http://arxiv.org/abs/1910.05063
A fraction of the light observed from edge-on disk galaxies is polarized due to two physical effects: selective extinction by dust grains aligned with the magnetic field, and scattering of the anisotropic starlight field. Since the efficiency of detectors and the response of optical devices depend on the polarization of incoming rays, this optical polarization produces both (a) a selection bias in favor of galaxies with specific orientations and (b) a polarization-dependent PSF. In this work we build toy models to obtain for the first time an estimate for the impact of polarization on PSF shapes and the impact of the selection bias due to the polarization effect on the measurement of the ellipticity used in shear measurements. In particular, we are interested in determining if this effect will be significant for WFIRST. We show that the systematic uncertainties in the ellipticity components are $7\times 10^{-5}$ and $1.1 \times 10^{-4}$ due to the selection bias and PSF errors respectively. Both of these systematic uncertainties are close to the WFIRST tolerance level, and hence more detailed studies of the polarization effects or more stringent requirements on polarization-sensitive instrumentation for WFIRST are required.
C. Lin, B. Tan, R. Mandelbaum, et. al.
Mon, 14 Oct 19
42/69
Comments: 10 pages, 4 figures
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