Dark Matter Contraction and the Stellar Content of Massive Early-type Galaxies: Disfavoring “Light” Initial Mass Functions. (arXiv:1007.2409v1 [astro-ph.CO])

We use stellar dynamics, strong lensing, stellar population synthesis models,
and weak lensing shear measurements to constrain the dark matter (DM) profile
and stellar mass in a sample of 53 massive early-type galaxies. We explore
three DM halo models (unperturbed Navarro Frenk & White [NFW] halos and the
adiabatic contraction models of Blumenthal and Gnedin) and impose a model for
the relationship between the stellar and virial mass (i.e., a relationship for
the star-formation efficiency as a function of halo mass). We show that, given
our model assumptions, the data clearly prefer a Salpeter-like initial mass
function (IMF) over a lighter IMF (e.g., Chabrier or Kroupa), irrespective of
the choice of DM halo. In addition, we find that the data prefer at most a
moderate amount of adiabatic contraction (Blumenthal adiabatic contraction is
strongly disfavored) and are only consistent with no adiabatic contraction
(i.e., a NFW halo) if a mass-dependent IMF is assumed, in the sense of a more
massive normalization of the IMF for more massive halos.

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