Intensity Mapping with Carbon Monoxide Emission Lines and the Redshifted 21 cm Line

TL;DR

This paper explores the potential of using CO emission line intensity mapping, combined with 21 cm line observations, to study the large-scale structure and reionization epoch of the early universe, highlighting cross-correlation advantages.

Contribution

It introduces a novel approach of combining CO intensity mapping with 21 cm observations to probe the Epoch of Reionization and discusses strategies to improve signal predictions.

Findings

CO intensity mapping can trace early galaxy molecular clouds.

Cross-correlation reduces foreground contamination.

Predicted signals are detectable with feasible surveys.

Abstract

We quantify the prospects for using emission lines from rotational transitions of the CO molecule to perform an `intensity mapping' observation at high redshift during the Epoch of Reionization (EoR). The aim of CO intensity mapping is to observe the combined CO emission from many unresolved galaxies, to measure the spatial fluctuations in this emission, and use this as a tracer of large scale structure at very early times in the history of our Universe. This measurement would help determine the properties of molecular clouds -- the sites of star formation -- in the very galaxies that reionize the Universe. We further consider the possibility of cross-correlating CO intensity maps with future observations of the redshifted 21 cm line. The cross spectrum is less sensitive to foreground contamination than the auto power spectra, and can therefore help confirm the high redshift origin of each signal. Furthermore, the cross spectrum measurement would help extract key information about the EoR, especially regarding the size distribution of ionized regions. We discuss uncertainties in predicting the CO signal at high redshift, and discuss strategies for improving these predictions. Under favorable assumptions, and feasible specifications for a CO survey mapping the CO(2-1) and CO(1-0) lines, the power spectrum of CO emission fluctuations and its cross spectrum with future 21 cm measurements from the MWA are detectable at high significance.