Probing individual sources during reionization and cosmic dawn using SKA HI 21-cm observations

TL;DR

This paper evaluates SKA1-low's potential to detect individual sources during reionization and cosmic dawn through their HI 21-cm signatures, proposing detection methods and analyzing expected signal strengths and observational requirements.

Contribution

It introduces visibility-based estimators for detecting HI 21-cm signals from sources during reionization and cosmic dawn, and assesses SKA1-low's capabilities for such detections.

Findings

Detection of ionized bubbles of radius >10 Mpc at z~8 with 100 hr of observations.

Possible 5σ detection of HII regions around bright QSOs with 600 hr of observations.

Detection of first X-ray and Ly-α sources at z=15 with ~1000 hr of observations.

Abstract

Detection of individual luminous sources during the reionization epoch and cosmic dawn through their signatures in the HI 21-cm signal is one of the direct approaches to probe the epoch. Here, we summarize our previous works on this and present preliminary results on the prospects of detecting such sources using the SKA1-low experiment. We first discuss the expected HI 21-cm signal around luminous sources at different stages of reionization and cosmic dawn. We then introduce two visibility based estimators for detecting such signal: one based on the matched filtering technique and the other relies on simply combing the visibility signal from different baselines and frequency channels. We find that that the SKA1-low should be able to detect ionized bubbles of radius $R_b \gtrsim 10$ Mpc with $\sim 100$ hr of observations at redshift $z \sim 8$ provided that the mean outside neutral Hydrogen fraction $ x_{\rm HI} \gtrsim 0.5$. We also investigate the possibility of detecting HII regions around known bright QSOs such as around ULASJ1120+0641 discovered by Mortlock et al. 2011. We find that a $5 \sigma$ detection is possible with $600$ hr of SKA1-low observations if the QSO age and the outside $ x_{\rm HI} $ are at least $\sim 2 \times 10^7$ Myr and $\sim 0.2$ respectively. Finally, we investigate the possibility of detecting the very first X-ray and Ly-$\alpha$ sources during the cosmic dawn. We consider mini-QSOs like sources which emits in X-ray frequency band. We find that with a total $\sim 1000$ hr of observations, SKA1-low should be able to detect those sources individually with a $\sim 9 \sigma$ significance at redshift $z=15$. We summarize how the SNR changes with various parameters related to the source properties.