Impact of intrinsic alignments on cosmic shear

1. 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)

2. Cosmic shear (2 point function)

3. Cosmic shear Face-on view Gravitationally sheared Gravitationally sheared Lensing by dark matter causes galaxies to appear aligned

4. 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

5. Intrinsic alignments (II) Face-on view Intrinsically Aligned (I) Intrinsically Aligned (I) Tidal stretching causes galaxies to align Adds to cosmic shear signal

6. Intrinsic-shear correlation (GI) Hirata & Seljak 2004 See also Heymans et al 2006, Mandelbaum et al 2006, Hirata et al 2007

7. Intrinsic-shear correlation (GI) Face-on view Gravitationally sheared (G) Intrinsically aligned (I) Galaxies point in opposite directions Partially cancels cosmic shear signal

8. Cosmic shear two point tomography

9. Cosmic shear tomography

11. Effect on cosmic shear of changing w by 1% Cosmic Shear Intrinsic Alignments (IA) Normalised to Super-COSMOS Heymans et al 2004

12. Effect on cosmic shear of changing w by 1% 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)

13. Elliptical galaxy-galaxy lensing Bridle & Abdalla

14. Elliptical galaxy-galaxy lensing Face-on view Bridle & Abdalla Background galaxy is gravitationally sheared tangentially around foreground lens

15. Bridle & Abdalla Contribution to ellipticity correlation function: Average shear around circular annulus Does not average to zero →net contamination

16. z1=0.3 z2=0.8 Cosmic shear signal Bridle & Abdalla Shear correlation function Average over population visible to R=24

17. z1=0.3 z2=0.8 Cosmic shear signal Bridle & Abdalla Shear correlation function Average over population visible to R=24 Change in cosmic shear signal for  w = 0.05

18. 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!

22. Perfect redshifts Least flexible model considered FoM is improved! Redshift dependence of IA (# bins) 2 3 5 No Intrinsic Alignments Dark energy Figure of Merit Reasonable model? (14 IA pars) Similar FoM to no IA case Very flexible (100 IA pars) FoM is roughly halved Scale dependence of IA (# bins)

23. Perfect redshifts Redshift dependence of IA (# bins) 2 3 5 Dark energy Figure of Merit Scale dependence of IA (# bins)

24. Realistic photozs σz=0.05(1+z) Redshift dependence of IA (# bins) 2 3 5 Dark energy Figure of Merit Scale dependence of IA (# bins)

25. No Intrinsic Alignments FoM / FoM(specz) Relatively flat (e.g. Hu 1999, Ma, Hu, Huterer 2006, Jain et al 2007, Amara & Refregier 2007 ....) Photoz error σz / (1+z)

26. Reasonable model? (14 IA pars) Very flexible (100 IA pars) FoM / FoM(specz) Photoz error σz / (1+z)

27. A factor of ~3 better photozs required! 0.8 FoM / FoM(specz) 0.02 (1+z) 0.08 (1+z) Photoz error σz / (1+z)

31. 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

32. Survey closes this Sunday

33. END

34. 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

35. z1=0.3 z2=0.8 Cosmic shear signal NFW Shear correlation function Average over population visible to R=24 ^

36. z1=0.3 z2=0.8 Cosmic shear signal Singular isothermal ellipsoid NFW Shear correlation function Average over population visible to R=24 ^

37. zlens=0.3 zsource=0.8 Bridle & Abdalla M200=1x1012 h-1 Mo Shear correlation function

38. 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

39. σz / (1+z)

42. 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

44. A toy model • Cluster counts • Lensing power spectrum

45. Full calculation Toy model

46. 100% Toy model 10% Cross correlation coefficient r

47. 100% Toy model 10% Cross correlation coefficient r 10% Full calculation 1%