Galaxy Evolution: Investigating Radial Trends in the Stellar Initial Mass Function using Stacked Spectra of Early-Type Galaxies

There is currently no consensus about the exact shape and, in particular, the universality of the stellar initial mass function (IMF). This is the distribution of masses of stars at the birth of a stellar population. For massive galaxies, it has been found that near-infrared (NIR) absorption features, which are sensitive to the ratio of dwarf to giant stars, deviate from a Milky Way-like IMF; their modelling seems to require a larger fraction of low mass stars. There are now increasing results looking at whether the IMF varies not only with galaxy mass, but also within galaxies.

The SDSS-IV/MaNGA integral-field survey will provide spatially resolved spectroscopy for 10,000 galaxies at R~2000 from 360-1000nm. Spectra of early-type galaxies were stacked to achieve high S/N which is particularly important for features in the NIR. These trends were compared with stellar population models for a range of absorption features in order to separate out degeneracies due to changes in stellar population parameters, such as age, metallicity and element abundances, with potential changes in the IMF. I will present our preliminary results for 615 galaxies and discuss the implications for galaxy formation models.