Weak Lensing Measurement of Galaxy Clusters in CFHTLS Wide W1 Fields

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Weak Lensing Measurement of Galaxy Clusters in
CFHTLS Wide W1 Fields
HuanYuan Shan (Tsinghua Univ.) Collaborators
J.-P. Kneib, C. Tao, Z.H. Fan, M. Jauzac, A.
Leauthaud, M. Limousin, R. Massey, J. Rhodes, K.
Thanjavur arXiv 1108.1981
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Outline

• Backgrounds
• Galaxy shape measurement
• Mass reconstructions
• Optical/X-ray counterparts
• Tomography analysis of lensing peaks
• Conclusions

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Galaxy Clusters

• Observe clusters Optical, X-ray, SZ effects,
  Lensing
• Why gravitational lensing?
• Independent of cluster mass model, purely
  geometrical method
• Independent of the cluster physics

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Weak Gravitational Lensing
- Weak distortions caused by LSS of the
universe common/weak - Clusters of galaxies are
important targets for weak-lensing studies
Individual
Statistical abundances mass
distribution
cosmological probes
Clowe et al. 2006
Hamana et al. 2004
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e.g., w123
CFHTLS-Wide T0006 release - 171 sq. degree
W1 72 sq. degree - multi-band u', g', r', i',
z'
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Shear Measurement Pipelines

• Our shear measurement pipelines are based on
  KSBf90 (Heymans et al. 2006)
• Objects detection and masking
• PSF modeling
• Galaxy shape measurement
• Calibration of the shear measurement pipeline

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CFHTLS-Wide W1 pointing W123 with
masking Effective sky coverage 58 sq. degree

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Star selection criteria - rh vs. Mag ?max
vs. Mag (?max Peak surface brightness) - S/N
gt100 elt2e (Stars number vs. S/N)
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PSF modeling - KSB Polynomial
model
Left Projection of the stellar ellipticities
before and after PSF anisotropy
correction. Right PSF ellipticity variation with
half light radius before and after PSF anisotropy
correction.
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Galaxy selection criteria - 4gt r gt1.1 rpsf,
S/Ngt10, 21.5lt maglt 24.5, elt1, d gt 3 arcsec
Galaxy number density of i' band
data ng 10.2 galaxies/arcmin2
I' band black R' band red Solid star-galaxy
separation Dotted all lensing cuts
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Calibration of Shear Measurement Pipelines
- Simulations STEP (Heymans et al. 2006 Massey
et al. 2007) Great08 (Bridle et al. 2009
2010) Disadvantage Shear and PSF do not vary
across an image - Real Data ACS-COSMOS vs.
CFHTLS-Deep 2 Space-based vs. Ground-based,
Cover the same sky area
- Matched shear P? fit P? (rh) vs. P?
(mag, rh)
Fu et al. (2008)
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- Real Data r' band vs. i' band data
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- Mean shear measurements from galaxies in
i'-band observations of the entire CFHTLS-Wide W1
field.
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- Shear signals vs. Star-galaxy correlation
function
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Mass Inversion
- KS inversion (Kaiser Squires 1993)
Positive and negative peaks (solid and dashed
contours 3, 4, 5 sigma)
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The probability distribution function (PDF) of
the peak height. a bimodal distribution
asymmetric excess at high S/N

Positive peaks

Negative peaks Different smoothing scales
0.5/1/2 arcmin blue/black/red lines
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The cumulative number of positive and negative
peaks

Positive peaks

Negative peaks
Pure
noise
Analytical
predictions (Fan, Shan Liu. 2010) circles

Different smoothing scales

1/2 arcmin-black/red
lines
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Comparison with Optical/X-ray counterparts
WL 301 positive peaks with S/Ngt3.5 I. Compare
with optical detection (Thanjavur et al. 2009
K2) - Bright Central Galaxy vs. WL peaks II.
Compare with X-ray detection (Adami et al. 2010)
- 6 sq. degree, XMM-LSS - 66 spectroscopically
confirmed clusters (0.05 lt z lt 1.5) - 31 X-ray
clusters are within W1 field
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/squares WL peaks with smoothing scale 1/2
arcmin Triangles K2 detection X X-ray
detection
The convergence S/N map of the w123 field
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Optical/X-ray counterparts
WL 301 positive peaks with
SNRgt3.5 I. Compare with optical detection
(Thanjavur et al. 2009) 126 candidate clusters
with SNRgt3.5 (purity 42) II. Compare with
X-ray detection (Adami et al. 2010) - 31 X-ray
clusters are within W1 field 7
counterparts offsets between X-ray and WL
center much larger than offset between optical
and WL measurements.
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Cluster redshift distribution for the matched
clusters

WL black solid
histogram
K2 red dashed
histogram
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Lens tomography
- SIS NFW mass model - Chi-square fitting
analysis with the error
(Hoekstra et
al. 2000) - Photometric redshift of source
galaxies (Arnouts et al. 2011)
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Results of a tomographic weak lensing analysis
SIS/NFW(solid/dashed)
E-mode black

B-mode red
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Scaling relations between velocity dispersion and
weak lensing mass
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Left Lens tomography redshift vs. photometric
redshift Right Matched velocity dispersion
X-ray vs. WL method
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Conclusions
1. We measure the galaxy shapes using KSB method,
and calibrate with HST image/other imaging
bands. 2. A 72 sq. degree DM map has been
reconstructed. 3. Considering the noise effects,
we get peak counts in the CFHTLS fields with
prediction from a ?CDM Universe 4. 85
groups/clusters have been confirmed 5. The good
agreement on the clusters redshift and velocity
dispersion implies no evidence of selection bias
compared to these other techniques