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Impact of intrinsic alignments on cosmic shear
• Shearing by elliptical galaxy halos
– SB + Filipe Abdalla astro-ph/0608002
• Intrinsic alignments and photozs
– SB + Lindsay King arXiv:0705.0166
• Cluster counts and cosmic shear – double counting?
– Masahiro Takada & SB arXiv:0705.0163
Sarah Bridle, UCL (London)
Gravitationallysheared
Gravitationallysheared
Lensing by dark matter causes galaxies to appear aligned
Cosmic shearFace-on view
Intrinsic alignments (II)
Croft & Metzler 2000, Heavens et al 2000, Crittenden et al 2001, Catelan et al 2001, Mackey et al, Brown et al
2002, Jing 2002, Hui & Zhang 2002
Tidal stretching causes galaxies to alignAdds to cosmic shear signal
IntrinsicallyAligned (I)
IntrinsicallyAligned (I)
Intrinsic alignments (II)Face-on view
Intrinsic-shear correlation (GI)
Hirata & Seljak 2004See also Heymans et al 2006, Mandelbaum et al 2006,
Hirata et al 2007
Galaxies point in opposite directionsPartially cancels cosmic shear signal
Gravitationallysheared (G)
Intrinsicallyaligned (I)
Intrinsic-shear correlation (GI)Face-on view
Cosmic shear two point tomography
Cosmic shear tomography
CosmicShear
IntrinsicAlignments (IA)
Normalised to Super-COSMOSHeymans et al 2004
If consider only wthen IA bias on wis ~10%
If marginalise 6 cosmologicalparametersthen IA bias on w is ~100% (+/- 1 !)
IntrinsicAlignments (IA)
Elliptical galaxy-galaxy lensing
Bri
dle
& A
bd
alla
Background galaxy is gravitationally sheared tangentially around foreground lens
Elliptical galaxy-galaxy lensingFace-on view
Bri
dle
& A
bd
alla
Bri
dle
& A
bd
alla
Contribution to ellipticity correlation function:Average shear around circular annulus
Does not average to zero →net contamination
z1=0.3 z2=0.8
Average over populationvisible to R=24
Cosmic shear signalS
hea
r co
rrel
atio
n f
un
ctio
n
Bri
dle
& A
bd
alla
Average over populationvisible to R=24
Cosmic shear signal
Change in cosmic shear signalfor w = 0.05
z1=0.3 z2=0.8S
hea
r co
rrel
atio
n f
un
ctio
n
Bri
dle
& A
bd
alla
Removal of intrinsic alignments
• Intrinsic – intrinsic (II) – Weight down close pairs (King & Schneider 2002,
Heymans & Heavens 2003, Takada & White 2004)
– Fit parameterized models (King & Schneider 2003)
• Shear – intrinsic (GI)– Fit parameterized models (King 2005, Bernstein DETF)
– Redshift weighting (Schneider talk)
Redshift quality is crucial!
Perfect redshifts
Scale dependence of IA (# bins)
Least flexible model consideredFoM is improved!
Reasonable model? (14 IA pars)Similar FoM to no IA case
Very flexible (100 IA pars)FoM is roughly halved
No Intrinsic AlignmentsRedshift
dependence of IA (# bins)
235
Scale dependence of IA (# bins)
Perfect redshifts
Redshiftdependence of IA (# bins)
235
Scale dependence of IA (# bins)
Realistic photozs σz=0.05(1+z)
Redshiftdependence of IA (# bins)
235
Photoz error σz / (1+z)
No Intrinsic AlignmentsF
oM
/ F
oM
(sp
ecz)
(e.g. Hu 1999, Ma, Hu, Huterer 2006, Jain et al 2007,Amara & Refregier 2007 ....)
Relatively flat
Photoz error σz / (1+z)
Reasonable model? (14 IA pars)
Very flexible (100 IA pars)
Fo
M /
Fo
M(s
pec
z)
Photoz error σz / (1+z)
Fo
M /
Fo
M(s
pec
z)A factor of ~3 better photozs required!
0.8
0.02 (1+z) 0.08 (1+z)
Conclusions
• Lensing by elliptical galaxy halos contributes to shear-intrinsic term (GI)
• 3x better photozs required to remove intrinsic alignments
• Cluster counts and lensing power spectra very complementary
AD
END
Shearing by elliptical galaxy halos
• Plan:– Calculate shear from elliptical halo– Calculate contribution to shear correlation fn– Average over a population of lenses– Compare with cosmic shear signal– Consider effect of halo profile– Investigate redshift dependence
Bridle & Abdalla 2007
Average over populationvisible to R=24
Cosmic shear signal
z1=0.3 z2=0.8
NFW
^
Sh
ear
corr
elat
ion
fu
nct
ion
Average over populationvisible to R=24
NFW
^
Singular isothermalellipsoid
Cosmic shear signal
z1=0.3 z2=0.8S
hea
r co
rrel
atio
n f
un
ctio
n
M200=1x1012 h-1 Mo
zlens=0.3 zsource=0.8S
hea
r co
rrel
atio
n f
un
ctio
n
Bri
dle
& A
bd
alla
How good to photozs need to be to remove intrinsic alignments?
• Plan:– Remove GI, II by marginalising over some
flexible model– Look at the effect of GI, II on dark energy errors– Dependence on flexibility of model?– Dependence on photoz errors?
Bridle & King 2007
σz / (1+z)
Dark energy from cluster counts and lensing: including the full covariance
• Plan:– Motivation: combining constraints– Shear power spectrum is from halos– Calculate covariance between cc and cs– Compare with toy model– Calculate signal to noise– Calculate effect on dark energy error bars
Takada & Bridle 2007
A toy model
• Cluster counts
• Lensing power spectrum
Toy model
Full calculation
Toy model
Cro
ss c
orr
elat
ion
co
effi
cien
t r
10%
100%
Toy model
FullcalculationC
ross
co
rrel
atio
n c
oef
fici
ent
r
10%
10%
1%
100%
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