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“My goal is simple.

Observational Cosmology: 2. The Cosmic Background. “My goal is simple. It is complete understanding of the universe, why it as it is and why it exists as all.” — Stephen Hawking. 2.1: The Isotropic Background. Is the Universe really homogeneous & isotropic ?? - Olbers Paradox revisited.

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“My goal is simple.

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  1. Chris Pearson : Observational Cosmology 2: The Cosmic Background - ISAS -2004 Observational Cosmology: 2.The Cosmic Background “My goal is simple. It is complete understanding of the universe, why it as it is and why it exists as all.” — Stephen Hawking.

  2. Chris Pearson : Observational Cosmology 2: The Cosmic Background - ISAS -2004 2.1: The Isotropic Background Is the Universe really homogeneous & isotropic ?? - Olbers Paradox revisited WHY IS THE SKY SO DARK ? Heinrich Olbers 1826 (Thomas Digges 1576) The Sky should be the average surface brightness of a star !!! Solution: The Universe has a finite age  Not all the light has had time to reach us yet ! This is the optical Olbers Paradox…. BUT … What if Mr Olber had microwave eyes ? The sky would be uniformly bright at l=5cm At a constant temperature of 2.73K

  3. Chris Pearson : Observational Cosmology 2: The Cosmic Background - ISAS -2004 CMB is like a heat map 4cm 2.1: The Isotropic Background Is the real Universe really homogeneous and isotropic ?? Actual Temperature Distribution 1 / 1000 Temperature variation 1 / 100, 000 Temperature variation

  4. Chris Pearson : Observational Cosmology 2: The Cosmic Background - ISAS -2004 2.1: The Isotropic Background • 1964: Penzias & Wilson - • Bell Laboratries Satellite Telecommunications at microwave wavelengths ~ 7.35cm • Found a value of 3.5K higher temperature than expected when turning antenna to blank sky • Serendipitously discover the 2.73K microwave background radiation The discovery of the microwave Background These photons are the redshifted relic or ashes of the Big Bang Originally high energy gamma rays, these primordial photons have cooled to be 2.73K 2mm microwaves today

  5. Chris Pearson : Observational Cosmology 2: The Cosmic Background - ISAS -2004 e- g e- e- g p g p p g p e- recombination t z T g H R H g H g H g De-coupling H g H g H g g H Last Scattering g 2.2: The Origin of the Microwave Background Recombination and Decoupling BIG BANG • matter in thermal equilibrium with the radiation. photons and electrons to interact via Thompson scattering • Temperature drops then p+e-H recombination • Eventually interactions stop allowing the photons to flow freely on scales of the horizon de-coupling • Era at which any photon last scattered off any electronsurface of last scattering

  6. Chris Pearson : Observational Cosmology 2: The Cosmic Background - ISAS -2004 2.2: The Origin of the Microwave Background The Surface of Last Scattering After Recombination and Decoupling the photons are no longer bound to matter and can stream freely Photons from the Big Bang fill the universe and we observe them as the 2.7K microwave background. These photons are the redshifted relic or ashes of the Big Bang Last time photons interacted Surface of Last Scattering This also means that we can not observe the Universe when it was younger than ~400,000 years

  7. Chris Pearson : Observational Cosmology 2: The Cosmic Background - ISAS -2004 Energy density of radiation Energy density of the matter Photon Number Density Baryon Number density 2.2: The Origin of the Microwave Background The Relic Background • Today : Energy density in Baryons is 800 times energy density in photons • But : Number density of Baryons to photon is 1 in 109

  8. Chris Pearson : Observational Cosmology 2: The Cosmic Background - ISAS -2004 Ionization energy of Hydrogen =13.6eV The baryon/photon ratio, ~5x10-10 Temperature drops then p+e-H recombination  depends on  Therefore define the fractional ionization Number densities of particles as a function of To given by Boltzmann function H binding energy = Q = (mp+me-mH)c2 mp~ mH Statistical weights mp= me=2, mH=4 SAHA EQUATION 2.2: The Origin of the Microwave Background The Physics of Recombination But even at lower temperatures sufficient photons with appropriate ionization energy

  9. Chris Pearson : Observational Cosmology 2: The Cosmic Background - ISAS -2004 Quadratic in c Saha Equation Ionization Fraction Black Body Energy Density Distribution 1 2 3 4 2 4 3 1 2.2: The Origin of the Microwave Background The Physics of Recombination Between temperatures of To~5000  2000, Ionization fraction drops 1  0

  10. Chris Pearson : Observational Cosmology 2: The Cosmic Background - ISAS -2004 2.2: The Origin of the Microwave Background The Physics of Recombination Decoupling Optical Depth

