Advancing Precision Cosmology with 21 cm Intensity Mapping

In this thesis we make progress toward establishing the observational method of 21 cm intensity mapping as a sensitive and efficient method for mapping the large-scale structure of the Universe. In Part I we undertake theoretical studies to better understand the potential of intensity mapping. This includes forecasting the ability of intensity mapping experiments to constrain alternative explanations to dark energy for the Universe's accelerated expansion. We also considered how 21 cm observations of the neutral gas in the early Universe (after recombination but before reionization) could be used to detect primordial gravity waves, thus providing a window into cosmological inflation. Finally we showed that scientifically interesting measurements could in principle be performed using intensity mapping in the near term, using existing telescopes in pilot surveys or prototypes for larger dedicated surveys. Part II describes observational efforts to perform some of the first measurements using 21 cm intensity mapping. We develop a general data analysis pipeline for analyzing intensity mapping data from single dish radio telescopes. We then apply the pipeline to observations using the Green Bank Telescope. By cross-correlating the intensity mapping survey with a traditional galaxy redshift survey we put a lower bound on the amplitude of the 21 cm signal. The auto-correlation provides an upper bound on the signal amplitude and we thus constrain the signal from both above and below. This pilot survey represents a pioneering effort in establishing 21 cm intensity mapping as a probe of the Universe.Ph