Principal Investigator Geoffrey V Bicknell Project q62

Mount Stromlo and Siding Spring Observatory Machine VP

Co-investigator Anton M. Koekemoer

Mount Stromlo and Siding Spring Observatory

Velocity Fields and Shock Waves in Gas from Merging Galaxies

The idea behind these simulations was to understand the fate of gas in merging galaxies and to see whether the velocity field obtained in simulations is similar to that observed in real galaxies. We were also particularly interested in whether the gas forms shocks since these can be a mechanism for the formation of emission line nebulosity in radio galaxies. For the comparison between theory and observation we had previously obtained excellent spectra from the Anglo Australian Telescope which had been used to provide three dimensional (two spatial dimensions plus one line of sight velocity dimension) data cubes.

What are the basic questions addressed?

What happens to the gas when a small gas rich galaxy merges with a large elliptical galaxy? Are shocks produced in the infalling gas and what is its velocity field?

What are the results to date and the future of the work?

We have shown that shocks are formed when the infalling stream orbits the nucleus, intersecting itself. This gas then "virializes" in the nucleus, forming a ball of shocked gas which has a velocity dispersion approximately equal to the velocity dispersion of the large galaxy. The resulting configuration from this simulation is very similar to the gas observed in the radio elliptical galaxy PKS 2356-61.

We are planning to repeat some of these calculations at higher resolution and with cooling of the shocked plasma taken into account.

What computational techniques are used and why is a supercomputer required?

We are using a vectorized version of a Smoothed Particle Hydrodynamics code which has been optimized for the VP2200. A supercomputer is required for both cpu speed and memory.

Publications:

The Fate of gas in Merging Galaxies, A M Koekemoer and G V Bicknell, in preparation