  11. Chris Pearson : Observational Cosmology 2: The Cosmic Background - ISAS -2004 c(z) c(T) 2.2: The Origin of the Microwave Background The Physics of Recombination Epoch of Recombination (kT~Q) To ~ 3740K z ~ 1370, Dz ~ 200 T ~ 240kyr, Dt ~ 70kyr Epoch of Decoupling (G~H) To ~ 3000 z ~ 1089, Dz ~ 195 T ~ 379,000yr, Dt ~ 118ky

  12. Chris Pearson : Observational Cosmology 2: The Cosmic Background - ISAS -2004 Early Universe was highly homogenous At the level of dT ~ 10-3 : Observe Dipole Anisotropy Subtract Dipole Distortion At the level of dT ~ 10-5 : Observe complicated fluctuations 2.3: Observations of the CMB Temperature Fluctuations Observations of CMB  Fluctuations in Temperature

  13. Chris Pearson : Observational Cosmology 2: The Cosmic Background - ISAS -2004 COBE 2.3: Observations of the CMB Temperature Fluctuations - Isotropy and Homogeneity Early Universe was highly homogenous • 1989: COBE • Cosmic Microwave Background Explorer • Diffuse Infrared Background Experiment • DIRBE 0.001mm < l < 0.24mm • Far Infrared Absolute Spectrometer • FIRAS 0.1mm < l < 10mm • Differential Microwave Radiometer • DMR l= 3.3, 5.7, 9.6mm

  14. Chris Pearson : Observational Cosmology 2: The Cosmic Background - ISAS -2004 Like the Ether ? Net Doppler Effect ZERO! Sweeps up cdt+vdtcosq more photons in direction of travel 1+bcosq Abberation effect (solid angle for moving observer decreases) (1+bcosq)-2 Io (no) = (1+bcosq)3 Ie (ne) q 1+ cos(q ) 2.3: Observations of the CMB At the level of 10-3 : Observe Dipole Anisotropy One half of sky seemingly blue shifted to higher temperatures One half of sky seemingly red shifted to lower temperatures Temperature Fluctuations - The Dipole Anisotropy Net motion of COBE wrt frame of reference in which CMB is isotropic Doppler Effect? 1) increases energy of photons seen in direction of motion ~ 1+bcosq Doppler Effect? 2) dn, interval of frequencies also increased ~ 1+bcosq (b=v/c~10-3) There is no quadrapole moment • COBE - Earth correction ~ 8 kms-1 • Earth - Sun correction ~ 30 kms-1 • Sun - Galactic Centre correction ~ 220 kms-1 • Galaxy - Local Group ~ 80 kms-1 •  Local Group moving towards Hydra at v~630±20kms-1 ~ 0.002c

  15. Chris Pearson : Observational Cosmology 2: The Cosmic Background - ISAS -2004 T2(q2,f2) T1(q1,f1) Temperature fluctuations defined of surface of sphere  Expand as spherical harmonics 2.3: Observations of the CMB Temperature Fluctuations • Early Universe was highly homogenous • Planck Time ~ quantum fluctuations • Inflation ~ amplified fluctuations  macroscopic • Fluctuations frozen until zdec • Fluctuations in the density (dr/r)~3(dT/T) Cl(q)= Correlation function (mean product over all points seperated by q) Value of Cl(q)as a function ofq (0< q <180o) gives a complete statistical description of the CMB

  16. Chris Pearson : Observational Cosmology 2: The Cosmic Background - ISAS -2004 Expand Cl(q)in spherical harmonics (Pl = Legendre Polynomials) 2.3: Observations of the CMB Temperature Fluctuations Cl(q)is scale dependent The value probed will depend on resolution of instrument Individual Cl ’s probe structure on different angular scales given by q=180o / l l = 0 the monopole l = 1 the dipole (due to our motion wrt CMB) l = >1 fluctuations imprinted on SLS

  17. Chris Pearson : Observational Cosmology 2: The Cosmic Background - ISAS -2004 Davis & Lineweaver 2003 2.3: Observations of the CMB • Particle horizon: the distance light can have traveled from t = 0 to any given time t • Event horizon: the distance light can travel from any given time t to t=∞ (or tmax). • Hubble Distance (Hubble Sphere): the distance beyond which recession velocity exceeds the speed of light. Horizons and Fluctuations

  18. Chris Pearson : Observational Cosmology 2: The Cosmic Background - ISAS -2004 horizon observer INFLATION L/2 qH For scales = Horizon scale at last scattering, dA horizon observer BIG BANG Horizon Distance given by particle horizon distance Angular Diameter Distance at SLS 2.3: Observations of the CMB The Horizon Distance at recombination and decoupling (Surface of Last Scattering SLS) Horizons and Fluctuations: Large Scale Fluctuations q>1o Scales of q>1o different origin to scales q<1o Spherical harmonics q=180o / l q>1o Corresponds to l<180 q<1o Corresponds to l>180 • Scales of q>1o outside horizon • fluctuations from inflation • Gravitational effect of primordial density fluctuations

