IMF shape constraints from stellar populations and dynamics from CALIFA
  In this letter we describe how we use stellar dynamics information to
constrain the shape of the stellar IMF in a sample of 27 early-type galaxies
from the CALIFA survey. We obtain dynamical and stellar mass-to-light ratios,
$\Upsilon_\mathrm{dyn}$ and $\Upsilon_{\ast}$, over a homogenous aperture of
0.5~$R_{e}$. We use the constraint $\Upsilon_\mathrm{dyn} \ge \Upsilon_{\ast}$
to test two IMF shapes within the framework of the extended MILES stellar
population models. We rule out a single power law IMF shape for 75% of the
galaxies in our sample. Conversely, we find that a double power law IMF shape
with a varying high-mass end slope is compatible (within 1$\sigma$) with 95% of
the galaxies. We also show that dynamical and stellar IMF mismatch factors give
consistent results for the systematic variation of the IMF in these galaxies.
