The Galaxy Dark Matter Connection
  What galaxy lives in what halo? The answer to this simple question holds important information regarding galaxy formation and evolution. We describe a new statistical technique to link galaxies to their dark matter haloes, or light to mass, using the clustering properties of galaxies as function of their luminosity. The galaxy-dark matter connection thus established, and parameterized through the conditional luminosity function, indicates the presence of two characteristic scales in galaxy formation: one at ~10^{11} Msun, where galaxy formation is most efficient, and another at ~10^{13} Msun, where a transition occurs from systems dominated by one brightest, central galaxy to systems with several dominant galaxies of comparable luminosity. We show that the relation between light and mass established from galaxy clustering alone is in excellent agreement with the dynamical masses inferred from satellite kinematics. We also present a new (halo-based) galaxy-group finder, and show that the multiplicity function of galaxy groups identified in the 2dFGRS suggests a relatively high mass-to-light ratio on the scales of galaxy clusters, or, alternatively, a relatively low value of sigma_8. These findings are also supported by our studies of pairwise peculiar velocities and satellite abundances. 
Frank C. van den Bosch (ETH), Xiaohu Yang (UMass), H.J. Mo (UMass)