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Programme area: Galaxies and Quasars: Galaxy Formation and Evolution

Disk Formation and Effect of Feedback on Galaxy Formation

In the context of her PhD thesis, Franziska Köckert is studying the structure and kinematics of spiral galaxies in cosmological scenarios under the supervision of Matthias Steinmetz. As part of the theoretical side of the RAVE project she is working on formation scenarios for disk galaxies in general and the Milky Way as an example. For this she is running simulations using the N-body code GADGET-2 by Volker Springel.
The standard hierarchical model for galaxy formation has severe problems forming realistic disk galaxies. Generally the produced disks are too small and centrally concentrated compared with observations. This is known as the angular momentum catastrophe. Also, star formation tends to be too efficient early on in the simulations, resulting in a large, slowly rotating bulge of old stars. They are trying to adress these problems by conducting a systematical study of recently proposed solutions for these problems - increasing resolution, various different recipes for star formation and feedback as well as including other physical processes like winds. First results have shown that the loss of angular momentum is most likely not a problem of insufficient resolution. In our simulations, the main loss happens in the phase of violent mergers early on in the formation history of the galaxy. After about z=1, when all mass is assembled, the loss is minimal compared to the time between z=3 and z=1.
  Results of a cosmological simulation of disk galaxy formation using gas cooling only.
Left: face-on view and face-off of the gas particles in a snaphot of the simulation. Right: time evolution of the specific angular momentum of the different components of the simulated galaxy.
© F. Köckert. All rights reserved.
Currently they are working on including star formation in the simulations. First attempts with the multiphase model by Springel & Hernquist (2003) have been flawed by the problem described above. A better way of treating supernova feedback might be necessary. In the future they hope to tie in our results to the results of the RAVE survey.
  Results of cosmological simulations of disk galaxy formation including star formation.
Left: Time evolution of the star formation rave. Right: snaphot of the simulation. Black particles (top panels) represent the gas. Colored particles are stellar disk particles color coded by age (red: > 10 Gyr, orange: 8

Last change 2007 April 5 by Arnaud Siebert