Mass assembly history and infall time of the Fornax dwarf spheroidal
  galaxy
  We use cosmological simulations to identify dark matter subhalo host
candidates of the Fornax dwarf spheroidal galaxy using the stellar kinematic
properties of Fornax. We consider cold dark matter (CDM), warm dark matter
(WDM), and decaying dark matter (DDM) simulations for our models of structure
formation. The subhalo candidates in CDM typically have smaller mass and higher
concentrations at z = 0 than the corresponding candidates in WDM and DDM. We
examine the formation histories of the ~ 100 Fornax candidate subhalos
identified in CDM simulations and, using approximate luminosity-mass
relationships for subhalos, we find two of these subhalos that are consistent
with both the Fornax luminosity and kinematics. These two subhalos have a peak
mass over ten times larger than their z = 0 mass. We suggest that in CDM the
dark matter halo hosting Fornax must have been severely stripped of mass and
that it had an infall time into the Milky Way of ~ 9 Gyr ago. In WDM, we find
that candidate subhalos consistent with the properties of Fornax have a similar
infall time and a similar degree of mass loss, while in DDM we find a later
infall time of ~ 3 - 4 Gyr ago and significantly less mass loss. We discuss
these results in the context of the Fornax star formation history, and show
that these predicted subhalo infall times can be linked to different star
formation quenching mechanisms. This emphasizes the links between the
properties of the dark matter and the mechanisms that drive galaxy evolution.
