Dark Matter Fraction in Lens Galaxies: New Estimates from Microlensing
  We present a joint estimate of the stellar/dark matter mass fraction in lens
galaxies and the average size of the accretion disk of lensed quasars from
microlensing measurements of 27 quasar image pairs seen through 19 lens
galaxies. The Bayesian estimate for the fraction of the surface mass density in
the form of stars is $\alpha=0.21\pm0.14$ near the Einstein radius of the
lenses ($\sim 1 - 2$ effective radii). The estimate for the average accretion
disk size is $R_{1/2}=7.9^{+3.8}_{-2.6}\sqrt{M/0.3M_\sun}$ light days. The
fraction of mass in stars at these radii is significantly larger than previous
estimates from microlensing studies assuming quasars were point-like. The
corresponding local dark matter fraction of 79\% is in good agreement with
other estimates based on strong lensing or kinematics. The size of the
accretion disk inferred in the present study is slightly larger than previous
estimates.
