Download The galaxy-galaxy lensing contribution to the cosmic shear two

Impact of intrinsic alignments on
cosmic shear
Sarah Bridle, UCL (London)
• 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
Cosmic shear (2 point function)
Cosmic shear
Face-on view
Gravitationally
sheared
Gravitationally
sheared
Lensing by dark matter causes galaxies to
appear aligned
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
Intrinsic alignments (II)
Face-on view
Intrinsically
Aligned (I)
Intrinsically
Aligned (I)
Tidal stretching causes galaxies to align
Adds to cosmic shear signal
Intrinsic-shear correlation (GI)
Hirata & Seljak 2004
See also Heymans et al 2006, Mandelbaum et al 2006,
Hirata et al 2007
Intrinsic-shear correlation (GI)
Face-on view
Gravitationally
sheared (G)
Intrinsically
aligned (I)
Galaxies point in opposite directions
Partially cancels cosmic shear signal
Cosmic shear two point tomography
Cosmic shear tomography
Cosmic
Shear
Intrinsic
Alignments (IA)
Normalised to Super-COSMOS
Heymans et al 2004
If consider only w
then IA bias on w
is ~10%
If marginalise 6
cosmological
parameters
then IA bias on w
is ~100% (+/- 1 !)
Intrinsic
Alignments (IA)
Bridle & Abdalla
Elliptical galaxy-galaxy lensing
Background galaxy is gravitationally sheared
tangentially around foreground lens
Bridle & Abdalla
Elliptical galaxy-galaxy lensing
Face-on view
Bridle & Abdalla
Contribution to ellipticity correlation function:
Average shear around circular annulus
Does not average to zero →net contamination
Cosmic shear signal
Average over population
visible to R=24
Bridle & Abdalla
Shear correlation function
z1=0.3 z2=0.8
Cosmic shear signal
Average over population
visible to R=24
Change in
cosmic shear signal
for  w = 0.05
Bridle & Abdalla
Shear correlation function
z1=0.3 z2=0.8
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
Least flexible model considered
FoM is improved!
Redshift
No Intrinsic Alignments
dependence
of IA (# bins)
2
3
Reasonable model? (14 IA pars)
5
Similar FoM to no IA case
Very flexible (100 IA pars)
FoM is roughly halved
Scale dependence of IA (# bins)
Perfect redshifts
Redshift
dependence
of IA (# bins)
2
3
5
Scale dependence of IA (# bins)
Realistic photozs σz=0.05(1+z)
Redshift
dependence
of IA (# bins)
2
3
5
Scale dependence of IA (# bins)
FoM / FoM(specz)
No Intrinsic Alignments
Relatively flat
(e.g. Hu 1999, Ma, Hu, Huterer 2006, Jain et al 2007,
Amara & Refregier 2007 ....)
Photoz error σz / (1+z)
FoM / FoM(specz)
Reasonable model? (14 IA pars)
Very flexible (100 IA pars)
Photoz error σz / (1+z)
FoM / FoM(specz)
A factor of ~3 better photozs required!
0.8
0.02 (1+z)
0.08 (1+z)
Photoz error σz / (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
Shear correlation function
z1=0.3 z2=0.8
Cosmic shear signal
NFW
Average over population
^
visible to R=24
Shear correlation function
z1=0.3 z2=0.8
Cosmic shear signal
Singular isothermal
ellipsoid
NFW
Average over population
^
visible to R=24
Shear correlation function
M200=1x1012 h-1 Mo
Bridle & Abdalla
zlens=0.3 zsource=0.8
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
Full calculation
Toy model
Cross correlation coefficient r
100%
10%
Toy model
Cross correlation coefficient r
100%
10%
Toy model
10%
1%
Full
calculation