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University of Durham
Institute for Computational CosmologyInstitute for Computational CosmologyInstitute for Computational Cosmology
Carlos S. Frenk Institute for Computational Cosmology,
Durham
Galaxy clusters
University of Durham
Institute for Computational CosmologyInstitute for Computational CosmologyInstitute for Computational Cosmology
Galaxy clusters - TiajinCarlos Frenk
Institute of Computational Cosmology University of Durham
• Introduction to the large-scale structure of the Universe
• The formation of dark matter halos
• The structure of dark matter halos
University of Durham
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What is the Universe made of?
University of Durham
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What is the universe made of?
critical density = density that makes univ. flat: = 1 for a flat univ.
(of which stars, Cole etal ‘02) s = 0.0023 ± 0.0003 • Baryons b = 0.044 ± 0.004
density critical density
• Radiation (CMB, T=2.726±0.005 oK) r = 4.7 x 10-5
• Dark matter (cold dark matter) dm =0.20 ± 0.04
• Dark energy (cosm. const. =0.75 ±
0.04 bdm(assuming Hubble parameter h=0.7)
• Neutrinos = 3 x 10-5 if m 6 x 10-2 (<mev)
mass+rel
+vac
University of Durham
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m=0.24±0.04 >>
b=0.044±0.004
all matter baryons
Dark matter must be non-baryonic
The nature of the dark matter
University of Durham
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Non-baryonic dark matter candidates
hot neutrino a few eV
warm ? a few keV
cold axion
neutralino10-5eV->100 GeV
Type candidate mass
University of Durham
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What is the Universe made of?
Dark energy
University of Durham
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Evidence for from high-z supernovae
SN type Ia (standard candles) at z~0.5 are fainter than
expected even if the Universe were empty
The cosmic expansion must have been
accelerating since the light was emitted
a/a0=1/(1+z)
University of Durham
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€
a.
+ kc 2 =8π
3Gρa2
€
H 2 1− Ωm − Ωγ − ΩΛ( ) = −kc 2
a2
Friedmann equations
For a homogeneous & isotropic Universe
a = expansion factor, k= curvature
mass+rel
+vacπ
GH 23
8=Ω
G
cvac π
8
2=
a
aH
.
=
University of Durham
Institute for Computational CosmologyInstitute for Computational CosmologyInstitute for Computational Cosmology
Evidence for from high-z supernovae
Distant SN are fainter than expected if expansion were decelerating
University of Durham
Institute for Computational CosmologyInstitute for Computational CosmologyInstitute for Computational Cosmology
€
a.
+ kc 2 =8π
3Gρa2
€
H 2 1− Ωm − Ωγ − ΩΛ( ) = −kc 2
a2
)(3 22 cpda
dac
+−=
)13(3
4..
+−= waGa π
Friedmann equations
For a homogeneous & isotropic Universe
a = expansion factor, k= curvature
2nd law of thermodynamics:
2cwp =
p= pressure
Equation of state:
mass+rel
+vacπ
GH 23
8=Ω
G
cvac π
8
2=
a
aH
.
=
University of Durham
Institute for Computational CosmologyInstitute for Computational CosmologyInstitute for Computational Cosmology
Friedmann equations
€
p = wρc 2where totmass+rel
+VAC a-3 a-4 const?
€
..
a = −4π
3Gρa(3w + 1)
€
c 2adρ
da= −3( p + ρc 2)
If VAC = VAC (z,x) and 3
1−<w quintessence
If vacconst ,dda
0 p c 2 w 1
Accelerated expansion
€
⇒ 3w + 1< 0 ⇒ ˙ ̇ a > 0 ⇒ Expansion accelerates
In general,
University of Durham
Institute for Computational CosmologyInstitute for Computational CosmologyInstitute for Computational Cosmology
2cwp =
)13(3
4..
+−= waGa π
Friedmann equations
013 >+w
where
At early times the universe is always decelerating
totmass+rel
+ a-3 a-4 const?
For matter or radiation:
There must be a transition between decelerating and accelerating expansion
University of Durham
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Supernovae Ia and dark energy
Reiss etal ‘04Redshift z
(m
-M)
(ma
g)
Transition from decelerated to accelerated expansion at z~0.5
16 new Sn Ia -- 6 @ z>1.25
University of Durham
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The large-structure of the Universe
University of Durham
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Results from the “2-degree field” galaxy survey
250 nights at 4m AAT 1997-2002
Anglo-Australian team
221,000 redshifts to bj<19.45
Median z=0.11
University of Durham
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100
0 m
illion lig
ht yea
rs
QuickTime™ and aYUV420 codec decompressor
are needed to see this picture.
University of Durham
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The origin of the large-structure of the Universe
University of Durham
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The beginning of the Universe
In 1980, a revolutionary idea was proposed: our universe started off in an unstable state (vacuum energy) and as a result expanded very fast in a short period of time cosmic inflation
Inflation
Initially, Universe is trapped in false vacuum
Scalar field
Universe decays to true vacuum keeping v~ const
Universe oscillates converting energy into particles
University of Durham
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†
Inflation for beginners
At early times k=0. So, Vacconst.
