Probing the Intergalactic Medium with Ly$\mathrm{\alpha}$ and 21 cm Fluctuations

TL;DR

This paper investigates the cross-correlation of 21cm and Lyα fluctuations to probe the intergalactic medium's state during reionization, demonstrating potential for upcoming surveys to constrain cosmic reionization history.

Contribution

It introduces a seminumerical simulation approach to analyze 21cm, Lyα, and Hα fluctuations, exploring their cross-correlations to infer IGM properties and reionization details.

Findings

Cross-correlation signal shows a characteristic morphology with a turnover from negative to positive at Mpc scales.

Demonstrates the use of 21cm and Hα cross-correlation to distinguish galactic and IGM Lyα emission.

Detectability of the cross-correlation signal at high SNR for upcoming instruments like SKA, SPHEREx, and CDIM.

Abstract

We study 21cm and Ly$\mathrm{\alpha}$ fluctuations, as well as H$\mathrm{\alpha}$, while distinguishing between Ly$\mathrm{\alpha}$ emission of galactic, diffuse, and scattered intergalactic medium (IGM) origin. Cross-correlation information about the state of the IGM is obtained, testing neutral versus ionized medium cases with different tracers in a seminumerical simulation setup. In order to pave the way toward constraints on reionization history and modeling beyond power spectrum information, we explore parameter dependencies of the cross-power signal between 21$\,$cm and Ly$\mathrm{\alpha}$, which displays a characteristic morphology and a turnover from negative to positive correlation at scales of a couple Mpc$^{-1}$. In a proof of concept for the extraction of further information on the state of the IGM using different tracers, we demonstrate the use of the 21$\,$cm and H$\mathrm{\alpha}$ cross-correlation signal to determine the relative strength of galactic and IGM emission in Ly$\mathrm{\alpha}$. We conclude by showing the detectability of the 21$\,$cm and Ly$\mathrm{\alpha}$ cross-correlation signal over more than one decade in scale at high signal-to-noise ratio for upcoming probes like SKA and the proposed all-sky intensity mapping satellites SPHEREx and CDIM, while also including the Ly$\mathrm{\alpha}$ damping tail and 21cm foreground avoidance in the modeling.