The Atacama Cosmology Telescope: The universe at 148 & 218 gigahertz

The Atacama Cosmology Telescope (ACT), located in the Atacama, Desert of Chile at an elevation of 5,190 m, represents a decade of work by a collaboration spanning multiple continents. ACT was designed to observe with arcminute angular resolution and a degree-sized field of view, resulting in an observed temperature anisotropy power spectrum that spans angular harmonic multipole 500 \u3c l \u3c 10,000 on the sky. This range spans the linear perturbation regime of the primary Cosmic Microwave Background (CMB) anisotropies into the secondary anisotropies created by nonlinear physical processes at later times. Low multipole coverage allows for cross-calibration with all-sky experiments such as the Wilkinson Microwave Anisotropy Probe (WMAP) and Planck, and high multipoles probe structures such as clusters of galaxies through the thermal Sunyaev-Zel\u27dovich effect (tSZE), and extragalactic point source populations. Millimeter wavelength-selected point, sources, most of which are high-redshift, galaxies, have only recently been systematically studied. The fidelity of CMB maps and galaxy cluster catalogs depend on understanding the galaxy populations, globally as well as on a local astrophysical level where they impact the ability to generate reliable mass-observable relations for galaxy clusters, which are important for cluster-derived cosmology. The multifrequency nature of ACT data permits the characterization of multiple galaxy populations through their spectral energy distributions (SEDs) in a relatively unexplored frequency regime. Analysis of ACT-selected galaxies informs the current understanding of the evolution of structure formation over cosmic time. This thesis begins by motivating the ACT science. A description of the ACT telescope and camera, with focus on the bandpass determination for the three optics tubes of the camera is followed by a synopsis of the observations to date. The map-making strategies used to produce the data analyzed for this thesis are reviewed, to provide background for the source analysis derived from ACT maps. ACT-detected source populations are analyzed in detail, including data taken during follow-up observations on the Australian Telescope Compact Array (ATCA) at 20GHz