HI and cosmological constraints from intensity mapping, optical and CMB surveys

We forecast constraints on neutral hydrogen (H I) and cosmological parameters using near-term intensity mapping surveys with instruments such as BINGO, MeerKAT and the Square Kilometre Array (SKA), and Stages III and IV optical galaxy surveys. If foregrounds and systematic effects can be controlled - a problem that becomes much easier in cross-correlation - these surveys will provide exquisite measurements of the HI density and bias, as well as measurements of the growth of structure, the angular diameter distance and the Hubble rate, over a wide range of redshift. We also investigate the possibility of detecting the late-time integrated Sachs-Wolfe effect using the Planck satellite and forthcoming intensity mapping surveys, finding that a large sky survey with Phase 1 of the SKA can achieve a near-optimal detection.