Dark influences II: gas and star formation in minor mergers of dwarf
  galaxies with dark satellites
  It has been proposed that mergers induce starbursts and lead to important
morphological changes in galaxies. Most studies so far have focused on large
galaxies, but dwarfs might also experience such events, since the halo mass
function is scale-free in the concordance cosmological model. Notably, because
of their low mass, most of their interactions will be with dark satellites. In
this paper we follow the evolution of gas-rich disky dwarf galaxies as they
experience a minor merger with a dark satellite. We aim to characterize the
effects of such an interaction on the dwarf's star formation, morphology, and
kinematical properties. We performed a suite of carefully set-up hydrodynamical
simulations of dwarf galaxies that include dark matter, gas, and stars merging
with a satellite consisting solely of dark matter. For the host system we vary
the gas fraction, disk size and thickness, halo mass, and concentration, while
we explore different masses, concentrations, and orbits for the satellite. We
find that the interactions cause strong starbursts of both short and long
duration in the dwarfs. Their star formation rates increase by factors of a few
to 10 or more. They are strongest for systems with extended gas disks and high
gas fractions merging with a high-concentration satellite on a planar, radial
orbit. In contrast to analogous simulations of Milky Way-mass galaxies, many of
the systems experience strong morphological changes and become spheroidal even
in the presence of significant amounts of gas. The simulated systems compare
remarkably well with the observational properties of a large selection of
irregular dwarf galaxies and blue compact dwarfs. This implies that mergers
with dark satellites might well be happening but not be fully evident, and may
thus play a role in the diversity of the dwarf galaxy population.
