Foregrounds and their mitigation

TL;DR

This paper reviews the nature of low-frequency radio foregrounds, primarily Galactic synchrotron and extragalactic sources, and discusses current methods for mitigating their impact on detecting the faint cosmological 21 cm signal.

Contribution

It provides a comprehensive overview of the physical properties of radio foregrounds and summarizes the latest techniques for their mitigation in 21 cm cosmology experiments.

Findings

Foreground emissions are significantly brighter than the 21 cm signal.

Understanding foreground properties is crucial for effective mitigation.

Current mitigation techniques are advancing but still face challenges.

Abstract

The low-frequency radio sky is dominated by the diffuse synchrotron emission of our Galaxy and extragalactic radio sources related to Active Galactic Nuclei and star-forming galaxies. This foreground emission is much brighter than the cosmological 21 cm emission from the Cosmic Dawn and Epoch of Reionization. Studying the physical properties of the foregrounds is therefore of fundamental importance for their mitigation in the cosmological 21 cm experiments. This chapter gives a comprehensive overview of the foregrounds and our current state-of-the-art knowledge about their mitigation.