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Galaxies and Cosmology

Galaxies and Cosmology

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Galaxies and Cosmology

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  1. Galaxies and Cosmology 5 points, vt-2007 Teacher: Göran Östlin Lectures 10-11

  2. FRW-models, summary

  3. Properties of the Universe set by 3 parameters: m, , k of Which only 2 are Independent: m + + k = 1

  4. Age of universe for: closed(1), critical(2), open(3), and acellerating(4) models

  5. CMBR spectrum A perfect black body -> thermal equilibrium when emitted

  6. Evolution of energy densities with scale factor R

  7. Evolution of fundamental interactions with time  inflation?

  8. Evolution of R during inflation

  9. What could have caused inflation? Equation of state: p = w  Radiation: w=1/3 Matter: w0 If w<-1/3 we would get acceleration i.e. Negative pressure makes gravity repulsive! Could w be a function of time? quintessence

  10. The early universe Gamov criterium: A reaction may be important as long as its interaction time scale is shorter than the expansion time scale of the universe Pair production. e.g.  +   e- + e+ reaction balance set by temperature, e.g: e + n  e- + p As long as mAc2 < kT a particle ’A’ may be kept in equilibrium, then ”freeze out”

  11. The early universe… • Baryogenesis: matter-antimatter equality broken, • Possibly by the decay of a so called X-boson • Net amount of matter • Photon to baryon ratio  = 109 Neutrino freeze out (decoupling) at t=0.7s Electron-positron pair production ceased and the Annihilation of existing pairs heated up radiation and Matter but not the neutrinos that had already decoupled

  12. Primordial nucleosynthesis • All fusion of hydrogen to heavier elements go through • the stage of deuterium. p + n  D +  • However, D can be dissociated by photons more • energetic than 2.2 Mev • Since there are many more photons than baryons • This will occur frequently enough also at much lower • Temperatures than kT=2.2 Mev ~1010 K • Nucleosynthesis inhibited until the D production rate was higher than the distruction rate (109K, t=200s) DEUTERIUM BOTTLENECK

  13. Primordial nucleosynthesis… However, neutron to proton ratio was fixed earlier (t=1s) when the neutrinos froze out: N(n)/N(p)=0.22 Since then until t=200s, some neutrons have decayed so N(n)/N(p)=0.16 Basically all leftover n ends up in D and almost all of that becomes He. Nothing heavier than Li is made. The He adundance is therefore determined by  (since we know the current CMBR photon density this gives us bar) Other trace elements: D, 3He, 7Li depend more strongly…

  14. Primordial nucleo-synthesis… Only a small Fraction of all Matter may be Baryonic Still larger than The luminous Matter density Galaxies could be baryonic?

  15. (re)combination Similarly to above, the vast amount of photons can Keep hydrogen ionised to temperatures well below 13.6 eV. But when T<4500 K the number of energetic Enough photons is to small and protons and electrons can combine to form neutral hydrogen Matter and radiation decouples Last scattering surface at z = 1100 (T=3000K) Leads to dramatic drop in pressure for the matter Observable as 3000/1100=3K CMBR, no lines since >>1 and z >>1

  16. Cosmic microwave Background Early universe Hot & Dense Dipole Penzias & Wilson CMBR according to COBE

  17. Last scattering ”surface”

  18. Structure/galaxy formation The concept of Jeans mass Gravity vs pressure, Static medium: M > Mjeans exponential growth Expanding EdS: M > Mjeans linear growth Expanding Open universe: M > Mjeans no growth Fluctuation spectrum: EdS: temperature fluctuations in CMBR expected at the 10-3 level, but only 10-5 observed Dark matter comes to rescue!

  19. Evolution of Jeans mass with scale factor with scale factor R

  20. Hierarchical growth of structure

  21. CMBR fluctuations First acoustic peak = standard rod! Height set by ΩBaryon At larger scales: Sachs-Wolfe

  22. Problems with standard BBI. Magnetic Monopoles

  23. Problems with standard BBII. Horizon problem

  24. Problems with standard BBIII. Flatness Problem

  25. Problems with standard BBIV. Origin of structure Inflation enlarges the scale of quantum fluctuations Microscopic Becomes Macroscopic

  26. The nature of dark matter Baryonic dark matter Hot vs cold non-baryonic dark matter: e.g. Nutrinos vs WIMPs

  27. Nature of dark energy • Cosmological constant • Vaccuum energy • Quintessence • String/Brane theory, extra dimensions

  28. Observations of the distant universe HST Ultra Deep Field 2 weeks of exposure Most distant galaxies at z=6 Problem: most of the light comes out in the infrared

  29. Lookback time and age

  30. Luminosity distance and angular size distance

  31. Redshifting galaxies LBGs LyaGs EROs

  32. ”Madau-plot”

  33. Madau plot is very sensitive to asssumptions about dust

  34. Hierarchical growth of structure Galaxy formation is a continous process Each big galaxy has had one major merger since z=1

  35. Closing in on the dark ages…

  36. JWST

  37. Some future observational tools ALMA, sub-mm, 64 antennae JWST “the first light machine” 6.5 m OWL the overwhelmingly large telescope +50m