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Cosmology and extragalactic astronomy

Cosmology and extragalactic astronomy. Mat Page. Mullard Space Science Lab, UCL. 8. The cosmic microwave background. Slide 2. 9. The cosmic microwave background. This lecture: Discovery of CMB COBE BOOMERANG WMAP, Planck. Slide 3. Discovery of CMB. 1965, Penzias & Wilson

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Cosmology and extragalactic astronomy

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

  2. Slide 2 9. The cosmic microwave background • This lecture: • Discovery of CMB • COBE • BOOMERANG • WMAP, Planck

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

  4. Slide 4 Where does it come from? • 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 z=1089 +- 1 (WMAP)

  5. Slide 5 So why do we see it now? • 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. Slide 6 So the Nobel prize has been won... • What now? • Build better detectors! • Better measurements probe density fluctuations in the early universe. • Problem – the atmosphere absorbs microwaves between 10mm and 1cm. • Peak of 2.7K blackbody spectrum is 1-3mm. • Solution: go up above the atmosphere!

  7. Slide 7 COBE • 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. Slide 8 Results from COBE • FIRAS: CMB has a blackbody spectrum with T=2.726K

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

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

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

  12. Slide 12 Once the dipole and Galactic emission have been removed:

  13. Slide 13 The famous COBE DMR result • 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 • < 1 part in 100,000

  14. Slide 14 How else can you get high?(I inherited this slide title!) • BOOMERANG • “Balloon Observations Of Millimetric Extragalactic Radiation ANd Geophysics • 1998 • 40 km altitude, in stratospheric polar vortex • Observed 3% of the sky • 10.5 days flight

  15. Slide 15 BOOMERANG results • Here is a sky map from BOOMERANG • Higher resolution than COBE, but it only observed 3% of the sky. • Spectrum shows angular variations in temperature • Interpreted as acoustic waves in pre-decoupling plasma.

  16. Slide 16 BOOMERANG: Cosmological parameters

  17. Slide 17 BOOMERANG: Cosmological parameters

  18. Slide 18 WMAP - results 2003. • Wilkinson Microwave Anisotropy Probe • Sits at L2, rotating and slowly precessing, to observe the whole sky twice a year.

  19. Slide 19 WMAP results

  20. Slide 20 WMAP: Key results • Reionization at z~10 • Warm dark matter ruled out, as WDM models cannot form structure till z=8. • 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 z=1089 +-1 • W0=1.02 +- 0.02 Wdark = 0.22 • WL = 0.73 Wbaryon = 0.05

  21. Slide 21 WMAP power spectrum

  22. Slide 22 Planck • ESA mission launched in 2009. • Europe’s first microwave background mission. • Resolution and precision so high that it should be the “final word” on structure at recombination. • 2m diameter primary mirror • Cryogenic payload (limited lifetime) • Situated at L2 like WMAP. • All sky survey. • Cosmology results released in 2013.

  23. Slide 23 • Scanned the whole sky at 10 arcminute resolution (no information on recombination on smaller scales) and with radiometry to 1 part in 106. • That is a factor 10 improvement in precision.

  24. Slide 24 Planck • Cosmology results out 2013 • Small revisions to cosmological parameters. • Ho=67.3 km/s • WL = 0.685 Wm = 0.315 • Age of Universe = 13.8 Gyrs. • And a few small effects which have attracted some radical interpretations. • Most notably, a large cold spot, first seen with WMAP, is confirmed.

  25. Slide 25 CMB: key points • 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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