1. Lecture 20-21: The Formation of Structure---Galaxies, Clusters, Voids
Astronomy 5: The Formation and Evolution of the Universe
Sandra M. Faber
Spring Quarter 2007
UC Santa Cruz

2. A major recent discovery: color bimodality

3. A redshift survey: 220,000 galaxies
Each small dot is a galaxy
We are here
History
1/4 of visible universe

4. 4 billion light years

5. 4 billion light years
Milky Way galaxy
Radius of cosmic horizon; 14 B lyr

6. 4 billion light years
Milky Way galaxy
Radius of cosmic horizon; 14 B lyr

7. A redshift survey: 220,000 galaxies
Each small dot is a galaxy
We are here
History
1/4 of visible universe

9. The seeds of galaxy and structure formation are small density fluctuations that were created by inflation
Density along a line in the early Universe:
Small group
Large cluster
Isolated galaxy
Void
The highest peaks collapse first, making small proto-galaxies. Then lower peaks collapse to make galaxies, and finally clusters and superclusters.

10. A chunk of the Universe first expanding and then collapsing
A chunk of the Universe first expanding and then collapsing. Dark matter only.
Redshift, z
Scale factor a = 1/(1+z). So Universe starts out 1/50th of present size.

11. Now the viewpoint steps back as the Universe expands to show detail inside the cube. The expansion seems to disappear, but this is an effect of the presentation. Dark matter only.

12. A thin slice through the cube. Still dark matter only.
Simulation courtesy of Springel, White, and Hernquist

13. Measles on the CMB map are the seeds of voids and superclusters.
Ripples in the CMB intensity on the celestial sphere, as mapped with the WMAP satellite.
The celestial sphere as portrayed from outside. The Milky Way is at the center of the sphere.

14. Cosmic history in 4 easy steps
Big Bang Zoom
Graphics from WMAP team

15. The Hubble Ultradeep Field to scale

16. Ultradeep field detail
Near
???
Far

17. DEEP2 looks 2/3 of the way back to the Big Bang
The DEEP2 Survey has gathered spectra of 50,000 galaxies using the DEIMOS spectrograph on the Keck 2 telescope. The typical galaxy is at z = 0.9 and is 100 times fainter than galaxies in low-redshift surveys like SDSS and 2dF.

19. Lumps continually collide to make bigger lumps. Hierarchical clustering.
Simulation courtesy of Springel, White, and Hernquist

20. Our matter makes up only a tiny fraction of galactic mass
Our matter makes up only a tiny fraction of galactic mass. The remainder is in a halo of dark matter roughly 10 times as big and 10 times as massive.

21. Visible galaxies embedded in the dark matter filaments

22. Visible galaxies embedded in the dark matter filaments
Formed stars