Testing adiabatic contraction with SDSS elliptical galaxies
  We study the profiles of 75 086 elliptical galaxies from the Sloan Digital
Sky Survey (SDSS) at both large (50-500 kpc/h) and small (~3 kpc/h) scales.
Weak lensing observations in the outskirts of the halo are combined with
measurements of the stellar velocity dispersion in the interior regions of the
galaxy for stacked galaxy samples. The weak lensing measurements are well
characterized by a Navarro, Frenk and White (NFW) profile. The dynamical mass
measurements exceed the extrapolated NFW profile even after the estimated
stellar masses are subtracted, providing evidence for the modification of the
dark matter profile by the baryons. This excess mass is quantitatively
consistent with the predictions of the adiabatic contraction (AC) hypothesis.
Our finding suggests that the effects of AC during galaxy formation are stable
to subsequent bombardment from major and minor mergers. We explore several
theoretical and observational systematics and conclude that they cannot account
for the inferred mass excess. The most significant source of systematic error
is in the IMF, which would have to increase the stellar mass estimates by a
factor of two relative to masses from the Kroupa IMF to fully explain the mass
excess without AC. Such an increase would create tension with results from
SAURON (Cappellari et al. 2006). We demonstrate a connection between the level
of contraction of the dark matter halo profile and scatter in the
size-luminosity relation, which is a projection of the fundamental plane.
Whether or not AC is the mechanism supplying the excess mass, models of galaxy
formation and evolution must reconcile the observed halo masses from weak
lensing with the comparatively large dynamical masses at the half light radii
of the galaxies.
