Field-level Reconstruction from Foreground-Contaminated 21-cm Maps

TL;DR

This paper introduces two innovative methods, an EFT-based inference and a diffusion model, to reconstruct the full 21-cm cosmological field from foreground-contaminated data, enabling access to previously inaccessible Fourier modes.

Contribution

It presents novel field-level reconstruction techniques combining physics-based modeling and deep generative models to recover missing Fourier modes in 21-cm cosmology data.

Findings

Successful reconstruction of missing Fourier modes.

Enhanced cosmological parameter constraints.

Potential for cross-experiment data integration.

Abstract

Current and upcoming 21-cm experiments will soon be able to map 21-cm spatial fluctuations in three dimensions for a wide range of redshifts. However, bright foreground contamination and the nature of radio interferometry create significant challenges, making it difficult to access rich cosmological information from the Fourier modes that lie within the "foreground wedge". In this work, we introduce two approaches aiming to reconstruct the full 21-cm density field, including the missing modes in the wedge: (a) a field-level inference under an effective field theory (EFT) framework; (b) a diffusion-based deep generative model trained on simulations. Under the EFT framework, we implement a fully differentiable forward model that maps the initial conditions of matter fluctuations to the observed, foreground-filtered 21-cm maps. This enables a gradient-based sampler to simultaneously sample the initial conditions and bias parameters, allowing a physically motivated mode reconstruction. Alternatively, we apply a variational diffusion model to perform 21-cm density reconstruction at the map level. Our model is trained on semi-numerical simulations over a wide range of astrophysical parameters. Our results from both approaches should provide improved cosmological constraints from the field level and also enable cross-correlation between experiments that have little or no overlapping modes.