Introduction to Cosmology

210 Dark Matter

20

10

0

• 10


• 20


• 20
  
  
  • 20 – 10 01020 – 20 – 10 01020
  
  
  
  


• 10

20

10

0

π/

• h
  1 Mpc

σ/h–^1 Mpc σ/h–^1 Mpc

π/

• h
  1 Mpc

Figure 9.2Plot of theoretically calculated correlation functions휉(휎,휋)as described in refer-
ence [2]. The lines represent contours of constant휉(휎,휋)= 4. 0 , 2. 0 , 0. 5 , 0. 2 , 0 .1. The models are:
top left, undistorted; bottom left, no infall velocities but훽= 0 .4; top right, infall velocity disper-
sion푎=500 kms−^1 ,훽=0; bottom right,푎=500km s−^1 ,훽= 0 .4. All models use Equation (9.15)
with푟c= 5. 0 ℎ−^1 Mpc and훾= 1 .7. Reproduced from [11] by permission of the 2dFGRS Team.

Introducing the phenomenological flattening parameter

훽=훺m^0.^6 ∕푏, (9.12)

one can write a linear approximation to the distortion as

휉(푠)

휉(푟)

= 1 +

2 훽

3

+

훽^2

5

. (9.13)

Estimates of훽and푏which we shall discuss in Equations (9.18–19) lead to a value of

훺mof the order of 0.25. Thus a large amount of matter in the LSC is dark.