Galaxy halo masses and satellite fractions from galaxy-galaxy lensing in the Sloan Digital Sky Survey: stellar mass, luminosity, morphology and environment dependencies

The relationship between galaxies and dark matter can be characterized by the halo mass of the central galaxy and the fraction of galaxies that are satellites. Here we present observational constraints from the SDSS on these quantities as a function of r-band luminosity and stellar mass using galaxy-galaxy weak lensing, with a total of 351,507 lenses. We use stellar masses derived from spectroscopy and virial halo masses derived from weak gravitational lensing to determine the efficiency with which baryons in the halo of the central galaxy have been converted into stars. We find that an L* galaxy with a stellar mass of 6x10¹⁰ Mₛᵤₙ is hosted by a halo with mass of 1.4x10¹² Mₛᵤₙ/h, independent of morphology, yielding baryon conversion efficiencies of 17₋₅⁺¹⁰ (early types) and 16₋₆⁺¹⁵ (late types) per cent at the 95 per cent CL (statistical, not including systematic uncertainty due to assumption of a universal initial mass function, or IMF). We find that for a given stellar mass, the halo mass is independent of morphology below Mₛₜₑₗₗₐᵣ=10¹¹ Mₛᵤₙ, in contrast to typically a factor of two difference in halo mass between ellipticals and spirals at a fixed luminosity. This suggests that stellar mass is a good proxy for halo mass in this range and should be used preferentially whenever a halo mass selected sample is needed. For higher stellar masses, the conversion efficiency is a declining function of stellar mass, and the differences in halo mass between early and late types become larger, reflecting the fact that most group and cluster halos with masses above 10¹³ Mₛᵤₙ host ellipticals at the center, while even the brightest central spirals are hosted by halos of mass below 10¹³ Mₛᵤₙ. (Abridged)