cmb observations with the cosmic background imager
DESCRIPTION
CMB Observations with the Cosmic Background Imager. Tim Pearson for the CBI team. Tony Readhead (Principal Investigator), Steve Padin (Project Scientist until 2002). CBI Timeline. 1995-1999: design and construction 1998-1999: testing in Pasadena 1999: ship to Chile and commission - PowerPoint PPT PresentationTRANSCRIPT
2005 March 24 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 3
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
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13 Cassegrain antennas0.9 m diameter26–36 GHz, 10 channelsHEMT amplifiers, Tsys ~ 27 KBaselines 1 m – 5.5 mAnalog correlatorAlt-az mount with parallactic rotation
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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 = 2 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
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Interferometry Advantages
• Insensitive to large-scale structure• Uncorrelated noise• Direct measurement of polarization Q ± iU• Beam uncertainty not very important• Very different systematics
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Chajnantor Observatory
Home of CBI, QUIET, and other experiments
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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
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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
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• 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!)
CBI Polarization
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Raw Images
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“Ground subtracted” images
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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)
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2.9σ above model
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Projecting Out Variable Sources
Marginalize over 1 parameter (flux) for each source,
Or 2 parameters (2000-01 and 2002-05 flux).
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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
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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, 87 . Requires 8~1.0
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Varying 6 parameters plus amplitude of SZ template component
2005 March 24 20
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
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CBI2
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NVSS Sources in CBI Field
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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 24
SZE SZE SecondarySecondaryCMB CMB
PrimaryPrimary
87
CBI2 Projection
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CBI Polarization Spectra
TT
BB
TE
EE
•TT consistent with earlier results•EE and TE consistent with predictions•BB consistent with zero
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Shaped Cl Fit• 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”
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Comparison of Experiments
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Comparison of Experiments
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Comparison of Experiments
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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.
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Isocurvature
Isocurvature puts peaks in differentplaces from adi-abatic. We use seed isocurvaturemodel and findboth EE and TEprefer adiabatic w/iso consistent withzero.
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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
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Foregrounds
WMAP synchrotron component(WMAP Science Team)
DRAO 1.4 GHz polarized intensity(Wolleben et al. astro-ph/0510456)
WMAP Ka-band polarization
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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)
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WMAP3
WMAP3+CBIcombinedTT+CBIpol
CMBall = Boom03pol+DASIpol +VSA+Maxima+WMAP3+CBIcombinedTT+CBIpol
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People
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• 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