A bias in cosmic shear from galaxy selection: results from ray-tracing simulations

Understand

We identify and study a previously unknown systematic effect on cosmic shear measurements, caused by the selection of galaxies used for shape measurement, in particular the rejection of close (blended) galaxy pairs.

• We use ray-tracing simulations based on the Millennium Simulation and a semi-analytical model of galaxy formation to create realistic galaxy catalogues.
• From these, we quantify the bias in the shear correlation functions by comparing measurements made from galaxy catalogues with and without removal of close pairs.
• A likelihood analysis is used to quantify the resulting shift in estimates of cosmological parameters.