Speaker
Description
During the Epoch of Reionization, luminous galaxies and quasars are expected to produce large ionized regions embedded within the neutral intergalactic medium. Detecting these individual ionized bubbles in the redshifted HI 21-cm signal offers a direct probe of the ionizing sources and the evolving IGM. However, such detections remain challenging for current radio interferometers due to sensitivity limitations. We propose a visibility-based matched-filter method to detect and characterize individual ionized bubbles using SKA1-Low AA* and AA4 observations, significantly reducing the required observing time. We develop and validate a computationally efficient estimator that operates on gridded visibilities to detect ionized bubbles. This serves as an accurate alternative to the more computationally demanding bare estimator that uses all baselines and frequency channels. Further, we employ a non-parametric foreground-subtraction method based on Gaussian process regression, which minimizes loss of the HI 21-cm signal and yields improved signal-to-noise ratios. Our analysis indicates that ionized bubbles at redshifts ~7-8 can be detected with SNR> 10 using 100 hours of SKA1-Low observations. We further derive a scaling relation that connects the SNR to the bubble radius, redshift, total observing time, and the mean neutral hydrogen fraction of the surrounding IGM. This helps to quickly predict the observational outcome for any planned observations and is, therefore, useful for devising observational strategies. Finally, we apply a Bayesian likelihood framework with MCMC sampling to the residual visibilities to recover ionized bubble properties. The resulting posterior distributions demonstrate accurate recovery of the bubble parameters. This confirms the feasibility of robustly characterizing individual ionized regions with the SKA1-Low. In this presentation, we shall discuss our method and simulation pipeline, the matched-filter and Bayesian analysis frameworks, and the implications of our results for probing reionization with upcoming SKA observations.
