  This work aims to study the distribution of luminous and dark matter in Coma
early-type galaxies. Dynamical masses obtained under the assumption that mass
follows light do not match with the masses of strong gravitational lens systems
of similar velocity dispersions. Instead, dynamical fits with dark matter halos
are in good agreement with lensing results. We derive mass-to-light ratios of
the stellar populations from Lick absorption line indices, reproducing well the
observed galaxy colours. Even in dynamical models with dark matter halos the
amount of mass that follows the light increases more rapidly with galaxy
velocity dispersion than expected for a constant stellar initial mass function
(IMF). While galaxies around sigma ~ 200 km/s are consistent with a Kroupa IMF,
the same IMF underpredicts luminous dynamical masses of galaxies with sigma ~
300 km/s by a factor of two and more. A systematic variation of the stellar IMF
with galaxy velocity dispersion could explain this trend with a Salpeter IMF
for the most massive galaxies. If the IMF is instead constant, then some of the
dark matter in high velocity dispersion galaxies must follow a spatial
distribution very similar to that of the light. A combination of both, a
varying IMF and a component of dark matter that follows the light is possible
as well. For a subsample of galaxies with old stellar populations we show that
the tilt in the fundamental plane can be explained by systematic variations of
the total (stellar + dark) mass inside the effective radius. We tested commonly
used mass estimator formulae, finding them accurate at the 20-30% level.
