LEMOMAF: Lensed Mock Map Facility

We present the Lensed Mock Map Facility (LEMOMAF), a tool designed to perform mock weak-lensing measurements on numerically simulated chunks of the Universe. Coupling N-body simulations to a semi-analytical model of galaxy formation, LEMOMAF can create realistic lensed images and mock catalogues of galaxies, at wavelengths ranging from the ultraviolet to the submillimetre. To demonstrate the power of such a tool, we compute predictions of the source-lens clustering (SLC) effect on the convergence statistics, and quantify the impact of weak lensing on galaxy counts in two different filters. We find that the SLC effect skews the probability density function of the convergence towards low values, with an intensity which strongly depends on the redshift distribution of galaxies. On the other hand, the degree of enhancement or depletion in galaxy counts due to weak lensing is independent of the SLC effect. We discuss the impact on the two-point shear statistics to be measured by future missions like SNAP and LSST. The SLC effect would bias the estimation of sigma(8) from two-point statistics up to 5 per cent for a narrow redshift distribution of mean z similar to 0.5, and up to 2 per cent in small angular scales for a redshift distribution of mean z similar to 1.5. We conclude that accurate photometric redshifts for individual galaxies are necessary in order to quantify and isolate the SLC effect.