Canceling out intensity mapping foregrounds

Understand

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.