Subgrid-scale modeling of turbulence regulated star formation in simulations of galaxy evolution

• Applicant: Professor Dr. Jens Niemeyer
• Subject Area: Astrophysics and Astronomy
• Term: from 2008 to 2013
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 48923236

• Final Report Year: 2013

Final Report Abstract

In numerical simulations of disk galaxies such as the Milky Way, the size of star-forming clouds is typically smaller than a single grid cell. For each grid cell, the density, the velocity, and the energy are computed by solving the Euler equations of gas dynamics. The numerical values of these variables represent mean values, averaged over the volume of a grid cell. The actual structure in each cell, however, is much more complicated. We approximate the multiphase structure of the interstellar medium (ISM) by a model in which small clouds of cold, dense gas are assumed to be embedded in a warm phase. The cold-gas clouds contain a certain fraction of molecular hydrogen, from which stars can form. The star formation rate depends on the density of the molecular hydrogen and the gas-depletion time scale. Both parameters are predicted by our model. The particular novelty of our model is the detailed treatment of the effects of turbulence on the subresultion processes that determine the star formation rate and efficiency. In the initial phase of the project (the subject of this report), the model was developed and successfully tested in stand-alone mode. It was later implemented into an adaptive mesh refinement (AMR) simulation code and coupled to a subgrid-scale model for unresolved turbulence, turning the model into a local description of the multiphase ISM that is self-consistently coupled to the resolved hydrodynamical variables. By means of AMR simulations with our subgrid-scale model for turbulence, star formation, and supernova feedback, we were able to reproduce basic properties of disk galaxies. In particular, our model demonstrates for the first time that the interplay between turbulence and feedback results in self-regulated star formation with an efficiency of around 1 % which agrees well with the observed values. In future work, we intend to apply the model in fully dynamical simulations of galaxy formation with cosmological initial conditions. Overall, the project proceeded as anticipated without any notable surprises or setbacks.

Publications

• 2012, MNRAS, 421, 1838
  Braun, H. & Schmidt, W.