An XMM-Newton Observation of NGC 1399 Reveals Two Phases of Hot Gas and Super-Solar Abundances in the Central Regions

Abstract

We present an initial analysis of a new XMM observation of NGC 1399, the central elliptical galaxy of the Fornax group. Spectral fitting of the spatially resolved spectral data of the EPIC MOS and pn CCDs reveals that a two-temperature model (2T) of the hot gas is favored over single-phase and cooling flow models within the central ~20 kpc. The preference for the 2T model applies whether or not the data are deprojected. The cooler component has a temperature (~0.9 keV) similar to the kinetic temperature of the stars while the hotter component has a temperature (~1.5 keV) characteristic of the virial temperature of a ~10^{13} M_sun halo. The two-phase model (and other multitemperature models) removes the ``Fe Bias&#39;&#39; within r < ~20 kpc and gives Z_Fe/Z_sun 1.5-2. At larger radii the iron abundance decreases until Z_Fe/Z_sun \~0.5 for r ~50 kpc. The Si abundance is super-solar (1.2-1.7 solar) within the central regions while Z_Si/Z_Fe ~0.8 over the entire region studied. These Fe and Si abundances imply that ~80% of the Fe mass within r ~50 kpc originates from Type Ia supernovae (SNIa). This SNIa fraction is similar to that inferred for the Sun and therefore suggests a stellar initial mass function similar to the Milky Way.