Exploring 21cm - Lyman Alpha emitter synergies for SKA

TL;DR

This study investigates the correlation between 21cm emission and Lyman Alpha Emitters during reionization using simulations, aiming to constrain the IGM ionization state and reionization topology with SKA and Subaru observations.

Contribution

It demonstrates how 21cm-LAE cross-correlations can constrain reionization parameters and supports the inside-out reionization scenario through simulation-based analysis.

Findings

LAEs strongly anti-correlate with 21cm emission.

SKA and Subaru can distinguish different ionization levels.

Observations support inside-out reionization topology.

Abstract

We study the signatures of reionization and ionizing properties of the early galaxies in the cross-correlations between the 21cm emission from the spin-flip transition of neutral hydrogen (HI) and the underlying galaxy population, in particular a sub-population of galaxies visible as Lyman Alpha Emitters (LAEs). With both observables simultaneously derived from a $z\simeq6.6$ hydrodynamical simulation (GADGET-2) snapshot post-processed with a radiative transfer code (pCRASH) and a dust model, we perform a parameter study and aim to constrain both the average intergalactic medium (IGM) ionization state ($1-\langle \chi_{HI} \rangle$) and the reionization topology (outside-in versus inside-out). We find that in our model LAEs occupy the densest and most-ionized regions resulting in a very strong anti-correlation between the LAEs and the 21cm emission. A 1000h SKA-LOW1 - Subaru Hyper Suprime Cam experiment can provide constraints on $\langle \chi_{HI} \rangle$, allowing us to distinguish between IGM ionization levels of 50%, 25%, 10% and fully ionized at scales $r<10$ comoving Mpc (assuming foreground avoidance for SKA). Our results support the inside-out reionization scenario where the densest knots (under-dense voids) are ionized first (last) for $\langle \chi_{HI} \rangle >= 0.1$. Further, 1000h SKA-LOW1 observations should be able to confirm the inside-out scenario by detecting a lower 21cm brightness temperature (by about 2-10 mK) in the densest regions ($> 2$ arcminute scales) hosting LAEs compared to lower-density regions devoid of them.