Large scale radio cosmology with 21cm intensity mapping

Neutral hydrogen (HI) has been shown to be a tracer of the underlying matter field in our Universe. Thus by probing the large scale clustering structure of HI, we can indirectly probe the cosmic structure and from this, infer constraints on cosmological parameters. 21cm intensity mapping with radio telescopes is an efficient method for this purpose, although the success of this novel technique relies on overcoming a number of challenges which I will discuss. The ultra-large scales of our Universe host potential signatures for new physics, but conventional galaxy surveys struggle to probe these scales with statistical significance. 21cm intensity mapping should be better suited to this task since it can rapidly survey large cosmic volumes. However, to access the largest scales with the much anticipated Square Kilometre Array (SKA), the single-dish intensity mapping method will be relied on. I will therefore also discuss the work being undertaken with MeerKAT (an SKA pathfinder telescope) to successfully demonstrate single-dish intensity mapping, which represents an important milestone for using the SKA as a large-scale structure probe.