The big blue bump-accretion disk connection in type1 active galactic nuclei: a new way to estimate the mass of super-massive black hole

Active Galactic Nuclei (AGN) are among the most powerful sources of energy in the Universe. The “central engine” is likely a super massive (M >~ 10^6 M_sun) black hole accreting matter from the nuclei of host galaxies. In order to study the AGN demography, formation, evolution, accretion physics and galaxy feedback processes we need a reliable method to estimate the black hole mass. The most reliable ones (direct methods) can be applied only to a few tens of nearby AGNs, strongly limiting the possibility to perform statistical studies on large samples and high redshift sources. The issue of black hole mass estimation on large samples of Type 1 AGN is addressed using an indirect (hence less reliable) procedure: the Single Epoch Virial (SEV) method. In this thesis I discuss the assumptions, biases and possible systematic errors affecting the SEV estimates, and propose a completely independent method to estimate the Type 1 AGN black hole mass. The method is based on the assumption that accretion occur through a standard Shakura & Sunyaev (1973) accretion disk. The calibration is performed by studying the statistical relationships between the broad–band spectral features of Type 1 AGN and the optical emission line luminosities. I apply the method to a sample of 23 radio–loud narrow–line Seyfert 1 galaxies, for which the SEV masses were suspected to be strongly biased. The resulting black hole mass estimates are significantly greater than SEV ones. I discuss the reliability of these estimates, and the consequence on the physical interpretation of the class of narrow–line Seyfert 1 galaxies in the framework of the AGN unified model.