A novel method for unbiased measurements of growth with cosmic shear

Abstract

I present a new technique for the measurement of the growth of cosmic structures via the power spectrum of weak lensing cosmic shear. It is based on a template-fitting approach, where a redshift-dependent amplitude of lensing modulates a fixed template power spectrum. Such an amplitude, which is promoted to a free parameter and fit against tomographic cosmic shear data, reads $D(z)\,\sigma_8\,\Omega_{{\rm m},0}=:\Omega\sigma_8(z)$, with $D(z)$ the growth factor, $\sigma_8$ a proxy for the overall amplitude of the matter power spectrum, and $\Omega_{{\rm m},0}$ the present-day matter abundance. I show that this method is able to correctly reconstruct $\Omega\sigma_8$ at the per cent level across redshift, thus allowing us to measure the growth of structures unbiased by observing discrete tracers. Moreover, I only makes use of measurements on linear scales. The method is highly complementary to measurements of the bias and growth, $b\sigma_8(z)$ and $f\sigma_8(z)$, from galaxy clustering analysis. I also demonstrate that the method is robust against an incorrect choice of cosmological parameters in the template, thanks to the inclusion of an Alcock-Paczy\'nski parameter.