  19. Chris Pearson : Observational Cosmology 2: The Cosmic Background - ISAS -2004 Fluctuations in density  fluctuations in gravitational potential  Gravitational Wells SACHS - WOLFE EFFECT (1967) Red spots - higher temperature - potential maxima Blue spots - lower temperature - potential minima 2.3: Observations of the CMB Horizons and Fluctuations: Sachs-Wolfe Effect • Scales of q>1o outside horizon • fluctuations from inflation • Gravitational effect of primordial density fluctuations Poisson eqn At surface of last scattering: • Photon a local potential minima (bottom of well) has to climb out  lose energy  Redshift • Photon a local potential maxima (top of well) falls in  gain energy  Blueshift

  20. Chris Pearson : Observational Cosmology 2: The Cosmic Background - ISAS -2004 horizon INFLATION Compression Acoustic Oscillations horizon Pressure BIG BANG Expansion Fundamental Overtones (l<180) l = 180 2.3: Observations of the CMB Horizons and Fluctuations: Small Scale Fluctuations q<1o • Scales of q<1o are inside the horizon  baryons & photons • Baryons and photons fall into DM potential well • At decoupling • Baryon/photon fluid in max compression  high r,T • Baryon/photon fluid in max expansion  low r,T Generally q~10(l=180) corresponds to potential wells in which Baryon/photon fluid had just reached max compression at time of decoupling (fundamental mode of oscillation). These potential wells had sizes of ~ dH,SLS (seen as qH today)

  21. Chris Pearson : Observational Cosmology 2: The Cosmic Background - ISAS -2004 odd peaks max compression even peaks max rarefaction Power in the fluctuations l2Cl(2p)1/2 Dobbs 2003 60’ 6’ 600’ Multipole (l)   Angular scale (q) 2.3: Observations of the CMB Different angular scales probing different Physical processes Horizons and Fluctuations Savage 2003

  22. Chris Pearson : Observational Cosmology 2: The Cosmic Background - ISAS -2004 http://planck.mpa-garching.mpg.de/Planck/experiments.html 2.3: Observations of the CMB CMB Experiments Different angular scales probing different Physical processes.

  23. Chris Pearson : Observational Cosmology 2: The Cosmic Background - ISAS -2004 2002 : Secondary acoustic peaks observed (Maxima,Boomerang DASI) 2001 : Fundamental acoustic peak observed (Boomerang, Maxima) 2015? : Discovery of B-modes ? (CMBPOL Einstein Probe Satellite) 2007? : Characterize E-modes, Discovery of B-modes ? (Planck) 2002 : CMB Polarization (E-modes) observed (DASI) 1977 : CMB Dipole Observed (Smoot et al) 2005 ? : Discovery of B-modes ? (Polar Bear) 1989 : CMB anisotropies observed (COBE) 1965 : CMB Discovery (Penzias & Wilson) 2001 : Acoustic Peaks mapped (WMAP) 2.3: Observations of the CMB CMB Experiments

  24. Chris Pearson : Observational Cosmology 2: The Cosmic Background - ISAS -2004 q ~ 70 q ~ 0.20 2.3: Observations of the CMB WMAP • Wilkinson Microwave Anisotropy Probe (2001 at L2) • Detailed full-sky map of the oldest light 380,000yr old in Universe. • It is a "baby picture" of the 380,000yr old Universe • Probe the CMB fluctuation Spectrum below the horizon scale • q ~ 900 - 0.2 (l=2-1000)

  25. Chris Pearson : Observational Cosmology 2: The Cosmic Background - ISAS -2004 2.3: Observations of the CMB WMAP

  26. Chris Pearson : Observational Cosmology 2: The Cosmic Background - ISAS -2004 Blue - cool Red - warm fundemental 1st harmonic 2.3: Observations of the CMB Resolving the Different Cosmological World Models • Relative heights and locations of these peaks  signatures of properties of the gas at this time Open Universe - photons move on faster diverging paths => angular scale is smaller for a given size Peak moves to smaller angular scales (larger values of l) *** THE UNIVERSE IS FLAT ***

  27. Chris Pearson : Observational Cosmology 2: The Cosmic Background - ISAS -2004 Wandelt et al. 2004 2.3: Observations of the CMB Resolving the Different Cosmological World Models

