WMAP 3 years of observations: Methods and cosmological insights Olivier Doré CITA / Princeton University on behalf of the WMAP science team
WMAP Science Team NASA - GSFC PRINCETON GODDARD C. Barnes C.Bennett (JHU) R. Bean (Cornell) G. Hinshaw O. Dor é (CITA) R. Hill M. Nolta (CITA) A. Kogut N. Jarosik M. Limon E. Komatsu (Texas) N. Odegard L. Page J. Weiland H. Peiris (Chicago) E. Wollack L. Verde (Penn) D. Spergel M. Halpern (UBC) S. Meyer (Chicago) G. Tucker (Brown) E. Wright (UCLA)
David Wilkinson 1935-2002
What has WMAP-1 done for us ? Color codes temperature (intensity), here ±100 μ K Temperature traces gravitational potential at the time of recombination, when the Universe was 372 000 ±14000 years old The statistical analysis of this map entails detailed cosmological information WMAP-1 has improved over COBE by a factor of 45 in sensitivity and 33 in angular resolution Doing so, the mission met all its requirements after the first year... ”Mission Accomplished!”... but...
What has WMAP-3 done for us? ... the insights expected on Inflation theory (~10 -18 s after BB) and the Universe reionization (364 +124/-74 Myr) from large scale CMB polarization measurements were too tempting to not be pursued WMAP-3 has measured the CMB polarization on very large angular scales To do so required us to improve control the systematics at a level 50 times higher than originally proposed!
Outline A CMB Primer Recap on WMAP and analysis improvements over the last 2 years A case for large scale polarized CMB detection Cosmological implications Phenomenological success of Λ CDM cosmology WMAP already addresses new set of questions risen by this success (Dark Energy, Inflation, Reionization, Non-Gaussianities...) I can’t cover it all now. Please ask questions and interrupt me!
A CMB Primer
The CMB is a leftover from when the Universe was 380 000 yrs old The Universe is expanding and cooling Once it is cool enough for Hydrogen to form, (T~3000K, t~3.8 10 5 yrs), the photons start to propagate freely (the CMB comes from t=380 000 Thomson mean free path is greater than years after Big Bang the horizon scale) Reionization This radiation has the imprint of the small anisotropies that grew by gravitational instability into the large structures we see today Today: 13.7 Gyrs after Big Bang
Confronting sky maps with theoretical predictions It is both theoretically sound and observationally supported to consider the CMB temperature fluctuations as a gaussian random field so that a lm ’s are Gaussian random variables Thus sufficient to consider the power spectrum Physics in the linear regime well described by a 3000K plasma photo-baryon fluid oscillating in dark matter potential wells 0.5 o 0.2 o Θ ~ π /l 90 o 2 o Θ > Θ dec ~2 o Silk damping Sachs-Wolfe plateau Acoustic regime Sunyaev & Zeldovich 70 Peebles & Yu 70 Bond & Efstathiou 87 Hu & White 97
Confronting sky maps with theoretical predictions It is both theoretically sound and observationally supported to consider the CMB temperature fluctuations as a gaussian random field so that a lm ’s are Gaussian random variables Thus sufficient to consider the power spectrum Physics in the linear regime well described by a 3000K plasma photo-baryon fluid oscillating in dark matter potential wells 0.5 o 0.2 o Θ ~ π /l 90 o 2 o Θ > Θ dec ~2 o Silk damping Sachs-Wolfe plateau S/N per l <1 Acoustic regime Cosmic variance Sunyaev & Zeldovich 70 >Noise Peebles & Yu 70 Bond & Efstathiou 87 Hu & White 97
The CMB is weakly polarized Linear polarization of the CMB is: Produced by Thomson scattering of a quadrupolar radiation pattern on free electrons ⇒ probe recombination and reionization e- Partially correlated with temperature (velocity pert. correlates with density pert.) Two types of Polarization Scalar perturbation to the metric produce E- mode polarization Tensor perturbations to the metric produce B-mode polarization, i.e. Gravity waves e- Polarization probes both perturbations themselves and ionization history Numerical calculation show that the polarization fraction is weak, ~1% of only
The WMAP mission
WMAP Launch June 30, 2001 at 3:47 EDT Delta II Model 7425-10 Delta Launch Number 286 Star-48 third stage motor Cape Canaveral Air Force Station Pad SLC-17B
Trajectory to L2
The spacecraft
