RadioLensfit: Bayesian weak lensing measurement in the visibility domain

TL;DR

RadioLensfit adapts a model-fitting shear measurement method for radio weak lensing, working directly in the visibility domain to reduce systematics, and shows promising simulation results for SKA-like data.

Contribution

It introduces RadioLensfit, a novel radio weak lensing measurement technique that operates in the visibility domain, avoiding imaging systematics.

Findings

Shear bias amplitude is comparable to SKA1 requirements.

Method performs well with realistic galaxy flux and size distributions.

Simulation results support feasibility for SKA-like surveys.

Abstract

Observationally, weak lensing has been served so far by optical surveys due to the much larger number densities of background galaxies achieved, which is typically by two to three orders of magnitude compared to radio. However, the high sensitivity of the new generation of radio telescopes such as the Square Kilometre Array (SKA) will provide a density of detected galaxies that is comparable to that found at optical wavelengths, and with significant source shape measurements to make large area radio surveys competitive for weak lensing studies. This will lead weak lensing to become one of the primary science drivers in radio surveys too, with the advantage that they will access the largest scales in the Universe going beyond optical surveys, like LSST and Euclid, in terms of redshifts that are probed. RadioLensfit is an adaptation to radio data of "lensfit", a model-fitting approach for galaxy shear measurement, originally developed for optical weak lensing surveys. Its key advantage is working directly in the visibility domain, which is the natural approach to adopt with radio data, avoiding systematics due to the imaging process. We present results on galaxy shear measurements, including investigation of sensitivity to instrumental parameters such as the visibilities gridding size, based on simulations of individual galaxy visibilities performed by using SKA1-MID baseline configuration. We get an amplitude of the shear bias in the method comparable with SKA1 requirements for a population of galaxies with realistic flux and scalelength distributions estimated from the VLA SWIRE catalog.