  Using data from the COSMOS survey, we perform the first joint analysis of
galaxy-galaxy weak lensing, galaxy spatial clustering, and galaxy number
densities. Carefully accounting for sample variance and for scatter between
stellar and halo mass, we model all three observables simultaneously using a
novel and self-consistent theoretical framework. Our results provide strong
constraints on the shape and redshift evolution of the stellar-to-halo mass
relation (SHMR) from z=0.2 to z=1. At low stellar mass, we find that halo mass
scales as Mh M*^0.46 and that this scaling does not evolve significantly with
redshift to z=1. We show that the dark-to-stellar ratio, Mh/M*, varies from low
to high masses, reaching a minimum of Mh/M*~27 at M*=4.5x10^10 Msun and
Mh=1.2x10^12 Msun. This minimum is important for models of galaxy formation
because it marks the mass at which the accumulated stellar growth of the
central galaxy has been the most efficient. We describe the SHMR at this
minimum in terms of the "pivot stellar mass", M*piv, the "pivot halo mass",
Mhpiv, and the "pivot ratio", (Mh/M*)piv. Thanks to a homogeneous analysis of a
single data set, we report the first detection of mass downsizing trends for
both Mhpiv and M*piv. The pivot stellar mass decreases from
M*piv=5.75+-0.13x10^10 Msun at z=0.88 to M*piv=3.55+-0.17x10^10 Msun at z=0.37.
Intriguingly, however, the corresponding evolution of Mhpiv leaves the pivot
ratio constant with redshift at (Mh/M*)piv~27. We use simple arguments to show
how this result raises the possibility that star formation quenching may
ultimately depend on Mh/M* and not simply Mh, as is commonly assumed. We show
that simple models with such a dependence naturally lead to downsizing in the
sites of star formation. Finally, we discuss the implications of our results in
the context of popular quenching models, including disk instabilities and AGN
feedback.
