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Dark Matter and the Large Scale Structure of the Universe 暗物質及宇宙建構

Dark Matter and the Large Scale Structure of the Universe 暗物質及宇宙建構. Lam Hui 許林 Columbia University. This is the second in a series of 3 talks. July 5: Dark energy and the homogeneous universe Today: Dark matter and the large scale

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Dark Matter and the Large Scale Structure of the Universe 暗物質及宇宙建構

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  1. Dark Matter and the Large Scale Structure of the Universe 暗物質及宇宙建構 Lam Hui 許林 Columbia University

  2. This is the second in a series of 3 talks. July 5: Dark energy and the homogeneous universe Today: Dark matter and the large scale structure of the universe July 18: Inflation and the early universe

  3. Outline Review: the inhomogeneous universe Basic mechanism: gravitational instability Basic ingredient: dark matter Basic statistical tool: correlation function Basic problem: mass

  4. Blandton & Hogg

  5. Hubble deep field

  6. CfA survey

  7. Sloan Digital Sky Survey

  8. recombination WMAP website

  9. CMB: cosmic microwave background

  10. Sloan Digital Sky Survey

  11. Gravitational Instability Interested quantity: overdensity

  12. LANL

  13. Scale factor a(t) time = t’ time=t x=0 x=1 x=2 x=0 x=1 x=2 distance = a(t)Δx distance = a(t’)Δx

  14. Fundamental equations mass conservation: momentum conservation i.e. F = ma : Poisson’s equation:

  15. From: Obtain: Growing mode:

  16. Gravitational Instability Interested quantity: overdensity

  17. Problem: There is not enough time for structure to grow from recombination to today! γ γ e- p+ H Solution: Dark matter - no/little interaction with photons; pressureless.

  18. Blandton & Hogg

  19. Evidence from rotation curve (Vera Rubin) Credit: Richard Pogge

  20. WMAP

  21. What makes up dark matter? Most plausible candidate: Weakly Interacting Massive Particle (WIMP) If annihilation cross section , naturally get the right left over abundance.

  22. Direct detection of WIMPs credit: U. Zaragoza

  23. Current structure formation paradigm: Pressureless (cold) dark matter, which makes up about 20% of the universe, forms structure via gravitational instability. To understand the quantitative success of this model, we need to learn one statistical tool: the2 point correlation function.

  24. Two-point correlation function ξ and power spectrum P r Common to plot: quantifies amplitude of fluctuations at scale 1/k.

  25. Hierarchical clustering: small things form first threshold

  26. Problem: usually don’t observe mass directly. CMB: observe temperature Galaxies: observe counts Want: mass

  27. Rauch ☼ n=2 1216 Å n=1

  28. Gravitational lensing image ☀ ☀ lens source observer image ☀ deflection angle = 4GM/r

  29. Jain

  30. Tegmark

  31. Summary -Structure formation occurs via the gravitational instability of cold dark matter. - Small galaxies form first, which then merge to form bigger things. - A major goal of observational cosmology is to measure the mass fluctuations. - We still don’t know what dark matter is.

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