Gravitational lensing evidence against extended dark matter halos
  It is generally thought that galaxies are embedded in dark matter halos
extending well beyond their luminous matter. The existence of these galactic
halos is mainly derived from the larger than expected velocities of stars and
gas in the outskirts of spiral galaxies. Much less is known about dark matter
around early-type (elliptical or lenticular) galaxies. We use gravitational
lensing to derive the masses of early-type galaxies deflecting light of
background quasars. This provides a robust measurement of the total mass within
the Einstein ring, a circle whose diameter is comparable to the separation of
the different quasar images. We find that the mass-to-light ratio of the
lensing galaxies does not depend on radius, from inner galactic regions out to
several half-light radii. Moreover, its value does not exceed the value
predicted by stellar population models by more than a factor two, which may be
explained by baryonic dark matter alone, without any need for exotic matter.
Our results thus suggest that, if dark matter is present in early-type
galaxies, its amount does not exceed the amount of luminous matter and its
density follows that of luminous matter, in sharp contrast to what is found
from rotation curves of spiral galaxies.
