SKA weak lensing – III. Added value of multiwavelength synergies for the mitigation of systematics

Abstract

In this third paper of a series on radio weak lensing for cosmology with the Square Kilometre Array, we scrutinise synergies between cosmic shear measurements in the radio and optical/near-IR bands for mitigating systematic effects. We focus on three main classes of systematics: (i) experimental systematic errors in the observed shear; (ii) signal contamination by intrinsic alignments; and (iii) systematic effects due to an incorrect modelling of non-linear scales. First, we show that a comprehensive, multiwavelength analysis provides a self-calibration method for experimental systematic effects, only implying < 50% increment on the errors on cosmological parameters. We also illustrate how the cross-correlation between radio and optical/near-IR surveys alone is able to remove residual systematics with variance as large as 10 −5 , i.e. the same order of magnitude of the cosmological signal. This also opens the possibility of using such a cross-correlation as a means to detect unknown experimental systematics. Secondly, we demonstrate that, thanks to polarisation information, radio weak lensing surveys will be able to mitigate contamination by intrinsic alignments, in a way similar but fully complementary to available self-calibration methods based on position-shear correlations. Lastly, we illustrate how radio weak lensing experiments, reaching higher redshifts than those accessible to optical surveys, will probe dark energy and the growth of cosmic structures in régimes less contaminated by non-linearities in the matter perturbations. For instance, the higher-redshift bins of radio catalogues peak at z ≃ 0.8 − 1, whereas their optical/near-IR counterparts are limited to z 0.5 − 0.7. This translates into having a cosmological signal 2 to 5 times less contaminated by non-linear perturbations.

SKA Science and Coordination with Multi-messenger facilities

“…By allowing cross-correlations of different tracers. [1] illustrates the power of cross-correlation to remove systematics for a Weak Lensing (WL) survey performed in the radio with SKA1 and in optical/IR. Moreover, cross-correlations can be sensitive to a specific component of the total signal, thus improving the constraint.…”

SuperCLASS – II. Photometric redshifts and characteristics of spatially resolved μJy radio sources

“…The SuperCLASS survey's primary science goals are to: (1) provide a test-bed for weak lensing studies at radio wavelengths for the future Square Kilometer Array (SKA) and other SKA progenitors and (2) obtain internal ∼ kpc maps of µJy radio sources for statistically large samples, determining their evolutionary origins through morphological analysis. High resolution e-MERLIN imaging combined with observations from the Karl G. Janksy Very Large Array (VLA) provides results similar to that expected of the SKA, allowing for the development of the tools required for shape measurement and a quantitative assessment of the physical properties of radio sources that can be used for cosmic shear measurements (Brown & Battye 2011;Harrison et al 2016;Bonaldi et al 2016;Camera et al 2017).…”

Developing a unified pipeline for large-scale structure data analysis with angular power spectra – I. The importance of redshift-space distortions for galaxy number counts

“…This will be a major advantage to tackle systematic effects (see e.g. Camera et al 2017), and possibly to mitigate cosmic variance (McDonald & Seljak 2009;Seljak 2009;Fonseca et al 2015). By doing so, multiple probes will achieve high precision and yield strengthened results on the evaluated cosmological model (Weinberg et al 2013).…”