The impact of intrinsic alignment on current and future cosmic shear surveys

• Published in: Monthly notices of the Royal Astronomical Society Vol. 456; no. 1; pp. 207 - 222
• Main Authors: Krause, Elisabeth, Eifler, Tim, Blazek, Jonathan
• Format: Journal Article
• Language: English
• Published: London Oxford University Press 11.02.2016
• Subjects: Alignment; Astrophysics; Cosmology; Dark energy; Errors; Galaxies; Luminosity; Mathematical models; Normal distribution; Shear; Simulation; Star & galaxy formation; Telescopes; cosmology: theory
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1093/mnras/stv2615

Intrinsic alignment (IA) of source galaxies is one of the major astrophysical systematics for weak lensing surveys. Several IA models have been proposed and their impact on cosmological constraints has been examined using the Fisher information matrix in conjunction with approximate, Gaussian covariances. This paper presents the first forecasts of the impact of IA on cosmic shear measurements for future surveys using simulated likelihood analyses and covariances that include higher order moments of the density field. We consider a range of possible IA scenarios and test mitigation schemes which parametrize IA by the fraction of red galaxies, normalization, luminosity and redshift dependence of the IA signal. Compared to previous studies, we find smaller biases in time-dependent dark energy models if IA is ignored in the analysis. The amplitude and significance of these biases vary as a function of survey properties (depth, statistical uncertainties), luminosity function and IA scenario. Due to its small statistical errors and relatively shallow depth, Euclid is significantly impacted by IA. Large Synoptic Survey Telescope (LSST) and Wide-Field Infrared Survey Telescope (WFIRST) benefit from increased survey depth, while larger statistical errors for Dark Energy Survey (DES) decrease IA's relative impact on cosmological parameters. The proposed IA mitigation scheme removes parameter biases for DES, LSST and WFIRST even if the shape of the IA power spectrum is only poorly known; successful IA mitigation for Euclid requires more prior information. We explore several alternative IA mitigation strategies for Euclid; in the absence of alignment of blue galaxies we recommend the exclusion of red (IA-contaminated) galaxies in cosmic shear analyses.