Abundance ratios and IMF slopes in the dwarf elliptical galaxy NGC 1396 with MUSE

Abstract

Deep observations of the dwarf elliptical (dE) galaxy NGC 1396 (M V = −16.60, Mass ∼ 4 × 10 8 M ), located in the Fornax cluster, have been performed with the VLT/ MUSE spectrograph in the wavelength region from 4750 − 9350 Å. In this paper we present a stellar population analysis studying chemical abundances, the star formation history (SFH) and the stellar initial mass function (IMF) as a function of galacto-centric distance. Different, independent ways to analyse the stellar populations result in a luminosity-weighted age of ∼ 6 Gyr and a metallicity [Fe/H]∼ −0.4, similar to other dEs of similar mass. We find unusually overabundant values of [Ca/Fe] ∼ +0.1, and under-abundant Sodium, with [Na/Fe] values around −0.1, while [Mg/Fe] is overabundant at all radii, increasing from ∼ +0.1 in the centre to ∼ +0.2 dex. We notice a significant metallicity and age gradient within this dwarf galaxy.To constrain the stellar IMF of NGC 1396, we find that the IMF of NGC 1396 is consistent with either a Kroupa-like or a top-heavy distribution, while a bottom-heavy IMF is firmly ruled out.An analysis of the abundance ratios, and a comparison with galaxies in the Local Group, shows that the chemical enrichment history of NGC 1396 is similar to the Galactic disc, with an extended star formation history. This would be the case if the galaxy originated from a LMC-sized dwarf galaxy progenitor, which would lose its gas while falling into the Fornax cluster.

Colors of Dwarf Ellipticals from GALEX to WISE

“…In a similar analysis, Mentz et al (2016) find the age and metallicity of NGC1396 (a well-studied Fornax dE) to be −0.4 and 6 Gyrs. Geha et al (2015) find values of −1.0 and 10 Gyrs for NGC185 and −0.5 and 6 Gyrs for NGC147, the other two dE companions to M31.…”

Evolution of the Stellar Mass–Metallicity Relation. II. Constraints on Galactic Outflows from the Mg Abundances of Quiescent Galaxies

“…This means that the measured age is expected to be younger than both light-and mass-weighted ages derived in models with extended star-formation histories (Choi et al 2014). The metallicities are less affected (Mentz et al 2016 The fitting method is the same as that in Paper I. In summary, we first mask out the most prominent telluric band in the 7591-7703Å wavelength range.…”

Combining stellar populations with orbit-superposition dynamical modelling: the formation history of the lenticular galaxy NGC 3115

“…Similarly to dynamical models, stellar population models have been used to uncover new relationships between galaxy structural parameters through a variety of scaling relations (see Gallazzi et al 2008;Graves et al 2009a,b;McDermid et al 2015;Walcher et al 2015, for some such relations). Again, stellar population models of individual (or handfuls of) galaxies in great detail offer insight into the specific formation path of these galaxies, as well as the presence of sub-structures with distinct stellar populations (for instance, see Barbosa et al 2016;Mentz et al 2016;Streich et al 2016).…”