Probing Cosmology with Weak Lensing Effects Zuhui Fan

Probing Cosmology with Weak Lensing Effects Zuhui Fan Dept. of Astronomy, Peking University

§ § Weak gravitational lensing effects Cosmological applications Current Future

§ Lensing Effects Gravitational lensing effects arise from the light deflection by the intervening structures

§ Weak Lensing Effects Weak distortions caused by the large-scale structures of the universe: common but weak v v “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

density inhomogeneity background source galaxy distribution Weak lensing effects

Involve almost all cosmological parameters notably: Ωm, σ8 , mν, w(z)

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

Observational advances Statistical methods theoretical studies Fast developing forefront of research

n Cosmological Applications map out dark matter distribution Bullet cluster COSMOS Massey et al. 2007

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

n Hoekstra & Jain 2008 astro-ph/08050139

Li, H. et al. 2008 (RCS, VIRMOS, Ga. Bo. DS, CFHT(22)) total ~100 deg*deg, varying depth

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). . .

Future surveys Hoekstra & Jain 2008 5000 deg 2 zm=0. 9 3 zbins Sun, L. , Zhao, G. B. et al.

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

Because of the weakness of the lensing signals, systematic effects can affect their cosmological applications considerably. * 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 * ……

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