2017MNRAS.464..453D

We here present the first spatially resolved study of the initial mass function (IMF) in external galaxies derived using a dynamical tracer of the mass-to-light ratio (M/L). We use the kinematics of relaxed molecular gas discs in seven early-type galaxies (ETGs) selected from the ATLAS^3D survey to dynamically determine 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 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 normalizations derived using molecular gas kinematics and those derived using other techniques. Despite this, we do not see find any correlation between the IMF normalization 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.