Elliptical galaxy masses out to five effective radii: the realm of dark
  matter
  We estimate the masses of elliptical galaxies out to five effective radii
using planetary nebulae and globular clusters as tracers. A sample of 15
elliptical galaxies with a broad variation in mass is compiled from the
literature. A distribution function-maximum likelihood analysis is used to
estimate the overall potential slope, normalisation and velocity anisotropy of
the tracers. We assume power-law profiles for the potential and tracer density
and a constant velocity anisotropy. The derived potential power-law indices lie
in between the isothermal and Keplerian regime and vary with mass: there is
tentative evidence that the less massive galaxies have steeper potential
profiles than the more massive galaxies. We use stellar mass-to-light ratios
appropriate for either a Chabrier/KTG (Kroupa, Tout & Gilmore) or Salpeter
initial mass function to disentangle the stellar and dark matter components.
The fraction of dark matter within five effective radii increases with mass, in
agreement with several other studies. We employ simple models to show that a
combination of star formation efficiency and baryon extent are able to account
for this trend. These models are in good agreement with both our measurements
out to five effective radii and recent SLACS measurements within one effective
radii when a universal Chabrier/KTG initial mass function is adopted.
