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Understanding Cosmic Microwave Background: Insights from Extragalactic Astronomy

This lecture delves into the intriguing properties of the Cosmic Microwave Background (CMB) and its significance in cosmology. It discusses the CMB's origins during critical epochs such as recombination and decoupling, along with its role as a remnant from the early universe's hot phase following the Big Bang. Key topics include temperature fluctuations in the CMB, Saha's equation, and the statistical tools used to analyze anisotropies. Additionally, insights from the Planck satellite findings provide a deeper understanding of the universe's structure, content, and evolution.

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Understanding Cosmic Microwave Background: Insights from Extragalactic Astronomy

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Presentation Transcript

  1. Physics 133: Extragalactic Astronomy and Cosmology Lecture 14; March 3 2014

  2. Previously. Applications of lensing • Measure mass of galaxies, clusters planets. • Test the cosmological model by measuring substructure • Cosmography • Test gravity • Properties of dark matter

  3. Outline: • Cosmic microwave background • Summary of properties • Saha’s Equation and recombination • (Re)combination and decoupling • Temperature fluctuations • Origin of the fluctuations • Cosmography: results from Planck

  4. The CMB: basic properties • CMB photons: • Energy density: 0.261 MeV/m3 • Number density: 4e8/m3 • Baryons: • Energy density 210 MeV/m3 • Number density: 0.22/m3 • Ratio: • η = n(baryons)/n(CMB)=5e-10

  5. What are the three main COBE results? • The CMB is a blackbody within 1 part in 10,000 • There is a dipole corresponding to the motion of the Earth with respect to the CMB • There are temperature fluctuations: • <(δT/T)2>1/2 = 1.1e-5 The standard interpretation is that the CMB is left over from an early Epoch when the universe was hot (Hot Big Bang)

  6. The origin of the CMB:Where/When does it come from?

  7. Three key epochs • Recombination • z~1370 • Decoupling • z~1100 • Last scattering surface • z~1100

  8. Recombination [Hydrogen case: blackboard]

  9. Decoupling and last scattering surface [blackboard]

  10. The CMB: current view How do we interpret this map? We need statistical tools.

  11. The CMB: current view What is this? Anisotropy of the CMB as a function of angular scale

  12. Anisotropy and cosmography.

  13. Planck XVI

  14. Summary • The CMB gives us a view of the universe at z~1100 (last scattering surface) • This is very close to the epoch of recombination, when nuclei captured electrons to form atoms z~1300 • CMB fluctuations are generated by fluctuations in the gravitational field at the time of last scattering • The angular scale of the fluctuations gives us information on the content of the universe.

  15. The End See you on Wednesday!

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