論文 - 須佐 元
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The effects of early cosmic reionization on the substructure problem in galactic halos
Susa H, Umemura M.
Astrophysical Journal 610 ( 1 II ) 2004年7月
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Recent observations of the cosmic microwave background by the Wilkinson Microwave Anisotropy Probe strongly suggest that the reionization of the universe took place quite early (z~17). On the other hand, it has been pointed out that the cold dark matter cosmology suffers from a substructure problem in which more subgalactic halos are produced in the Local Group than dwarf galaxies. In this Letter, as a potential mechanism for solving this problem, we consider the feedback effects of early reionization on the formation of small-scale structures. For this purpose, we perform three-dimensional radiation hydrodynamic simulations, incorporating the radiative transfer for ionizing photons. As a result, it is found that the early reionization is devastating for low-mass systems with Mvir<~108 Msolar or vcirc<~20 km s-1, and almost all gas is photoevaporated in more than 95% of low-mass systems. Such a strong negative feedback on the formation of low-mass galaxies may solve the substructure problem and support the picture that Local Group dwarf galaxies are descendants of the more massive halos that experienced and survived tidal stripping....
DOI： 10.1086/423199
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Galaxy Formation in the Presence of Ultraviolet Background Radiation Field --- A Simulation by Radiation-SPH ---
Hajime Susa, Masayuki Umemura
Proceedings of Japan-German Seminar, held in Sendai, Japan, July 24-28, 2001, Eds.: N. Arimoto and W. Duschl 83 - 86 2004年2月
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担当区分：筆頭著者
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Galaxy Formation in the Presence of Ultraviolet Background Radiation Field --- A Simulation by Radiation-SPH ---
須佐 元
Studies of Galaxies in the Young Universe with New Generation Telescope 2004年2月
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We studied galaxy formation with Radiation-SPH simulations in order to find the effects of UVB field on the star formation in the forming galaxies. We find the UVB radiation field can delay the star formation in protogalactic clouds, especially at low redshift (z < 2). This result suggests that galaxies formed at lower redshift tend to be late type galaxies and early type galaxies tend to be formed at higher redshift....
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The Epoch of Cosmic Reionization
須佐 元
Studies of Galaxies in the Young Universe with New Generation Telescope 2004年2月
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Full radiative transfer for ionizing photons in 3D space has been solved to pursue the reionization history in an inhomogeneous universe. It has been shown that the inhomogeniety of the universe delays the reionization considerably. Also, QSO absorption line systems are simulated with using the results of radiative transfer calculations. Lyα continuum depression implies that the metagalactic UV intensity decreases rapidly with z at z > 5, and the reionization must have taken place between z = 6 and 10. Finally, it is stressed that Hα forest is a more powerful tool to probe the reionization history and the density fluctuations in the universe at z > 5....
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Formation of dwarf galaxies in reionized universe with heterogeneous multi-computer system
Boku T, Susa H, Onuma K, Umemura M, Sato M, Takahashi D.
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) 3039 629 - 636 2004年
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Heterogeneous remote computing system for computational astrophysics with OmniRPC
Onuma K, Boku T, Sato M, Takahashi D, Susa H, Umemura M.
Proceedings - International Symposium on Applications and the Internet Workshops 623 - 629 2004年
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Quasar Mesolensing - Direct Probe to Substructures around Galaxies
Yonehara A, Umemura M, Susa H.
Publications of the Astronomical Society of Japan 55 ( 6 ) 1059 - 1078 2003年12月
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Recently, a ``CDM crisis'' is being discussed. The main point of this crisis is that the number of substructures presented by cosmological N-body simulations based on the CDM scenario for structure formation is much larger than the observed substructures. Therefore, it is crucial for this crisis to discriminate whether the expected number of CDM substructures really exist without detectable radiation, or do not exist. In this paper, we present a new idea to detect such invisible substructures by utilizing gravitational lensing. Here, we consider quasars that are gravitationally lensed by a foreground galaxy. A substructure around a lensing galaxy may superposed on one of the lensed images of such quasars. In this situation, additional image splitting should occur in the image behind the substructure, and additional multiple images are created. From our estimations, the separation and time delay between the additional multiple images are expected to be 1-30 milli-arcsecond and 1-103 second, respectively. Furthermore, we evaluate that the optical depth for such events is sim 0.1. Consequently, future fine-resolution imaging and/or high-speed monitoring will unable us to find invisible substructures in one of a few multiple quasars....
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Radiative transfer in astrophysics
須佐 元
Astronomical Herald 2003年12月
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Lots of astrophysical issues are closely related to the problem of radiation transfer. In this paper, I try to outline the recent results on the cosmic reionization, and radiative feedback on the formation of galaxies, in which the multi-dimensional radiative tranfer problem is quite important. I also mention the future prospects on these issues....
