2006 Fiscal Year Final Research Report Summary
Dark Matter Structure in Galaxies
| Project/Area Number |
17540210
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Astronomy
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| Research Institution | Tohoku University |
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Principal Investigator |
CHIBA Masashi Tohoku University, Graduate School of Science, Professor, 大学院理学研究科, 教授 (50217246)
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| Co-Investigator(Kenkyū-buntansha) |
TAKADA Masahiro Tohoku University, Graduate School of Science, Assistant Professor, 大学院理学研究科, 助手 (40374889)
MINEZAKI Takeo Tokyo University, Graduate School of Science, Assistant Professor, 大学院理学系研究科, 助手 (60292835)
KASHIKAWA Nobunari National Astronomical Observatory of Japan, Optical and Infrared Division, Assistant Professor, 光赤外研究部, 主任研究員(研究職) (00290883)
INOUE Kaiki Kinki University, Graduate School of Science, Associate Professor, 理工学部, 講師 (70388495)
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| Project Period (FY) |
2005 – 2006
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| Keywords | Astrophysics / Dark Matter |
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| Research Abstract |
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.
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