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Title:
Part 3: Weak gravitational lensing
Authors:
Schneider, P.
Publication:
In: Gravitational lensing: strong, weak and micro. Saas-Fee Advanced Course 33. The Course took place from 8-12 April 2003, in Les Diablerets, Switzerland. Swiss Society for Astrophysics and Astronomy. Edited by G. Meylan, P. Jetzer and P. North. Lecturers: P. Schneider, C. Kochanek, J. Wambsganss. Berlin: Springer, ISBN 3-540-30309-X, ISBN 978-3-540-30309-1, 2006, p. 269 - 451
Publication Date:
00/2006
Origin:
ARI
ARI Keywords:
Gravitational Lensing
Abstract Copyright:
Springer
Comment:
ISBN: 3-540-30309-X
Bibliographic Code:
2006glsw.conf..269S

Abstract

We shall start by describing the basics of weak lensing in Sect. 2, namely how the shear, or the projected tidal gravitational field of the intervening matter distribution can be determined from measuring the shapes of images of distant galaxies. Practical aspects of observations and the measurements of image shapes are discussed in Sect. 3. The next two sections are devoted to clusters of galaxies; in Sect. 4, some general properties of clusters are described, and their strong lensing properties are considered, whereas in Sect. 5 weak lensing by clusters is treated. As already mentioned, this allows us to obtain a parameter-free map of the projected (2-D) mass distribution of clusters. We then turn to lensing by the inhomogeneously distributed matter distribution in the Universe, the large-scale structure. Starting with Gunn (1967), the observation of the distortion of light bundles by the inhomogeneously distributed matter in the Universe was realized as unique probe to study the properties of the cosmological (dark) matter distribution. The theory of this cosmic shear effect, and its applications, was worked out in the early 1990's (e.g., Blandford et al. 1991). In contrast to the lensing situations studied in the rest of this book, here the deflecting mass is manifestly three-dimensional; we therefore need to generalize the theory of geometrically-thin mass distributions and consider the propagation of light in an inhomogeneous Universe. As will be shown, to leading order this situation can again be described in terms of an "equivalent" surface mass density. The theoretical aspects of this large-scale structure lensing, or cosmic shear, are contained in Sect. 6. Although the theory of cosmic shear was well in place for quite some time, it took until the year 2000 before it was observationally discovered, independently and simultaneously by four groups. These early results, as well as the much more extensive studies carried out in the past few years, are presented and discussed in Sect. 7. In Sect. 8, we consider the weak lensing effects of galaxies, which can be used to investigate the mass profile of galaxies. As we shall see, this galaxy-galaxy lensing, first detected by Brainerd et al. (1996), is directly related to the connection between the galaxy distribution in the Universe and the underlying (dark) matter distribution; this lensing effect is therefore ideally suited to study the biasing of galaxies; we shall also describe alternative lensing effects for investigating the relation between luminous and dark matter. In the final Sect. 9 we discuss higher-order cosmic shear statistics and how lensing by the large-scale structure affects the lens properties of localized mass concentrations. Some final remarks are given in Sect. 10.
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