Insights from probability distribution functions of intensity maps

In the next few years, intensity-mapping surveys that target lines such as CO, Lyα and C II stand to provide powerful probes of high-redshift astrophysics. However, these line emissions are highly non-Gaussian, and so the typical power-spectrum methods used to study these maps will leave out a significant amount of information. We propose a new statistic, the probability distribution of voxel intensities, which can access this extra information. Using a model of a CO intensity map at z ∼ 3 as an example, we demonstrate that this voxel intensity distribution (VID) provides substantial constraining power beyond what is obtainable from the power spectrum alone. We find that a future survey is similar to the planned CO Mapping Array Pathfinder (COMAP). Full experiment could constrain the CO luminosity function to the order of ∼10 per cent. We also explore the effects of contamination from continuum emission, interloper lines and gravitational lensing on our constraints and find that the VID statistic retains significant constraining power even in pessimistic scenarios.