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Galaxies And the Foundation of Modern Cosmology

Galaxies And the Foundation of Modern Cosmology. What are the three major types of galaxies?. Hubble Ultra Deep Field. Hubble Ultra Deep Field. Hubble Ultra Deep Field. Spiral Galaxy. Hubble Ultra Deep Field. Spiral Galaxy. Hubble Ultra Deep Field. Elliptical Galaxy. Elliptical Galaxy.

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Galaxies And the Foundation of Modern Cosmology

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  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 EllipticalGalaxy Spiral Galaxy

  8. Hubble Ultra Deep Field Elliptical Galaxy EllipticalGalaxy Spiral Galaxy

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

  10. halo disk bulge Spiral Galaxy

  11. Disk Component: stars of all ages, many gas clouds Type Sa Galaxy 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 (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

  26. How are galaxies grouped together?

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

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

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

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

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

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

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

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

  35. Why don’t all galaxies have similar disks?

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

  37. 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

  38. 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

  39. We must also consider the effects of collisions

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

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

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

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

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

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

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

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