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Abstract
In this thesis work, I examine the ensemble properties of quasars at increasing redshift regimes toward early epochs in the universe, with the goal of understanding the distribution and evolution of these objects that populate distant space. Using observations and simulations of quasar spectra that model expected quasar photometry, I predict and examine the properties of quasars in the redshift ranges z ∼ 3, 5, and 6, as well as beyond the yet unobserved z > 7 frontier. Practical observations were carried out in the course of this work, and we have discovered new samples of objects in each of these ranges: 340 quasars have been found at z ∼ 3, ten quasars at z ∼ 5, and a sample of 71 L and T dwarfs observed in the course of our z ∼ 6 quasar search.
Throughout this work, I describe and employ the quasar spectral cloning technique---a numerical tool used to provide statistical information that improves estimates of observed quasar numbers. The cloning of quasar spectra and the generation of semi-synthetic photometric colors can guide the planning of candidate selection before observation, increasing the completeness of observed samples. Cloned quasar colors can also be used to measure the effectiveness of existing selection techniques. Finally, quasar cloning provides predictions about colors and selection methods for those objects not yet observed in the distant universe.
At z ∼ 3, I describe the planning and execution of a dedicated survey for quasars at this peak epoch of activity in the early universe. We use the Sloan Digital Sky Survey to find quasars hidden from optical surveys due to stellar contamination, and with the Two-Degree Field spectrograph, retrive a sample of 340 newly discovered quasars in this redshift regime. Analysis of the resulting quasar optical luminosity function is carried out, and compared with existing and ongoing quasar investigations. We find that our discovered sample yields a peak in quasar activity both stronger and higher in redshift than recent work using broadly targeted and shallower samples. This may suggest that the pace of quasar evolution is more rapid in time (and redshift) than previously modeled.
At z ∼ 5, I have used quasar cloning to refine SDSS riz target selection techniques, and we have carried out a dedicated search for these quasars which were once at the frontier of observability. We have discovered 10 new faint quasars at redshifts z > 4.7, and I use this result to estimate the completeness and future discovery potential of the Sloan Digital Sky Survey quasar observing program. (Abstract shortened by UMI.)
