1. 16 Galaxies Island Universes

2. 16 Copyright – FORS1 VLTI, European Southern Observatory

3. 16 Hubble Tuning Fork

4. 16 Ellipticals

5. 16 Huge No gas. No dust. No young stars. Nothing but old stars. –Random orbits.

6. 16 M 87 Copyright – Anglo-Australian Telescope Board Copyright - HST

7. 16 Hubble Tuning Fork

8. 16 Copyright – Adam Block, KPNO

9. 16 Spirals

10. 16 Like Milky Way. Disks and bulge. Young stars and old. Gas and dust. Stars forming. Stars dying. M81 and M82 – Copyright R. Gendler

11. 16 M63 Copyright – S. Miyazaki, Suburu

12. 16 NGC1365 Copyright – VLT

13. 16 M31 The Andromeda Galaxy Copyright – Jason Ware Copyright – S. Miyazaki, Suburu

14. 16 M33 – Copyright NOAO

15. 16 M51 - Copyright HST John P. Gleason

16. 16 NGC 4314

17. 16 NGC 891 – Copyright J.C. Barentine, NOAO NGC 891 – Copyright WIYN

18. 16 Sombrero Galaxy – Copyright P. Barthel VLT M10 – copyright Credner and Kohle

19. 16 NGC 4526

20. 16 Irregulars

21. 16 Distance to Near Galaxies Need a standard candle. If there is something in a galaxy which has a known luminosity we can determine a distance. Several candidates: –Variable stars –Supernovae –“Brightest” stars

22. 16 M3 Variables in Clusters Copyright – K. Stanek (Harvard)

23. 16 Variable Stars For RR Lyrae stars: –Average luminosity is a standard candle –Always ~ 100 x Sun For Cepheid variables: –Pulsation period is proportional to average luminosity –Observe the period  find the luminosity Good to 15 Mpc!

24. 16 Nearby Galaxies Cepheids Period Luminosity  M v Know m v Get Distance

25. 16 For Cepheid in M100 P = 20 days. From P-L: L = 10000 x Sun M sun = 5, so M Cep = -5 m = 20 m – M = 25 So 25/5 = 5 = log(d/10pc) How log works: –What is 100 = 10 x ? –Same as saying 2 = log(100) So 5 = log(d/10pc) d/10pc = 100000 D = 1,000,000 pc How it works

26. 16 The Local Group

27. 16 Groups

28. 16 The Virgo Cluster

29. 16 Clusters

30. 16 Concept Test A standard candle can be any object (or class of object) that: a.Always has the same luminosity. b.Has some means of knowing its luminosity without first needing to know its distance. c.Can vary in brightness (as long as it always has the same average luminosity). d.Has a known absolute magnitude. e.Always gives off the same amount of energy, regardless of distance from us.

31. 16

32. 16 NGC 1316 – Copyright VLT

33. 16

34. 16 Distant Galaxies Can’t see individual stars. Supernovae rare. Can use nearby galaxies to get distances to further galaxies. Distance ladder: –Parallax  nearby stars –Nearby stars  H-R diagram –H-R diagram  distant stars (variables) –Variable stars  nearby galaxies –Nearby galaxies  Hubble’s Law

35. 16 21cm Radiation Neutral hydrogen (HI) gives off light, = 21cm. Milky Way HI emission – Copyright J. Dickey

36. 16 Extragalactic HI Observe HI in other galaxies. Measure wavelength of 21 cm radiation. Doppler Shift: Get velocity away from us.

37. 16 Hubble’s Law Measure the velocity of every galaxy. Nearly all are redshifted. Use Cepheids to measure distances to nearby galaxies. Result: The faster it’s moving, the farther away it is. H o = 71 km/s/Mpc

38. 16 Map the Universe v = H o D If you know H o : 71 km/s/Mpc Measure v Get D Find: Voids Walls Clusters

39. 16 140 Mpc 70 Mpc

40. 16 Concept Test Imagine that Cepheid variables were more luminous than previously thought. As a result, Hubble’s constant would be: a.Smaller than previously thought. b.Larger than previously thought. c.Unchanged since we aren’t changing either the velocity or position of the galaxy. d.None of the above.

41. 16 Limits to Hubble’s Law Negative velocity? Galaxy pairs? Clusters? Orbits?

42. 16 Homework #16 For Friday Read: Bennett Ch 22.1 – 22.4 Do Ch22: –Problems: 9, 12