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Dark Energy Survey Year 1 results: the impact of galaxy neighbours on weak lensing cosmology with IM3SHAPE

Dark Energy Survey Year 1 results: the impact of galaxy neighbours on weak lensing cosmology with IM3SHAPE
Dark Energy Survey Year 1 results: the impact of galaxy neighbours on weak lensing cosmology with IM3SHAPE
We use a suite of simulated images based on Year 1 of the Dark Energy Survey to explore the impact of galaxy neighbours on shape measurement and shear cosmology. The hoopoe image simulations include realistic blending, galaxy positions, and spatial variations in depth and PSF properties. Using the im3shape maximum-likelihood shape measurement code, we identify four mechanisms by which neighbours can have a non-negligible influence on shear estimation. These effects, if ignored, would contribute a net multiplicative bias of m∼0.03−0.09 in the DES Y1 im3shape catalogue, though the precise impact will be dependent on both the measurement code and the selection cuts applied. This can be reduced to percentage level or less by removing objects with close neighbours, at a cost to the effective number density of galaxies neff of 30%. We use the cosmological inference pipeline of DES Y1 to explore the cosmological implications of neighbour bias and show that omitting blending from the calibration simulation for DES Y1 would bias the inferred clustering amplitude S8≡σ8(Ωm/0.3)0.5 by 2σ towards low values. Finally, we use the hoopoe simulations to test the effect of neighbour-induced spatial correlations in the multiplicative bias. We find the impact on the recovered S8 of ignoring such correlations to be subdominant to statistical error at the current level of precision.
0035-8711
Smith, M.
8bdc74e1-a37b-434d-ae75-82763109bf7a
DES Collaboration
Smith, M.
8bdc74e1-a37b-434d-ae75-82763109bf7a

Smith, M. , DES Collaboration (2018) Dark Energy Survey Year 1 results: the impact of galaxy neighbours on weak lensing cosmology with IM3SHAPE. Monthly Notices of the Royal Astronomical Society. (doi:10.1093/mnras/stx3282).

Record type: Article

Abstract

We use a suite of simulated images based on Year 1 of the Dark Energy Survey to explore the impact of galaxy neighbours on shape measurement and shear cosmology. The hoopoe image simulations include realistic blending, galaxy positions, and spatial variations in depth and PSF properties. Using the im3shape maximum-likelihood shape measurement code, we identify four mechanisms by which neighbours can have a non-negligible influence on shear estimation. These effects, if ignored, would contribute a net multiplicative bias of m∼0.03−0.09 in the DES Y1 im3shape catalogue, though the precise impact will be dependent on both the measurement code and the selection cuts applied. This can be reduced to percentage level or less by removing objects with close neighbours, at a cost to the effective number density of galaxies neff of 30%. We use the cosmological inference pipeline of DES Y1 to explore the cosmological implications of neighbour bias and show that omitting blending from the calibration simulation for DES Y1 would bias the inferred clustering amplitude S8≡σ8(Ωm/0.3)0.5 by 2σ towards low values. Finally, we use the hoopoe simulations to test the effect of neighbour-induced spatial correlations in the multiplicative bias. We find the impact on the recovered S8 of ignoring such correlations to be subdominant to statistical error at the current level of precision.

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More information

Accepted/In Press date: 7 August 2017
e-pub ahead of print date: 26 December 2017
Published date: 21 April 2018

Identifiers

Local EPrints ID: 418670
URI: https://eprints.soton.ac.uk/id/eprint/418670
ISSN: 0035-8711
PURE UUID: 954782ce-7ef3-4dca-87a4-9d268c517164
ORCID for M. Smith: ORCID iD orcid.org/0000-0002-3321-1432

Catalogue record

Date deposited: 16 Mar 2018 17:30
Last modified: 17 May 2019 00:30

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Author: M. Smith ORCID iD

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