1. The Structure of the Universe AST 112

2. Galaxy Groups and Clusters A few galaxies are all by themselves Most belong to groups or clusters Galaxy Groups: – Loose collections of about 5-50 galaxies – Many spirals found in groups Galaxy Clusters: – Hundreds or thousands of galaxies – Dominated by ellipticals

3. Galaxy Groups Hickson Compact Group 87 170,000 LY in diameter

4. Local Group Two heavyweights – Milky Way – Andromeda One intermediate – Triangulum Galaxy 30-40 dwarf galaxies

5. Galaxy Clusters Abell 1689 2 million LY across

6. Galaxy Clusters Galaxies being drawn into clusters The structure of the Universe is still evolving!

7. Nearby Groups and Clusters

8. Nearby or part of something larger? Measurements on all of these groups and clusters show that they are interacting, but not gravitationally bound

9. This suggests that separate groups and clusters interact as a larger structure: Supercluster

10. The Local Supercluster

11. Superclusters Superclusters sometimes have a large central concentration They have filaments of galaxies that branch off These filaments are like connections between superclusters

12. Superclusters We don’t see superclusters through telescopes. We make velocity measurements on separate clusters – See if they interact gravitationally They show up in large-scale maps

13. Large-Scale Motion If we look at velocities of galaxies nearby, we see some variation due to: – Random motion within group / cluster – Large scale motion of groups / clusters Groups and clusters often seem to be “flowing” somewhere!

14. The Great Attractor The Local Group and all matter within 150 million LY appear to be moving toward the “Great Attractor” Calculated mass of tens of thousand of Milky Ways! What is it? There was no obvious cause for this!

15. The Great Attractor It’s behind the band of the Milky Way! One cluster (Abell 3627) near the center of the “Great Attractor” Probably extremely large supercluster

16. Structure of the Universe Are galaxy superclusters distributed in any particular way?

17. Redshift Surveys Large surveys attempt to answer that. We can make a map of observable galaxies and clusters, including their distances Dark matter plays a significant role – Holds galaxies and clusters together

18. Redshift Surveys Maps of galaxies: very time / resource / data intensive – We need long exposures with large telescopes to even see distant galaxies – We need their distance too Determines distance using Hubble’s Law

19. CfA Redshift Survey They surveyed “wedges” Carroll and Ostlie, 3 rd Edition

20. CfA Redshift Survey Galaxies not distributed randomly Chains and filaments with superclusters at intersections Voids live in between Carroll and Ostlie, 3 rd Edition

21. CfA Redshift Survey Another CfA wedge Carroll and Ostlie, 3 rd Edition

22. CfA2 Survey Another CfA survey (different declinations) – Great Wall – South Wall “Walls” are large superclusters

23. 2dF Survey

24. Sloan Digital Sky Survey (SDSS) Outer circle is 2 billion LY Spectra for 800,000 galaxies

25. Great Wall 1 billion LY from end to end Largest known structure in the Universe Sub-structure – Filaments – Voids

26. Deep Sky Surveys

27. Cosmological Principle At some scale, universe should start to look the same everywhere – 1 billion LY “The End of Greatness”

28. Structure of the Universe The structure of the Universe consists of walls of galaxies (superclusters) connected together by filaments of galaxies.

29. Structure Formation Simulations show that dark matter forms the structure of the Universe and it “corrals” light matter.

30. Structure Formation Light matter is thought to “map out” dark matter Dark matter structure forms a “framework”, light matter follows and collects where dark matter is most dense

31. Structure of the Universe Combine: – Our deep sky surveys – Our knowledge of dark matter – Physics Millenium Simulation models what the Universe looks like (as though we can see dark matter).

32. Structure of the Universe