Michael Brown (University of Edinburgh) 1 results from the QUaD CMB polarisation experiment

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29 June 2006 Bernard's Cosmic Stories 1

1 st results from the QUaD CMB polarisation experiment

Michael Brown (University of Edinburgh)


Polarisation of the CMB


Polarisation Temperature

Polarisation Matrix: P = Q + U


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The E/B Decomposition

Can decompose Q & U into:

E-modes (even-parity):

(or grad)

B-modes (odd-parity):

(or curl)

Density perturbations produce only E-modes.

Gravitational waves produce both E & B-modes.



Cold Spot: Hot Spot:


The CMB Power Spectra

Have 4 possible spectra: TT, TE, EE, BB (TB = EB = 0).

Primary effects Secondary effects


Gravitational Lensing Diffusion

Damping Sachs-Wolfe

Acoustic Oscillations

Gravitational Wave `Bump’

QUaD l-range


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The QUaD experiment

QUaD is the QUEST telescope installed on the DASI mount at the South Pole.

2.6 m primary mirror.

31 pixel polarisation sensitive bolometer (PSB) camera.

100GHz and 150GHz observing frequencies.

Secondary supported on foam cone.

DASI infrastructure re-used for QUaD.

Extended ground shield.


QUaD people

Cardiff: Peter Ade, Walter Gear, Simon Melhuish, Angiola Orland, Lucio Piccirillo, Nutan Rajguru, Mike Zemcov.

Caltech: Andrew Lange, Jamie Bock, John Kovac, Ken Ganga (Paris).

Chicago: John Carlstrom, Tom Culverhouse, Robert Friedmann, Eric Leitch (JPL), Clem Pryke, Robert Schwarz (South Pole).

Edinburgh: Michael Brown, Patricia Castro, Andy Taylor

Maynooth: Gary Cahill, Anthony Murphy, Fabio Noviello, Creidhe O’Sullivan.

Stanford: Melanie Bowden, Sarah Church, Jamie Hinderks, Ben Rusholme, Keith Thompson, Ed Wu.


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QUaD in extended ground shield:


Focal plane:

12 feeds @ 100GHz (6 arcmin), 19 feeds at 150GHz (4 arcmin).


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1 st season’s observations

Each hour of observations is split between a lead and trail field – separated by 0.5 hrs (7.5°) in RA – exact same scan pattern with respect to ground.

Two 8-hour CMB runs/day: 2


run repeats same scan

pattern as 1


with telescope rotated 60° about line of sight axis (deck angle rotation).

Relative calibration from source (RCW38) + “el-nods”

(small el scan to inject atmospheric ramp).

99 days of CMB data taken in 1


season covering a 10°×6°

patch of the B03 (low-foreground) deep field region.


Beams measured from RCW38

Used to construct a T-dependent

beam model for each detector.


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1 st year T maps:

100 GHz: 150 GHz:

. Inverse-variance weighted maps.



order polynomial removed from each az-scan.


1 st year Q/U maps at 150GHz:

Smoothed at scale ~5 arcmin in attempt to bring out structure.

Q: U:


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T, Q & U jacknife maps:

100 GHz T

150 GHz U 150 GHz Q

150 GHz T


Field differencing

Difference lead & trail fields to remove possible ground signal (sensitivity hit: S/N ↓ by √2).

100 GHz T 150 GHz T

150 GHz Q 150 GHz U


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Using Monte-Carlo based power spectrum estimator so need to simulate the experiment extremely accurately:

Measure auto- and cross-spectra of time-ordered data (TOD) for each pair of PSBs. Using these, inject correlated noise into simulations in fourier space.

Add a CMB signal convolved with a temperature-dependent beam model measured for each bolometer.

Process simulated TOD in exact same way as the real data.

Simulations → noise bias, beam/filtering transfer functions, errors & covariances.

' '

' 1

' ~ ~ ) /

( l l l

ll C N F


C l


Simulated maps:

100 GHz T

150 GHz U 150 GHz Q

150 GHz T


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Jacknife power spectra – 150 GHz real /sims


Weiner filtered E and B maps


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Power spectra from simulations





season completed, 2


season underway.

Measuring polarisation from ground is hard!!!

Field-difference to remove ground contamination.

QUaD will run for 3 years, funding permitted (lensing of CMB, isocurvature modes, non-trivial test of ΛCDM

model. Possible detection of lensing B-modes).

Upcoming ground & balloon-borne experiments (Clover, Ebex, Spider etc. ~2008/09) will search for gravitational wave signature of inflation.

Planck may measure large-angle B-mode polarisation.




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