Observational constraints on the assembly of galaxies and galaxy clusters

This dissertation uses observations of galaxies and galaxy clusters as probes of the assembly of structure in the Universe. Galaxy mergers are key drivers of structure assembly, and we develop a new observational technique for identifying galaxy mergers. Our method identifies galaxy merger remnants by the spectral signatures of their inspiralling black holes, and we identify 32 such objects in the DEEP2 Galaxy Redshift Survey. Based on this sample, we find that mergers may trigger active galactic nucleus (AGN) activity in red galaxies and estimate a merger rate of ∼ 3 mergers Gyr -1 for red galaxies at redshifts 0.3 < z < 0.8. We also survey the additional insights into galaxy assembly possible with an extended sample of such objects and with measurements of the spatial offsets of the AGN within their host galaxies.;In addition, we use observations of galaxy clusters to test predictions from the standard Λ cold dark matter (ΛCDM) model of structure formation. Using gravitational arcs as tracers of cluster mass distributions, we find that the mass profiles of observed lensing clusters are compatible with the profiles implied by ΛCDM simulations of structure formation. Similarly, we find that observed cluster concentrations, which are measures of the clusters' central densities, and masses follow the correlation expected from simulations. However, observed lensing clusters exhibit systematically higher concentrations, which we argue are the result of projection effects and cluster substructure.;Our cluster analysis also reveals that lensing clusters have unique formation histories. We find a correlation between the brightest cluster galaxy luminosities and cluster masses that implies lensing clusters were assembled via more mergers with other clusters, or mergers with more massive clusters, than the general cluster population. Finally, we explore means of reducing the scatter on cluster property correlations that provide constraints on cosmological parameters. Minimizing this scatter enables more precise measurements of cosmological parameters. We argue that exploiting both gravitational lensing for improved cluster mass estimates and the interdependencies of cluster concentration, mass, and X-ray temperature can tighten the correlations used to derive cosmological parameters.