Cosmology and extragalactic astronomy

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Cosmology and extragalactic astronomy
Mat Page
Mullard Space Science Lab, UCL
8. The cosmic microwave background
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9. The cosmic microwave background
Slide 2

• This lecture
• Discovery of CMB
• COBE
• BOOMERANG, DASI
• MAP

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Discovery of CMB
Slide 3

• 1965, Penzias Wilson
• Atmospheric noise for Telstar
• Unexplained noise in microwave antenna
• Isotropic, consistent with a 3K blackbody

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Where does it come from?
Slide 4

• Early Universe
• hot, energetic protons and electrons
• As Universe expands, it cools
• Protons and electrons recombine to form
  hydrogen
• Universe becomes transparent to light
• Matter and radiation decouple
• 380,000 years after the big bang, at z1089 - 1
  (WMAP)

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So why do we see it now?
Slide 5

• Recombination happens at the same time everywhere
  - why do we see the CMB?
• CMB thermal glow emitted isotropically from
  everywhere in space
• Some of it is reaching us now.

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So youve won your Nobel prize...
Slide 6

• What now?
• Build better detectors!
• Better measurements probe density fluctuations in
  early universe
• Problem - atmosphere absorbs microwaves between
  10mm and 1cm.
• Peak of 2.7K blackbody spectrum is 1-3mm
• Solution go up!

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COBE
Slide 7

• The Cosmic Background Explorer
• FIRAS - Far InfraRed Absolute Spectrometer
• Measure spectrum of CMB
• DMR - Differential Microwave Radiometer
• Compare CMB from different parts of the sky, look
  for anisotropy
• DIRBE - Diffuse InfraRed Background Experiment
• Cosmic infrared background
• IR from distant stars in early Universe

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Results from COBE
Slide 8

• FIRAS CMB has a blackbody spectrum with T2.726K

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Spectrum very close to blackbody
Slide 9

• These are the residuals to the blackbody fit

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COBE DMR
Slide 10

• Two horns at 60o
• Differential measurement

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COBE results DMR dipole
Slide 11

• CMB dipole anisotropy
• Doppler shift 370 km/s
• Shows Solar system motion relative to CMB

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Once the dipole and Galactic emission have been
removed
Slide 12
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The famous COBE DMR result
Slide 13

• Subtract dipole anisotropy
• Subtract dust, gas synchrotron radiation from
  the Milky Way
• Left with anisotropies in the CMB
• These are density fluctuations in the early
  Universe
• Fluctuations 20 mK
• lt 1 part in 100,000

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How else can you get high?
Slide 14

• BOOMERANG
• Balloon Observations Of Millimetric
  Extragalactic Radiation ANd Geophysics
• 1998
• 40 km, in stratospheric polar vortex
• Observed 3 of sky
• 10.5 days flight

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BOOMERANG results
Slide 15

• Here is a sky map from BOOMERANG
• Higher resolution than COBE, but only observed 3
  of the sky.
• Spectrum shows angular variations in temperature
• Interpreted as acoustic waves in pre-decoupling
  plasma.

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BOOMERANG Cosmological parameters
Slide 16
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BOOMERANG Cosmological parameters
Slide 17
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DASI
Slide 18

• Degree Angular Scale Interferometer
• On the ground at the South Pole
• Detects polarisation of CMB
• Further constrains cosmological models

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WMAP - results 2003!
Slide 19

• Wilkinson Microwave Anisotropy Probe
• Sits at L2, rotating and slowly precessing

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WMAP results
Slide 20
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WMAP Key results
Slide 21

• Reionization at z10
• Warm dark matter ruled out, as WDM models cannot
  form structure till z8
• Global fit to WMAP supernovae, 2dF etc
• Age of Universe 13.7 - 0.2 x 109 years.
• Decoupling occurred after 379 -8 x 103 years
• at a redshift of z1089 -1
• W01.02 - 0.02 Wdark 0.22
• WL 0.73 Wbaryon 0.05

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WMAP power spectrum
Slide 22
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CMB key points
Slide 23

• The CMB was discovered in 1965 and is a crucial
  piece of evidence for the big bang
• It is the radiation from the optically thick
  early Universe
• It is highly Uniform, but contains small
  fluctuations
• these tiny fluctuations were the seeds for
  present day galaxies and clusters
• The spectrum of fluctuations allows us to put
  tight constraints on cosmological parameters