Tuesday, April 9, 2013

1304.2164 (Masato Shirasaki et al.)

Effect of Mask Regions on Weak Lensing Statistics    [PDF]

Masato Shirasaki, Naoki Yoshida, Takashi Hamana
Sky masking is unavoidable in wide-field weak lensing observations. We study how masks affect the measurement of statistics of matter distribution probed by weak gravitational lensing. We first use 1000 Gaussian simulations in order to examine in detail the impact of mask regions on the weak lensing Minkowski Functionals (MFs). We consider actual sky masks used for a Subaru Suprime-Cam imaging survey. The masks increase the variance of the convergence field and thus the expected values of the MFs are biased even for a Gaussian random field. The bias is caused by two effects. One is owing to the reduced number of sampling Fourier modes, which can be accounted for analytically by considering the survey geometry appropriately. The other is owing to variation of the variance of the convergence field for each field of view. Lensing MFs are biased systematically when the reconstructed convergence field is normalized by its variance. We then use a large number of cosmological ray-tracing simulations in order to address if the lensing MFs measured for a Subaru 2-deg^2 survey are consistent with those of the standard cosmology. The resulting chi^2/n_dof = 29.6/30 for combined three MFs, obtained by taking the mask effects into account, suggests that the observational data are indeed consistent with the standard LCDM model. Finally, we explore how masked covariance matrices affect cosmological parameter estimation. We conclude that the lensing MFs are powerful probe of cosmology only if the effect of masking is correctly taken into account.
View original: http://arxiv.org/abs/1304.2164

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