Subtraction of point sources from interferometric radio images through an algebraic forward modeling scheme

TL;DR

This paper introduces an algebraic forward modeling method for subtracting point sources from interferometric radio images, significantly improving dynamic range and residual noise characteristics, especially useful for 21 cm cosmology.

Contribution

The paper presents a novel algebraic nonlinear minimization approach for point source subtraction that is effective with image-only data and scalable to large radio arrays.

Findings

Residual maps match thermal noise after subtraction

Recovered sources have ~10 arcsec position error

Achieved ~3 orders of magnitude increase in dynamic range

Abstract

We present a method for subtracting point sources from interferometric radio images via forward modeling of the instrument response and involving an algebraic nonlinear minimization. The method is applied to simulated maps of the Murchison Wide-field Array but is generally useful in cases where only image data are available. After source subtraction, the residual maps have no statistical difference to the expected thermal noise distribution at all angular scales, indicating high effectiveness in the subtraction. Simulations indicate that the errors in recovering the source parameters decrease with increasing signal-to-noise ratio, which is consistent with the theoretical measurement errors. In applying the technique to simulated snapshot observations with the Murchison Wide-field Array, we found that all 101 sources present in the simulation were recovered with an average position error of 10 arcsec and an average flux density error of 0.15%. This led to a dynamic range increase of approximately 3 orders of magnitude. Since all the sources were deconvolved jointly, the subtraction was not limited by source sidelobes but by thermal noise. This technique is a promising deconvolution method for upcoming radio arrays with a huge number of elements, and a candidate for the difficult task of subtracting foreground sources from observations of the 21 cm neutral Hydrogen signal from the epoch of reionization.