De-contamination of cosmological 21-cm maps

TL;DR

This paper introduces a MAP-based method to extract the cosmological 21-cm signal from reionization data, effectively removing foregrounds and noise, and demonstrates its accuracy through detailed simulations and tests.

Contribution

The novel contribution is the development and testing of a MAP formalism that leverages line-of-sight coherence and 3D correlations to decontaminate 21-cm maps from complex foregrounds and noise.

Findings

Accurate signal recovery at low noise levels (1-5 mK) with rms differences around 1.7-4.2.

Successful reconstruction of the 1D power spectrum across all noise levels tested.

Good reconstruction of Minkowski functionals only at noise levels of a few mK.

Abstract

We present a method for extracting the expected cosmological 21-cm signal from the epoch of reionization, taking into account contaminating radiations and random instrumental noise. The method is based on the maximum a-posteriori probability (MAP) formalism and employs the coherence of the contaminating radiation along the line-of-sight and the three-dimensional correlations of the cosmological signal. We test the method using a detailed and comprehensive modeling of the cosmological 21-cm signal and the contaminating radiation. The signal is obtained using a high resolution N-body simulation where the gas is assumed to trace the dark matter and is reionized by stellar radiation computed from semi-analytic galaxy formation recipes. We model contaminations to the cosmological signal from synchrotron and free-free galactic foregrounds and extragalactic sources including active galactic nuclei, radio haloes and relics, synchrotron and free-free emission from star forming galaxies, and free-free emission from dark matter haloes and the intergalactic medium. We provide tests of the reconstruction method for several rms values of instrumental noise from $\sigma_{N}=1$ to 250 mK. For low instrumental noise, the recovered signal, along individual lines-of-sight, fits the true cosmological signal with a mean rms difference of $d_{rms}\approx 1.7\pm 0.6$ for $\sigma_{N}=1$ mK, and $d_{rms}\approx 4.2\pm 0.4$ for $\sigma_{N}=5$ mK. The one-dimensional power spectrum is nicely reconstructed for all values of $\sigma_{N}$ considered here, while the reconstruction of the two-dimensional power spectrum and the Minkowski functionals is good only for noise levels of the order of few mK.