| This dissertation reports various results from the first large-scale observational survey of galaxy groups and clusters as they existed between ten and seven billion years ago, when the Universe was roughly half its present age. By observing such systems and comparing them to similar objects at more recent times, we can learn a great deal about the history and composition of the cosmos. To this end, we make use of data from the DEEP2 (Deep Extragalactic Evolutionary Probe 2) Galaxy Redshift Survey. This large, spectroscopic survey was performed using the DEIMOS spectrograph on the Keck II telescope and has mapped the spatial distribution of some 40, 000 galaxies over three square degrees of the sky, focusing primarily on the redshift range 0.7 ≤ z ≤ 1.4.;We present four distinct studies relating to DEEP2 groups and clusters. First, we refine an automated group-finding algorithm, calibrate it for use with DEEP2 data, and construct a catalog of DEEP2 groups and clusters. We then analyze the color distribution of the galaxies in those systems, compared to the distribution for isolated galaxies, and we find substantial evolution in the former distribution, with important implications for the history of galaxy formation. Next, we present detailed observations of a single, interesting galaxy in DEEP2---the remnant of a collision between two red galaxies, formerly a group---which appears to host two active nuclei. Finally, we develop a theoretical framework within which it will soon be possible, using the abundance of DEEP2 groups and clusters, to place interesting constraints on cosmological parameters, including the equation of state of the dark energy. |
