Upcoming intensity mapping surveys will provide a powerful probe of astrophysics and cosmology in the distant universe. However, in order to realize the potential of this new technique, we must improve our understanding of the link between intensity maps and physics on all scales. In this thesis, we develop a number of tools for analyzing intensity maps. For most of this work, we illustrate our methods using the example of a CO intensity map at redshift z~3, though our results are applicable to many other lines.
We first present the formalism for computing intensity mapping power spectra, and use it to study the detectability of the CO signal. We find that, though the signal amplitude is highly uncertain, a well-designed experiment can detect CO under most assumptions. We then describe a method of simulating intensity maps, and use it to study the problem of foreground line contamination. By masking out the brightest regions of a map, we find that the cosmological information contained in surveys targeting Lyman alpha and CO can be recovered, though astrophysical information is lost. Unfortunately, due to instrumental constraints and high-intensity foreground contamination, this method is less effective for CII surveys. We also demonstrate that the astrophysical information content of foreground lines can be recovered through cross-correlations. By correlating pairs of CO frequency bands, we show that the 13CO isotopologue line can allow unprecedented constraints on molecular gas properties within distant galaxies.
Line emission in intensity maps is highly non-Gaussian, so power spectra alone cannot fully constrain the properties of target populations. To resolve this, we introduce the Voxel Intensity Distribution (VID), which gives the one-point probability distribution of voxel intensities. We demonstrate that the VID provides substantial constraining power beyond what is obtainable from the power spectrum, even in the presence of foreground contamination. We then apply the VID to a hypothetical measurement of the cosmic star formation rate density from a CO survey. We show that, despite model uncertainties, such an observation could place competitive constraints on this crucial quantity while eliminating systematics which hamper existing measurements
