1. Towards the first detection using SPT polarisation
CMB cluster lensing
Towards the first detection using SPT polarisation
ASA 2016 meeting, Sydney
Srinivasan Raghunathan
School of Physics
University of Melbourne

2. In a nutshell … South Pole Telescope – Observes CMB (both T, and P).
Identifies galaxy clusters using tSZ effect.
Observed CMB is lensed due to the LSS and galaxy clusters.
Lensed CMB is important to extract cosmological information.
Optimal estimators can reconstruct the cluster profiles using the lensed CMB –> mass estimator.
CMB cluster lensing using temperature data reported by SPT-SZ.
This work – aimed towards the first detection of CMBpol cluster lensing.

3. Cosmic Microwave Background
Remnant radiation from the Big-Bang.
Discovered by Arno Penzias and Robert Wilson – Bell Labs in 1964.
Extremely homogenous and isotropic; Very close to black-body ≈ 2.7K; ∆T/T ≈ 10-5.

4. South Pole Telescope - Polarisation
10 South Pole.
Surveys:
SPT – SZ ( )
SPTpol (2012 – 2016)
SPT-3G ( )
Beam: 1.2 arcmin (approximately) Gaussian.
Background: Planck 143 GHz polarisation intensity map
Operating frequency: 95, 150, (and 220 for SPT-SZ) GHz.
500 sq. deg field with noise levels = 5.5, 7.7 uk-arcmin for T and P at 150 GHz.

5. South Pole Telescope – Galaxy clusters
Free streaming CMB photons from the lss
Thermal SZ
effect
Hot gas – presence of free electrons
Galaxy cluster
in the LOS
No change in the CMB spectrum
Shifts the CMB frequency
CMB photons:
< 220 Ghz =
220 GHz = Null
> 220 GHz =
Cluster detection using matched filter
Close to 500 clusters;
25 per cent with redshift info.
(Bleem et al. in preparation)
Observed by the SPTpol. Temperature map - preliminary

6. CMB cluster lensing serve as a mass calibrator
CMB lensing
CMB lensed by the large-scale structures and by individual galaxy clusters.
Lensing contains info. about neutrinos and D.E. Also useful for inflationary physics.
Expected distortions: 1 arcmin for a massive high redshift cluster
Proportional to mass of the galaxy cluster
CMB cluster lensing serve as a mass calibrator
Look at Anthony D.’s poster #2 for other mass proxies
Not a single cluster but averaged over the entire cluster sample

7. CMB cluster lensing -∇y ɸ -∇x ɸ
CMB lensed by the large-scale structures and by individual galaxy clusters.
Kappa map
-∇y ɸ
-∇x ɸ
Cluster:
Mass = 2 x 1014 solar mass
Concentration c = 3.0
redshift z = 0.6

8. ? CMB cluster lensing -∇y ɸ -∇x ɸ
CMB lensed by the large-scale structures and by individual galaxy clusters.
The grav. potential can be reconstructed using modified quadratic - estimators. ?
Kappa map
-∇y ɸ
-∇x ɸ
Goal: Reconstruct kappa map from the lensed CMB – QE estimator.

9. CMB cluster lensing – Quadratic estimator
Refer: Hu et al. 2007;
arXiv:astro-ph/
Gradient field
Lensed field
Six estimators:
X = T, E
Y = T, E, B
TT estimator
stacking 1000 clusters
for different experiments
Redshift information is not required.

10. CMB “galaxy” lensing – Quadratic estimator
First detection using ACTPol experiment Madhavacheril et al arXiv:
Combining measurements from CMB around 12,000 CMASS galaxies from SDSS-III/BOSS.
Detection significance: 3.2 sigma.
Inferred mass M200 = 1013 solar mass.
TT estimator – Reconstructed kappa map

11. CMB cluster lensing - ML approach
Template fitting:
Refer: Baxter et al. 2015;
arXiv:
d – 14 x 14 arcmin cutouts of SPTpol maps centered on various galaxy clusters.

12. CMB cluster lensing - ML approach
Template fitting:
Refer: Baxter et al. 2015;
arXiv:
From data
CCMB – signal covariance matrix: computed using 30,000 simulations <sT s>
Generate unlensed CMB.
Lens the CMB with different cluster masses and look for the increase in likelihood. Redhshift obtained by xcorr with other surveys.
Combine likelihood for various clusters.

13. CMB cluster lensing
First CMB cluster lensing detection using SPT-SZ data arXiv:
Combining measurements from 513 clusters at mean z = 0.55 (0.14 < z < 1.25).
Detection significance: 3.1 sigma.
Cluster mass M200= 5.1+/-2.5 x 1014 solar mass.
Mass estimate biased for high mass clusters due to cluster tSZ emission.
No tSZ contamination for polarisation estimators.
Mention about linear combination of 3 frequencies to remove tSZ signals.
220 GHz not available for SPTpol.

14. CMB cluster lensing – current status
Noiseless simulations
8 different pipeline runs after combining likelihood values of 10 clusters.
Excepted likelihood peak values.
Null test – no lensing –
Likelihood correctly peaks near zero. T Q U

15. (Immediate) next steps + Summary
SPTpol has identified close to 500 clusters in 500 sq. deg. field.
CMB is lensed by galaxy clusters and the signal can be used as a mass proxy.
3.1 sigma detection using temperature was reported by SPT-SZ in 2015.
We expect >2.5 sigma detection for polarisation.
Handling systematics: NFW profile, lensing due to LSS, cluster mis-centering, insufficient redshift information, beam ellipticites, T to P leakage.
More clusters + redshifts: Dark Energy Survey.
Improved quadratic estimator.