との相関を見つけ、核反応率の不定性を取り除く新しい方法を提案し、天体核反応率パラメータS34を5%の精度で決定した。CNOサイクル反応^<14>N+p->^<15>O+γの核反応率が持つ最も大きな不確定さは、閾値以下504keVに位置する複合核励起状態の陽子幅の不定性による。クーロン励起反応法を用いた実験によって、従来の低い精度の値に比べて約1/10の陽子幅であることを実験的に見つけた。宇宙、銀河団、銀河、星の構造・化学進化に及ぼすニュートリノの影響を調べるために、宇宙ニュートリノ・レプトン数の破れとビッグバン元素合成、宇宙背景輻射への影響、超新星爆発で発生する高エネルギーニュートリノが速中性子捕獲元素合成(R元素合成)過程に与える影響を詳細に調べた。精密な太陽モデルと精緻なる核反応率を用いたニュートリノ振動現象の解析、および、ニュートリノ振動現象が超新星元素合成に及ぼす影響の研究が進行中である。
R-process Elements in the First Generation Stars and High-redshift Objects and the Galactic-and Cosmic-Age Problem.

KAJINO Toshitaka, CHIBA Masashi, YOSHII Yuzuru, NOMOTO Kenichi, TOKI Hiroshi, SADAKANE Kozo

Offer Organization: Japan Society for the Promotion of Science

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

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

Institution: National Astronomical Observatory

1998 - 1999

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Observational study of the r-process elements was one of the utlimate purposes in this project, and it has just started in the year 2000 with the construction of SUBARU TELESCOPE which is equipped with High-Dispersion-Spectrograph (HDS) at the top of Mt.Kea. We have already carried out several test observations of SUBARU-HDS, which proves to work very well as we designed. Using this spectrograph, several metal-deficient halo stars have already been observed in order to detect metal absorption lines from Th232 (half life 14.1 Gy), U238 (4.5 Gy), Re187 (43.5 Gy), and many others. Data analysis is now underway. Theoretical studies of the r-process nucleosynthesis in supernova explosions also have been carried out to reach deep understanding of the nucleosynthesis mechanism. Actinoids are ideal heavy radioactive nuclei whose half life is of order of cosmic age. In this project, it was theoretically clarified that most heavy r-process elements, including some amounts of actinoids, are produced in explosive nucleosynthesis associated with Type II SN explosions. Dependence of the calculated yields of these elements on the physical conditions of stellar environments were studied in detail : It was clarified the relation between r-process abundance yields and physical parameters such as neutrino flux from the center of proto-neutron star, mass and radius of the neutron star, entropy and dynamic time scale which are closely related to the neutrino heating proceses in the neutrino- driven winds.
New Light on Galactic Astronomy Based on the Hipparcos Catalog

CHIBA Masashi, KAJINO Toshitaka, GOUDA Naoteru, SOFUE Yoshiaki, YOSHII Yuzuru, TOSA Makoto

Offer Organization: Japan Society for the Promotion of Science

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

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

Institution: National Astronomical Observatory

1997 - 1998

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The Hipparcos mission was the first space experiment dedicated to astrometry, and was accepted within the ESA scientific program in 1980. The primary objective of the mission was the determination of accurate astrometric data - positions, annual proper motions and absolute trigonometric parallaxes, at levels of I milliarcsec - for about 120000 stars. The Hipparcos Catalogue, the primary result of the observations and reduction of the satellite-acquired data, has provided great impacts on various research fields that include positional astronomy, stellar evolution, galactic astronomy, and cosmology. Among the whole sample in the catalogue, the astrometric observations of RR Lyrae variables and metal-deficient red giants have been parts of the Hipparcos program assigned to our research group. Analyzing the data of these stars which arrived us prior to the release of the catalogue, we have found that (1) ages of old globular clusters, calibrated from the absolute magnitudes of RR Lyrae variables, put severe limits on the range of cosmological parameters, and that (2) the formation of the Galaxy from the halo to disk components, as probed by kinematics of metal-poor stars, involved the slow collapse lasting several billion years. We have also conducted the assembly of spectroscopic and photometric information for numerous metal-poor stars, for the purpose of studying early dynamical evolution of the Galaxy in the cosmological context. This is mainly because in recent years, the numbers of recognized stars with metal abundances significantly less than solar has grown enormously. So too has the quality and quantity of information available concerning their detailed abundances, velocities, and proper motions. Using newly determined (and/or refined) proper motions for over 1000 of these stars, based on results from the Hipparcos mission and various catalogs including the Southern Proper Motion catalog, the Northern Proper Motion catalog, the Astrographic Catalog, and the Digital Sky Survey obtained at STScI, we have arrived at the comprehensive view of the kinematics of the thick disk and halo components of the Galaxy. A number of interesting differences were also found between the observed properties of our non-kinematically selected sample, as compared with similar-sized, but kinematically biased samples of metal-poor stars.
銀河形成と進化の理論的研究に基づく観測的宇宙論の考察

千葉柾司

Offer Organization: 日本学術振興会

System: 科学研究費助成事業基盤研究(C)

Category: 基盤研究(C)

Institution: 国立天文台

1996 - 1996

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クウェーサ-のスペクトルには、ライマンアルファの森と呼ばれる多数の吸収線が観測されており、これらは銀河間にあって小さなサイズの暗黒物質(ミニハロ-)によって束縛された中性水素雲による現象であると考えられてきた。そして、このような雲は銀河になり損ねたガスであるとするモデルで良く説明されてきた。ところが、最近の観測によれば、吸収線系の多くが系外銀河周辺のガスに直接関連していることが示唆されており、さらに、Keckによる高分散観測によって、吸収線系の半分以上に重元素が見つかっており、ミニハロ-起源以外の吸収線系を示唆する。そこで我々は、ミニハロ-ならびに銀河ハロ-に束縛された星間ガスの物理状態を考察し、これらの観測結果を自然に説明できる理論模型を提案した。特に、吸収線系のうち重元素を含む割合は、ミニハロ-か又は銀河ハロ-かを区別する質量スケールと密接に関係しており、この質量として光電離を考慮した銀河形成モデルで与えられる値を採用すれば、重元素を含む吸収線系の割合を再現できることを初めて示した。また、吸収線系における重元素量は、標準的な銀河形成論で与えられる銀河形成の時期と銀河系ハロ-星で報告されている年齢と重元素量との間の相関関係を用いて説明できることを示した。また、我々は、膨張宇宙の基本定数を決定する方法の有力な一つである、クウェーサ-の重力レンズ統計に関して検討を行った。これまでのレンズモデルに従えば、大きな値の宇宙項Aは否定されると考えられてきた。しかし、この結論は、レンズ現象を実質的に引き起こす早期型銀河の数分布及び質量分布の情報に強く依存している。我々は、早期型銀河に関する最新の観測情報を取り入れることによって新たなレンズ統計のモデルを構築し、HSTによるレンズ探査の観測結果を説明するためには、大きなAでかつ平坦な宇宙が示唆されることを明らかにした。

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Social Activities 2

仙台市天文台ブレインサポーター

2008/07/15 - Present

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仙台市天文台の運営に関して助言・支援を行なう。
仙台市天文台運営協議会

2009/11/18 - 2020/03/31

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仙台市天文台運営事業に対する意見委員会

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理科年表の監修・執筆