Abstract:
In this thesis the standard paradigm for the explanation of activity in galaxies is tested and extended. It is proposed that most galaxies harbor a massive black hole in their nuclei with a closely coupled accretion disk/jet system. The level of activity is mainly determined by the overall accretion flow. A model is developed to describe the broad-band (radio to X-ray) emission of a coupled jet/disk system and it is shown that a sample of radio loud and radio quiet quasars as well as the Galactic Center source Sgr A* can be explained by such a model the latter resembling an ``AGN on a starvation diet''. The parameters for jets in luminous AGN are consistent with previously found values and there is evidence for the presence of relativistic jets also in radio weak quasars. An important mechanism for injecting synchrotron emitting particles in radio loud jets could be secondary pair production in hadronic cascades following pp-collisions leading to an electron distribution with low-energy cut-off. Finally, it is proposed that the difference between radio loud and radio weak quasars, the rarity of FR I type quasars and the difference between FR I and FR II radio galaxies is simply due to a different environment on the pc-scale (`obscuring torus') the jet/disk system is interacting with. It is postulated that the opening angle of obscuring tori in AGN depend on the power of the central engine and the host galaxy type where the tori in elliptical galaxies narrow to the jet beaming angle at L_disk<10^46 erg/sec.
Other publications can be found here.
Questions: Heino Falcke, hfalcke@astro.umd.edu