The stellar population and initial mass function of NGC1399 with MUSE

Abstract

We present spatially resolved measurements of the stellar initial mass function (IMF) in NGC1399, 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., 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 NGC1399 is heavier than the Milky Way in its centre and remains radially constant at a super-Salpeter slope out to 0.7 Re. At radii larger than this, the IMF slope decreases to becomemarginally consistent with aMilkyWay IMF just beyond Re. The inferred central V-band M/L ratio is in excellent agreement with the previously reported dynamical M/L measurement from Houghton et al. 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 ionized gas extending 4 arcsec (404 pc at DL = 21.1Mpc) from the centre of NGC1399, with very narrow equivalent width and low-velocity dispersion (65 ± 14 km s-1). The location of the emission, combined with an analysis of the emission line ratios, leads us to conclude that NGC1399's AGN is the source of ionizing radiation.