Intensity Mapping without Cosmic Variance

TL;DR

This paper proposes a method to improve intensity mapping surveys by cross-correlating with galaxy redshift surveys, enabling sensitivity beyond cosmic variance limits and aiding in the study of galaxy evolution and large-scale structure.

Contribution

It introduces a Fisher matrix-based framework for optimizing cross-correlation surveys to evade cosmic variance, guiding future survey design.

Findings

Optimal sensitivity achieved by matching survey depths.

Cross-correlation can surpass cosmic variance limits.

Applicable to infrared space telescopes and galaxy surveys.

Abstract

Current and future generations of intensity mapping surveys promise dramatic improvements in our understanding of galaxy evolution and large-scale structure. An intensity map provides a census of the cumulative emission from all galaxies in a given region and redshift, including faint objects that are undetectable individually. Furthermore, cross-correlations between line intensity maps and galaxy redshift surveys are sensitive to the line intensity and clustering bias without the limitation of cosmic variance. Using the Fisher information matrix, we derive simple expressions describing sensitivities to the intensity and bias obtainable for cross-correlation surveys, focusing on cosmic variance evasion. Based on these expressions, we conclude that the optimal sensitivity is obtained by matching the survey depth, defined by the ratio of the clustering power spectrum to noise in a given mode, between the two surveys. We find that mid- to far-infrared space telescopes could benefit from this technique by cross-correlating with coming galaxy redshift surveys such as those planned for the Nancy Grace Roman Space Telescope, allowing for sensitivities beyond the cosmic variance limit. Our techniques can therefore be applied to survey design and requirements development to maximize the sensitivities of future intensity mapping experiments to tracers of galaxy evolution and large-scale structure cosmology.