Title: KINETyS: Constraining spatial variations of the stellar initial mass function in early-type galaxies,
Abstract: The heavyweight stellar initial mass function (IMF) observed in the cores of
massive early-type galaxies (ETGs) has been linked to formation of their cores
in an initial swiftly-quenched rapid starburst. However, the outskirts of ETGs
are thought to be assembled via the slow accumulation of smaller systems in
which the star formation is less extreme; this suggests the form of the IMF
should exhibit a radial trend in ETGs. Here we report radial stellar population
gradients out to the half-light radii of a sample of eight nearby ETGs.
Spatially resolved spectroscopy at 0.8-1.35{\mu}m from the VLT's KMOS
instrument was used to measure radial trends in the strengths of a variety of
IMF-sensitive absorption features (including some which are previously
unexplored). We find weak or no radial variation in some of these which, given
a radial IMF trend, ought to vary measurably, e.g. for the Wing-Ford band we
measure a gradient of +0.06$\pm$0.04 per decade in radius.
Using stellar population models to fit stacked and individual spectra, we
infer that the measured radial changes in absorption feature strengths are
primarily accounted for by abundance gradients which are fairly consistent
across our sample (e.g. we derive an average [Na/H] gradient of
-0.53$\pm$0.07). The inferred contribution of dwarf stars to the total light
typically corresponds to a bottom heavy IMF, but we find no evidence for radial
IMF variations in the majority of our sample galaxies.