The galaxy-mass correlation and the Kilo-Degree Survey (KiDS)

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Within this project, we will conduct a detailed analysis of galaxy-galaxy lensing (GGL), a versatile tool to study the mass profile of galaxies and the relative distribution of galaxies and (dark) matter in the Universe. Galaxies do not faithfully trace the distribution of the underlying mass distribution, a fact called galaxy bias. A detailed knowledge of the bias is needed to be able to relate the observable galaxy distribution to the (dark) matter distribution, which is predicted from cosmological models. The magnitude of bias and its dependence on galaxy properties depends on the formation processes of galaxies and their evolutionary history. GGL provides themost direct measurement of this bias, which we will study as a function of galaxy type, luminosity (or stellar mass), redshift and,more generally, the relative distribution of galaxies and the underlying dark matter distribution. Furthermore, the radial massprofile of galaxies and their dark matter halos will be probed with high statistical accuracy out to large radii. The interpretation ofthe results will be conducted in the framework of the so-called halo model; together with the clustering properties of galaxies,information on cosmological parameters can be derived. In addition, we will study higher-order correlations between galaxies andmatter. These results will provide substantial constraints on models of galaxy formation and evolution, as demonstrated by earlier work.The ESO Public Survey KiDS (Kilo Degree Survey) provides a unique data resource for such studies, owing to its sky coverage, larger depth compared to the Sloan Digital Sky Survey (SDSS), superb imaging properties of the instrument/telescope, and its waveband coverage. We will conduct a full weak gravitational lensing analysis of the 1500 square degrees imaging survey in four optical bands. KiDS is complemented with a near-infrared counterpart VIKING, covering the same area in 5 near infrared band, to provide accurate source catalogs and, in particular, robust estimates of galaxy shapes and photometric redshifts. Capitalising on the past experience of our group in terms of data processing, pipeline development, shape and photometric redshift measurements, and methodological and theoretical developments in weak lensing, we are in an excellent position to play a leading role in an international collaboration where this KiDS/VIKING survey will be fully explored.