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Chapter 6 Cosmic Microwave Background

Chapter 6 Cosmic Microwave Background. COBE. COBE. WMAP CMB anisotropy. CMB anisotropy: a toy tutorial †. † : mainly from Wayne Hu ( http://background.uchicago.edu/~whu ). Gravity : attracting force Photon pressure : driving force

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Chapter 6 Cosmic Microwave Background

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  1. Chapter 6 Cosmic Microwave Background Particle Astrophysics & Cosmology SS 2008

  2. Particle Astrophysics & Cosmology SS 2008

  3. Particle Astrophysics & Cosmology SS 2008

  4. Particle Astrophysics & Cosmology SS 2008

  5. Particle Astrophysics & Cosmology SS 2008

  6. COBE Particle Astrophysics & Cosmology SS 2008

  7. COBE Particle Astrophysics & Cosmology SS 2008

  8. WMAP CMB anisotropy Particle Astrophysics & Cosmology SS 2008

  9. CMB anisotropy: a toy tutorial † † : mainly from Wayne Hu (http://background.uchicago.edu/~whu) Particle Astrophysics & Cosmology SS 2008

  10. Gravity : attracting force Photon pressure : driving force baryonic matter coupled to photons  photon pressure prevents collapse prior to recombination (while DM is already forming structure much earlier!) Particle Astrophysics & Cosmology SS 2008

  11. Oscillations produce T > 0 or T < 0 bluered Lowest mode (or wave number) corresponds to acoustic waves that managed to contract (or expand) once until recombination 2nd mode managed to contract and expand once until recombination, a.s.o. n = n · cs · s*-1 = n · c/3 · s-1 = n · 10-13 Hz  not “audible” ... Tn = trec/n = n-1 · 300000 yr Particle Astrophysics & Cosmology SS 2008

  12. Angular distribution in the sky: prior to recombination, photons correspond to higher and lower temp- erature After recombination, photons travel freely and convey their last information - hot or cold, as a function of angular position - to the observer; spatial inhomogeneity is con-verted into an angular anisotropy The larger the distance they arrive from, the more complex the angular pattern  higher multipoles Particle Astrophysics & Cosmology SS 2008

  13. taken from de Bernardis Particle Astrophysics & Cosmology SS 2008

  14. taken from de Bernardis Particle Astrophysics & Cosmology SS 2008

  15. Particle Astrophysics & Cosmology SS 2008

  16. The first peak: spatial curvature Fundamental scale at recombination (the distance that sound could travel) is converted into a fundamental angular scale on the sky today The first (and strongest) peak measures the geometry of the universe caveat: change in  produces slight shift, too ( causes slight change in distance that light travels from recombination to the observer) 1st peak, current score: 0 = 1.02 ± 0.02 Particle Astrophysics & Cosmology SS 2008

  17. The second peak: baryons and inertia: baryons add inertia to the plasma  contraction goes stronger, while the rarefaction remains the same! compression corresponds to odd peaks rarefaction corresponds to even peaks  higher baryon loading enhances odd over even peaks Particle Astrophysics & Cosmology SS 2008

  18. Particle Astrophysics & Cosmology SS 2008

  19. 2nd peak, current score: b ·h2 = 0.0224 ± 0.0009 in nice agreement with b from deuterium abundance (QSO absorption lines) Two more effects related to b: (i) increasing baryon load slows oscillations down  long waves don’t have enough time to build up  larger k preferred if b increases  power spectrum pushed to slightly higher l (ii) increasing b leads to more efficient damping of waves (s.b.), which is stronger for shorter wavelengths  spectrum falls of more rapidly towards large l (iii) decreasing msmaller baryon-loading effect Particle Astrophysics & Cosmology SS 2008

  20. The third peak: decay of potentials Poisson equation Since r  R-4 and m  R-3 ,  is governed by r in the state of highest compression However, rapid expansion of the universe leads to instant- aneous decay of ! The fluid now sees no gravitation to fight against  amplitude of oscillations goes way up: driving force! Particle Astrophysics & Cosmology SS 2008

  21. Driving force obviously more important in smaller (younger) universe, i.e. for r » m Since modes with small wavelengths started first, it is the higher acoustic peaks that are more prone to this effect. Increasing m ·h2 decreases the driving force  amplitudes of waves decrease Influence of m only separable from that of b by measuring at least the first three peaks 3rd peak, current score: m = 0.27  0.04  = 0.73  0.04 in good agreement with other, independent methods (galaxy clusters, SNe) Particle Astrophysics & Cosmology SS 2008

  22. effect of damping Particle Astrophysics & Cosmology SS 2008

  23. Damping depends on both, b and m b : increasing baryon density couples the photon-baryon fluid more tightly, hence shifts the damping tail to smaller angular scales, i.e. higher l m : increasing total matter density increases relative age of the universe, hence the angular scale of the damping is increased, shifting the damping tail to lower l Particle Astrophysics & Cosmology SS 2008

  24. Particle Astrophysics & Cosmology SS 2008

  25. deriving the power spectrum Particle Astrophysics & Cosmology SS 2008

  26. WMAP CMB anisotropy Particle Astrophysics & Cosmology SS 2008

  27. WMAP power spectrum Particle Astrophysics & Cosmology SS 2008

  28. Sunyaev-Zeldovich effect Particle Astrophysics & Cosmology SS 2008

  29. Particle Astrophysics & Cosmology SS 2008

  30. Particle Astrophysics & Cosmology SS 2008

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