Question

1. The cause of radio galaxies, Seyfert galaxies, and quasars is the same phenomenon. What is this phenomenon and why do these objects appear to have quite different properties?
2. If we assume that Active Galaxy Nucleus galaxies are caused by supermassive black holes consuming gas and dust, how many AGN galaxies should we expect to see as we look farther away compared to the number we see close to us and why?
3. If elliptical galaxies are formed by the merger of spiral galaxies, why do elliptical galaxies have such different properties than spirals?

Answer 1

These galaxies are linked by the presence of an active galactic nuclei. The common explanation of this activity is that a rotating supermassive black hole with an accretion disk emmiting radiation lies at the centre of the galaxy. The spinning can also produce jets of material pointing along the axis of rotation and according to this model the different properties are a result of the viewing angle. Radio galaxies and Seyferts correspond to views of active galaxies which are inclined. Quasars are billions of ly away and with a very large luminosity, which suggests that the black hole is surrounded by a lot of material.

AGN galaxies are more likely to be found further away, a majority of normal galaxies are expected to be found closer to us. This is beacuse when we look at distant galaxies we actually see how they were millions of years ago. The Quasars which are the more distant are also the younger galaxies. At the beggining a large amount of gas and dust was present in the vecinity of the black hole's accretion disk. As times goes by this material is consumed and the galaxy becomes less luminous, evolving into Radio or Seyfert galaxies and eventually to regular galaxies.

The collision of such massive and complex systems can give rise to radical change in properties in time. However according to recent studies it has been proven that in the early stages of merging the properties of the spiral mergers are indeed evolving towards the properties of elliptical galaxies.