Supermassive Black Hole Accretion Across the Age of the Universe

This work searches for common grounds for the diversity of properties exhibited by the emission-line nuclei of galaxies, from large look-back times to the local universe. The studies presented here include: (1) a program of high signal-to-noise spectroscopy for 44 high redshift (z>4) quasars using the MMT and Keck observatories; (2) a detailed analysis of the ultraviolet and optical spectral behavior of 22 Narrow Line Seyfert 1 (NLS1) galaxies based on archival Hubble Space Telescope (HST) spectra; (3) an in-depth investigation of the proposed link between NLS1s and z>4 quasars, by means of comparison of composite spectra, and a Principal Component Analysis; (4) a simulation of Seyferts/quasars designed to explore the role of dust in modifying their observed spectral energy distribution; and (5) a sensitive search for accretion signatures in a large sample of nearby emission-line galaxy nuclei, employing a quantitative comparison of the nebular line flux ratios in small (HST) and large (ground-based) apertures.