Direct reconstruction of the Reionization history from 21cm 2D Power Spectra

TL;DR

This paper introduces EoRFlow, a simulation-based inference framework that reconstructs the reionization history directly from 2D 21cm power spectra, enabling efficient and unbiased estimation of the neutral hydrogen fraction during the Epoch of Reionization.

Contribution

The paper presents a novel SBI method for directly inferring the reionization timeline from 21cm power spectra without explicit likelihoods, validated on realistic SKA-Low mock data.

Findings

Enables fast, unbiased estimation of $x_{HI}(z)$ in narrow redshift slices.

Successfully reconstructs the global reionization history from simulated SKA data.

Provides a scalable approach for 21cm cosmology in the SKA era.

Abstract

The 21cm line from the spin-flip transition of neutral hydrogen (HI) provides a unique window into the Epoch of Reionization (EoR), the final phase transition of our Universe. The Square Kilometre Array (SKA) enables precise measurements of 21cm fluctuations that trace ionization, temperature, and density fluctuations of the intergalactic medium (IGM). Nevertheless, a direct reconstruction of the timeline of the EoR in terms of the progress of ionization remains an ongoing challenge due to the highly non-Gaussian nature and thus intractable likelihood of the 21cm signal. Here, we present EoRFlow, a simulation-based inference (SBI) framework for reconstructing the global neutral hydrogen fraction $x_{\mathrm{HI}}(z)$ directly from 2D cylindrically averaged power spectra (2DPS) of the 21cm signal. We validate our method on realistic mock datasets for SKA-Low. Bypassing the need for explicit likelihood formulations, our approach enables fast, unbiased posterior estimation of the $x_{\mathrm{HI}}$ evolution in narrow redshift slices, allowing for piecewise reconstruction of the global reionization history. By directly inferring the reionization history from 21cm power spectra, our framework provides a scalable and robust path forward for 21cm cosmology in the SKA era.