Objects at the highest observable redshifts (greater than 4) are systematically studied by means of their emission-line properties, hence revealing information on the timescale of star formation and chemical enrichment in the young universe.
Direct comparisons of the emission properties of z > 4 sources with those at low and intermediate redshift provide valuable insights regarding accretion-powered activity in relation to star formation and galaxy evolution. In particular, a detailed study of the optical and UV properties of the NLS1s is performed, and a comparative analysis of their emission characteristics relative to those of the z > 4 QSOs is conducted in order to probe the proposed NLS1 -- high z QSO connection.
Observational biases that almost invariably accompany any AGN survey are investigated in-depth along with the role of the absorbing dust in modifying the shape of the quasar spectral energy density distribution.
Nearby galactic nuclei are studied through high quality Hubble Space Telescope archival spectra that expose spatial scales much smaller than those observed in the past surveys, allowing us to probe in detail the degree to which the underlying continuum sources are related or not to some form of activity substantially different from normal star formation.