Outline: Introduction Noise peaks from intrinsic ellipticites Results Summary

1. "Dark clumps" near clustersfrom Weak Lensing Effects Zuhui Fan Dept. of Astronomy, Peking University

2. Outline: • Introduction • Noise peaks from intrinsic ellipticites • Results • 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. Cosmological Applications map out constrain cosmology dark matter distribution

8. “Dark clumps” around clusters Erben et al 2000 Linden et al. 2006 “Dark clumps” S/N ~4 M~1014Msun at z~0.2 If real, would be significant for the theory of structure formation

9. Galaxies are not intrinsically spherical shear intrinsic ellipticites

10. -> noise in the mass distribution constructed from weak lensing effects pure noise

11. Noise peaks from intrinsic ellipticities • Noise peaks have no optical counterparts (However, Dark clumps) • Lensing signals from real clumps have certain redshift dependency -- lensing tomography • On average, high S/N noise peaks (>4) are rare Use average number density of noise peaks: P~8*10-3(>4.5) Unlikely to be a noise peak, then real “dark clumps”? However, around real clusters, the probability of high noise peaks can be higher than average

12. -> Presence of real clusters affects the statistics of noise peaks Smoothed noise field can well be discribed by a Gaussian random field

13. Smoothed quantities: dpend on cluster profiles cored isothermal NFW

14. NFW ISO • Results : Rc=Rs=1.7 arcmin, Rvir=5Rc (Rs), θG=0.5arcmin, peak height=5.6 Profiles peak numbers in R>Rc (Rs)

15. κ reconstruction: mass-sheet degeneracy <K>=0 within the survey area <K >=0 for the outer most ring --> depend on survey area For a survey area much larger than the typical size of a cluster, the mass-sheet degeneracy does not affect much.

16. different normalizations on K cored isothermal NFW <K>=0 K=0(ring) true

17. Number of high S/N noise peaks are significantly boosted (~10 times for S/N>4.5 for cored isothermal cluster with <K>=0 within 5Rc)

18. Noise peaks above certain threshold are closely correlated with clusters, in a way similar to the biased halo formation. However, the mass- sheet degenerancy in weak lensing reconstruction should be taken into account. ---> To evaluate the probability of noise peaks, one must consider the cluster evironment ---> For large scale surveys, the correlation of clusters and noise peaks may cause contaminations on cluster correlations

19. Around a real cluster -> Noise affects cluster lensing signals cluster peak height νbiased by ~+1 for cored iso

20. Cluster peak height distribution With central , one can calcuate the distribution --> provide an analytical way to make a better prediction of cluster abundance from weak lensing surveys * (Hamana et al. 2004, fitting formula)

21. Summary * noise peaks and clusters are correlated * One must consider both coherently in weak lensing studies --> enhance the probability of high noise peaks (can be an order of magnitude higher) ---> true peak height is affected: cluster abundance