Transcript A correlation of the CMB and large scale structure

What have we learnt from WMAP?
Robert Crittenden
Institute of Cosmology and Gravitation,
Portsmouth, UK
Over 100 papers in the past year just with ‘WMAP’
in the title!
What is qualitatively new in WMAP?
Outline
• Introduction to WMAP
• Polarization on the largest scales
• Correlations with large scale structure
• Large scale power deficit
• Topology of the universe
• Evidence of non-Gaussianity
Wilkinson Microwave Anisotropy Probe
David Wilkinson
CMB Pioneer
WMAP satellite
Launched June 2001
Reached L2 August 2001
WMAP science team
• Charles Bennett, PI
G. Hinshaw, M. Limon,
A. Kogut, E. Wollack
• L. Page, N. Jarosik,
D. Spergel, D. Wilkinson
• E. Wright
• G. Tucker
• S. Meyer
• M. Halpern
NASA Goddard
Princeton
UCLA
Brown
Chicago
UBC
Many thanks to them for their hard work as well as
images and data products used in this talk!
what’s so great about WMAP?
Mostly quantitative:
• More pixels: nearly 1,000,000 independent pixels
• More frequencies: five frequency channels
 better foreground removal, even the through galaxy
• Full sky coverage
 tight calibration from the dipole (0.5%)
 compare and unify other CMB observations
 cosmic variance limited to l=350
• Better systematic error control
five frequency maps
23, 33, 41, 61 and 93 GHz
derived maps
Dust map
Free-free map
Synchrotron map
CMB map
Power spectrum of WMAP
Hinshaw et al.
Cosmic variance limited
to l=350
S/N > 1 for l<650
Features:
• Doppler peak well
characterized
• missing small scale
power?
• glitches at l=40,
210
Remarkably consistent with earlier data, apart from 10%
calibration issue.
cosmological parameters
The power spectrum has confirmed earlier best fit
models, with smaller error bars
Bottom line: very close to flat
significant dark matter (25%)
dominated by dark energy (70%)
adiabatic, n=1
Most papers have focused on using spectrum to
constraint variants of the lambda CDM model
But the full sky nature of WMAP has allowed us
to discover a number of things which we
could not have known otherwise…
Large scale CMB polarization
On the last scattering surface, polarisation is
generated effectively by the fluid velocity
gradient
Thus, we do not expect it to be large for modes
outside the horizon (l < 100)
Any polarization we see on these scales must
have been generated by later scattering!
WMAP is the first experiment to see the
polarization on the largest scales (though it
was seen in earlier measurements by DASI)
Temperature-polarization cross correlation
WMAP’s polarization sensitivity is poor, making direct
detection very difficult, but large sky coverage means
finding correlation with temperature is relatively easy.
Advantage is that we know the polarization we see is
cosmological!
WMAP saw both
reionization and
polarization from
last scattering!
First calculations of
T-P by Coulson, RC
and Turok, 1994
Kogut et al. 2003
Reionization
Polarization on very large scales means some
fraction of the light was recently rescattered
The amplitude indicates 1/6 photons scattered,
which can only be done if the universe
reionized fairly early (z = 20  10)
Optical depth,
 = 0.17  0.04
This will be discussed
in detail in talks by J.
Ostriker, M. Kaplinghat
Polarization from last scattering
WMAP also measured the polarization from the
largest modes at last scattering
The sign of the cross correlation tells us
something about the direction of the velocity
flows at that time.
The sign was consistent with that predicted by
adiabatic fluctuations, but not isocurvature.
Inflow
Radial
Outflow
Tangential
Correlation with large scale structure
The large sky coverage of WMAP means that
one is able to detect even weak correlations
with other surveys.
There are a number of reasons why such
correlations might exist:
• The integrated Sachs-Wolfe effect
• The Sunyaev-Zeldovich effect in clusters
• Unremoved foreground sources
integrated Sachs-Wolfe effect
while most cmb anisotropies arise on the last scattering surface, some
may be induced by passing through a time varying gravitational potential:
T
  2  d 



T
linear regime – integrated Sachs-Wolfe (ISW)
non-linear regime – Rees-Sciama effect
when does the linear potential change?
  4 G a  
2
2
Poisson’s equation
• constant during matter domination
• decays after curvature or dark energy come to dominate (z~1)
induces an additional, uncorrelated layer of large scale anisotropies
two independent maps
Integrated Sachs-Wolfe map
Mostly large angular features
Observed map is total of
these, and has features of
both (3 degree resolution)
Early time map (z > 4)
Mostly from last scattering surface
compare with large scale structure
ISW fluctuations are correlated with the galaxy distribution!
observer
time dependent
gravitational potential
potential depth
changes as cmb
photons pass
through
density of galaxies traces
the potential depth
since the decay happens slowly, we need to see galaxies at
high redshifts (z~1)
 active galaxies (quasars, radio, or hard x-ray sources)
 possibility of accidental correlations means full sky needed
how do we trace the matter?
X-rays from active
galaxies
HEAO-1 x-ray satellite
Galaxy and virtually all
visible structures
cleaned out
Radio galaxies
NRAO VLA Sky
Survey (NVSS)
ISW correlations detected!
Correlations seen with
both at the 2.5 –
3.0 sigma level
Also seen to some
extent in galaxy
surveys: SDSS,
2MASS, APM
S. Boughn & RC, Nature2004
Amplitudes are largely consistent with dark
energy model and argue against any pure dark
matter model. (See E. Copeland talk.)
