Cosmological 21cm experiments: Searching for a needle in a haystack

TL;DR

This paper reviews the challenges of detecting the faint 21cm cosmological signal during the Epoch of Reionization amidst foreground contamination, highlighting observational constraints, modeling efforts, and foreground removal techniques, with a focus on LOFAR-EoR results.

Contribution

It provides an overview of observational and theoretical approaches to foreground modeling and removal in 21cm experiments, emphasizing the LOFAR-EoR findings.

Findings

Foreground contamination is a major obstacle in 21cm signal detection.

Theoretical models help in understanding and mitigating foreground effects.

LOFAR-EoR results demonstrate progress in constraining the EoR signal.

Abstract

There are several planned and ongoing experiments designed to explore the Epoch of Reionization (EoR), the pivotal period during which the gas in the intergalactic medium went from being entirely neutral to almost entirely ionized. These experiments will probe the EoR, through the redshifted 21 cm line from neutral hydrogen, using radio arrays: e.g. Low Frequency Array (LOFAR) and Murchinson Widefield Array (MWA). Unfortunately however, the cosmological 21 cm signal is highly contaminated by astrophysical foregrounds and by non-astrophysical and instrumental effects. Therefore, to reliably detect the cosmological signal, it is essential to understand very well all data components, their influence on the desired signal and explore additional complementary or corroborating probes of the EoR. These proceedings give an overview of observational constrains of the foregrounds, present theoretical efforts to model the foregrounds, and discuss a problem of the foreground removal. The major results are presented for the LOFAR-EoR experiment.