CMB lensing reconstruction biases in cross-correlation with large-scale structure probes

Fabbian, Giulio, Lewis, Antony and Beck, Dominic (2019) CMB lensing reconstruction biases in cross-correlation with large-scale structure probes. Journal of Cosmology and Astroparticle Physics, 2019 (10). pp. 1-50. ISSN 1475-7516

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The cross-correlation between cosmic microwave background (CMB) gravitational lensing and large-scale structure tracers will be an important cosmological probe in the coming years. Quadratic estimators provide a simple and powerful (if suboptimal) way to reconstruct the CMB lensing potential and are widely used. For Gaussian fields, the cross-correlation of a quadratic-estimator CMB lensing reconstruction with a tracer is exactly unbiased if the power spectra are known and consistent analytic lensing mode response functions are used. However, the bispectrum induced by non-linear large-scale structure growth and post-Born lensing can introduce an additional bias term (NL(3/2)) in the cross-correlation spectrum, similar to the NL(3/2) bias in the auto-spectrum demonstrated in recent works. We give analytic flat-sky results for the cross-correlation bias using approximate models for the post-Born and large-scale structure cross-bispectra, and compare with N-body simulation results using ray-tracing techniques. We show that the bias can be at the 5–15% level in all large-scale structure cross-correlations using small-scale CMB temperature lensing reconstruction, but is substantially reduced using polarization-based lensing estimators or simple foreground-projected temperature estimators. The relative magnitude of these effects is almost three times higher than in the CMB lensing auto-correlation, but is small enough that it can be modelled to sufficient precision using simple analytic models. We show that NL(3/2) effects in cross-correlation will be detected with high significance when using data of future surveys and could affect systematic effects marginalization in cosmic shear measurements mimicking galaxy intrinsic alignment.

Item Type: Article
Schools and Departments: School of Mathematical and Physical Sciences > Physics and Astronomy
Research Centres and Groups: Astronomy Centre
Subjects: Q Science
Q Science > QB Astronomy
Q Science > QB Astronomy > QB0980 Cosmogony. Cosmology
Q Science > QB Astronomy > QB0980 Cosmogony. Cosmology > QB0991.L37 Large scale structure
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Depositing User: Giulio Fabbian
Date Deposited: 29 Oct 2019 10:16
Last Modified: 19 Nov 2019 11:45

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Project NameSussex Project NumberFunderFunder Ref
Precision cosmological parameters : CosmoParsG1365EUROPEAN UNION616170 ERC-2013-CoG
University of Sussex Astronomy Consolidated Grant 2017-2020G2050STFC-SCIENCE AND TECHNOLOGY FACILITIES COUNCILST/P000525/1