Quick Look

Capability Development for Modeling the Structure and Dynamics of
Barred Spiral Galaxies, 15-R9577

Principal Investigator
David E. Kaufmann

Inclusive Dates:  09/12/05 – 01/12/06

Background - The study of the structure and dynamics of spiral galaxies is fundamental to the scientific goals of the National Science Foundation (NSF) and NASA. For example, life is believed most likely to arise within planetary systems that form more or less concurrently with their host stars. Star formation, at least in the current epoch, is taking place predominantly in the disks of spiral galaxies. More specifically, it is occurring in the spiral arms of these galaxies. Spiral structure, in turn, depends on the structure and dynamics of the galaxies themselves. We focus on barred spiral galaxies because it is now recognized that the majority of spiral galaxies possess bar-like features to some degree, and these bars can significantly affect the dynamical evolution of these systems. Figure 1 shows a suspected barred galaxy seen edge-on, with a pronounced peanut-shaped central bulge. One of the more fruitful approaches to studying galaxy dynamics in recent years has been with computer simulations using N-body models. The most efficient N-body technique for simulating galaxies that retain a fairly consistent geometry throughout their evolution is the so-called particle-mesh, or PM, method. The overall goal of this project was to extend our capability to model barred spiral galaxies via the PM method.

Approach - The specific objective of this quick-look project was to modify and extend our existing two-dimensional (2D) PM galaxy simulation code so that it could be used to model the full three-dimensional (3D) structure and dynamics of barred spiral galaxies (e.g., see Figure 1), including both stellar and gaseous components. In our effort to extend our 2D polar grid code to a full 3D cylindrical polar grid (see Figure 2), we were guided by an important paper of Pfenniger & Friedli (ref. Pfenniger, D. & Friedli, D. 1993. Astronomy & Astrophysics, 270, 561.). To compute the dynamical evolution of stars and gas in the "halo" of the galaxy, in which matter is distributed more or less spherically about the center of the galaxy (and hence beyond the limits of the cylindrical grid), we supplemented the cylindrical polar grid with a spherical grid of much greater radial extent. With this hybrid grid code, we can compute the dynamical evolution of stars and gas both within the disk of the galaxy as well as in the galactic halo. We include the effects of gas by means of a "sticky particle" scheme.

Accomplishments - We have completed the code enhancements described above and have performed a small number of test simulations with it. Although the parameter space covered by the test runs made to date is somewhat limited, we are continuing the testing process. All testing completed so far has been successful. We believe that the resultant code is unique in the field. We are not aware of any other code that combines the described state-of-the-art 3D gravity modeling with the ability to model the gaseous component using the sticky particle technique. We are seeking funding from the NSF and NASA for projects whose work is substantially based on the use of the new code.

Side view of the 3D cylindrical polar grid. Only the middle and extreme mesh lines in the vertical dimension are shown (figure taken from Pfenniger & Friedli 1993).

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