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CMB Observations with the Cosmic Background Imager

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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).

2005 March 24

- 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

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

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

2005 March 24

- Insensitive to large-scale structure
- Uncorrelated noise
- Direct measurement of polarization Q ± iU
- Beam uncertainty not very important
- Very different systematics

2005 March 24

Home of CBI, QUIET, and other experiments

2005 March 24

- 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

- 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

• 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!)

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2005 March 24

- 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

2.9σ above model

2005 March 24

Marginalize over 1 parameter (flux) for each source,

Or 2 parameters (2000-01 and 2002-05 flux).

2005 March 24

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

- 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

- 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

2005 March 24

2005 March 24

- 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

SZE

Secondary

CMB

Primary

~ s87

2005 March 24

- TT consistent with earlier results
- EE and TE consistent with predictions
- BB consistent with zero

TT

EE

TE

BB

2005 March 24

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

2005 March 24

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2005 March 24

- 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 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

- 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

WMAP Ka-band polarization

DRAO 1.4 GHz polarized intensity

(Wolleben et al. astro-ph/0510456)

WMAP synchrotron component

(WMAP Science Team)

2005 March 24

- 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

WMAP3+CBIcombinedTT+CBIpol

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

2005 March 24

2005 March 24

- 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