Theoretical astrophysics and plasma physics at RPC

Abstract:

Three-dimensional hydrodynamical simulations are used to investigate the structural stability of cooling flows that are episodically heated by jets from a central AGN. The radial profile of energy deposition is controlled by (a) the power of the jets, and (b) the pre-outburst density profile. A delay in the ignition of the jets causes more powerful jets to impact on a more centrally concentrated medium. The net effect is a sufficient increase in the central concentration of energy deposition to cause the post-outburst density profile to be less centrally concentrated than that of an identical cluster in which the outburst happened earlier and was weaker. These results suggest that the density profiles of cooling flows oscillate around an attracting profile, thus explaining why cooling flows are observed to have similar density profiles. The possibility is raised that powerful FR II systems are ones in which this feedback mechanism has broken down and a runaway growth of the source parameters has occurred.

Abstract:

We have investigated the dynamics of the merging process in the minor merger hypothesis for active galactic nuclei. We find that for a satellite galaxy to be able to merge directly with the nucleus of the host galaxy (for example, to give rise to the compact dust discs which are seen in early-type active galaxies), the initial orbit of the satellite is required to be well aimed. For the case of the host galaxy being a disc galaxy, if the initial orbits of the satellites are randomly oriented with respect to the host galaxy, then the orbits of those which reach the host nuclear regions in a reasonable time are also fairly randomly oriented once they reach the nucleus. We note that this result might be able to provide an explanation of why the jet directions in the nuclei of Seyfert galaxies are apparently unrelated to the plane of the galaxy discs.