Unified model of AGN

Comment on the unified model of AGN

Originally the unified model of AGN says that intrinsically all AGN have the same structure: a torus, an accretion disk, jets, etc. The different observed AGN types can then be explained only by the different viewing angles.
Recently I was on two conferences in which the participants came to very different conclusions: in one the unified model was declared as dead while in the next conference it was declared as alive!
On first sight people seem to have very different views. However, I think that both views are actually based on the same idea:
Of course AGN do not all look the same! However, they can all be described with the same components given by the unified model, if we accept the following:

  • the different components can be more or less dominant or even not present at all! For example, I don’t think that a torus is always necessary to explain an AGN.
  • AGN evolve over time. For example during/after a merger they go through different phases.
  • There can also be other external factors which shape the spectra of AGN like dust lanes near the AGN.

In addition to the viewing angle, these factors can explain the different observed AGN types.
So whether you declare the unified model as dead or alive is just a matter of definition.