CMB Observations with the Cosmic Background Imager

1. CMB Observations with the Cosmic Background Imager Tim Pearson for the CBI team Tony Readhead (Principal Investigator), Steve Padin (Project Scientist until 2002). 2005 March 24

2. CBI Timeline • 1995-1999: design and construction • 1998-1999: testing in Pasadena • 1999: ship to Chile and commission • 2000-2001: CMB T and SZE observations (Stokes L) • 2-field differencing • 2002-2005: CMB polarization observations (Stokes L&R) • 6-field common mode • Jun 2005 - present: idle (unfunded) • May-Dec 2006: upgrade to larger antennas, T/SZE observations • 2007- : replace with QUIET receivers 2005 March 24

3. 13 Cassegrain antennas 0.9 m diameter 26–36 GHz, 10 channels HEMT amplifiers, Tsys ~ 27 K Baselines 1 m – 5.5 m Analog correlator Alt-az mount with parallactic rotation 2005 March 24

4. An interferometer cross-correlates the signals received by two separated antennas: the response (“visibility”) is proportional to a Fourier component with spatial frequency u = d/λ. The power spectrum Cl is the expectation of the square of the Fourier transform of the sky intensity distribution: i.e., closely related to the square of the visibilityVV*. Multipole l = 2p u Estimate spectrum by squaring visibility and subtracting noise bias. The observed sky is multiplied by the primary beam, corresponding to convolution (smoothing) in the (u,v) plane: so the interferometer measures a smoothed version of the power spectrum. Mosaicing several fields is equivalent to using a larger primary beam, thus improving resolution in l. CMB interferometers CAT, DASI, CBI, VSA, MINT, Amiba The CBI – Interferometry of the CMB 2005 March 24

5. Interferometry Advantages • Insensitive to large-scale structure • Uncorrelated noise • Direct measurement of polarization Q ± iU • Beam uncertainty not very important • Very different systematics 2005 March 24

6. Chajnantor Observatory Home of CBI, QUIET, and other experiments 2005 March 24

7. Total Intensity Observations • Observations made in 1999-2002 • Problem 1: Ground spillover • Differencing of two fields observed at same AZ/EL • Problem 2: Foreground point sources • Measure with higher resolution instrument • “Project out” of dataset sources of known position • Statistical correction to power spectrum 2005 March 24

8. Mosaic images • Emission from ground (horizon) dominant on 1-meter baselines • Observe 2 fields separated by 8 min of RA, lead for 8 min followed by trail for 8 min; subtract corresponding visibilities. Ground emission cancels. • Images show lead field minus trail field • Also eliminates low-level spurious signals 2005 March 24

9. CBI Polarization • Compact array • switchable RCP or LCP 36 RR or LL baselines measure I 42 RL or LR baselines measure Q+iU or E+iB • New ground strategy: strips of 6 fields, remove common mode (mean);(Lose 1 mode per strip to ground) • CBI observes 4 patches of sky – 3 mosaics & 1 deep strip Pointings in each area separated by 45’. Mosaic 6x6 pointings, for 4.5deg square, deep strip 6x1. • 2.5 years of data, Aug 02 – Apr 05. * Note bug in earlier analysis: omitted one antenna (12/78 baselines!) 2005 March 24

10. Raw Images 2005 March 24

11. “Ground subtracted” images 2005 March 24

12. Data Reduction • Editing and calibration • Noise estimation • Gridding of RR+LL, RL, LR or T, E, and B with full covariance matrix calculation • Project out common ground (downweight linear combination of data) • Project out point sources in T • Ignore point sources in polarization • Images of E and B (FT of gridded estimators) • Power spectrum estimation by max likelihood 2005 March 24

13. CBI Combined TT (2000-2005)

14. 2.9σ above model 2005 March 24

15. Projecting Out Variable Sources Marginalize over 1 parameter (flux) for each source, Or 2 parameters (2000-01 and 2002-05 flux). 2005 March 24

