EMU: Cross-correlating EMU Pilot Survey 1 with Dark Energy Survey to constrain the radio galaxy redshift distribution

TL;DR

This paper demonstrates how cross-correlating radio continuum surveys with optical galaxy maps can accurately determine the redshift distribution, improving cosmological analyses of large-scale structure.

Contribution

It introduces a statistical method to infer the redshift distribution of radio galaxies by cross-correlating EMU Pilot Survey data with the Dark Energy Survey, outperforming existing models.

Findings

Recovered redshift distribution peaks at higher redshift.

Model fits data significantly better than simulated distributions.

Method applicable to future large-scale radio surveys.

Abstract

Radio continuum galaxy surveys can provide a relatively fast map of the projected distribution of structure in the Universe, at the cost of lacking information about the radial distribution. We can use these surveys to learn about the growth of structure and the fundamental physics of the Universe, but doing so requires extra information to be provided in the modelling of the redshift distribution, $dN/dz$. In this work, we show how the cross-correlation of the two dimensional radio continuum map with another galaxy map (in this case a photometric optical extragalactic survey), with a known redshift distribution, can be used to determine the redshift distribution through statistical inference. We use data from the Evolutionary Map of the Universe (EMU) Pilot Survey 1 and cross-correlate it with optical data from the Dark Energy Survey to fit the parameters of our $dN/dz$ model. We show that the recovered distribution fits the data much better than current simulated $dN/dz$ models available in the literature, and peaks at a much higher redshift. These results will have significance for future cosmological analyses with large-scale radio continuum surveys such as the full EMU, or with the SKAO.