# Cross-correlation between the 21-cm signal and [OIII] emitters during early cosmic reionization

## TL;DR

This study explores the cross-correlation between 21-cm signals and [OIII] emitters during early cosmic reionization, revealing how their relationship evolves and can be used to probe the reionization process.

## Contribution

It introduces a novel method of using [OIII] line emitters to cross-correlate with 21-cm signals, supported by simulations, to study the reionization epoch.

## Key findings

- Positive correlation between 21-cm and [OIII] emitters during early reionization
- Correlation sign changes from positive to negative as reionization progresses
- Potential detectability with SKA and [OIII] surveys

## Abstract

We study statistics of the 21-cm signal from the epoch of reionization. We propose to use [OIII] line emitting galaxies to cross-correlate with the 21-cm signal from $z = 7 - 10$. To this aim, we employ simulations of reionization obtained post-processing the high-resolution cosmological hydrodynamic simulation Massive Black-II with the three-dimensional (3D) radiative transfer code CRASH to follow the propagation of ionizing photons from a variety of sources. We show that, during the early phases of reionization, the 21-cm signal is positively correlated with the spatial distribution of the [OIII] emitters on large scales $(k < 1h~\rm cMpc^{-1})$. This positive correlation is generated by the temperature-galaxy correlation and it is a few times larger than when we assume that the heating is saturated. As the reionized regions expand, the correlation changes its sign to negative from $z = 10$ to 8. The signals at this epoch can be detected by combining the Square Kilometre Array (SKA) and a wide-field [OIII] emitter survey. We also calculate the cross-power spectrum with a 3D [OIII] intensity field, aiming at exploiting future intensity mapping observations. We conclude that high-redshift [OIII] line emitters can be used to probe the reionization process when the intergalactic medium is largely neutral.