€
˙ a
a= const Universe expands exponentially
Inflation ends when Vac decay and Universe reheats
a.
kc 2 8π3
Ga22
University of Durham
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Conventionalinflation
Chaoticinflation
Cosmic Inflation
t=10-35 s
Inflation theory predicts:
1. Flat geometry (=1)
(eternal expansion)
2. Small ripples in mass distribution
University of Durham
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Quantum fluctuations are blown up to macroscopic scales during inflation
Generation of primordial fluctuations
Because of quantum fluctuations, different parts of the Universe finish inflating at slightly different times
University of Durham
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Spectrum of inhomogeneities
x
University of Durham
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Standard inflation predicts:
1. FLAT GEOMETRY:
2. 2~ k
3
k
2
k2
kn
n = 1
Gaussian amplitudes
123=
+
Hm
Cosmic Inflation
University of Durham
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University of Durham
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University of Durham
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Evolution of an adiabatic perturbation in CDM universe
M=1015 Mo=1, h=0.5
Dak matter baryons
radiationFlu
ctu
atio
n a
mpl
itud
e
Log a(t)/a0
Horizon entry
University of Durham
Institute for Computational CosmologyInstitute for Computational CosmologyInstitute for Computational Cosmology
The origin of cosmic structureQUANTUM FLUCTUATIONS:
k2
kn
n = 1
Gaussian amplitudes
Inflation (t~10-35 s)
P(k)=Akn T2(k,t)
Damping (nature of dark matter)+
n=1
Mezaros damping
Free streaming
P(k)
Transfer functionRh(teq)
• Hot DM (eg ~30 ev neutrino)
- Top-down formation
• Cold DM (eg ~neutralino)
- Bottom-up (hierachical)
University of Durham
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The microwave background radiation
z =1000
The microwave background radiation
Plasma
z =
T=2.73 K
380 000 years after the big Bang
inflation
University of Durham
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Temperature anisotropies in the CMBIntrinsic anisotropies at last scattering:• Gravitational redshift: Sachs-Wolfe effect• Doppler effect• Adiabatic perturbationsLine of sight effects:
• Time varying potentials: ISW effect• Compton scattering: SZ effect
University of Durham
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The origin of cosmic structure
n=1
Mezaros damping
Free streaming
Large scales
P(k)
Rh(teq)
Small scales
• Hot DM (eg ~30 ev neutrino)
- Top-down formation
• Cold DM (eg ~neutralino)
- Bottom-up (hierachical)
QUANTUM FLUCTUATIONS:
k2
kn
n = 1
Gaussian amplitudes
Inflation (t~10-35 s)
P(k)=Akn T2(k,t)
Damping (nature of dark matter)+
Transfer function
• Hot DM (eg ~30 ev neutrino)
- Top-down formation
• Cold DM (eg ~neutralino)
- Bottom-up (hierachical)
CMB
University of Durham
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QuickTime™ and aGIF decompressor
are needed to see this picture.
The acoustic peaks in the CMB
Wayne hu
http://background.uchicago.edu/~whu/
If M<Mjeans the photon-baryon fluid oscillates
of CMB acoustic peak sound horizon at trec
University of Durham
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The cosmic microwave background radiation (CMB) provides a window to the universe at t~3x105 yrs
In 1992 COBE discovered temperature fluctuations (T/T~10-5) consistent with inflation predictions
The CMB
1992
University of Durham
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The CMB
1992
2003
University of Durham
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WMAP temperature anisotropies in the CMB
Bennett etal ‘03
University of Durham
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The Emergence of the Cosmic Initial Conditions
curvature
total density
baryons
University of Durham
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The Emergence of the Cosmic Initial Conditions
• > 105 independent ~ 5 measurements of T are fit by an a priori model with 6 (physical) parameters
• Best CDM model has: t
o= 13.7±0.2 Gyr
h=0.71±0.03 8=0.84±0.04
t=1.02±0.02
m=0.27±0.04
b=0.044±0.004
e=0.17±0.07 (Bennett etal 03)
• Parameters in excellent agreement with other data T-P x-corr Adiabatic fluctns
curvature
total density
baryons
University of Durham
Institute for Computational CosmologyInstitute for Computational CosmologyInstitute for Computational Cosmology
123=
+
H1. FLAT GEOMETRY:
2. QUANTUM FLUCTUATIONS: k2
kn
n = 1
Gaussian amplitudes
Inflation (t~10-35 s)
adiabatic
Dark matter
CMB (t~3x105 yrs)Structure
(t~13x109yrs)
The origin of cosmic structure
University of Durham
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Evolution of spherical perturbations
University of Durham
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n=1
damping
Free streaming
Calculating the evolution of cosmic structure
N-body simulation
“Cosmology machine”