# Dark ages reionization & galaxy formation simulation XII: Bubbles at dawn

## TL;DR

This paper explores the potential of combining low-frequency radio observations with infrared data to detect cosmic reionization by stacking 21-cm spectra around known galaxies, enabling insights into the epoch of reionization and IGM properties.

## Contribution

It proposes a novel stacking technique using SKA and WFIRST data to detect ionized bubbles during the cosmic dawn, providing a new observational approach to study reionization.

## Key findings

- Stacking 21-cm spectra can detect the EoR at redshifts 9-12.
- The method can constrain the IGM's spin temperature evolution.
- Detection of ionized bubbles can reveal if the IGM is in absorption or emission.

## Abstract

Direct detection of regions of ionized hydrogen (HII) has been suggested as a promising probe of cosmic reionization. Observing the redshifted 21-cm signal of hydrogen from the epoch of reionization (EoR) is a key scientific driver behind new-generation, low-frequency radio interferometers. We investigate the feasibility of combining low-frequency observations with the Square Kilometre Array and near infra-red survey data of the Wide-Field Infrared Survey Telescope to detect cosmic reionization by imaging HII bubbles surrounding massive galaxies during the cosmic dawn. While individual bubbles will be too small to be detected, we find that by stacking redshifted 21-cm spectra centred on known galaxies, it will be possible to directly detect the EoR at $z \sim 9-12$, and to place qualitative constraints on the evolution of the spin temperature of the intergalactic medium (IGM) at $z \geq 9$. In particular, given a detection of ionized bubbles using this technique, it is possible to determine if the IGM surrounding them is typically in absorption or emission. Determining the globally-averaged neutral fraction of the IGM using this method will prove more difficult due to degeneracy with the average size of HII regions.