Speaker
Description
The redshifted 21 cm line is a powerful tool for studying the state of the intergalactic medium (IGM) before the epoch of reionization. The MWA’s ultra-low-frequency band, spanning 75 MHz to 100 MHz, covers the 21 cm line from redshift of 15. This redshift corresponds to the epoch when the first stars formed and the IGM was heated by X-ray radiation. However, observations at these frequencies are significantly contaminated by foregrounds such as Galactic synchrotron radiation. Additionally, measurements in this band suffer from systematics, including ionospheric effects.
Therefore, detecting 21 cm fluctuations at these redshifts requires a deep understanding of the low-frequency sky, instrumental systematics, and calibration strategies. In this talk, we report progress in our data analysis of MWA drift-scan observations at ultra-low frequencies. The observation covers right ascensions from −45° to +75° with zenith pointing. Calibration was performed using MWA Hyperdrive with the latest calibration source catalog. Our key findings include: (1) short baselines are dominated by Fornax A and Pictor A around LST ≈ 50; (2) Fornax A is effectively subtracted, though residuals from other sources remain; (3) the power spectrum’s dynamic range varies with LST; (4) the level of systematics dominating the power spectrum depends on nights; and (5) current upper limits are constrained primarily by gain calibration errors. We also report ongoing analysis related to ionospheric conditions, RFI from the Moon, gain smoothing, and statistical analysis of visibilities.
