Detecting ionized bubbles around luminous sources during the reionization era using HI 21-cm signal

TL;DR

This study assesses the detectability of ionized bubbles around luminous sources during the Epoch of Reionization using simulated HI 21-cm observations, demonstrating the potential of uGMRT and SKA1-Low for probing the early universe.

Contribution

It introduces a visibility-based matched filter technique for detecting ionized bubbles in 21-cm data and evaluates observational requirements with uGMRT and SKA1-Low.

Findings

Ionized bubbles can be detected with >5σ significance using ~2000-3000 hours with uGMRT.

SKA1-Low can detect these bubbles with >8σ significance in about 100 hours.

The method allows measurement of bubble radius and neutral hydrogen fraction.

Abstract

Measuring the properties of the intergalactic medium (IGM) and sources during the Epoch of Reionization (EoR) is of immense importance. We explore the prospects of probing the IGM and sources through redshifted 21-cm observations of individual ionized bubbles surrounding known luminous sources during the EoR. Accordingly, we simulate HI 21-cm maps, foreground contaminants, and system noise which are specific to the uGMRT and SKA1-Low observations. Following the subtraction of the foreground from the total visibility, we employ a visibility-based matched filter technique to optimally combine the desired HI 21-cm signal while minimizing the system noise. Our analysis suggests that these ionized bubbles can be detected with more than $5 \sigma$ significance using approximately $\sim 2000$ and $\sim 3000$ hours of observation time with the uGMRT at redshift $7.1$ and $8.3$, respectively, when the mean neutral hydrogen fraction outside the targeted bubble is $ \sim 0.9$. The SKA1-Low should be able to detect these bubbles with more than $8 \sigma$ significance using only $\sim 100$ hrs of observations. The total observing time increases both for the uGMRT and SKA1-Low when the mean neutral hydrogen fraction outside the targeted bubble decreases. Further, we investigate the impact of foreground subtraction on the detectability and find the signal-to-noise ratio decreases when smaller bandwidth is used. More importantly, we show that the matched filtering method can measure ionized bubble radius and constrain HI-neutral fraction reasonably well, providing deeper insights into the source properties and the intergalactic medium.