1. What have we learnt from WMAP? Robert Crittenden Institute of Cosmology and Gravitation, Portsmouth, UK

2. Over 100 papers in the past year just with ‘WMAP’ in the title! What is qualitatively new in WMAP? Outline Introduction to WMAP Polarization on the largest scales Correlations with large scale structure Large scale power deficit Topology of the universe Evidence of non-Gaussianity

3. Wilkinson Microwave Anisotropy Probe David Wilkinson CMB Pioneer WMAP satellite Launched June 2001 Reached L2 August 2001

4. WMAP science team Charles Bennett, PI NASA Goddard G. Hinshaw, M. Limon, A. Kogut, E. Wollack L. Page, N. Jarosik, Princeton D. Spergel, D. Wilkinson E. Wright UCLA G. Tucker Brown S. MeyerChicago M. HalpernUBC Many thanks to them for their hard work as well as images and data products used in this talk!

5. what’s so great about WMAP? Mostly quantitative: More pixels: nearly 1,000,000 independent pixels More frequencies: five frequency channels  better foreground removal, even the through galaxy Full sky coverage  tight calibration from the dipole (0.5%)  compare and unify other CMB observations  cosmic variance limited to l=350 Better systematic error control

6. five frequency maps 23, 33, 41, 61 and 93 GHz

7. derived maps Dust mapSynchrotron map Free-free mapCMB map

8. Power spectrum of WMAP Cosmic variance limited to l=350 S/N > 1 for l<650 Features: Doppler peak well characterized missing small scale power? glitches at l=40, 210 Remarkably consistent with earlier data, apart from 10% calibration issue. Hinshaw et al.

9. cosmological parameters

10. The power spectrum has confirmed earlier best fit models, with smaller error bars Bottom line: very close to flat significant dark matter (25%) dominated by dark energy (70%) adiabatic, n=1 Most papers have focused on using spectrum to constraint variants of the lambda CDM model But the full sky nature of WMAP has allowed us to discover a number of things which we could not have known otherwise…

11. Large scale CMB polarization On the last scattering surface, polarisation is generated effectively by the fluid velocity gradient Thus, we do not expect it to be large for modes outside the horizon (l < 100) Any polarization we see on these scales must have been generated by later scattering! WMAP is the first experiment to see the polarization on the largest scales (though it was seen in earlier measurements by DASI)

12. Temperature-polarization cross correlation WMAP’s polarization sensitivity is poor, making direct detection very difficult, but large sky coverage means finding correlation with temperature is relatively easy. Advantage is that we know the polarization we see is cosmological! WMAP saw both reionization and polarization from last scattering! First calculations of T-P by Coulson, RC and Turok, 1994 Kogut et al. 2003

13. Reionization Polarization on very large scales means some fraction of the light was recently rescattered The amplitude indicates 1/6 photons scattered, which can only be done if the universe reionized fairly early (z = 20  10) Optical depth,  = 0.17  0.04 This will be discussed in detail in talks by J. Ostriker, M. Kaplinghat

14. Polarization from last scattering WMAP also measured the polarization from the largest modes at last scattering The sign of the cross correlation tells us something about the direction of the velocity flows at that time. The sign was consistent with that predicted by adiabatic fluctuations, but not isocurvature. Inflow Radial Outflow Tangential

15. Correlation with large scale structure The large sky coverage of WMAP means that one is able to detect even weak correlations with other surveys. There are a number of reasons why such correlations might exist: The integrated Sachs-Wolfe effect The Sunyaev-Zeldovich effect in clusters Unremoved foreground sources

16. integrated Sachs-Wolfe effect while most cmb anisotropies arise on the last scattering surface, some may be induced by passing through a time varying gravitational potential: linear regime – integrated Sachs-Wolfe (ISW) non-linear regime – Rees-Sciama effect when does the linear potential change? Poisson’s equation constant during matter domination decays after curvature or dark energy come to dominate (z~1) induces an additional, uncorrelated layer of large scale anisotropies

17. two independent maps Integrated Sachs-Wolfe map Mostly large angular features Early time map (z > 4) Mostly from last scattering surface Observed map is total of these, and has features of both (3 degree resolution)

18. compare with large scale structure potential depth changes as cmb photons pass through time dependent gravitational potential observer density of galaxies traces the potential depth ISW fluctuations are correlated with the galaxy distribution! since the decay happens slowly, we need to see galaxies at high redshifts (z~1)  active galaxies (quasars, radio, or hard x-ray sources)  possibility of accidental correlations means full sky needed

19. how do we trace the matter? X-rays from active galaxies HEAO-1 x-ray satellite Galaxy and virtually all visible structures cleaned out Radio galaxies NRAO VLA Sky Survey (NVSS)

20. ISW correlations detected! Correlations seen with both at the 2.5 – 3.0 sigma level Also seen to some extent in galaxy surveys: SDSS, 2MASS, APM Amplitudes are largely consistent with dark energy model and argue against any pure dark matter model. (See E. Copeland talk.) S. Boughn & RC, Nature2004

21. SZ cross correlation Hot gases in clusters can upscatter CMB photons, also producing a correlation on smaller angular scales. Evidence for this is growing, but still somewhat contradictory Apparently detected with some surveys, not seen in others, seems to depend on the method used to trace clusters. This will lead to a constraint on the size and temperature of hot gas in clusters (Compton y-parameter) see also S. Majumdar talk.

