Central dark matter trends in early-type galaxies from strong lensing,
  dynamics and stellar populations
  We analyze the correlations between central dark matter (DM) content of
early-type galaxies and their sizes and ages, using a sample of
intermediate-redshift (z ~ 0.2) gravitational lenses from the SLACS survey, and
by comparing them to a larger sample of z ~ 0 galaxies. We decompose the
deprojected galaxy masses into DM and stellar components using combinations of
strong lensing, stellar dynamics, and stellar populations modeling. For a given
stellar mass, we find that for galaxies with larger sizes, the DM fraction
increases and the mean DM density decreases, consistently with the cuspy halos
expected in cosmological formation scenarios. The DM fraction also decreases
with stellar age, which can be partially explained by the inverse correlation
between size and age. The residual trend may point to systematic dependencies
on formation epoch of halo contraction or stellar initial mass functions. These
results are in agreement with recent findings based on local galaxies by
Napolitano, Romanowsky & Tortora (2010) and suggest negligible evidence of
galaxy evolution over the last ~ 2.5 Gyr other than passive stellar aging.
