Jet-Feedback in Galaxy Formation
Despite enormous successes in understanding the formation of galaxies, cosmological simulations still suffer from incomplete modelling of massive galaxies: Since observations indicate that these galaxies formed their stars early and during a short time period, some mechanism is needed to suppress cooling flows and star formation at later times and avoid the formation of too massive and blue present-day galaxies. Feedback from active galactic nuclei (AGN) is a very promising candidate for this due to the large powers involved. It is generally divided into a "quasar mode" with  high black hole accretion rates, a radiatively efficient accretion disk and quasar winds in the central part of the galaxy and a "radio mode" with jets (bipolar, relativistic and collimated plasma outflows) originating from the AGN with large kinetic power and reaching to large distances - even far out of the galaxy.
 
Simulated X-ray emission from the ambient gas
  1.  Negative Feedback
We have carried out simulations of jets on large scales and simulated the interaction with the ambient cluster gas. Jets efficiently thermalize a large fraction of their kinetic energy and heat up the surrounding gas. The jet inflates a cocoon of hot and very diffuse radio-emitting plasma, which also forms cavities visible at X-ray energies. We now try to understand what amounts of energy is transferred to the different components of a multi-phase interstellar medium on the galaxy scale and whether only the hot gas component received the heating or the cold phase of a galactic gas disk also can be heated up or destroyed. Simulated X-ray emission from the ambient gas
  1.  Positive Feedback
It has been conjectured that interaction of jets with cold gas clouds could compress these clouds, make them gravitationally unstable and thus possibly induce star formation. Observations of high-redshift galaxies indicate that this may indeed occur. By having a clumpy cold gas phase included in our simulations, we explore the relative importance of this mechanism to the opposing negative feedback.
Interaction of a powerful jet with a galactic gas disk
  1.  Extended emission line regions in distant radio galaxies
Observations of ionized gas in high-redshift radio galaxies shows that enormous amounts of gas are spread out in direction of the jet axis and accelerated to large systematic (several hundreds of km/s) and turbulent velocities (1000 km/s and more). Our simulations of the interaction between jet and a gaseous disk may help understanding these outflows and the amount of energy transferred to them from the jet.
 
 
Model for emission line nebulae in high-redshift radio galaxies