The inner structure of Active Galactic Nuclei from spectroscopy of large samples of quasars

Active Galaxies are peculiar galaxies, characterized by non-stellar emission from the central regions of their nuclei (Active Galactic Nuclei, AGN), with luminosities from 10^40 to 10^48 erg s^-1. The energy source for this radiation is the accretion onto a SuperMassive Black Hole (10^6-10^10 Msun ). The discovery that Supermassive Black Holes are present in quiescent galaxies as well as in active ones, along with the finding that AGN activity peaks at z~2-3, suggests that this phase is common to all galaxies and likely influences their evolution. The study of AGN is therefore crucial to understand how galaxies formed and evolved in the Universe. The small size and the distance of these sources imply that the emitting regions are spa- tially unresolved, making the spectroscopic analysis the only tool available for their study. AGN are characterised by strong emission features, coming from specific regions: the Broad Line Region and the Narrow Line Region. These lines show profiles far broader than the normal galactic emissions and are hence necessarily emitted by gas under the influence of a very strong gravitational field. Their presence in AGN spectra is therefore a confirmation that the central engine of AGN consists of a SMBH; furthermore, it enables us to give an estimation of the mass of the central body and, through the analysis of their shape, makes us able to study the geometry and the kinematics of the emitting regions. This thesis fits in this context. We are interested in the study of emissions coming from the structures depicted in the AGN Unified Model and, particularly, in the emission lines coming from the BLR, the closest to the SMBH and therefore the one providing information on its mass.