EDP Sciences
Free Access
Volume 398, Number 1, January IV 2003
Page(s) 23 - 30
Section Extragalactic astronomy
DOI https://doi.org/10.1051/0004-6361:20021614

A&A 398, 23-30 (2003)
DOI: 10.1051/0004-6361:20021614

Separating cosmic shear from intrinsic galaxy alignments: Correlation function tomography

L. J. King and P. Schneider

Institut für Astrophysik und Extraterrestrische Forschung, Universität Bonn, Auf dem Hügel 71, 53121 Bonn, Germany
(Received 23 September 2002 / Accepted 22 October 2002)

During the past few years, secure detections of cosmic shear have been obtained, manifest in the correlation of the observed ellipticities of galaxies. Constraints have already been placed on cosmological parameters, such as the normalisation of the matter power spectrum $\sigma_{8}$. One possible systematic contaminant of the lensing correlation signal arises from intrinsic galaxy alignment, which is still poorly constrained. Unlike lensing, intrinsic correlations only pertain to galaxies with small physical separations, the correlation length being a few Mpc. We present a new method that harnesses this property, and isolates the lensing and intrinsic components of the galaxy ellipticity correlation function using measurements between different redshift slices. The observed signal is approximated by a set of template functions, making no strong assumptions about the amplitude or correlation length of any intrinsic alignment. We also show that the near-degeneracy between the matter density parameter $\Omega_{\rm m}$ and $\sigma_{8}$ can be lifted using correlation function tomography, even in the presence of an intrinsic alignment signal.

Key words: cosmology: dark matter -- cosmology: observations -- methods: data analysis

Offprint request: L. J. King, lindsay@astro.uni-bonn.de

© ESO 2003

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