Exploring Galaxy Morphology with GalCrash

Getting Started

To get to the GalCrash page, start at the Dynamical Astronomy JavaLab, (Note you will probably want to open another browser window for the JavaLab, so you can see the Simulation and these instructions at the same time). From the main JavaLab page, select "applets" from the buttons along the side, and then select "GalCrash". Important Note: before running the applet, it is a good idea to read the "Background" page, that describes what the applet does, and the "Controls" page, so you have some idea of how you will control the simulation.

When you have read up on what the applet does, select the "Applet" button and try running the thing for yourself. First try running the applet with its default settings, just to get an idea of what the simulation does.

1. Click Reset to set the simulation to its beginning value, then click start to begin it running.
2. After the simulation has run for about 20 seconds or so, click the stop button to pause the simulation. Put the cursor in area of the screen and hold down the right mouse button. Notice that when you do this, you can move the mouse around and change the orientation you view the simulation with.
3. Let the simulation run further; does it look like the two galaxies in this simulation will merge into a single galaxy? What parameter (or parameters!) in the collision do you think control whether that happens or not?
4. Now try rerunning the simulation several times, each time changing the different parameters that GalCrash lets you control. The idea here is to just get a rough idea how things change with different settings before you try to model some actual galaxies.

Exercise 1: The Antenna Galaxies

1. Look at figure 23-16 in your textbook, which shows a picture of a famous pair of interacting galaxies people sometimes call the Antenna. Try and find a set of starting conditions that will cause GalCrash to create a model galaxy that looks something like the Antenna. (Hint: try your initial runs with 250 particles per galaxy. Then, when you have a rough idea of the correct starting parameters, rerun the simulation with 2000 particles. The simulation will run slower with more particles, but will give you a better looking result for comparison.)

Exercise 2: The Cartwheel Ring Galaxy

1. Now try a simulation of the Cartwheel galaxy, which is shown in figure 23-17 of the textbook. How do the starting parameters that create the cartwheel compare to those that created the Antenna?
2. A larger version of the Cartwheel Galaxy image is available from the Space Science Telescope Institute, that shows the Cartwheel along with two neighboring galaxies, each of which could possibly be the galaxy the cartwheel collided with. Can you tell unambiguously from your simulation which of the two it actually was?

Exercise 3: Forming an elliptical galaxy

1. In section 23.2, the textbook discusses two possible ways to form an elliptical galaxy, the second of which is colliding two spiral galaxies together. Try and run a simulation to create something that looks like an elliptical galaxy.
2. Given the two different scenarios for how elliptical galaxies form, can you think of a way to tell the difference between ellipticals formed by the two different mechanisms? (Hint: This is not an easy question to answer!!)

Exercise 4: More Mergers, and a Merger Sequence

The following questions use the Galaxy Pair/Interacting Galaxies Picture Gallery, at the University of Alabama. The page is maintained by Bill Keel, one of the leading researchers on the topic of galaxy interactions.

1. Look at the images of different pairs of galaxies. Do all of the galaxies shown show obvious signs of interaction? If not, can you think of any reason (or reasons) that 2 galaxies that appear to be near one another may not seem to be interacting?
2. Pick a few of the galaxies that seem to be interacting. Can you reproduce the appearance of these galaxies using GalCrash?
3. Notice that the first picture in the gallery is a sequence of images of actual galaxies that Dr. Keel suggests can be thought of as representing different steps in the evolution of a galaxy merger. Can you produce that sequence (at least approximately) with a single GalCrash simulation?

Send Page maintainer email: andersen@shasta.phys.uh.edu