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Quasar Mesolensing - Direct Probe to Substructures around Galaxies
須佐元
Publications of the Astronomical Sciety of Japan 55 ( 1059 ) 2003年11月
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Radiation-Hydrodynamical Simulations of Primordial Galaxy Formation in the UV Background
Tetsu Kitayama, Hajime Susa, Masayuki Umemura, Satoru Ikeuchi
ASP Conference Proceedings 208 417 2003年11月
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A Simulation of Galaxy Formation by Radiation-SPH
Hajime Susa, Masayuki Umemura
ASP Conference Proceedings 208 323 2003年11月
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担当区分：筆頭著者
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HMCS-G : グリッド環境における計算宇宙物理のためのハイブリッド計算システム(グリッド応用)
朴, 泰祐, 佐藤, 三久, 小沼, 賢治, 牧野, 淳一郎, 須佐, 元, 高橋, 大介, 梅村, 雅之
情報処理学会論文誌. コンピューティングシステム 44 ( 11 ) 1 - 13 2003年8月
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出版者・発行元：一般社団法人情報処理学会
我々は,グリッド環境上に分散した汎用並列計算機群と専用並列計算機を結合し,各種物理現象の複合シミュレーションを可能とする計算環境HMCS-Gを設計し,重力専用計算機GRAPE-6クラスタを中心とする計算宇宙物理学用のシステムを実装した.アプリケーションプログラミングの簡便さとシステム全体のスループット向上のため,グリッドRPCとしてOmniRPCを用い,HMCS-Gの特性に合わせた効率的なシステムを実現した.各種ネットワーク環境における初期性能評価の結果,ある程度のネットワークバンド幅のもとで,HMCS-Gは実アプリケーションの現実的な実行に耐える性能を提供できることが確認された.また,HMCS-Gにより,貴重な専用計算リソースであるGRAPE-6のようなシステムを,世界規模で共有することが可能となる.
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Formation of Dwarf Galaxies in Reionized Universe
Hajime Susa, Masayuki Umemura
The Local Group as an Astrophysical Laboratory; poster papers from the Space Telescope Science Institute Symposium held in May, 2003. Edited by Mario Livio and Thomas M. Brown. Published by the Space Telescope Science Institute 94 2003年5月
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担当区分：筆頭著者
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Towards Direct Detection of Substructure around Galaxies -- Quasar Mesolensing
Atsunori Yonehara, Masayuki Umemura, Hajime Susa
ASP Conference Proceedings 289 496 - 472 2003年5月
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Formation of Dwarf Galaxies in Reionized Universe
須佐 元
The Local Group as an Astrophysical Laboratory 2003年5月
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Towards Direct Detection of Substructure around Galaxies -- Quasar Mesolensing
須佐 元
The Proceedings of the IAU 8th Asian-Pacific Regional Meeting, Volume 1 2003年5月
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We discuss about detectability of substructure around galaxies by utilizing a quasar which is gravitationally lensed by an intervening galaxy. In this situation, background quasars have already shown multiple images. If a substructure in the lens galaxy is superposed on one of the images, additional gravitational lensing by the substructure will occur. The typical image separation due to the substructures with mass 10^8 M_o is on the order of micro-arcseconds. Even if we cannot resolve these images, the total flux variations of these images are expected to be observed, both as its own flux variation plus the ``echo"-like variation due to time delay between the images. The time delay of this ``echo"-like variation is estimated to be several tens of minutes....
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Role of ultraviolet background radiation field on the formation of galaxies
須佐 元
Astronomical Herald 2003年2月
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There are various types of galaxies in our universe. They are distributed over six orders of magnitude in mass, and have wide varieties of morphologies and colors. It is one of the main and far-reaching research themes in the present cosmology how these galaxies are formed and they come to have such diversity. These varieties might be caused by ultraviolet background radiation field (UVB) filled the universe in the era of galaxy formation, because UVB introduces a few physical scales to the formation processes of galaxies. In this paper, I will try to outline the effects of ultraviolet background radiation field on the formation of galaxies....
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A Simulation of Galaxy Formation by Radiation-SPH
須佐 元
Astrophysical Supercomputing using Particle Simulations 2003年
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HMCS-G: Grid-enabled hybrid computing system for computational astrophysics
Boku T, Sato M, Onuma K, Makino J, Susa H, Takahashi D, Umemura M, Ukawa A.
Proceedings - CCGrid 2003: 3rd IEEE/ACM International Symposium on Cluster Computing and the Grid 558 - 567 2003年
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Radiation-Hydrodynamical Simulations of Primordial Galaxy Formation in the UV Background
須佐 元
Astrophysical Supercomputing using Particle Simulations 2003年