1. Steward Observatory – Gregory RudnickSept 2006 RECIPE FOR A GALAXY CLUSTER: A LOT OF DARK MATTER, A BUNCH OF HOT GAS, AND A SPRINKLING OF GALAXIES Dr. Gregory Rudnick (NOAO/Kitt Peak)

2. Steward Observatory – Gregory RudnickSept 2006 Some BIG questions about galaxy clusters?  What are they?  How do they form?  Where do they live?  Why are they interesting?  What are some current efforts to study them?

3. Steward Observatory – Gregory RudnickSept 2006 A review of gravity  Gravity is a force  Everything attracts everything else  Without gravity everything would move in straight lines

4. Steward Observatory – Gregory RudnickSept 2006 What are galaxy clusters? Large groups of galaxies held together by gravity. 6 Million light years

5. Steward Observatory – Gregory RudnickSept 2006 What are galaxy clusters? Ben Moore Large groups of galaxies held together by gravity.

6. Steward Observatory – Gregory RudnickSept 2006 What are clusters made of? galaxies Hercules cluster

7. Steward Observatory – Gregory RudnickSept 2006 An Interlude: Galaxies 101 (in 3 minutes) There are hundreds of billions of stars in every galaxy That’s about 200,000,000,000 stars!! Galaxies are large collections of stars with gas and dust

8. Steward Observatory – Gregory RudnickSept 2006  Hundreds of galaxies  That’s trillions of stars!!  Elliptical and S0 galaxies are the most common types of galaxies

9. Steward Observatory – Gregory RudnickSept 2006 How massive are clusters?  Use motions of galaxies.  Calculate how much mass you need to hold cluster together. clusters are 10 15 times as massive as the sun Stars make up only 5% of cluster mass! Where is the missing mass?

10. Steward Observatory – Gregory RudnickSept 2006 Stars aren’t the only game in town  Matter emits at other wavelengths too.  Hot (10 million degree) gas emits in the x-ray  Twice as much hot intra- cluster gas as stars  Hot gas makes up 10% of total mass

11. Steward Observatory – Gregory RudnickSept 2006 Where is the rest of the mass?  Only 5% stars + 10% hot gas has been seen  Where is other 85%?  Can we verify the large mass? Gravitational lensing Galaxy clusters are mostly made of “Dark Matter”

12. Steward Observatory – Gregory RudnickSept 2006 What do we know  Clusters are made of:  galaxies (5%)  hot gas (10%)  dark matter (85%)

13. Steward Observatory – Gregory RudnickSept 2006 How do they form? volker springel

14. Steward Observatory – Gregory RudnickSept 2006 Where do clusters live? The nearest two clusters Coma (260 million light years) Virgo (55 million light years)

15. Steward Observatory – Gregory RudnickSept 2006 The Big Picture

16. Steward Observatory – Gregory RudnickSept 2006 The Big Picture

17. Steward Observatory – Gregory RudnickSept 2006 Why are clusters interesting and useful? Providing evidence for dark matter Gravitational lensing

18. Steward Observatory – Gregory RudnickSept 2006

19. Steward Observatory – Gregory RudnickSept 2006 The Bullet Cluster - testing the existence of Dark Matter Douglas Clowe If gravity is stronger on large scales and dark matter doesn’t exist then the gravitational force should be located at the center of the “visible” matter.

20. Steward Observatory – Gregory RudnickSept 2006 The Bullet Cluster Douglas Clowe Use gravitational lensing to measure total mass.

21. Steward Observatory – Gregory RudnickSept 2006 Clusters as Laboratories of Galaxy Evolution Can clusters tell us how galaxies might transform their types? How can a spiral turn into an elliptical?

22. Steward Observatory – Gregory RudnickSept 2006 What happens to gas in a galaxy when it flies through the hot intra- cluster gas Ram Pressure Stripping

23. Steward Observatory – Gregory RudnickSept 2006 Galaxy Harassment

24. Steward Observatory – Gregory RudnickSept 2006 Galaxy Harassment

25. Steward Observatory – Gregory RudnickSept 2006 Observing the Evolution of Clusters How can we see clusters when they were younger? Astronomy is like archaeology. increasing distance back in time

26. Steward Observatory – Gregory RudnickSept 2006 CL1202.4-1224 4.3 Billion years CL1232.3-1250 5.1 Billion years CL1037.5-1243 5.3 Billion years CL1054.4-1245 6.3 Billion years CL1354.1-1231 6.3 Billion years Clusters through cosmic time

27. Steward Observatory – Gregory RudnickSept 2006 Galaxies in Young Clusters cl1037-1243 5.3 Billion years cl1216-1201 6.5 Billion years

28. Steward Observatory – Gregory RudnickSept 2006 Summary  Galaxies don’t matter: Clusters are dominated by Dark Matter (5% stars, 10% hot gas, 85% dark matter)  Cosmic meeting points: Clusters are concentrations of galaxies at the intersection of filaments of cosmic structure  Cosmic Laboratories: Clusters are useful in studying dark matter and the evolution of galaxies