# Calibrating photometric redshifts with intensity mapping observations

## TL;DR

This paper proposes a method combining intensity mapping and clustering redshifts to calibrate galaxy redshift distributions, significantly improving photometric redshift accuracy for large imaging surveys.

## Contribution

It introduces a novel approach to calibrate photometric redshifts using intensity mapping data, enhancing redshift precision in galaxy surveys.

## Key findings

- Intensity mapping can calibrate galaxy redshifts with high accuracy.
- Method reduces photometric redshift uncertainties below DES and LSST requirements.
- Effectiveness depends on instrumental parameters and systematic error control.

## Abstract

Imaging surveys of galaxies will have a high number density and angular resolution yet a poor redshift precision. Intensity maps of neutral hydrogen (HI) will have accurate redshift resolution yet will not resolve individual sources. Using this complementarity, we show how the clustering redshifts approach, proposed for spectroscopic surveys can also be used in combination with intensity mapping observations to calibrate the redshift distribution of galaxies in an imaging survey and, as a result, reduce uncertainties in photometric redshift measurements. We show how the intensity mapping surveys to be carried out with the MeerKAT, HIRAX and SKA instruments can improve photometric redshift uncertainties to well below the requirements of DES and LSST. The effectiveness of this method as a function of instrumental parameters, foreground subtraction and other potential systematic errors is discussed in detail.