First steps toward probing ultra-large-scales with the SKAO

Abstract: Wide-sky surveys with radio telescopes such as the Square Kilometre Array Observatory (SKAO) have the potential to lead the way in probing density fluctuations on the largest scales. This will be achieved by surveying diffuse 21cm emission from extragalactic neutral hydrogen (HI), a technique known as HI intensity mapping. This will be a primary aim for the future SKAO once constructed. However, pathfinder experiments such as the 64-dish MeerKAT telescope are already operational and will provide spectroscopic surveys with competitive volumes. I will present the first detection of the cosmological signal using HI intensity mapping with a multi-dish array. This detection was achieved by cross-correlating MeerKAT pilot survey intensity maps with overlapping optical galaxies from the WiggleZ Dark Energy Survey. A measurement of the power spectrum between these fields provided a 7.7σ detection of a cross-correlation. To achieve this detection, the multi-dish array must map the radio emission using the single-dish data from each element of the array rather than as a conventional interferometer. This detection is the first practical demonstration of the multi-dish auto-correlation intensity mapping technique, which is crucial for the SKAO's capability to probe ultra-large scales. This marks an important milestone in the roadmap for the cosmology science case with the full SKAO.