Suppressing the contribution of intrinsic galaxy alignments to the shear two-point correlation function

Details Suppressing the contribution of intrinsic galaxy alignments to the shear two-point correlation function Suppressing the contribution of intrinsic galaxy alignments to the shear two-point correlation function

2002-08-13

arxiv.org/abs/astro-ph/0208256v2

Astron.Astrophys. 396 (2002) 411-418

Astronomy and Astrophysics

Astrophysics

17 pages, 5 figures, Accepted in A&A, incorporates minor Comments from referee

Scientific paper

10.1051/0004-6361:20021372

Cosmological weak lensing gives rise to correlations in the ellipticities of faint galaxies. This cosmic shear signal depends upon the matter power spectrum, thus providing a means to constrain cosmological parameters. It has recently been proposed that intrinsic alignments arising at the epoch of galaxy formation can also contribute significantly to the observed correlations, the amplitude increasing with decreasing survey depth. Here we consider the two-point shear correlation function, and demonstrate that photometric redshift information can be used to suppress the intrinsic signal; at the same time Poisson noise is increased, due to a decrease in the effective number of galaxy pairs. The choice to apply such a redshift-depending weighting will depend on the characteristics of the survey in question. In surveys with a mean z of about 1, although the lensing signal dominates, the measurement error bars may soon become smaller than the intrinsic alignment signal; hence, in order not to be dominated by systematics, redshift information in cosmic shear statistics will become a necessity. We discuss various aspects of this.

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