SZ cross correlation
Hot gases in clusters can upscatter CMB
photons, also producing a correlation on
smaller angular scales.
Evidence for this is growing, but still somewhat
contradictory
Apparently detected with some surveys, not
seen in others, seems to depend on the
method used to trace clusters.
This will lead to a constraint on the size and
temperature of hot gas in clusters (Compton
y-parameter) see also S. Majumdar talk.
Are there missing large scale
correlations?
The WMAP papers reported a
deficit of large scale power
to that expected in
cosmological constant
dominated models
One statistic showed that this
was likely only at a level of
1 chance in 700.
(Posterior statistic?)
Missing power also observed
for COBE.
Difficult to measure given
cosmic variance.
Spergel et al.
Why has this received so much attention?
Other glitches are more statistically significant, but this
is at a very interesting scale, the present horizon, and
is not constrained on larger scales
Difficult to produce by additional effects because it
requires cancelling large scale power
Some proposed solutions:
1) Running spectra tilt
2) Some minimum k cutoff
3) Related to curvature scale
4) High frequency oscillations in spectrum
5) SZ from local supercluster
6) Related to topology of the universe
Is the deficit significant?
Efstathiou argues that the WMAP analysis suffers from a
number of problems:
• Low estimates of power spectrum given the
uncertainties in the masking
• Biases from frequentist statistics
• Decided on the test based on seeing the data
He argues that the discrepancy is more like 1 chance in
10 or 20 and is consistent with lambda CDM.
Can only be improved by better subtraction of the
galaxy.
Remains a tempting target for theorists.
Could we be seeing the effects of a
finite universe?
Based on the WMAP low l
power spectrum, it has
been suggested that our
space could be
dodecahedral (shaped like a
soccer ball)
This model is slightly closed
and positively curved,
 = 1.013
No indications have been
found using correlation of
patches
Luminet, Weeks, Riazuelo, Lehoucq
and Uzan, 2003.
More general searches have given only
upper limits
So far general searches for
topology have only placed upper
limits
Focus has been on looking for
matched ‘circles in the sky’ or
symmetries in the temperature
patterns
While the dodecahedral model hasn’t been specifically
excluded, evidence is against most models with a
topology scale less than 24 GPc (Cornish et al, de
Oliveira-Costa et al., Bond, Pogosyan & Souradeep)
Future tests – looking for statistical isotropy (Hajian &
Souradeep)
Non-Gaussianity in WMAP?
Initial analyses indicated that the WMAP results were
consistent with Gaussianity:
1) Three point tests are consistent up to known point
source contribution (Komatsu et al., Gaztanaga & Wagg)
2) Apparent non-Gaussianities in COBE bispectrum do not
appear in WMAP (Magueijo & Madeiros)
3) Topological tests (Minkowski functionals, genus) are
also consistent (Komatsu et al., Colley & Gott)
So far the limits are not sufficient to endanger the levels of
non-Gaussianity that might be predicted by inflation
Some trouble on the horizon?
Some recent analyses have pointed to possible
inconsistencies:
1) Evidence that north ecliptic hemisphere has less
large scale power than southern (Eriksen et al.)
2) A wavelet analysis shows evidence for nonGaussianity in the southern Galactic hemisphere
(Vielva et al.)
3) Asymmetry between some genus statistics for
north and south Galactic hemispheres (Park)
4) Some strange alignments seen in the quadrupole
and octopole moments (Tegmark et al.)
5) Multipole vector analysis indicates unexpected
alignments at low l (Copi et al.)
6) Evidence for some strange phase correlations at
l=16 (Coles et al.) and at very high l (Chiang et al.)
Is it significant?
Most authors argue against foreground being
responsible, but its not impossible
Possibly a problem with a posteriori statistics, but many
seem to be pointing to similar problems
Could it be similar to COBE problems, where some of
the data was contaminated? This seems unlikely for
the large scale problems.
The jury is still out, and more investigation is
needed!
Conclusions
WMAP has not only improved our understanding on a
quantitative level, but also in qualitatively new ways
thanks to its all sky coverage
1) Large scale polarization data shows that the CMB was
significantly rescattered – new physics of reionization?
2) The velocity flows after last scattering were consistent
with adiabatic fluctuations
3) Evidence that some fluctuations were produced
recently due to ISW, consistent with predictions of
lambda CDM
4) Interesting hints at a lack of power on large scales,
but its still consistent with the standard picture
Conclusions continued…
5)
6)
One interesting explanation for it, a ‘soccerball’
universe has not been ruled out, but most small
topological universes are unlikely.
The fluctuations appear largely Gaussian as would be
expected by inflation, but some interesting aspects of
the data still puzzle us, particularly on large scales
Future:
Two year data should be out soon
WMAP Polarization auto-correlation (E-E)
Small scale temperature and polarization experiments
Planck is just 3.5 years away!
large scale correlations
The anisotropies created by the
ISW effect are primarily on large
scales and are largely uncorrelated
with those produced earlier
  0.73 h  0.72 n 1.0
WMAP best fit scale invariant spectrum
On small scales, positive and
negative ISW effects will tend to
cancel out. However, on larger
scales photons receive fewer kicks
of larger amplitude
The early and late power is fairly
weakly correlated, so the power
spectra add directly:
Cltotal  Clearly Clisw
Highest correlations are for the
quadrupole, but it is still very weak
C2 / C2iswC2early  0.08