Deep Investigation of Neutral Gas Origins (DINGO): Options for robust Deep Spectral Line Imaging in the SKA-Era

TL;DR

This paper introduces a uv-grid stacking method for deep spectral line imaging with next-generation radio telescopes, demonstrating it recovers more flux and reduces artefacts compared to traditional image stacking, thus improving data quality.

Contribution

The paper presents a novel uv-grid stacking technique that outperforms traditional image stacking in deep spectral line imaging, with potential applications for SKA-era surveys.

Findings

uv-grid stacking recovers 99% of true HI flux

Traditional image stacking recovers only 92% of flux

Image stacking introduces artefacts like negative bowls around sources

Abstract

The data storage requirements for deep spectral line observations with next-generation radio interferometers like the Australian Square Kilometre Array Pathfinder (ASKAP) and the Square Kilometre Array (SKA) are extremely challenging. The default strategy is to reduce data after each daily observation and stack the resulting images. Although this approach is computationally efficient, it risks propagating systematic errors and significantly degrades the final data quality. However, storage and computation requirements for a traditional way to image the entire deep dataset together are prohibitively expensive. We present an alternative \textit{uv}-grid stacking method and compare its scientific outcomes with both the traditional approach, which processes all data jointly and serves as the best-possible result, and the default image-stacking method. Our technique involves halting the standard imaging pipeline after the daily residual visibility grids are formed. These grids are then stacked and jointly deconvolved to combine many epochs of data. Using the traditional approach as a benchmark, we show that image-stacking recovers only 92\% of the true {\HI} flux. In contrast, our \textit{uv}-grid stacking method recovers 99\%, which is in excellent agreement with the traditional method within the noise limits. Furthermore, image-stacking introduces significant non-physical artefacts, such as negative bowls around strong sources, indicating poor deconvolution and a loss of physical information. Based on these findings, we intend to apply the \textit{uv}-grid stacking to the Deep Investigation of Neutral Gas Origins (DINGO) survey on ASKAP and strongly recommend this or a similar approach for future radio astronomy facilities.