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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

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slide1

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

cbi timeline
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

slide3

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 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

interferometry advantages
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
Chajnantor Observatory

Home of CBI, QUIET, and other experiments

2005 March 24

total intensity observations
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
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
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

raw images
Raw Images

2005 March 24

data reduction
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

slide14

2.9σ above model

2005 March 24

projecting out variable sources
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
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

slide17

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

cbi upgrade
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

slide20
CBI2

2005 March 24

gbt observations
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
CBI2 Projection

SZE

Secondary

CMB

Primary

~ s87

2005 March 24

cbi polarization spectra
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 c l fit
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

slide29
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

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

isocurvature1
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

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

foregrounds1
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

slide34

WMAP3

WMAP3+CBIcombinedTT+CBIpol

CMBall = Boom03pol+DASIpol +VSA+Maxima+WMAP3+CBIcombinedTT+CBIpol

2005 March 24

people
People

2005 March 24

slide36

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