The distribution of mass around galaxies

We explore the distribution of mass about the expected sites of galaxy formation in a high-resolution hydrodynamical simulation of a LCDM cosmology which includes cooling, star-formation and feedback. We show that the evolution of the galaxy bias is non-trivial and non-monotonic and that the bias is stochastic. We discuss the galaxy-mass cross-correlation function and highlight problems with the interpretation of galaxy-galaxy lensing as due to extended dark matter halos around ``typical'' galaxies. Finally we show that the ``external shear'' around strong gravitational lenses is likely to be closely aligned with the direction of the nearest massive galaxy and to have a power-law distribution which can be predicted from the galaxy auto-correlation function.