The SAMI-Fornax Dwarfs Survey - III. Evolution of [α/Fe] in dwarfs, from Galaxy Clusters to the Local Group

Using very deep, high spectral resolution data from the SAMI Integral Field Spectrograph, we study the stellar population properties of a sample of dwarf galaxies in the Fornax Cluster, down to a stellar mass of 10(7) M-circle dot, which has never been done outside the Local Group. We use full spectral fitting to obtain stellar population parameters. Adding massive galaxies from the ATLAS3D project, which we re-analysed, and the satellite galaxies of the Milky Way, we obtained a galaxy sample that covers the stellar mass range 10(4) -10(12) M-circle dot. Using this large range, we find that the mass-metallicity relation is not linear. We also find that the [alpha/Fe]-stellar mass relation of the full sample shows a U-shape, with a minimum in [alpha/Fe] for masses between 10(9) and 10(10) M-circle dot. The relation between [alpha/Fe] and stellar mass can be understood in the following way: when the faintest galaxies enter the cluster environment, a rapid burst of star formation is induced, after which the gas content is blown away by various quenching mechanisms. This fast star formation causes high [alpha/Fe] values, like in the Galactic halo. More massive galaxies will manage to keep their gas longer and form several bursts of star formation, with lower [alpha/Fe] as a result. For massive galaxies, stellar populations are regulated by internal processes, leading to [alpha/Fe] increasing with mass. We confirm this model by showing that [alpha/Fe] correlates with clustercentric distance in three nearby clusters and also in the halo of the Milky Way.