The stellar population and initial mass function of NGC 1399 with MUSE
  We present spatially resolved measurements of the stellar initial mass
function (IMF) in NGC 1399, the largest elliptical galaxy in the Fornax
Cluster. Using data from the Multi Unit Spectroscopic Explorer (MUSE) and
updated state-of-the-art stellar population synthesis models from Conroy et. al
2018, we use full spectral fitting to measure the low-mass IMF, as well as a
number of individual elemental abundances, as a function of radius in this
object. We find that the IMF in NGC 1399 is heavier than the Milky Way in its
centre and remains radially constant at a super-salpeter slope out to 0.7
R$_{e}$. At radii larger than this, the IMF slope decreases to become
marginally consistent with a Milky Way IMF just beyond R$_{e}$. The inferred
central V-band M/L ratio is in excellent agreement with the previously reported
dynamical M/L measurement from Houghton et. al 2006. The measured radial form
of the M/L ratio may be evidence for a two-phase formation in this object, with
the central regions forming differently to the outskirts. We also report
measurements of a spatially resolved filament of ionised gas extending 4
arcseconds (404 pc at $D_{\mathrm{L}}=21.1$ Mpc) from the centre of NGC 1399,
with very narrow equivalent width and low velocity dispersion ($65\pm14$ \kms).
The location of the emission, combined with an analysis of the emission line
ratios, leads us to conclude that NGC 1399's AGN is the source of ionising
radiation.
