Robust IMF measurements in Early Type Galaxies
Galaxy structure in the low-redshift universe
Sam Vaughan
University of Oxford
Roger Davies (University of Oxford), Ryan Houghton (University of Oxford), Simon Zieleniewski (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)