Not to scale: Earth-L2 distance Earth — L2 distance is 22.5 deg. 22.5° half-angle 1% of Sun — Earth 1hour precession cone Distance 3 Months 129 sec. (0.464rpm) Spin A-side line of site MAP at L 2 B-side line of site 6 Months - Earth full sky coverage 1 Day Sun
WMAP summary L2 orbit Constant survey mode Spin rate: 0.464rpm Thermal stability Precession rate: 1rph Passive cooling 22.5 o half angle Rapid and complex sky scan Observe 30% of the sky every day A line of sight Most of pixels are observed with evenly distributed orientations Lagrange point L2 B line of sight Differential measurement only Most of the common modes cancel Two radiometers per feed Earth T 1 +T 2 ∝ Intensity T 1 -T 2 ∝ Polarization 10 feeds, 20 DA total 5 microwave frequencies to monitor foregrounds SUN K, Ka, Q, V, W bands 22, 33, 40, 60, 93 GHz Accurate calibration on the cosmological dipole and beam measurements on Jupiter Design optimized for temperature measurements
Mapping temperature fluctuations
Foreground Spectra
WMAP Sky Maps: 23 to 94 GHz 41 GHz 23 GHz 61 GHz 33 GHz 94 GHz Absolute Calibration: 0.5% Bandwidth: ~20% Beam FWHM: 0.85˚ (23 GHz) to 0.21˚(94 GHz) Systematic around 15 μ K 2 for C 2 TT vs the ~1000 μ K 2 nominal TT and ~100 (EE), and less for higher l
K Band (23 GHz) -200 +200 Temperature (µK)
Ka Band (33 GHz) -200 +200 Temperature (µK)
Q Band (41 GHz) -200 +200 Temperature (µK)
V Band (61 GHz) -200 +200 Temperature (µK)
W Band (94 GHz) -200 +200 Temperature (µK)
Systematic Error Cross-Checks (Q1+Q2)/2 (Q1-Q2)/2 (V1+V2)/2 (V1-V2)/2 (W12+W34)/2 (W12-W34)/2
COBE-WMAP Comparison COBE DMR 53 GHz Difference: WMAP - DMR WMAP Q/V Combined (to approximate 53 GHz) Simulated DMR Noise (for comparison) -100 +100 Temperature (µK)
Foreground Removal for Spectrum Analysis Q V W -70 +70 Temperature ( µ K) External templates H α maps from Finkbeiner et al. 03 WHAM Haslam et al. 1981 Finkbeiner, Davis & Schlegel 2001
Mapping polarization fluctuations
Remarks on the analysis over the last 2 years Differential measurement and interlocked scanning strategy suppresses polarization systematics as for temperature. No new systematics, but the weak nature of the spinorial polarized signal requires extra-care to avoid any coupling to the much stronger T field (100 times). Non-trivial interactions between the slow drift gain, non-uniform weighting across the sky, time series masking, 1/f noise, galactic foregrounds, band-pass mismatch, off-set sensitivity and loss imbalance. The handling of these effect had to be propagated from the map-making till the power-spectrum measurement. To understand them required numerous end-to-end simulations (enough to have good statistics). Most of 2004-5 was spent running those and realizing that the previous short-cuts did not work anymore. A new pipeline was eventually required and has been designed, written and optimized. We rely heavily on null tests in map (various frequency) and C l space to assess the quality of this processing
Temperature maps V band year 1 (pub) year 3 year 3 - year 1 V-band W band W-band -200 +200 -30 +30
Polarization maps K band V band Ka band W band Q band Color code P=(Q 2 +U 2 ) 1/2 smoothed with a 2 o fwhm Direction shown for S/N > 1
K band - 23 GHz
Ka band - 33 GHz
Q band - 41 GHz
V band - 61 GHz
W band - 94 GHz
Polarization mask +90° NEP 0° +180° GC -180° SEP -90° p02 p04 p06 p08 p10 Dust Sources
Uncleaned power spectra Foregrounds dominate over all l of interest and all frequencies unlike Outside p06 mask for temperature
Spiral magnetic field structures seen in external galaxies Bi-symmetric Spiral model
Polarized foregrounds predictions: synchrotron radiation Polarization directions 0° 180° Polarization amplitude K1 Polarization Amplitude K1 Polarization Prediction from Haslam Based on a model in which a 0 T(mK) 0.1 gas of cosmic rays electrons interact with a magnetic field following a bisymmetric spiral arm pattern
Foreground cleaned maps pre-cleaned cleaned Ka-band Q-band V-band W-band Q Stokes -20 20 T ABLE 4 C OMPARISON OF χ 2 B ETWEEN P RE - CLEANED AND CLEANED Due to correlations between w M APS n W 1.38 1.58 6144 -1229 a a foregrounds, a map based cleaning R e Ka 2.142 1.096 4534 4743 l is more powerful C Q 1.289 1.018 4534 1229 2 parameters/frequency fit only V 1.048 1.016 4534 145 W 1.061 1.050 4534 50
Final CMB spectra 100.00 10.00 { l ( l +1) C l / 2 � } 1/2 [ µ K] 1.00 0.10 0.01 1 10 100 1000 Multipole moment ( l )
Cosmological Implications
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