# KINETyS: Constraining spatial variations of the stellar initial mass function in early-type galaxies

## TL;DR

This study investigates the radial variation of the stellar initial mass function in early-type galaxies using spatially resolved spectroscopy, finding minimal evidence for IMF gradients and highlighting the role of abundance gradients.

## Contribution

It provides the first detailed radial analysis of IMF-sensitive features in ETGs, revealing that abundance gradients, not IMF variations, dominate the observed spectral changes.

## Key findings

- Weak or no radial IMF variation detected in most galaxies
- Abundance gradients, especially in [Na/H], explain spectral feature changes
- Dwarf star contribution indicates a bottom-heavy IMF without radial variation

## 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.