  28. Chris Pearson : Observational Cosmology 2: The Cosmic Background - ISAS -2004 DASI polarization measurement 2002 2.3: Observations of the CMB CMB photons may be polarized Polarization measurements Stokes vector S=(I,Q,U,V) characterizies the intensity and polarization of light. V=IRCP-ILCP Unpolarized light Q=U=V=0 polarized light, Q2+U2+V2=1 CMB Polarization V=0 U=I+45-I-45 Q=I0-I90 • Inflation  Gravitational wave background • CMB SLS gravity wave amplitude  B (curl) mode component to CMB polarization • The smoking gun of inflation • Extend observations from 380,000yrs  10-35 s after Big Bang !! • Combination of Scalar, Vector & Tensor fields carry information on temperature anisotropies, acoustic peaks, cosmological parameter. • Information on epoch of re-ionization

  29. Chris Pearson : Observational Cosmology 2: The Cosmic Background - ISAS -2004 2.3: Observations of the CMB Polarization measurements ~100mK Temperature E (Tensor)-modes ~4mK RMS B (curl)-modes ≤300nK 1 degree B-mode amplitude is Determined only by the energy scale of inflation. Characterized by Tensor to scalar ratio ~ < 0.71 (WMAP Hu et al. astro-ph/0210096

  30. Chris Pearson : Observational Cosmology 2: The Cosmic Background - ISAS -2004 2.4: Background Light Components Backgrounds or Foregrounds? (signals or noise?) The total integrated background light comes from many sources • Cosmic Microwave Background Radiation CMBR 3K, peaks at 5cm • Our Atmosphere: Sunlight scattered through atmosphere • Zodiacal Light: Dust in plane of Solar System illuminated by Sun peaks at 60mm • Galactic emission from dust, peaks at about 100mm • Emission from hot gas, Synchrotron & free-free radio emission • Extra galactic contributions from Radio Sources, Galaxies • S-Z Compton scattering of CMBR photons by relativistic e- in cluster gas

  31. Chris Pearson : Observational Cosmology 2: The Cosmic Background - ISAS -2004 2.4: Background Light Components Backgrounds or Foregrounds? (signals or noise?)

  32. Chris Pearson : Observational Cosmology 2: The Cosmic Background - ISAS -2004 2.4: Background Light Components Infrared Cirrus • Extended whispy neutral interstellar dust in the Milky Way heated by the interstellar radiation field. • Cirrus emission peaks at far IR wavelengths (100µm) but was detected in all 4 IRAS bands • The galactic cirrus is a function of galactic latitude and is serious for wavelengths longer than 60µm. B100 Contours at 1 and 2 MJy/sr

  33. Chris Pearson : Observational Cosmology 2: The Cosmic Background - ISAS -2004 2.4: Background Light Components Confusion to extragalactic sources • Extragalactic Background • The superposition of sources below the flux limit / resolution of the instrument

  34. Chris Pearson : Observational Cosmology 2: The Cosmic Background - ISAS -2004 Optical 2.4: Background Light Components Contributions to the Extragalactic Background

  35. Chris Pearson : Observational Cosmology 2: The Cosmic Background - ISAS -2004 CMB Galactic HI (correlated) Galactic HI (uncorrelated) Galactic Synchrotron Extragalactic Radio Sources Extragalactic IR Sources Instrument on sky noise level 2.4: Background Light Components Backgrounds or Foregrounds? (signals or noise?) Bouchet 1999

  36. Chris Pearson : Observational Cosmology 2: The Cosmic Background - ISAS -2004 2.5: Summary • The CMB is strong vindication for the Hot Big Bang Theory • The CMB • Isotropic to one part in 105 - An ideal Black Body • Shows a Dipole distortion due to the motion of the Earth wrt CMB frame • After Dipole Subtraction shows fluctuations on 30mK • The epoch of recombination and decoupling define the Surface of Last Scattering (SLS) • The SLS is the last time the CMB interacated with matter • The SLS is a fossil of the 380,000yr old Universe • Primoridial density fluctuations are imprinted on the SLS • The Fluctuations in the CMB has 2 origins • On scales > 1 degree  Primordial Fluctuations from Inflation (Sachs Wolfe effect) • On scales < 1 degree  acoustic oscillations in the baryon-photon plasma • Decomposing the CMB fluctuations into spherical harmonics • Plot the fluctuation power as a function of angular size • Discriminate between different world models • WMAP - THE UNIVERSE IS FLAT ! • Foreground (contamination) • Zodiacal Light • Discriminate between different world models • Extragalactic Background (unresolved galaxies) • ***** One man’s noise is another man’s signal ***** Summary BUT….

  37. Chris Pearson : Observational Cosmology 2: The Cosmic Background - ISAS -2004 2.5: Summary Summary

  38. Chris Pearson : Observational Cosmology 2: The Cosmic Background - ISAS -2004 2.5: Summary Summary 終 Observational Cosmology 2. The Cosmic Background Observational Cosmology 3. Structure Formation 次：

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