Recent Progress in 21-cm Intensity Mapping with the SKA Pathfinder uGMRT

Abstract

21-cm intensity mapping is a promising technique to probe large-scale structures in our Universe. To measure the 21-cm intensity mapping signal, we have carried out a deep radio continuum observation of the ELAIS-N1 field using the SKA pathfinder instrument uGMRT. We have used uGMRT’s high angular resolution and wide bandwidth (300-500 MHz) to make a deep image of the field, from which, we identified and removed the compact sources. We found that the residual foregrounds are still several orders of magnitude brighter than the expected 21-cm signal. In a series of subsequent works, we have systematically developed novel techniques to remove the residual foregrounds and reach the system noise. The methodology includes sidelobe suppression, RFI handling, a foreground removal technique that is robust against signal loss and the necessary ingredients for a wide bandwidth data analysis. With a mere 25 hours of observation, we have found an upper limit which is just 10 times above the expected 21-cm signal. This stringent upper limit has led us to 50 more hours of observations with uGMRT, which, combined with the refined pipeline, is expected to provide a substantial improvement and a much tighter constraint. The techniques and these results will underpin future observations with SKA.