1. Class 22 : Galaxy collisions & galaxy formation Collisions of galaxies. Formation of galaxies.

3. I : Collisions of galaxies Galaxy collisions are comparatively common (and spectacular!). Major collision… Collision of 2 big galaxies. Quite rare. Minor collision… Collision of a large galaxy with a small “dwarf” galaxy. Very common!

4. Movies of galaxy merger simulations… Chris Mihos & Sean Maxwell What happens when two galaxies pass close to one another?

5. Flyby… Chris Mihos & Sean Maxwell Notice the “tidal tails” that are thrown off and the disorganized “lump” at the center.

6. The Antennae Galaxy

7. The Cartwheel Galaxy

8. Cartwheel Simulation Chris Mihos & Sean Maxwell

9. Fate of the Milky Way?

10. Centaurus A shells CTIO Cen A is a peculiar galaxy with strong radio emission. Star shells are a common sign of recent mergers.

11. Minor (satellite) merger Chris Mihos & Sean Maxwell Most mergers are like this one: big guy eats little guy. Dumps a lot of gas and dust into big galaxy. Small galaxy completely disrupted.

12. Galaxy Harassment N-body shop, U Washington Multiple small interactions over time in clusters can tear galaxies apart.

13. Internal evolution Galaxy collision can drive “internal evolution” of galaxies… Rapid star formation Galactic collisions make gas clouds collapse and turn into stars. Makes galaxy look blue (since there can be many young, hot stars). Quasar activity Galactic collision drives gas into center of galaxy. Gas can rain onto central massive black hole and produce tremendous amounts of energy… More about this possibility soon…

14. II : Galaxy formation How did galaxies form? In the beginning… The BIG BANG! Universe started off very hot, and very uniform (matter smoothly filled all space). BUT, there were very small fluctuations in the uniform distribution of matter… Gravity caused fluctuations to grow. What happened next? Nowadays, can study this process using computer simulations…

15. Simulation from the “Virgo Consortium”… (CDM)

16. Zoom in on a forming galaxy cluster (Virgo Consortium) This movie zooms in on one patch of a larger simulation where we know that a galaxy cluster is about to form.

17. “Bottom-up” formation scenario… All driven by gravitational collapse. Some small things form first. Collisions/mergers cause bigger things to grow… Dwarf galaxies  galaxies  galaxy clusters  superclusters and so on.

19. Las Campanas Redshift survey

21. Sloan Digital Sky Survey