the cosmic microwave background · • since cmb fluctuations are on the 2-d sky, we need angular...
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The Cosmic Microwave Background
Compilation of extracts from:
A. Wetzel (Berkeley),
R. Bustos (UDEC),
D. Spergel (Princeton),
T. Richtler (UDEC)
NASA
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NASA
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Cosmological Parameters
k = 0 (because the universe is flat, i.e. Ωtot
~ 1)
τ : because CMB photons can be scattered, altering anisotropies
r : set to 0? since there is no evidence of tensor pertubations
Density pertubation amplitude: often expressed as σ8
Bias: between galaxy distribution and dark matter distribution
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Quantum Fluctuations in the early universe
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The state of the art …
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Large-scale structure in the distribution of galaxies
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Tiempo
Tam
año
BigBang
Inflación
Sopade
quarks
nnuucclleeoo
ssyynntthheessiiss
HydrogenHydrogen
&&
HeliumHelium
PlasmaPlasma
400,000años1 minuto10-35 sec10-41 sec
miles de millones de años
14
bbaarryyoonn
ggeenneessiiss
108 9
Granunificación
Fondo cósmico
CMBHoy: CBISan Pedro
Época oscura
1
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Ωnb
Ωb
ΩΛ
4 % materia normal
21 % materia oscura
75 % energía oscura
Consecuencias de los resultados del WMAP/CBI etc.:
vacío
Una revolución en la física fundamental
Edad del Universo: 13.5 mil millones de años
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Universe is flat (WMAP)
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Measuring the CMB Anisotropies
• First COBE image• No variation on the scale 1 part in 1000
Wayne Hu
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Measuring the CMB Anisotropies
• Turn up resolution slightly• Dipole - redshift from our motion
Wayne Hu
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Measuring the CMB Anisotropies
• Approach microKelvin precision• We see the early perturbations that give
rise to the structure of today
Wayne Hu
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Imágenes totales del cielo de las anisotropías del CMB.2.725 K +/- ~ 30 µK rms
Resolución !!!
1992
2003
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CMB Power Spectrum
• Measure the angular coherence of the temperature fluctuations
• We are familiar with decomposing signals in Fourier space with k modes
• Since CMB fluctuations are on the 2-D sky, we need angular decomposition in multipole space to study the amplitude
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Spherical Harmonics
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1.2x10-9
1.0
0.8
0.6
0.4
0.2
0.0
l ( l
+1)
Cl /
2π
(µK
)2
300025002000150010005000
Multipole (l)
Angular Scale on Sky1
o10
'5
'
acoustic peaks in photon-baryon fluid
soundhorizon
(Tem
per
atu
ra)2
K2
Large Features Small FeaturesEstructuras grandes Estructuras pequeñas
Escala angular en el cielo
l∝θ−1
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Systematic sources of error since recombination (affect primarily small scale power)
• Gravitational waves– Affect polarizations
• Integrated Sachs Wolf effect– Depth of potential well changes photon frequency as
universe expands
• Reionization– Eliminates anisotropies
• Lensing effects• Sunyaev Zeldovich effect
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31-October-2002 Mark Birkinshaw, U. Bristol 24
2. The origin of the SZ effect
Clusters of galaxies contain extensive hot atmospheres
Te ≈ 6 keV
np≈ 103 protons m-3
L ≈ 1 Mpc
2 Mpc
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What is it?: Inverse Compton
• Photon scatters off of moving e-
– Gains energy from e-
– ∆ 0 → increases
• Decrement in Rayleigh-Jeans
• Increment in Wein
[3]
Carlstrom, Holder, Reese, “Cosmology with the Sunyaev-Zel’dovich Effect,” 2002, astro-ph/0208192.
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• Need to assume value and error of some parameters a priori to fit other cosmological parameters to CMB power spectrum
Parameter Estimation
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Initial Fit to WMAP - 6 parameters
Fit Derivedbh
2=0 .024±0.001mh
2=0 .14±0.02h=0 .72±0 .05 t 0=13 .4±0 .3Gyr
m=0 .29±0 .07
Combine WMAP, CBI, ACBAR, 2dFGRS, Lyα Forest Data
b=0 .047±0.006
bh2=0 .0224±0.0009
mh2=0 .135±0 .009
h=0 .71±0 .04 t 0=13 .7±0 .2Gyr
b=0 .044±0 .004m=0 .27±0 .04
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Cosmological Parameters
k = 0 (because the universe is flat, i.e. Ωtot
~ 1)
τ : because CMB photons can be scattered, altering anisotropies
r : set to 0? since there is no evidence of tensor pertubations
Density pertubation amplitude: often expressed as σ8
Bias: between galaxy distribution and dark matter distribution
![Page 30: The Cosmic Microwave Background · • Since CMB fluctuations are on the 2-D sky, we need angular decomposition in multipole space to study the amplitude. Spherical Harmonics. 1.2x10-9](https://reader036.vdocuments.mx/reader036/viewer/2022071000/5fbc4f15050fe84b943c6f73/html5/thumbnails/30.jpg)