CMB Observations with the Cosmic Background Imager Tim Pearson for the CBI team The CBI site is located at an altitude of 5000 m in the Andes near Cerro Chajnantor, 40 km east of San Pedro de Atacama. We chose this site to minimize atmospheric noise at 30 GHz, but were unable to do competitive site testing. Alternatives we considered included Mauna Kea (Hawaii) and the South Pole. Tony Readhead (Principal Investigator), Steve Padin (Project Scientist until 2002). 2005 March 24

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

HEMT amplifiers, Tsys ~ 27 K Baselines 1 m – 5.5 m Analog correlator 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

The CBI – Interferometry of the CMB 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 visibility VV*. 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 2005 March 24

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

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

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

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

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 4.5 deg 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

Raw Images 2005 March 24

“Ground subtracted” images 2005 March 24

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

CBI Combined TT (2000-2005)

2.9σ above model 2005 March 24

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

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

Not consistent with any likely model of discrete source contamination 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

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

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

CBI2 2005 March 24

NVSS Sources in CBI Field 2005 March 24

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

CBI2 Projection SZE Secondary CMB Primary ~ s87 2005 March 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

Shaped Cl Fit EE qB = 0.97 ± 0.14 (68%) 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 Likelihood of EE Amplitude vs. “TT Prediction” 2005 March 24

Comparison of Experiments 2005 March 24

Comparison of Experiments CBI defines high l at present, and would defne it better if we had been able to observe over the last year! QUaD? 2005 March 24

Comparison of Experiments 2005 March 24

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

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

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

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

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

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

People 2005 March 24

Sievers et al. 2005, astro-ph/0509203 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