The data storage requirements for deep spectral line observations with next-generation radio interferometers like ASKAP and the SKA are extremely challenging. The default strategy is to reduce data after each observation and stack the resulting images. Rhee et al. present an alternative 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. The new 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, the team show that image-stacking recovers only 92% of the true HI flux. In contrast, the uv-grid stacking method recovers 99%, which is in excellent agreement with the traditional method within the noise limits. Based on these findings, the team intend to apply the uv-grid stacking to the Deep Investigation of Neutral Gas Origins (DINGO) survey on ASKAP. DINGO aims to carry out deep spectral-line (HI) observations over the G23 region of the Galaxy And Mass Assembly (GAMA) survey, which has rich multi-wavelength datasets, enabling both HI and continuum science.

The image above shows the ASKAP beam footprints used for DINGO observations over one tile of the G23 region. Two 36-beam patterns (blue for footprint A and red for footprint B, respectively) of each 6-by-6 beam configuration are interleaved to achieve the uniform sensitivity over the field. Beam IDs are overlaid on individual beams. For the study, two beams (dashed-line circles) were selected from each footprint, surrounding the bright HI galaxy NGC 7361 (denoted with a yellow star). The background is an optical image.