A new measure for cosmic shear

Details A new measure for cosmic shear A new measure for cosmic shear

1997-08-15

arxiv.org/abs/astro-ph/9708143v1

Mon.Not.Roy.Astron.Soc.296:873-892,1998

Astronomy and Astrophysics

Astrophysics

34 pages, plain TeX, including 9 figures, submitted to MNRAS

Scientific paper

10.1046/j.1365-8711.1998.01422.x

We consider here a new statistical measure for cosmic shear, the aperture mass Map, which is defined as a spatially filtered projected density field and which can be measured directly from the image distortions of high-redshift galaxies. By selecting an appropriate spatial filter function, the dispersion of the aperture mass is a convolution of the power spectrum of the projected density field with a narrow kernel, so that provides a well localized estimate of the power spectrum at wavenumbers s~5/theta. We calculate for various cosmological models, using the fully non-linear power spectrum of the cosmic density fluctuations. The non-linear evolution yields a significant increase of relative to the linear growth on scales below ~0.5 degree. The third-order moment of Map can be used to define a skewness, which is a measure of the non-Gaussianity of the density field. We present the first calculation of the skewness of the shear in the frame of quasi-linear theory of structure growth. We show that it yields a sensitive measure of the cosmological model; in particular, it is independent of the normalization of the power spectrum. Several practical estimates for are constructed and their dispersions calculated. We show that one sq.deg. of a high-quality image is sufficient to detect the cosmic shear with the Map-statistics on scales below ~10 arcmin, and to estimate its amplitude with an accuracy of ~30% on scales below ~5 arcmin. (abbreviated)

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