Formation of Dwarf Spheroidal Galaxies Via Mergers of Disky Dwarfs
  We perform collisionless N-body simulations to investigate whether binary
mergers between rotationally-supported dwarfs can lead to the formation of
dwarf spheroidal galaxies (dSphs). Our simulation campaign is based on a hybrid
approach combining cosmological simulations and controlled numerical
experiments. We select merger events from a Constrained Local UniversE (CLUES)
simulation of the Local Group (LG) and record the properties of the interacting
dwarf-sized halos. This information is subsequently used to seed controlled
experiments of binary encounters between dwarf galaxies consisting of
exponential stellar disks embedded in cosmologically-motivated dark matter
halos. These simulations are designed to reproduce eight cosmological merger
events, with initial masses of the interacting systems in the range ~ (5-60) x
10^7 Mo, occurring quite early in the history of the LG, more than 10 Gyr ago.
We compute the properties of the merger remnants as a distant observer would
and demonstrate that at least three of the simulated encounters produce systems
with kinematic and structural properties akin to those of the classic dSphs in
the LG. Tracing the history of the remnants in the cosmological simulation to
z=0, we find that two dSph-like objects remain isolated at distances larger
than 800 kpc from either the Milky Way or M31. These systems constitute
plausible counterparts of the remote dSphs Cetus and Tucana which reside in the
LG outskirts, far from the tidal influence of the primary galaxies. We conclude
that merging of rotationally-supported dwarfs represents a viable mechanism for
the formation of dSphs in the LG and similar environments.
