Spatially resolved variations of the IMF mass normalisation in
  early-type galaxies as probed by molecular gas kinematics
  We here present the first spatially-resolved study of the IMF in external
galaxies derived using a dynamical tracer of the mass-to-light ratio. We use
the kinematics of relaxed molecular gas discs in seven early-type galaxies
(ETGs) selected from the ATLAS3D survey to dynamically determine mass-to-light
ratio (M/L) gradients. These M/L gradients are not very strong in the inner
parts of these objects, and galaxies that do show variations are those with the
highest specific star formation rates. Stellar population parameters derived
from star formation histories are then used in order to estimate the stellar
initial mass function function (IMF) mismatch parameter, and shed light on its
variation within ETGs. Some of our target objects require a light IMF,
otherwise their stellar population masses would be greater than their dynamical
masses. In contrast, other systems seem to require heavier IMFs to explain
their gas kinematics. Our analysis again confirms that IMF variation seems to
be occurring within massive ETGs. We find good agreement between our IMF
normalisations derived using molecular gas kinematics and those derived using
other techniques. Despite this, we do not see find any correlation between the
IMF normalisation and galaxy dynamical properties or stellar population
parameters, either locally or globally. In the future larger studies which use
molecules as tracers of galaxy dynamics can be used to help us disentangle the
root cause of IMF variation.
