Weak Gravitational Lensing

Weak gravitational lensing is the small distortion of background galaxy shapes by a foreground matter distribution.

Weak Lensing Forecasts
Figure 1: Forecasts for constraints on dark energy for a future Euclid-like weak lensing survey and SKA-like weak lensing survey (Harrison et al. arXiv:1601.03947). Both experiments display similar constraining power. Moreover, cross-correlating the two experiments does not significantly degrade the precision but greatly increases robustness to systematic uncertainties.


This phenomenon is a consequence of the curvature of spacetime by matter and energy, as predicted by Einstein's General Theory of Relativity.

The weak lensing of a large number of background sources by the large-scale structure of the Universe, known as cosmic shear, produces coherent shape distortions which can be used to measure the distribution of matter in the Universe, and hence helps us to study the history of large-scale structure formation.

To date, weak lensing has primarily been done using optical surveys, such as the Canada-France-Hawaii-Telescope Lensing Survey (CFHTLenS) and the Kilo-Degree Survey (KiDS). The JBCA is a key contributor to the Dark Energy Survey (DES), which is an optical survey focussed on learning about the content and nature of dark energy. One of the primary tools used to achieve this goal is weak lensing, and early results from the DES science verification data have already produced promising constraints on the equation of state of dark energy and the fraction of matter in the Universe.

The JBCA is also involved in future high-precision optical weak lensing surveys, such as those that will be performed using the Euclid space telescope and the Large Synoptic Survey Telescope (LSST). These surveys are expected to provide an unprecedented insight into the composition and evolution of large-scale structure.

One exciting area of research being conducted at the JBCA is the prospect of performing weak lensing in the radio. Techniques for performing radio weak lensing are being developed using the Super-CLuster Assisted Shear Survey (SuperCLASS), which is a survey of 1.75 square degrees of the Northern sky using the e-MERLIN telescope array. The aim is to use the techniques developed with SuperCLASS in future high resolution radio surveys conducted with, for example, the Square Kilometre Array (SKA). Also, combining radio and optical weak lensing data can potentially remove some of the systematic observational and astrophysical uncertainties that will place limitations on the individual surveys. An example of this work is shown in Figure 1.

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