A Technique for Foreground Subtraction in Redshifted 21 cm Observations

TL;DR

This paper introduces a new multi-frequency foreground subtraction technique for 21 cm cosmology, leveraging differences in signal correlation across frequencies to accurately isolate the HI signal from dominant foregrounds.

Contribution

The proposed method exploits the uncorrelated nature of 21 cm signals across frequencies and the slow variation of foregrounds to improve foreground removal accuracy.

Findings

Effective separation of 21 cm signal from foregrounds demonstrated

Foreground power spectrum can be accurately estimated

Method enhances the detection prospects of the HI signal

Abstract

One of the main challenges for future 21 cm observations is to remove foregrounds which are several orders of magnitude more intense than the HI signal. We propose a new technique for removing foregrounds of the redshifted 21 cm observations. We consider multi-frequency interferometer observations. We assume that the 21 cm signals in different frequency channels are uncorrelated and the foreground signals change slowly as a function of frequency. When we add the visibilities of all channels, the foreground signals increase roughly by a factor of ~N because they are highly correlated. However, the 21 cm signals increase by a factor of ~\sqrt{N} because the signals in different channels contribute randomly. This enables us to obtain an accurate shape of the foreground angular power spectrum. Then, we obtain the 21-cm power spectrum by subtracting the foreground power spectrum obtained this way. We describe how to obtain the average power spectrum of the 21 cm signal.