1 / 37

Accurate Cosmology from LSST Cosmic Shear

Accurate Cosmology from LSST Cosmic Shear. Shear measurement The problem International Challenges Impact of morphologies Intrinsic alignments Must be taken into account Calibration using cross-correlations Photometric redshift requirements. The great potential of cosmic shear. Galaxy

malini
Download Presentation

Accurate Cosmology from LSST Cosmic Shear

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Accurate Cosmology from LSST Cosmic Shear • Shear measurement • The problem • International Challenges • Impact of morphologies • Intrinsic alignments • Must be taken into account • Calibration using cross-correlations • Photometric redshift requirements

  2. The great potential of cosmic shear Galaxy clustering Supernovae Cosmic shear Quality of dark energy constraint Example for optical ground-based surveys Dark Energy Task Force report astro-ph/0609591

  3. The Future HSC AFTA JDEM

  4. The great potential of cosmic shear Galaxy clustering Supernovae Cosmic shear Quality of dark energy constraint Example for optical ground-based surveys Dark Energy Task Force report astro-ph/0609591

  5. Cosmic Shear: Potential systematics Galaxy shape measurement Intrinsic alignments Photometric redshifts Accuracy of predictions See the DESC Whitepaper for much more detail

  6. Galaxy shape measurement Causes b/a ~ 0.03 Measure b/a +/- 0.3 The GREAT08 Challenge Handbook Bridle et al 2010

  7. Galaxy shape measurement Causes b/a ~ 0.03 Measure this to 1% Measure b/a +/- 0.3 The GREAT08 Challenge Handbook Bridle et al 2010

  8. Typical data

  9. Shear TEsting Programme • Brought together international shear measurement community • Revitalised research area • Set a benchmark for shear measurement • Current methods OK for current data (then) • Very non-trivial problem for future STEP 1:

  10. GREAT08: Separate the issues Bridle et al 2010

  11. GREAT08 Results in Detail See also GREAT10 Kitching et al Bridle et al 2010

  12. Sersic model fitting shear measurement codes • LensFit • Multifit • Im3shape See also currently popular non-Sersic methods: DEIMOS, FDNT, shapelets

  13. Model bias due to realistic galaxy morphologies Model bias Kacprzak, SB, et al 2013

  14. How many galaxies do we need to observe, to know enough about their morphologies? Hirsch et al in prep, Voigt et al in prep

  15. GREAT3 References:Mandelbaum, Rowe et al 2013 The GREAT3 Challenge Handbook Rowe, Mandelbaum et al 2013 The GalSim Toolkit

  16. Shear measurement issues for LSST • Iterative PSF reconstruction • Noise bias calibration • Knowledge of galaxy morphologies • Deblending • Stacking • Wavelength dependent PSF • Flux dependent PSF • Star selection effects

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

  18. 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

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

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

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

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

  23. Effect on cosmic shear of changing w by 1% Intrinsic Alignments (IA)

  24. Ignoring Intrinsic Alignments is Bad! Badness depends on assumed model Kirk, Rassat, Host, Bridle 2012

  25. Use of shear-position correlations Shear-shear correlations - Measure mostly dark matter Shear-position correlations - Measure mostly intrinsic alignments Position-position correlations - Traditional galaxy survey observable

  26. Forecast Joint Constraints from Position 2-point Observables Cosmic shear Intrinsic Alignments Galaxy clustering Cosmic magnification Shear-position correlation function Angular power spectra are sourced by underlying 3D power spectra: Dark matter P(k), galaxy P(k), IA P(k), galaxy-DM cross, IA-DM cross Joachimi & Bridle 2010

  27. Shear alone (ee), fixed IAs Kirk, Rassat, Host, Bridle 2012

  28. Shear alone (ee), fixed IAs Kirk, Rassat, Host, Bridle 2012 Shear alone (ee), marg IAs

  29. Shear alone (ee), fixed IAs ee, ne, nn, fixed IAs Kirk, Rassat, Host, Bridle 2012 Shear alone (ee), marg IAs ee, ne, nn, marg IAs

  30. Intrinsic Alignment work for LSST Build a physically motivated model f(z,k,L,c) from observational programme • Using existing/planned speczs and photozs • Self-calibration from imaging surveys • Calculate desired survey requirements • Synergy with photoz calibration fields? and come up with • motivated functional forms from simulations. • Test IA removal methods on simulations in non-linear regime

  31. Photometric Redshifts for LSST • Need precise redshifts to eliminate intrinsic alignments • Improved use of colour information • Use of additional e.g. morphology information?

  32. Requirements on Photoz Precision More stringent requirements on photoz accuracy with IAs Kirk, Laszlo, Bridle, Bean 2011

  33. Photometric Redshifts for LSST • Need precise redshifts to eliminate intrinsic alignments • Improved use of colour information • Use of additional e.g. morphology information? • Need accurate redshifts to measure cosmology • Spectra from representative training set • Development and use of cross-correlation methods

  34. Requirements on Photoz Accuracy Need the mean redshift of galaxies to better than 0.01 (0.003 with no cross-correlations) Same for knowledge of scatter Translates to 100s of galaxies per z bin in a complete sample Or cross-correlation between spectra and imaging catalogues Kirk, Laszlo, Bridle, Bean 2011

  35. Conclusions • Shear measurement • International Challenges to set the pace • Check necessary knowledge of galaxy morphologies • Long list of calculations still to do (see DESC WP) • Intrinsic alignments • Can’t be ignored • Can be self-calibrated • Lots of additional information available • Photometric redshift calibration • Accuracy a greater worry than precision • May determine LSST depth usable for lensing

  36. GREAT3 PSFs and PSF variation Mandelbaum, Rowe et al 2013 The GREAT3 Challenge Handbook

  37. Cross-correlation of shapes and spectra Red: different sky Blue: same sky Southern Hemisphere spectra MOONS 4MOST SKA HI Euclid

More Related