This figure compares the closure phase power spectrum derived from the observational data (DATA) with the forward model predictions (Model). The foreground model (FG) and the combined foreground plus cosmological 21-cm signal model (FG+HI), representing the expected signal levels to be reached by future experiments.

Novel Interferometric Techniques for Detecting the 21-cm Signal from the Epoch of Reionisation

Himanshu Tiwari (Curtin University)

Abstract:
Detecting the cosmological 21-cm signal from the Epoch of Reionisation (EoR) presents a significant challenge due to foreground contamination and instrumental limitations. Therefore, alternative approaches can be explored to overcome some of these challenges. This work presents two independent approaches: Lunar Occultation for estimating the global 21-cm signal and closure phases for measuring the 21-cm power spectrum. Lunar Occultation utilises the Moon as a thermal reference to measure the foreground sky temperature, with results demonstrated using Murchison Widefield Array (MWA) observations. A key aspect of this method is mitigating reflected FM Radio Frequency Interference (RFI) from the Moon, which is addressed through modelling and statistical techniques.

The second method employs radio interferometric closure phases to estimate the 21-cm power spectrum, providing a calibration-independent alternative to traditional visibility-based methods. Our analysis of MWA data reveals systematic contaminants that impact sensitivity, which are mitigated using statistical techniques. These methods lay basic foundation which can be beneficial for the upcoming radio experiments, especially SKA-low, to further our understanding of the early Universe through the 21-cm signal.

Caption:
The figure shown illustrates the closure phase power spectra of the EoR1 field (RA: 4h, Dec: -30º) obtained using three redundant baseline triads (14m, 24m, 28m) from approximately 9 hours of MWA Phase-II observations. This figure compares the closure phase power spectrum derived from the observational data (DATA) with the forward model predictions (Model). The foreground model (FG) and the combined foreground plus cosmological 21-cm signal model (FG+HI), representing the expected signal levels to be reached by future experiments. While the observational data still lies 2-3 orders of magnitude above the theoretical limits, a consistent agreement between the DATA and the Model is evident, which has been verified through rigorous statistical testing. This consistency is a result of incorporating baseline-dependent systematics in the forward modelling process. This approach, which effectively accounts for systematics and enhances the sensitivity to the 21-cm signal, shows great promise for future radio experiments, particularly with SKA-Low.