Sarah Bridle and Lindsay King 2007 New J. Phys. 9 444 doi:10.1088/1367-2630/9/12/444
Dark energy constraints from cosmic shear power spectra: impact of intrinsic alignments on photometric redshift requirements
Focus on Gravitational LensingSarah Bridle1,3 and Lindsay King2
Show affiliationsPart of Focus on Gravitational Lensing
Cosmic shear constrains cosmology by exploiting the apparent alignments of pairs of galaxies due to gravitational lensing by intervening mass clumps. However, galaxies may become (intrinsically) aligned with each other, and with nearby mass clumps, during their formation. This effect needs to be disentangled from the cosmic shear signal to place constraints on cosmology. We use the linear intrinsic alignment model as a base and compare it to an alternative model and data. If intrinsic alignments are ignored then the dark energy equation of state is biased by ~50%. We examine how the number of tomographic redshift bins affects uncertainties on cosmological parameters and find that when intrinsic alignments are included two or more times as many bins are required to obtain 80% of the available information. We investigate how the degradation in the dark energy figure of merit depends on the photometric redshift scatter. Previous studies have shown that lensing does not place stringent requirements on the photometric redshift uncertainty, so long as the uncertainty is well known. However, if intrinsic alignments are included the requirements become a factor of three tighter. These results are quite insensitive to the fraction of catastrophic outliers, assuming that this fraction is well known. We show the effect of uncertainties in photometric redshift bias and scatter. Finally, we quantify how priors on the intrinsic alignment model would improve dark energy constraints.
- PACS
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98.62.Sb Gravitational lenses and luminous arcs
98.62.Py Distances, redshifts, radial velocities; spatial distribution of galaxies
- Subjects
- Dates
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Issue 12 (December 2007)
Received 4 May 2007
Published 17 December 2007
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Dark energy constraints from cosmic shear power spectra: impact of intrinsic alignments on photometric redshift requirements
Sarah Bridle and Lindsay King 2007 New J. Phys. 9 444
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