Journal Club
Galactic thick disks in the Fornax Cluster

Abstract

We analyze the stellar kinematics and populations of a sample of three edge-on S0 galaxies in the Fornax cluster. Maps of unprecedented spatial resolution of the mean stellar age, metallicity and [Mg/Fe] abundance show the differences in the structures of the three galaxies. Whereas one galaxy appears overall old, the other two show relatively young stars in their thin disks and nuclear regions. However, a clear-cut distinction separates in the three galaxies the metal-rich and less [Mg/Fe]-enhanced populations in the thin disk and the more metal-poor and [Mg/Fe]-enhanced stars in the thick disk. Since these galaxies are located at different distances from the Fornax cluster center, we discuss possible evolutionary paths in relation to their environment. 
A structural decomposition allows us to define geometrically the different components of the three galaxies and describe the nature of their thick disks. These share a composite star formation history, revealing a significant fraction of younger stars co-exists with a main older population. The chemical properties of the younger sub-populations suggest that they were formed in a less chemically enriched satellite. We propose a complex thick-disk formation scenario combining in-situ formation at high redshift with later accretion.