Weak Gravitational Lensing Magnification

Weak gravitational lensing is one of the most powerful techniques to study the nature of the accelerating expansion of the Universe, to test general relativity, and to understand the relationship between visible and dark matter structures.

While most researchers in this field use the shear effect of weak lensing for their studies we have begun to establish the magnification effect as a competitive tool, which complements the shear and allows some new, unique measurements that are not possible with the shear. Our Emmy Noether group develops this method and applies it to large imaging surveys. We measure the magnification induced by galaxies and galaxy clusters out to large redshifts from data sets like the "Canada France Hawaii Telescope Lensing Survey" and the European "Kilo Degree Survey". In this way we constrain dark matter halo masses and relate them to stellar masses, spectral types, optical richness, etc. As a by-product we also measure the dust profiles of these objects out to several Megaparsec using colour information. By combining the dust- and DM- halo measurements of galaxies with clustering measurements at different redshifts we are planning to measure magnification tomography and thereby testing our theory of gravity and constrain the physical nature of the mechanism that is responsible for the accelerating expansion.