1 / 27

Outline: Introduction Cosmological applications Systematics Summary

Cosmological studies with Weak Lensing Effects Zuhui Fan Dept. of Astronomy, Peking University. Outline: Introduction Cosmological applications Systematics Summary. Introduction Gravitational lensing effects arise from the light deflection by the intervening structures.

elaina
Download Presentation

Outline: Introduction Cosmological applications Systematics Summary

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. Cosmological studies with Weak Lensing Effects Zuhui Fan Dept. of Astronomy, Peking University

  2. Outline: • Introduction • Cosmological applications • Systematics • Summary

  3. Introduction Gravitational lensing effects arise from the light deflection by the intervening structures

  4. Weak Lensing Effects Weak distortions caused by the large-scale structures of the universe: common but weak • “see” the dark matter directly  powerful probes of the distribution of dark matter • sensitive to the formation of large-scale structures and the global geometry of the universe  highly promising in dark energy studies

  5. Observationally challenging accurate shape measurements: lensing induced shape distortions are much weaker than the intrinsic ellipticities of galaxies  statistical measurements of the coherent distortions PSF corrections accurate calibration of the redshift distribution of source galaxies

  6. Observational advances Statistical methods theoretical studies  Fast developing forefront of research

  7. density inhomogeneity • Cosmological Applications background source galaxy distribution

  8. map out dark matter distribution

  9. Weak lensing clusters: avoid complicated gas physics Tang & Fan (2005, ApJ) CFHTLS Deep

  10. Cosmic shear : constraining cosmological parameters Fu et al. 2008 A&A (CFHTLS)

  11. Li, H. et al. (2009,PhLB) (RCS, VIRMOS,GaBoDS,CFHT(22)) total ~100deg*deg, varying depth

  12. Weak lensing observations start to provide useful and complementary constraints on Ωm, σ8 , and mν. Current data are largely limited by statistical errors due to relatively small survey areas and relatively shallow depth. Future weak lensing observations: go wide and deep LSST, Euclid, SNAP, (DOME A)......

  13. Future surveysSun, L., Zhao, G.B. et al. Hoekstra & Jain 2008 5000deg2 zm=0.9 3 zbins

  14. Systematics * redshift distribution of source galaxies magnitude distribution  redshift distribution photo-z measurement * intrinsic alignments of source galaxies shear-ellipticity correlation * Nonlinear power spectrum * observational systematics * ……

  15. Catastrophic Errors in photo-z(ApJ, 2009) Weak lensing effects are sensitive to the redshift distribution of source galaxies It is impractical to measure the redshift of vast number of galaxies with z>1 spectroscopically The technique developed to estimate the redshift of galaxies photometrically is tremendously important : multi-filter broad band measurements

  16. (Adelberger et al, 2004) 9 filters 390-1700nm

  17. Effects on parameter determination Ma et al. 2006 degradation

  18. Effects on parameter determination We concentrate on the catastrophic island, and emphasize the bias Major island: (0.35,3.5) Overall fraction ~1% Biasing the parameter determination

  19. Bias on dark energy parameter estimates 5 redshift bins

  20. Without knowledge on the catastrophic errors both chi-square fitting and Fisher matrix linear analysis fitted fiducial large bias is induced >> 3σ

  21. Spectral calibrations are needed to gain knowledge on catastrophic errors [Nspec:zp=(3,4)]

  22. Calibration requirement fsky=0.25 (10000deg2 ) Nspec > 8600 (zp 3-4)

  23. remove problematic galaxies zp<0.5 and zp>3 degradation factor ~1.4

  24. Summary * catastrophic redshift errors can lead to large biases on parameter determinations * spectral calibration are required * remove galaxies in problematic bins ---> degradation factor ~ 1.4 * other calibration methods fsky=0.25 (10000deg2 ) Nspec > 8600 (zp 3-4)

  25. Weak lensing effects hold great potential in cosmological studies Much more investigations are needed

More Related