1. Galaxies And the Foundation of Modern Cosmology

2. What are the three major types of galaxies?

3. Hubble Ultra Deep Field

4. Hubble Ultra Deep Field

5. Hubble Ultra Deep Field
Spiral Galaxy

6. Hubble Ultra Deep Field
Spiral Galaxy

7. Hubble Ultra Deep Field
Elliptical Galaxy
Elliptical Galaxy
Spiral Galaxy

8. Hubble Ultra Deep Field
Elliptical Galaxy
Elliptical Galaxy
Spiral Galaxy

9. Hubble Ultra Deep Field
Elliptical Galaxy
Elliptical Galaxy
Irregular Galaxies
Spiral Galaxy

10. halo
disk
bulge
Spiral Galaxy

11. Type Sa Galaxy Disk Component: stars of all ages, many gas clouds
Spheroidal Component:
bulge & halo, old stars,
few gas clouds

12. Sa Galaxies Sa Galaxies: Dominant nuclear bulge
Tightly wound spiral pattern
Few (but some) newly formed stars, HII regions or other evidence of active star formation

13. Sb Galaxies Moderate nuclear bulge Intermediate spiral pattern
Some evidence for massive young stars, HII regions, star formation

14. Type Sc Galaxy Blue-white color indicates ongoing star formation
Disk Component:
stars of all ages,
many gas clouds
Spheroidal Component:
bulge & halo, old stars,
few gas clouds
Red-yellow color indicates older star population

15. Sc Galaxies Small to nearly non-existent nuclear bulge
(Some classify Messier as as Type Sd)
Small to nearly non-existent nuclear bulge
Open spiral pattern
Active star-formation

16. Disk Component:
stars of all ages,
many gas clouds
Blue-white color indicates ongoing star formation
Spheroidal Component:
bulge & halo, old stars,
few gas clouds
Red-yellow color indicates older star population

17. Barred Spiral Galaxy
Has a bar of stars across the bulge

18. Barred Spiral Types
SBa SBb SBc

19. S0 Lenticular Galaxy
Has a disk like a spiral galaxy but very little dust or gas (intermediate between spiral and elliptical)

20. S0 Edge-on
Note the clear presence of a disk, but absence of dust band in this S0 galaxy: NGC 3115

21. Elliptical Galaxy:
All spheroidal (bulge) component, no disk

22. Elliptical Galaxy:
All spheroidal component, virtually no disk component
Red-yellow color indicates older star population

23. Irregular Galaxies Irregular I Galaxy
Blue-white color indicates ongoing star formation

24. Irr II Galaxy - Messier 82

25. Hubble’s Galaxy Classes
Spheroid
Dominates
Disk Dominates

27. How are galaxies grouped together?

28. Spiral galaxies are often found in groups of galaxies
(up to a few dozen galaxies)

29. Our Galaxy & Andromeda belong to a small “Local Group”
of about 20 or so galaxies

30. Elliptical galaxies are much more common in huge clusters of galaxies
(hundreds to thousands of galaxies)

31. How do we observe the life histories of galaxies?

32. Deep observations show us very distant galaxies as they were much earlier in time
(Old light from young galaxies)

35. Denser regions contracted, forming protogalactic clouds
H and He gases in these clouds formed the first stars

36. Supernova explosions from first stars kept much of the gas from forming stars
Leftover gas settled into spinning disk
Conservation of angular momentum

37. Why do galaxies differ?
M87
NGC 4414
But why do some galaxies end up looking so different?

39. Nature: Conditions in Protogalactic Cloud?
Spin: Initial angular momentum of protogalactic cloud could determine size of resulting disk

40. Conditions in Protogalactic Cloud?
Density: Elliptical galaxies could come from dense protogalactic clouds that were able to cool and form stars before gas settled into a disk

41. Distant Red Ellipticals
Observations of some distant red elliptical galaxies support the idea that most of their stars formed very early in the history of the universe

42. We must also consider the effects of collisions

43. Collisions were much more likely early in time, because galaxies were closer together

44. Many of the galaxies we see at great distances (and early times) indeed look violently disturbed

45. The collisions we observe nearby trigger bursts of star formation

46. Modeling such collisions on a computer shows that two spiral galaxies can merge to make an elliptical

47. Modeling such collisions on a computer shows that two spiral galaxies can merge to make an elliptical

48. Shells of stars observed around some elliptical galaxies are probably the remains of past collisions

49. Collisions may explain why elliptical galaxies tend to be found where galaxies are closer together

50. Giant elliptical galaxies at the centers of clusters seem to have consumed a number of smaller galaxies