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Cosmology and extragalactic astronomy

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So you've won your Nobel prize... What now? Build better detectors! ... Age of Universe = 13.7 - 0.2 x 109 years. Decoupling occurred after 379 -8 x 103 years ... – PowerPoint PPT presentation

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Title: Cosmology and extragalactic astronomy


1
Cosmology and extragalactic astronomy
Mat Page
Mullard Space Science Lab, UCL
8. The cosmic microwave background
2
9. The cosmic microwave background
Slide 2
  • This lecture
  • Discovery of CMB
  • COBE
  • BOOMERANG, DASI
  • MAP

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

4
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)

5
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.

6
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!

7
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

8
Results from COBE
Slide 8
  • FIRAS CMB has a blackbody spectrum with T2.726K

9
Spectrum very close to blackbody
Slide 9
  • These are the residuals to the blackbody fit

10
COBE DMR
Slide 10
  • Two horns at 60o
  • Differential measurement

11
COBE results DMR dipole
Slide 11
  • CMB dipole anisotropy
  • Doppler shift 370 km/s
  • Shows Solar system motion relative to CMB

12
Once the dipole and Galactic emission have been
removed
Slide 12
13
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

14
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

15
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.

16
BOOMERANG Cosmological parameters
Slide 16
17
BOOMERANG Cosmological parameters
Slide 17
18
DASI
Slide 18
  • Degree Angular Scale Interferometer
  • On the ground at the South Pole
  • Detects polarisation of CMB
  • Further constrains cosmological models

19
WMAP - results 2003!
Slide 19
  • Wilkinson Microwave Anisotropy Probe
  • Sits at L2, rotating and slowly precessing

20
WMAP results
Slide 20
21
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

22
WMAP power spectrum
Slide 22
23
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
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