1. Spiral Galaxies

2. Elliptical Galaxies

3. Irregular Galaxies

4. Classification of Galaxies

5. Properties of Galaxies SpiralsEllipticalsIrregulars Mass [typical; range] (solar masses) 10 11 ; 10 9 - 10 12 10 11.5 ; 10 6 - 10 13 10 10 ; 10 8 - 10 11 Size (pc)10 4 - 10 5.5 10 4 - 10 6 10 3 - 10 5 ColorBlue arms, reddish bulge reddishbluish Luminosity10 8 - 10 10 10 5 - 10 11 10 7 - 10 9 Stellar PopulationsPops I & IIPop IIPop I (Pop II) Interstellar mediumYesVery littleStill some RotationYes (disk)noNot a lot Fraction30%20%50% Other galaxy types : Peculiar, Interacting, Ring, Starburst, Dwarf, Luminous Infrared, Active Nuclei, Damped Lyman-alpha

6. Stephan’s Quintet – Colliding galaxies

7. The “Anntenae” Galaxies – a case study

8. Galactic Train Wrecks

9. Collisional Aftermath

10. Ring Galaxies – the “splash” Head-on collisions can produce a “ripple” of star formation that expands outwards.

11. Galactic Superwinds

12. The Magellanic Clouds Large Magellanic Cloud Small Magellanic Cloud Southern Hemisphere only

13. The Galactic Neighborhood

14. The “Local Group” of Galaxies

15. Members of the Local Group

16. And outward…

17. Galaxy Clusters Virgo Coma Notice the giant ellipticals at the centers of many clusters. These are an example of “galactic cannibalism”.

18. Galactic Cannibals – Central CD Ellipticals At the heart of rich clusters, galaxies pass through the center and are disrupted and collected.

19. Making a CD galaxy

20. into the Universe…

21. Large Scale Structure On the largest scales (100 million ly) the Universe takes on a “foamy” appearance, with great filaments and walls of galaxies and clusters, surrounding great “voids” that are relatively empty.

22. Dark Matter - rotation curves Rotation curves imply the mass-to-light ratios of galaxies go up as we look on larger scales: Sun  M/L=1, solar neighborhood  M/L=3, galaxy  M/L=50

23. Dark Matter – cluster speeds galaxy clusters  M/L=200-500 From average speed of galaxies – the cluster would fly apart From X-ray gas held in – several million degrees and extensive

24. What could the dark matter be? 1)Normal but dark matter (“baryonic”) : rocks, white or brown dwarfs? 2) Black holes or neutron stars? Too much metals would have been produced. Anyway, there is a fundamental reason from the Big Bang this can’t be it…

25. Dark Matter :gravitational lensing The mass required to produce the observed lensing is much higher than the luminous mass. This is a direct observation of gravity due to dark matter.

26. WIMPS and Cold Dark Matter Could dark matter be some kind of new particles which interact very weakly with matter (like neutrinos do) but massive, and not moving relativistically? Experiments at Berkeley and elsewhere are looking for them (guaranteed Nobel prize!).