script, 2.3 DM

Question 1

properties of DM?

Answer 1

non collisional, non interacting, non baryonic

Question 2

mark n explain rotational curve plot

Answer 2

x

Question 3

relation of DM w radius of gal?

Answer 3

inc w r

at large radius: v_rot ~ r^-1/2
expected profile: dec
obs: flat
cause: DM

Question 4

find m/l of spiral gal?

Answer 4

x

Question 5

comparison w stellar m/l?

Answer 5

M/L* = 6.5
M/L_gal = 150

Question 6

inventory of cluster mass? calc % of each mass contribution?

Answer 6

x

Question 7

optical gives mass of? + calc

Answer 7

stars

M*= 1/50 M_cl

Question 8

x rays give mass of? calc?

Answer 8

gas

M_gas = 1/7 M_cl

Question 9

explain bullet cluster? what does it prove?

Answer 9

prove: that DM os collision less

Question 10

is DM grav interacting?

Answer 10

yes

observed grav effects

Question 11

is DM collisionless? proof?

Answer 11

yes

bullet cluster

Question 12

is DM cold?

Answer 12

yes

if warm: rel at cmb: large str form first: top down

it was non-relativistic at the time of decoupling from weak interactions – otherwise structure formation would have proceeded ‘top-down’, in contrast to our hierarchical structure formation scenario (Ly-α forest, structure formation)

Question 13

proof that DM is non-baryonic, does not interact em?

Answer 13

cmb fluctuations

if DM interact em: DM grav oppo to photon pressure and even out DM in homo– no DM growth before cmb – in that case:

DM den fluctuations at cmb: 10^-5

DM den fluc now (if DM interact electromag) = DM den fluctuations at cmb * a /a_rec
= 10^-5+3 = 10^-2

obs DM den fluctuations now&raquo_space; 1

i. e DM fluc grow well before cmb
i. e DM does not interact em & is non-baryonic