Quantifying the samplng in uv-plane: Implications for imaging extended radio sources

Abstract

Radio interferometers measure the Fourier transform of the sky at the spatial frequencies sampled by the interferometer baselines. Inherently, the shortest projected baseline in an observation towards a source limits the largest sampled angular scale. The sampling in the ‘uv-plane’ — the plane in which the projected baseline vectors are measured — is critical for obtaining high sensitive images and to quantify the angular structures which may be missed in an observation. In this work we define a filling fraction Ffm of the uv-plane in a given data and the overlap fraction (Fov) between the uv-coverages of two data. These fractions have applications in calculating the errors introduced by interpolation in the process of gridding the visibilities for imaging. The methods are demonstrated using data from the Giant Me-trewave Radio Telescope. With wide-band receivers in the upcoming upgrade of existing interferometers and the future Square Kilometer array, the uv-overlap fraction will be much higher leading to much better spectral index mapping and impact the related science.