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

20  Download (0)

Full text

(1)

29 June 2006 Bernard's Cosmic Stories 1

1 st results from the QUaD CMB polarisation experiment

Michael Brown (University of Edinburgh)

(2)

Polarisation of the CMB

Temperature

Polarisation Temperature

Polarisation Matrix: P = Q + U

(3)

29 June 2006 Bernard's Cosmic Stories 3

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.

B E

B E

Cold Spot: Hot Spot:

(4)

The CMB Power Spectra

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

Primary effects Secondary effects

Reionisation

Gravitational Lensing Diffusion

Damping Sachs-Wolfe

Acoustic Oscillations

Gravitational Wave `Bump’

QUaD l-range

(5)

29 June 2006 Bernard's Cosmic Stories 5

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.

(6)

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.

(7)

29 June 2006 Bernard's Cosmic Stories 7

QUaD in extended ground shield:

(8)

Focal plane:

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

(9)

29 June 2006 Bernard's Cosmic Stories 9

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

nd

run repeats same scan

pattern as 1

st

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

st

season covering a 10°×6°

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

(10)

Beams measured from RCW38

Used to construct a T-dependent

beam model for each detector.

(11)

29 June 2006 Bernard's Cosmic Stories 11

1 st year T maps:

100 GHz: 150 GHz:

. Inverse-variance weighted maps.

3

rd

order polynomial removed from each az-scan.

(12)

1 st year Q/U maps at 150GHz:

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

Q: U:

(13)

29 June 2006 Bernard's Cosmic Stories 13

T, Q & U jacknife maps:

100 GHz T

150 GHz U 150 GHz Q

150 GHz T

(14)

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

(15)

29 June 2006 Bernard's Cosmic Stories 15

Simulations:

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

M

C l

(16)

Simulated maps:

100 GHz T

150 GHz U 150 GHz Q

150 GHz T

(17)

29 June 2006 Bernard's Cosmic Stories 17

Jacknife power spectra – 150 GHz real /sims

(18)

Weiner filtered E and B maps

(19)

29 June 2006 Bernard's Cosmic Stories 19

Power spectra from simulations

(20)

Conclusions

1

st

season completed, 2

nd

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.

Figure

Updating...

References

Related subjects :