16. Cosmology Results CBI has measured power spectrum to much higher l than previous experiments, well into damping tail Flat universe with scale-invariant primordial fluctuation spectrum Low matter density, baryon density consistent with BBN, non-zero cosmological constant Agreement with Boomerang, DASI, VSA and Maxima at l < 1000 is excellent 2005 March 24

17. At 2000 < l <3500, CBI finds power ~ 3 sigma above the standard models • Not consistent with any likely model of discrete source contamination • Suggestive of secondary anisotropies, especially the SZ effect • Comparison with predictions from hydrodynamical calculations: strong • dependence on amplitude of density fluctuations, s87 . Requires s8~1.0 2005 March 24

18. Varying 6 parameters plus amplitude of SZ template component 2005 March 24

19. CBI Upgrade • Larger 1.4-m dishes (Oxford University) • Lower ground pickup, lower noise • Ground screen • Close-packed array • Concentrate on high-l excess and SZE in clusters • 9–12 months of observing before QUIET 2005 March 24

20. CBI2 2005 March 24

21. NVSS Sources in CBI Field 2005 March 24

22. GBT observations • Green Bank telescope 30 GHz measurements of NVSS sources in CBI fields • New Caltech Continuum Backend for switched observations • 1580 (of ~4000) sources observed so far under photometric conditions • 175 detected S > 2.5 mJy (5σ) at 32 GHz • Non-detections can be safely ignored in CBI! • Additional GBT observations to characterize faint source population • Brian Mason, Larry Weintraub, Martin Shepherd 2005 March 24

23. CBI2 Projection SZE Secondary CMB Primary ~ s87 2005 March 24

24. CBI Polarization Spectra • TT consistent with earlier results • EE and TE consistent with predictions • BB consistent with zero TT EE TE BB 2005 March 24

25. Shaped Cl Fit Likelihood of EE Amplitude vs. “TT Prediction” • Use WMAP’03+CBI TT+ Acbar best-fit Cl as fiducial model • Results for CBI • EE qB = 0.97 ± 0.14 (68%) • EE likelihood vs. zero : significance 10.1 σ • TE qB = 0.85 ± 0.25 • BB qB = 1.2 ± 1.8 μK2 2005 March 24

26. Comparison of Experiments 2005 March 24

27. Comparison of Experiments 2005 March 24

28. Comparison of Experiments 2005 March 24

29. θ/θ0 • Angular size of sound horizon at LSS should be same for TT and EE. • CBI only has multiple solutions (shift spectrum by one peak). • DASI removes degeneracy, but less sensitive. • CBI EE + DASI EE give scale vs. TT of 0.98 +/- 0.03. 2005 March 24

30. Isocurvature Isocurvature puts peaks in different places from adi- abatic. We use seed isocurvature model and find both EE and TE prefer adiabatic w/ iso consistent with zero. 2005 March 24

31. Isocurvature • Normalize seed iso spectrum to total power expected from TT adiabatic prediction • Fit shapes for both EE, TE • EE adi =1.00±0.24, iso=0.03±0.20 • TE adi = 0.86±0.26, iso=0.04±0.25 2005 March 24

32. WMAP Ka-band polarization Foregrounds DRAO 1.4 GHz polarized intensity (Wolleben et al. astro-ph/0510456) WMAP synchrotron component (WMAP Science Team) 2005 March 24

33. Foregrounds • TT: template comparisons • 2.5σ detection of correlation with 100 μm template • CHFT observations to provide SZ template • Polarization: No evidence (yet) for foreground contamination: • No B-mode detection • No indication of discrete sources (power ∝ l2) • Upper limit on synchroton component (DASI) 2005 March 24

34. WMAP3 WMAP3+CBIcombinedTT+CBIpol CMBall = Boom03pol+DASIpol +VSA+Maxima+WMAP3+CBIcombinedTT+CBIpol 2005 March 24

35. People 2005 March 24

36. http://astro.caltech.edu/~tjp/CBI/ • Readhead et al. 2004, ApJ, 609, 498 • Readhead et al. 2004, Science 306, 836 • Sievers et al. 2005, astro-ph/0509203 2005 March 24