Galaxy structure in the low-redshift universe
Robust IMF measurements in Early Type Galaxies
Sam Vaughan
Roger Davies (University of Oxford), Ryan Houghton (University of Oxford), Simon Zieleniewski (University of Oxford)
University of Oxford
The assumption of a universal Initial Mass Function (IMF) has been challenged in recent years. Evidence from dynamical Mass-to-Light (M/L) measurements point to a relationship between IMF slope and global velocity dispersion, whilst studies using dwarf-sensitive absorption line indices suggest a link between IMF slope and alpha enhancement. However, the reasons behind such correlations are still not understood and the two methods appear to disagree on a galaxy-by-galaxy basis (Smith 2014).

We present an integral field spectrograph (IFS) study using the Oxford SWIFT instrument of the far-red dwarf-sensitive indices (Na0.82, CaT, FeH0.99) in two massive early type galaxies: NGC 1277 and IC 843. The choice of galaxies facilitates direct comparison between the methods of dynamical and spectroscopic IMF determination, as both have published dynamical measurements already. . SWIFT's extended wavelength coverage and 2D field of view allow radial measurements of the Wing-Ford (FeH) index in these galaxies for the first time. FeH is a particularly robust dwarf-sensitive feature, as iron abundance is well understood and readily measured. This is not true for indices based on sodium (Zieleniewski et al. 2014; Smith et al. 2015) or titanium oxide (Kobayashi et al. 2006). Comparing FeH to the other dwarf-sensitive indices with stellar population models, we disentangle abundance and IMF variations to provide radial measurements of the IMF, stellar age and element abundances out to one effective radius.
09:00 - 10:30
BS - Lecture Theatre A25 (121)