Journal Article

The cosmological impact of intrinsic alignment model choice for cosmic shear

Donnacha Kirk, Anais Rassat, Ole Host and Sarah Bridle

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 424, issue 3, pages 1647-1657
Published in print August 2012 | ISSN: 0035-8711
Published online August 2012 | e-ISSN: 1365-2966 | DOI:
The cosmological impact of intrinsic alignment model choice for cosmic shear

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We consider the effect of galaxy intrinsic alignments (IAs) on dark energy constraints from weak gravitational lensing. We summarize the latest version of the linear alignment model of IAs, following a brief note of Hirata & Seljakand further interpretation by Laszlo et al. We show the cosmological bias on the dark energy equation of state parameters w0 and wa$ that would occur if IAs were ignored. We find that w0 and wa are both catastrophically biased, by an absolute value of just greater than unity under the Fisher matrix approximation. This contrasts with a bias several times larger for the earlier IA implementation. Therefore, there is no doubt that IAs must be taken into account for future stage III experiments and beyond. We use a flexible grid of IA and galaxy bias parameters as used in previous work and investigate what would happen if the Universe is described by used the latest IA model, but we assumed the earlier version. We find that despite the large difference between the two IA models, the grid flexibility is sufficient to remove cosmological bias and recover the correct dark energy equation of state. In an appendix, we compare observed shear power spectra to those from a popular previous implementation and explain the differences.

Keywords: galaxies: evolution; cosmology: observations; large-scale structure of Universe

Journal Article.  7887 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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