1. Galaxies Types Dark Matter Active Galaxies Galaxy Clusters & Gravitational Lensing

2. What is a galaxy? A vast, self-organized collection of: –Stars –Planets –Interstellar dust, gases & ices –Dark Matter

3. Types of Galaxies Spiral Elliptical Irregular (maybe a combination of the two)

4. Spiral Galaxies

9. Barred-Spiral Galaxies

10. Elliptical Galaxies

11. Irregular Galaxies

13. Why do we have different types of galaxies? –mostly due to collisions/captures

17. Summary: The Hubble Fork A classification scheme, not an evolution scheme.

18. Dark Matter Stated that galaxies are embedded in this giant cloud of dark matter –How do we know? Rotation of the galaxies.

19. How to measure galactic rotation speeds –Doppler Shift (again)! –Use any convenient spectral line Hα line in visible spectrum (hot Hydrogen: tracks rotation of stars) 21 cm Hydrogen line in radio spectrum (cold Hydrogen: tracks rotation of IS clouds)

20. If a galaxy’s mass were all stars & gas, would expect curve B (Kepler’s 3 rd Law) But, when we measure the rotation of almost every galaxy, we observe profiles like curve A

22. Conclusion: the galaxy has some “unseen” mass that we cannot directly observe –Planets & planet-like bodies –Brown dwarfs –Cool white dwarfs and/or neutron stars –Black holes –Neutrinos or some other exotic matter No evidence for dark matter on solar system scales (planets’ orbital speeds are Keplerian)

23. Active Galaxies Radio Galaxies Seyfert Galaxies Quasars Starburst Galaxies

24. Radio Galaxies –Generally elliptical galaxies –Have “radio lobes” up to millions of ly long High-speed electron gas flowing from poles Similar to pulsars Synchrotron radiation: intense galactic magnetic fields

25. Radio Galaxies emit millions of times more radio energy than a “normal” spiral or elliptical galaxy, like M81

27. Seyfert Galaxies –Generally spiral galaxies –Incredibly bright nucleus The central 1 ly 3 are typically brighter than other (entire) galaxies –Broadband: radiates at many frequencies across the EM spectrum

28. Interacting Seyfert galaxies

29. Quasars –“Quasi-stellar radio source” –Some of the farthest objects ever seen –Very bright –High redshifts = large distance (Hubble’s Law) –Ultra-fast relativistic jets

30. 1973: Quasar 3C279 appears to have a jet that is moving at least 9 times faster than the speed of light! This is an “optical illusion” of motion at near light-speed –Subsequent studies have shown the beam expanding at 99.9% light-speed

31. What causes the activity? –Supermassive black holes! –Feeding on galactic-center material Recall accretion and frictional heating Recall role of magnetic field

32. Recall an atom’s speed in a gas dependson temperature. At the high temperatures in the inner parts of the accretion disk, some gases can be “boiled away” and escape the pull of gravity. If there is a magnetic field present (which there is if the BH formed from stellar collapse), it can guide the boiled-off gases into the polar jets we observe.

34. Galaxy Clusters

35. Andromeda Small Magellanic CloudLarge Magellanic Cloud

36. Clusters of galaxy clusters

38. The Einstein Cross: 4 images of the same quasar

41. The first-ever determination of the distribution of dark matter made from lensing studies

43. The Expansion of the Universe Hubble’s Law –The more distant a galaxy is, the faster it is moving away from us

44. Hubble’s Law: V = H 0 D, where modern estimates give H 0 ~ 70 km/sec/Mpc 1/H 0 = ?

45. NEXT TIME Cosmology –The study of the large scale properties of the Universe –Origin & fate of the Universe