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Polarization-assisted WMAP-NVSS
Cross Correlation
Guo Chin Liu (ASIAA)
Collaborators:
K-W Ng(IoP, AS)
Ue-Li Pen (CITA)
Dark energy -- SNe Ia
1. Supernovae look
farther/fainter than
prediction by the model of
universe composed by
matter.
2. Model with three quarters of
“energy”, which accelerates
the expansion of universe,
explains data very well.
Dark energy – Microwave Background Sky
Geometry of our universe
Power spectrum from CMB
gives two hints for dark
energy
1. Position of first peak
proves the curvature of
our universe is small
2. The enhancement on
large-scale may prove the
existence of dark energy
ISW effect
Dark energy – Microwave Background Sky
Observation of CMB first
peak alone does not
guarantee the existence of
dark energy.
1. We are living in low
density universe, m0.3
m+k+=1
Allen et al. 2002
Carlberg et al. 1997
2. Hubble constant is not so
small, for example, from
SZ clusters measurement,
H0=60-70
Reese et al. 2002
Udomprasert et al 2004.
Spergal et al. 2007
Astronomical Observations for Dark Energy
Need to be sensitive on
1. Geometry of universe (distance vs. redshift relation)
2. Structure formation
Current used observations
1. Supernova type Ia : probe the geometry of universe
Caution: assuming uniform intrinsic luminosity
2. CMB : good constraint on small curvature
Caution : no time evolution data
3. Large scale structure : evolution of geometry of universe and
growth factor D(z)
Caution: depend on CDM model for structure formation
Future observation
Weak lensing: Size of distortion image depends on
distance traveled and growth factor
BAO: Baryon Acoustic Oscillation is sensitive to dark
energy through its effect on the angular-diameter
distance vs. redshift relation and through its effect on
the time evolution of the expansion rate.
ISW Effect
1. If the potential decays between the time a photon falls into
a potential well and when it climbs out it gets a boost in
temperature of due to the differential gravitational redshift
and due to an accompanying contraction of the wavelength
2. No ISW effect in matter dominate epoch.
3. The dark energy dominating on late epoch creates the
temperatures anisotropies on large scales.
E=|1-2|
2
1
T/T=-2  d d/d
ISW Effect
1. Signature of dark energy
2. Probe of evolution of structure
3. Sensitive on large scale
4. Detection is limited by cosmic
variance.
Try to look for correlation of CMB with matter
Cross correlation of CMB with matter in local
universe Proposed by Crittenden & Turok (1996)
Density fluctuation
Form structures
CMB gains energy
Possible tracers
1. NRAO VLA Sky Survey (NVSS)
2. Hard X-ray background (HEAO-1)
3. Sloan Digital Sky Survey (SDSS)
4. Two Micron All Sky Survey Extended Source Catalogue
(2MASS XSC)
Previous work
1. Real space : Diego et al. 2003, Boughn & Crittenden
2004, Cabre et. al. 2006, Nolta et al. 2004, Giannantonin
et al. 2006, Rassat et al. 2006
2. Multipole l space: Afshordi et al. 2004
3. Wavelet space: Viela et al. 2006, McEwen et al. 2007
Example of cross-correlation
1. The curve is sensitive on model
of dark energy, bias factor, power
spectrum of density perturbation,
n_g(z)
2. Peaks at l~ few tens, less trouble
on cosmic variance
3. Noise is dominated by CMB from
recombination and reionization
Douspis et al. 2008
First detection of the cross-correlation
Correlating CMB sky to
hard X-rays (HEAO-1) and
radio galaxy (NVSS)
wiNiwjTj/wiwj
3 sigma detection for hard
X-rays and 2.5 sigma for
radio galaxy
Boughn & Crittenden, nature, 2004
CMB anisotropies & polarization on large scales
CMB last scattering surface
△TSW, z=1100
Generate P.
△Treion, z=10
Generate P.
△TISW, z<2
Dark energy dominates
Observer
Correction by the information of polarization
At large scales T=TSW + Tre + TISW
Eno ISW =aTno ISW + n
<TE>noisw = a <TT>noisw
<EE>noisw=a2<TT>noisw + n2
No ISW above
T(ISW) =T – Enoisw/a * WF
WF=a2<TT>/<EE>
<TT>, <EE> and <TE> are
obtained by CMBfast, forcing
ISW=0
Applying to CMB power spectrum
Total
Polarization corrected
ISW
Details of this work
1. We work at harmonic space
SZ and radio emission is ignorable.
Low correlation between each mode
2. Using NVSS as matter distribution tracer.
3. ClNW=<aNlmaT*lm>
△T/T()=aTlmYlm()
4. Healpix software is used for
visualization and calculating alm
NVSS data
1. 1.4GHz , 82% sky coverage (>-40)
2. Sensitivity 2.5 mJy contains 1.8 million sources
3. Typical luminosity function models indicate 0z2 distribution
CMB SKY
61GHz
41GHz
T
T
T
Q
Q
Q
U
U
U
Result
1. Using polarization
information narrows down
the uncertainties from
primary CMB about 3-7%
2. Better instrument noise
estimation is necessary
(mainly from 1/f)
Error bars are obtained by correlation of 500
simulated CMB maps with real NVSS data
Summary
1. Working in harmonics space, signal with 2-sigma is detected
in l~ 10-20.
2. Primary CMB is the dominated noise in this cross-correlation.
Using polarization information, we can filter out part of it.
3. It suppress the noise about 3--7% in band power, giving a
better constrain on dark energy model.
Contamination
1. Sunyaev-Zeldovich Effect: anisotropies generated through
the inverse Compton scattering with free e- correlates with
the galaxy itself.
On small scales
2. Emission from the radio galaxy
Emission at f<few tens GHz contaminates the microwave
sky.
On small scales
3. Primary CMB itself: △T(ISW) < 30% of △T(total)