A microlensing measurement of dark matter fractions in three lensing
  galaxies
  Direct measurements of dark matter distributions in galaxies are currently
only possible through the use of gravitational lensing observations.
Combinations of lens modelling and stellar velocity dispersion measurements
provide the best constraints on dark matter distributions in individual
galaxies, however they can be quite complex. In this paper, we use observations
and simulations of gravitational microlensing to measure the smooth (dark)
matter mass fraction at the position of lensed images in three lens galaxies:
MG 0414+0534, SDSS J0924+0219 and Q2237+0305. The first two systems consist of
early-type lens galaxies, and both display a flux ratio anomaly in their close
image pair. Anomalies such as these suggest a high smooth matter percentage is
likely, and indeed we prefer ~50 per cent smooth matter in MG 0414+0534, and
~80 per cent in SDSS J0924+0219 at the projected locations of the lensed
images. Q2237+0305 differs somewhat in that its lensed images lie in the
central kiloparsec of the barred spiral lens galaxy, where we expect stars to
dominate the mass distribution. In this system, we find a smooth matter
percentage that is consistent with zero.
