Tuesday

The Square Kilometre Array (SKA) radio telescope will have sufficient sensitivity to detect a density of galaxies comparable to that found in optical surveys, allowing weak lensing measurements in the radio band. A radio lensing survey probes to higher redshift than the equivalent optical surveys and will have different systematics. Most of the techniques available for the measurement of cosmic shear are based on the best fitting of galaxy shapes from images, as they have been developed for optical surveys. However, radio interferometers measure visibilities, i.e. the Fourier transform of the sky image at a finite sampling. They are usually transformed into images, corrected for the interferometer sidelobe response, by an iterative non-linear process, which may introduce residuals that dominate the cosmological signal. A more natural approach to adopt with radio data is to work directly in the visibility domain, avoiding systematics due to the imaging process and where the noise is Gaussian. I will show work on the development of such methods, adopting a Bayesian approach, with results from SKA simulations. In particular I will present RadioLensfit, an adaptation to the Fourier domain of the model fitting method lensfit (Miller et al. 2013), recently used in several optical surveys, where a single source is measured at a time. It can be combined with another approach, exploiting the HMC technique, to perform a joint fitting in higher density regions of the SKA field of view.

Miller L. et al., 2013, MNRAS, 429, 2858