A Troublesome Past: Chemodynamics of the Fornax dwarf spheroidal

Abstract

We present compelling evidence for the complexity of the Fornax dwarf spheroidal. By disentangling three different stellar subpopulations in its red giant branch, we are able to study in detail the dependence between kinematics and metallicity. A well-defined ordering in velocity dispersion, spatial concentration, and metallicity is evident in the subpopulations. We also present evidence for a significant misalignment between the angular momentum vectors of the old and intermediate-age populations. According to the HST measurement of Fornax's proper motion, this corresponds to counter-rotation. These ingredients are used to construct a novel evolutionary history of the Fornax dwarf spheroidal, characterized as a late merger of a bound pair.