# Matched filtering with interferometric 21cm experiments

## TL;DR

This paper evaluates the potential of interferometric 21cm experiments to detect large-scale cosmic structures like voids using a matched filter approach, emphasizing the importance of foreground control.

## Contribution

It introduces a Fourier space matched filter formalism tailored for interferometric 21cm surveys to assess large-scale structure detection capabilities.

## Key findings

- Without foregrounds, instruments could catalog many voids with high completeness.
- Foreground contamination significantly impacts the ability to detect large-scale structures.
- Finite u-v coverage affects the detection sensitivity and accuracy.

## Abstract

A new generation of interferometric instruments is emerging which aim to use intensity mapping of redshifted $21\,$cm radiation to measure the large-scale structure of the Universe at $z\simeq 1-2$ over wide areas of sky. While these instruments typically have limited angular resolution, they cover huge volumes and thus can be used to provide large samples of rare objects. In this paper we study how well such instruments could find spatially extended large-scale structures, such as cosmic voids, using a matched filter formalism. Such a formalism allows us to work in Fourier space, the natural space for interferometers, and to study the impact of finite $u-v$ coverage, noise and foregrounds on our ability to recover voids. We find that in the absence of foregrounds such instruments would provide enormous catalogs of voids, with high completeness, but that control of foregrounds is key to realizing this goal.