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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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Presentation on theme: "Dark Matter and the Large Scale Structure of the Universe 暗物質及宇宙建構"— Presentation transcript:

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

11

12 Sloan Digital Sky Survey

13 Gravitational Instability
Interested quantity: overdensity

14 LANL

15

16 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

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

18 From: Obtain: Growing mode:

19 Gravitational Instability
Interested quantity: overdensity

20 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.

21 Blandton & Hogg

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

23 WMAP

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

25 Direct detection of WIMPs
credit: U. Zaragoza

26 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: the 2 point correlation function.

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

28 Hierarchical clustering: small things form first
threshold

29

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

31 Rauch n=2 1216 Å n=1

32 deflection angle = 4GM/r
Gravitational lensing image lens source observer image deflection angle = 4GM/r

33

34

35 Jain

36 Tegmark

37 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.

38


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