1. Spiral Galaxies Ron Buta University of Alabama

2. What are spiral galaxies? l Flattened systems of stars, gas, and dust l stars seem to concentrate in spiral “arms” l all bound by gravity into a single unit l typical size:50,000-100,000 light years l typical mass: 10billion-500billion suns l often there is also a prominent bulge

3. Face-on spiral galaxy

4. Highly inclined spiral galaxy

5. Edge-on spiral galaxy

6. Edge-on Spiral Galaxy

7. Why are spirals interesting? l An intriguing morphology l difficult to explain l common and widespread thoughout the Universe l new stars tend to form in spirals but not in other types of galaxies l part of process of galaxy evolution and interaction l our Galaxy is a spiral

8. Discovery of Spirals l 1845 William Parsons, Third Earl of Rosse, Ireland l 72-inch reflector l visually detected spiral arms in the Whirlpool Nebula M51 l many other “nebulae” found to be spirals

9. William Parsons, “Lord Rosse” 1800-1867

10. Discovery of spiral structure in M51

12. What causes spiral structure? l Natural phenomenon in flat, rotating stellar disks l possibly triggered by an interaction with another galaxy l or generated by bars l “density waves”

13. Spiral galaxy research at UA l morphology l sense of winding of spiral arms l gravitational torques due to bars and spiral arms l star formation in galactic rings

14. The de Vaucouleurs Atlas of Galaxies Gerard de Vaucouleurs 1918-1995

15. The de Vaucouleurs Atlas: what is it? l Authors: R. J. Buta (U. Alabama) l H. G. Corwin, Jr. (Caltech) l S. C. Odewahn (U. Arizona) l publisher: Cambridge Univ. Press l Purpose: to illustrate the de Vaucouleurs revised Hubble classification system with modern digital images

16. NGC 7457 SA(rs)0-

17. NGC 1553 SA( r )0

18. NGC 1291 (R)SB(s)0/a

19. NGC 2713 (R’)SB(rs)ab

20. NGC 4736 (R)SA( r )ab

21. NGC 5850 SB( r )b

22. NGC 4501 (M88) SA(rs)b

23. NGC 4321 (M100) SAB(s)bc

24. NGC 1566 SAB(s)bc

25. NGC 6643 SA(rs)c

26. NGC 7479 SB(s)c

27. NGC 6946 SAB(rs)cd

28. NGC 5585 SAB(s)d

29. NGC 4618 SB(rs)m

31. Sense of winding of spiral arms l Trailing arms: follow direction of rotation l Leading arms: oppose direction of rotation l most spiral arms trail l but one galaxy has leading arms!

32. Trailing arm spiral M81

33. Leading arm spiral galaxy NGC 4622

34. Barred spiral galaxies l A bar-like pattern of old stars crosses the center l arms break from the ends of this bar l 70% of spirals have a bar, including the Milky Way

35. Barred spiral galaxy NGC 1365

36. Barred spiral NGC 1300

37. How stars move in presence of a bar l In solar system, planets follow elliptical paths with Sun at one focus l no torque on planet as it orbits l in presence of a bar, star may follow a centered elliptical orbit l there is a torque on star as it orbits l amount of torque is a measure of “bar strength”

40. Rings of Star Formation l Real bar orbit l “lit up” by new stars l often not circular

43. Gallery of spirals from the Hubble Space Telescope

44. Typical spiral galaxy: NGC 4414

45. Starburst spiral galaxy NGC 3310

46. Ringed spiral galaxy NGC 7742

47. Superposed spiral galaxies NGC 3314

48. Edge-on spiral galaxy ESO 510-13

49. Edge-on spiral galaxy NGC 4013

51. Peculiar ring galaxy: Hoag’s Object

52. Barred spiral galaxy NGC 4319 with quasar

53. Polar ring galaxy NGC 4650A

54. Compact galaxy group

55. Colliding spiral galaxies: NGC 6745

57. The Spiral Menagerie: Visual Observations of Spirals from McDonald and Siding Spring Observatories l 1977-1984 l photoelectric galaxy photometry runs l McDonald 30, 36, 82, and 107-inch telescopes l Siding Spring 40-inch telescope

58. NGC 5194-5 (M51) - McDonald 30-inch

59. NGC 1566, SSO 40-inch

60. NGC 2403, McD 30-inch

61. NGC 3034 (M82), McD 36-inch

62. NGC 3893(36McD), 4449(36McD), 4676(107McD), 3646(36McD), and 5921(36McD)

63. NGC 4631 (left) and NGC 4565(right) (both 30McD)

64. M99, M100, M88, and M61 (all 30McD)

65. M77(36McD), NGC4535(30McD), NGC5394-5(36McD), NGC3395-6(36McD), NGC5426- 7(36McD), NGC5247(36McD)

66. Thank you!