# Cosmic variance

in weak gravitational lensing

In this work, we highlight the shortcomings of using a deep narrow sample as a training sample to obtain redshift-dependent shear calibration biases for large surveys. Using COSMOS catalog, which is the largest contiguous survey from the Hubble Space Telescope, we showed that individual redshift bins were dominated by a single (or few) overdensities and voids. Thus, they cannot be used to obtain the redshift-dependent calibration for shear estimates since the sample is dominanted by local environment and is not a representative sample of the Universe. We tried a few possible techniques to mitigate this effect, but nonetheless, the environment effects were too strong to obtain a useful training sample from COSMOS.

Papers that have come out of this project:

- The impact of cosmic variance on simulating weak lensing surveys

**A. Kannawadi**, R. Mandelbaum, C. Lackner (2015) MNRAS 449 (4), 3597-3612 - The third gravitational lensing accuracy testing (GREAT3) challenge handbook

R. Mandelbaum, B. Rowe, J. Bosch, C. Chang, F. Courbin, M. Gill, M. Jarvis,**A. Kannawadi**, T. Kacprzak, C. Lackner, A. Leauthaud, H. Miyatake, R. Nakajima, J. Rhodes, M. Simet, J. Zuntz, B. Armstrong, S. Bridle, J. Coupon, J. P. Dietrich, M. Gentile, C. Heymans, A. S. Jurling, S. M. Kent, D. Kirkby, D. Margala, R. Massey, P. Melchior, J. Peterson, A. Roodman, T. Schrabback (2014) ApJS, 212 (1), 5