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Dark Energy Survey Year 1 Results: Constraints on Intrinsic Alignments and their Colour Dependence from Galaxy Clustering and Weak Lensing

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Original languageEnglish
Pages (from-to)5453-5482
Number of pages30
JournalMonthly Notices of the Royal Astronomical Society
Issue number4
Early online date16 Aug 2019
Publication statusPublished - 1 Nov 2019


We perform a joint analysis of intrinsic alignments and cosmology using tomographic weak lensing, galaxy clustering, and galaxy–galaxy lensing measurements from Year 1 (Y1) of the Dark Energy Survey. We define early- and late-type subsamples, which are found to pass a series of systematics tests, including for spurious photometric redshift error and point spread function correlations. We analyse these split data alongside the fiducial mixed Y1 sample using a range of intrinsic alignment models. In a fiducial non-linear alignment model analysis, assuming a flat Λ cold dark matter cosmology, we find a significant difference in intrinsic alignment amplitude, with early-type galaxies favouring AIA=2.38+0.32−0.31 and late-type galaxies consistent with no intrinsic alignments at 0.05+0.10−0.09⁠. The analysis is repeated using a number of extended model spaces, including a physically motivated model that includes both tidal torquing and tidal alignment mechanisms. In multiprobe likelihood chains in which cosmology, intrinsic alignments in both galaxy samples and all other relevant systematics are varied simultaneously, we find the tidal alignment and tidal torquing parts of the intrinsic alignment signal have amplitudes A1=2.66+0.67−0.66⁠, A2=−2.94+1.94−1.83⁠, respectively, for early-type galaxies and A1=0.62+0.41−0.41⁠, A2=−2.26+1.30−1.16 for late-type galaxies. In the full (mixed) Y1 sample the best constraints are A1=0.70+0.41−0.38⁠, A2=−1.36+1.08−1.41⁠. For all galaxy splits and IA models considered, we report cosmological parameter constraints consistent with the results of the main DES Y1 cosmic shear and multiprobe cosmology papers.

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