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)

Cosmic shear (2 point function)

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%