Modeling Galaxy-Mass Correlations in Dissipationless Simulations

We use high-resolution dissipationless simulations of the concordance flat LCDM model to make predictions for the galaxy--mass (GM) correlations and compare them to the recent SDSS weak lensing measurements.We use a simple observationally motivated scheme to assign luminosities and colors to the halos.This allows us to closely match the selection criteria used to define observational samples.The simulations reproduce the observed GM correlation function and its observed dependencies on luminosity and color.The luminosity dependence of the correlation function is primarily determined by the changing relative contribution of central and satellite galaxies at different luminosities. The color dependence of the GM correlations reflects the difference in the typical environments of blue and red galaxies. We also find agreement between the predicted and observed cross-bias, b_x=b/r,at all probed scales.The GM correlation coefficient, r, is close to unity on scales >1/h Mpc.The cross bias is thus expected to measure the actual bias of galaxy clustering on these scales.The aperture mass-to-light ratio is independent of galaxy color.The aperture mass scales approximately linearly with luminosity at L_r>10^{10}h^{-2} Lsun, while at lower luminosities the scaling is shallower: L_r^{0.5}. We show that most of the luminous galaxies (M_r<-21) are near the centers of their halos and their GM correlation function at r<100/h kpc can therefore be interpreted as the average dark matter density profile of these galaxies. We find that for galaxies in a given narrow luminosity range, there is a broad and possibly non-gaussian distribution of halo virial masses. Therefore, the average relation between mass and luminosity derived from the weak lensing analyses should be interpreted with caution.