Basics of the Cosmic Microwave Background
Eiichiro Komatsu (UT Austin)
Lecture at Max Planck Institute
August 14, 2007
Night Sky in Optical (~0.5nm)
Night Sky in Microwave (~1mm)
A. Penzias & R. Wilson, 1965
R. Dicke and J. Peebles, 1965
3.5KNOW
P. Roll and D. Wilkinson, 1966
D.Wilkinson
“The Father of CMB Experiment”
David Wilkinson (1935~2002)
• Science Team Meeting, July, 2002
Plotted the “second point” (3.2cm) on the CMB spectrum The first confirmation of a black-body spectrum (1966)
Made COBE and MAP happen and be successful“The Father of CMB Experiment”MAP has become WMAP in 2003
COBE/DMR, 1992
•Isotropic?
•CMB is anisotropic! (at the 1/100,000 level)
COBE to WMAPCOBE
WMAP
COBE1989
WMAP2001
[COBE’s] measurements also marked the inception of cosmology as a precise science. It was not long before it was followed up, for instance by the WMAP satellite, which yielded even clearer images of the background radiation.
Press Release from the Nobel Foundation
CMB: The Most Distant Light
CMB was emitted when the Universe was only 380,000 years old. WMAP has measured the distance to this epoch. From (time)=(distance)/c we obtained 13.73 0.16 billion years.
WMAP 3-yr Power Spectrum
What Temperature Tells Us
Distance to z~1100
Baryon-to-Photon Ratio
Matter-Radiation Equality Epoch
Dark Energy/New Physics?
CMB to Cosmology
&Third
Baryon/Photon Density Ratio
Low Multipoles (ISW)
Constraints on Inflation Models
Determining Baryon Density
Determining Dark Matter Density
Measuring Geometry
Power SpectrumScalar T
Tensor T
Scalar E
Tensor E
Tensor B
Jargon: E-mode and B-mode• Polarization is a rank-2 tensor field.
• One can decompose it into a divergence-like “E-mode” and a vorticity-like “B-mode”.
E-mode B-mode
Seljak & Zaldarriaga (1997); Kamionkowski, Kosowsky, Stebbins (1997)
Primordial Gravity Waves• Gravity waves create quadrupolar temperat
ure anisotropy -> Polarization
• Directly generate polarization without kV.
• Most importantly, GW creates B mode.
Polarization From Reionization
• CMB was emitted at z~1088.• Some fraction of CMB was re-scattered in a reionized
universe.• The reionization redshift of ~11 would correspond to 3
65 million years after the Big-Bang.
z=1088, ~ 1
z~ 11, ~0.1
First-star formation
z=0
IONIZED
REIONIZED
NEUTRAL
Measuring Optical Depth• Since polarization is generated by scattering, the amplitude is given by the number of scattering, or optical depth of Thomson scattering:
which is related to the electron column number density as
Polarization from Reioniazation
“Reionization Bump”
WMAP Results
Parameter Determination: First Year vs Three Years
• The simplest LCDM model fits the data very well.– A power-law primordial power spectrum– Three relativistic neutrino species– Flat universe with cosmological constant
• The maximum likelihood values very consistent– Matter density and sigma8 went down slightly
Constraints on GW• Our ability to
constrain the amplitude of gravity waves is still coming mostly from the temperature spectrum.– r<0.55 (95%)
• The B-mode spectrum adds very little.
• WMAP would have to integrate for at least 15 years to detect the B-mode spectrum from inflation.
What Should WMAP Say About Inflation Models?
Hint for ns<1
Zero GW The 1-d marginalized constraint from WMAP alone is ns=0.95+-0.02.
GW>0The 2-d joint constraint still allows for ns=1 (HZ).
What Should WMAP Say About Flatness?
Flatness, or very low Hubble’s constant?
If H=30km/s/Mpc, a closed universe with Omega=1.3 w/o cosmological constant still fits the WMAP data.
What Should WMAP Say About Dark Energy?
Not much!
The CMB data alone cannot constrain w very well. Combining the large-scale structure data or supernova data breaks degeneracy between w and matter density.
What Should WMAP Say About Neutrino Mass?
WMAP alone (95%):
- Total mass < 2eV
WMAP+SDSS (95%)
- Total mass < 0.9eV
WMAP+all (95%)
- Total mass < 0.7eV