1. Cosmic shear and intrinsic alignments Rachel Mandelbaum April 2, 2007 Collaborators: Christopher Hirata (IAS), Mustapha Ishak (UT Dallas), Uros Seljak (Zurich/Princeton)

2. Dark matter clustering  Why should we care about this? Cosmological model predicts clustering of dark matter more simply than that of baryons Cosmological model predicts clustering of dark matter more simply than that of baryons Measures of dark matter clustering and its evolution teach us about cosmology Measures of dark matter clustering and its evolution teach us about cosmology  Why is it difficult to study? Telescopes see light = galaxies = baryons Telescopes see light = galaxies = baryons Baryon behavior is harder to understand Baryon behavior is harder to understand We need probes of dark matter We need probes of dark matter

3. Galaxy-dark matter relationship  Why should we care about this? Allows us to understand observations of galaxies better Allows us to understand observations of galaxies better Allows us to relate simulations, models, and observations Allows us to relate simulations, models, and observations  Why is this question difficult to answer? Need simultaneous probes of both galaxy and dark matter Need simultaneous probes of both galaxy and dark matter

4. What is lensing? Gravitational lensing: Gravitational lensing: Weak: small effect, can be treated perturbatively as shape distortion Weak: small effect, can be treated perturbatively as shape distortion Sensitive to all matter along line of sight, including dark matter!

5. Cosmic shear What is it? Weak lensing by large-scale structure (depends on matter power spectrum) What is it? Weak lensing by large-scale structure (depends on matter power spectrum) How is it measured? Various statistics, e.g. shear variance in cells, correlation function of galaxy ellipticities, … How is it measured? Various statistics, e.g. shear variance in cells, correlation function of galaxy ellipticities, … Critical assumption? Independence of galaxy ellipticities in the absence of lensing Critical assumption? Independence of galaxy ellipticities in the absence of lensing

6. The power of cosmic shear Allows constraints on power spectrum amplitude at different z than CMB, SNe (Upadhye et al. 2005)  constrain w Allows constraints on power spectrum amplitude at different z than CMB, SNe (Upadhye et al. 2005)  constrain w Lensing tomography gives even better improvement when added to Planck + SN, constraints on w and w a tighter by factors of 3-5 (Ishak 2005) Lensing tomography gives even better improvement when added to Planck + SN, constraints on w and w a tighter by factors of 3-5 (Ishak 2005) Assumption: systematics understood very well Assumption: systematics understood very well

7. Violation of assumptions? ? OR… Hirata & Seljak (2003)

8. The physical picture  Low-z galaxies aligned with tidal field High-z galaxy lensed by overdensities

9. The problem? Intrinsic alignments relate to galaxy-dark matter connection (alignment of baryons with local tidal fields) Intrinsic alignments relate to galaxy-dark matter connection (alignment of baryons with local tidal fields) Galaxy dynamics insufficiently understood to predict alignments Galaxy dynamics insufficiently understood to predict alignments Need to measure with real data Need to measure with real data Use results to relate to models Use results to relate to models When physics is understood, relate to effects on cosmic shear measurements When physics is understood, relate to effects on cosmic shear measurements

10. II, GI measurement with SDSS Use ~300,000 spectroscopic galaxies Use ~300,000 spectroscopic galaxies Find correlation function of ellipticities with small radial separation: Find correlation function of ellipticities with small radial separation: Find ellipticity - galaxy cross-correlation: Find ellipticity - galaxy cross-correlation: e r e r = (-e)(-e)=e 2 e r e r = (e)(-e)=-e 2

11. GI in reality Small scales: Binggeli effect, Holmberg effect, many other works Small scales: Binggeli effect, Holmberg effect, many other works Large scales: detection to 60 Mpc/h with SDSS (Mandelbaum et al. 2006, Hirata et al. 2007) Large scales: detection to 60 Mpc/h with SDSS (Mandelbaum et al. 2006, Hirata et al. 2007) Consistent with zero for typical L* galaxies Consistent with zero for typical L* galaxies Amplitude increases rapidly with luminosity above 2L* Amplitude increases rapidly with luminosity above 2L* Destructive interference with cosmic shear Destructive interference with cosmic shear

12. The Data Data sourceL ColorRedshifts Ngals SDSS Main sample (York et al., 2000) SDSS LRG sample L*/3 < L < 7L* L >~ 3L* All Red 0.05<z< 0.25 0.15<z<0.35 2SLAQ LRG sample (Cannon et al., 2006) L>~2.5L*Red0.4<z<0.7 36,278 265,908 7758

13. Results: MAIN sample Power-law fits: Confidence contours (1, 2, 3  ) shown in luminosity bins Detection in two brighter bins to 60 Mpc/h at 99.96% and >99.99% CL! No detection for L<~L* galaxies.

14. Results: SDSS LRG sample Split into luminosity bins(1=faintest) Conclusion: >3  detection for all SDSS LRG subsamples.

15. Scaling relations (red galaxies) (decreasing with transverse sep) (increasing with luminosity) (decreasing with redshift, poorly constrained) Note: 2  errors

16. To predict contamination… Use COMBO-17 R-band luminosity function (spectral type, redshift- dependent); Wolf et al. (2003) Use COMBO-17 R-band luminosity function (spectral type, redshift- dependent); Wolf et al. (2003) Choose a limiting depth in that band Choose a limiting depth in that band Associate spectral types with red vs. blue, get distribution of L(z) Associate spectral types with red vs. blue, get distribution of L(z) Do so not just for central model, but limits in either direction Do so not just for central model, but limits in either direction

17. Projected contamination Cosmic shear power spectrum Most pessimistic model,  8 = -0.10 Central model,  8 = -0.02 Most optimistic model,  8 = -0.004 GI power spectra Hirata et al. 2007

18. Future work Key weakness in constraints: GI contamination from blue galaxies; low redshift Key weakness in constraints: GI contamination from blue galaxies; low redshift Need theoretical modeling, not just with DM simulations: Need theoretical modeling, not just with DM simulations: See Heymans et al. 2006 modeling with N-body simulations, were able to match SDSS observations with a mix of galaxy types See Heymans et al. 2006 modeling with N-body simulations, were able to match SDSS observations with a mix of galaxy types Goes back to “difficult questions”: galaxy/DM connection not fully understood Goes back to “difficult questions”: galaxy/DM connection not fully understood

19. Conclusions Cosmic shear can constrain cosmological parameters and break degeneracies in analyses using other types of data Cosmic shear can constrain cosmological parameters and break degeneracies in analyses using other types of data Future surveys: S/N ~ 100-1000 Future surveys: S/N ~ 100-1000 More intrinsic alignments work (observational, theoretical) necessary to allow it to fulfill its potential More intrinsic alignments work (observational, theoretical) necessary to allow it to fulfill its potential