An Improved Method for 21cm Foreground Removal

TL;DR

This paper presents a novel Fourier-space based method for 21cm foreground removal that improves cleaning on small spatial scales without additional computational cost.

Contribution

It introduces a new Fourier-space formalism and an improved foreground cleaning method that outperforms previous line-of-sight approaches on small scales.

Findings

Enhanced foreground removal on small spatial scales.

Method matches previous results on large scales.

No extra computational cost compared to existing methods.

Abstract

21 cm tomography is expected to be difficult in part because of serious foreground contamination. Previous studies have found that line-of-sight approaches are capable of cleaning foregrounds to an acceptable level on large spatial scales, but not on small spatial scales. In this paper, we introduce a Fourier-space formalism for describing the line-of-sight methods, and use it to introduce an improved new method for 21 cm foreground cleaning. Heuristically, this method involves fitting foregrounds in Fourier space using weighted polynomial fits, with each pixel weighted according to its information content. We show that the new method reproduces the old one on large angular scales, and gives marked improvements on small scales at essentially no extra computational cost.