22. Are there missing large scale correlations? The WMAP papers reported a deficit of large scale power to that expected in cosmological constant dominated models One statistic showed that this was likely only at a level of 1 chance in 700. (Posterior statistic?) Missing power also observed for COBE. Difficult to measure given cosmic variance. Spergel et al.

23. Why has this received so much attention? Other glitches are more statistically significant, but this is at a very interesting scale, the present horizon, and is not constrained on larger scales Difficult to produce by additional effects because it requires cancelling large scale power Some proposed solutions: 1) Running spectra tilt 2) Some minimum k cutoff 3) Related to curvature scale 4) High frequency oscillations in spectrum 5) SZ from local supercluster 6) Related to topology of the universe

24. Is the deficit significant? Efstathiou argues that the WMAP analysis suffers from a number of problems: Low estimates of power spectrum given the uncertainties in the masking Biases from frequentist statistics Decided on the test based on seeing the data He argues that the discrepancy is more like 1 chance in 10 or 20 and is consistent with lambda CDM. Can only be improved by better subtraction of the galaxy. Remains a tempting target for theorists.

25. Could we be seeing the effects of a finite universe? Based on the WMAP low l power spectrum, it has been suggested that our space could be dodecahedral (shaped like a soccer ball) This model is slightly closed and positively curved,  = 1.013 No indications have been found using correlation of patches Luminet, Weeks, Riazuelo, Lehoucq and Uzan, 2003.

26. More general searches have given only upper limits So far general searches for topology have only placed upper limits Focus has been on looking for matched ‘circles in the sky’ or symmetries in the temperature patterns While the dodecahedral model hasn’t been specifically excluded, evidence is against most models with a topology scale less than 24 GPc (Cornish et al, de Oliveira-Costa et al., Bond, Pogosyan & Souradeep) Future tests – looking for statistical isotropy (Hajian & Souradeep)

27. Non-Gaussianity in WMAP? Initial analyses indicated that the WMAP results were consistent with Gaussianity: 1) Three point tests are consistent up to known point source contribution (Komatsu et al., Gaztanaga & Wagg) 2) Apparent non-Gaussianities in COBE bispectrum do not appear in WMAP (Magueijo & Madeiros) 3) Topological tests (Minkowski functionals, genus) are also consistent (Komatsu et al., Colley & Gott) So far the limits are not sufficient to endanger the levels of non-Gaussianity that might be predicted by inflation

28. Some trouble on the horizon? Some recent analyses have pointed to possible inconsistencies: 1)Evidence that north ecliptic hemisphere has less large scale power than southern (Eriksen et al.) 2)A wavelet analysis shows evidence for non- Gaussianity in the southern Galactic hemisphere (Vielva et al.) 3)Asymmetry between some genus statistics for north and south Galactic hemispheres (Park) 4)Some strange alignments seen in the quadrupole and octopole moments (Tegmark et al.) 5)Multipole vector analysis indicates unexpected alignments at low l (Copi et al.) 6)Evidence for some strange phase correlations at l=16 (Coles et al.) and at very high l (Chiang et al.)

29. Is it significant? Most authors argue against foreground being responsible, but its not impossible Possibly a problem with a posteriori statistics, but many seem to be pointing to similar problems Could it be similar to COBE problems, where some of the data was contaminated? This seems unlikely for the large scale problems. The jury is still out, and more investigation is needed!

30. Conclusions WMAP has not only improved our understanding on a quantitative level, but also in qualitatively new ways thanks to its all sky coverage 1)Large scale polarization data shows that the CMB was significantly rescattered – new physics of reionization? 2)The velocity flows after last scattering were consistent with adiabatic fluctuations 3)Evidence that some fluctuations were produced recently due to ISW, consistent with predictions of lambda CDM 4)Interesting hints at a lack of power on large scales, but its still consistent with the standard picture

31. Conclusions continued… 5)One interesting explanation for it, a ‘soccerball’ universe has not been ruled out, but most small topological universes are unlikely. 6)The fluctuations appear largely Gaussian as would be expected by inflation, but some interesting aspects of the data still puzzle us, particularly on large scales Future: Two year data should be out soon WMAP Polarization auto-correlation (E-E) Small scale temperature and polarization experiments Planck is just 3.5 years away!

32. large scale correlations The anisotropies created by the ISW effect are primarily on large scales and are largely uncorrelated with those produced earlier On small scales, positive and negative ISW effects will tend to cancel out. However, on larger scales photons receive fewer kicks of larger amplitude The early and late power is fairly weakly correlated, so the power spectra add directly: WMAP best fit scale invariant spectrum Highest correlations are for the quadrupole, but it is still very weak