SKA Weak Lensing I: Cosmological Forecasts and the Power of Radio-Optical Cross-Correlations

TL;DR

This paper forecasts the potential of SKA radio weak lensing surveys to constrain cosmological parameters and highlights the significant benefits of cross-correlating radio and optical shear maps for improved accuracy and systematic error reduction.

Contribution

It demonstrates that SKA1 can be competitive with Stage III experiments and SKA2 can surpass Stage IV optical surveys, emphasizing the power of radio-optical cross-correlations.

Findings

SKA1 can match Stage III optical experiments in constraining cosmology.

SKA2 can outperform Stage IV optical weak lensing surveys.

Cross-correlations reduce systematic errors and improve constraints by about 5%.

Abstract

We construct forecasts for cosmological parameter constraints from weak gravitational lensing surveys involving the Square Kilometre Array (SKA). Considering matter content, dark energy and modified gravity parameters, we show that the first phase of the SKA (SKA1) can be competitive with other Stage III experiments such as the Dark Energy Survey (DES) and that the full SKA (SKA2) can potentially form tighter constraints than Stage IV optical weak lensing experiments, such as those that will be conducted with LSST, WFIRST-AFTA or Euclid-like facilities. Using weak lensing alone, going from SKA1 to SKA2 represents improvements by factors of $\sim10$ in matter, $\sim10$ in dark energy and $\sim5$ in modified gravity parameters. We also show, for the first time, the powerful result that comparably tight constraints (within $\sim5\%$) for both Stage III and Stage IV experiments, can be gained from cross-correlating shear maps between the optical and radio wavebands, a process which can also eliminate a number of potential sources of systematic errors which can otherwise limit the utility of weak lensing cosmology.