Intensity Mapping of Molecular Gas at High Redshift

The origin and evolution of structure in the Universe is one of the major challenges of observational astronomy. How and when did the first stars and galaxies form? How does baryonic structure trace the underlying dark matter? A multi-wavelength, multi-tool approach is necessary to provide the complete story or the evolution of structure in the Universe. Intensity mapping, which relies on the ability to detect many objects at once through their integrated emission rather than direct detection of individual objects, is a critical part of this mosaic. Intensity mapping provides a window on lower luminosity objects that cannot be detected individually but that collectively drive important processes. In particular, our understanding of the molecular gas component of massive galaxies is being revolutionized by ALMA and EVLA but the population of smaller, star-forming galaxies, which provide the bulk of star formation cannot be individually probed by these instruments.In this talk, I will summarize two intensity mapping experiments to detect molecular gas through the carbon monoxide (CO) rotational transition. We are currently completing sensitive observations with the Sunyaev-Zel'dovic Array (SZA) telescope at a wavelength of 1 cm that are sensitive to emission at redshifts 2.3 to 3.3. The SZA experiments sets strong limits on models for the CO emission and demonstrates the ability to reject foregrounds and telescope systematics in very deep integrations. I also describe the development of an intensity mapping capability for the Y.T. Lee Array, a 13-element interferometer located on Mauna Loa. In its first phase, this project focuses on detection of CO at redshifts 2.3 - 3.3 with detection via power spectrum and cross-correlation with other surveys. The project includes a major technical upgrade, a new digital correlator and IF electronics component to be deployed in 2015/2016. The Y.T. Lee Array observations will be more sensitive and extend to larger angular scales than the SZA observations.