# Canceling out intensity mapping foregrounds

## TL;DR

This paper introduces a novel analysis method combining intensity maps with galaxy surveys to effectively cancel foreground contamination in 21 cm intensity mapping, enabling more precise measurements of the HI mass function.

## Contribution

The paper proposes a new one-point statistic that is unbiased by foregrounds and leverages combined data to improve HI mass function measurements.

## Key findings

- Method can measure HI mass function with high precision
- Foreground bias is effectively canceled
- Applicable to current 21 cm observations

## Abstract

21 cm intensity mapping has arisen as a powerful probe of the high-redshift universe, but its potential is limited by extremely bright foregrounds and high source confusion. In this Letter, we propose a new analysis which can help solve both problems. From the combination of an intensity map with an overlapping galaxy survey we construct a new one-point statistic which is unbiased by foregrounds and contains information left out of conventional analyses. We show that our method can measure the HI mass function with unprecedented precision using observations similar to recent 21 cm detections.