High-resolution three-dimensional simulations of gas removal from
  ultrafaint dwarf galaxies. I. Stellar feedback
  The faintest Local Group galaxies found lurking in and around the Milky Way
halo provide a unique test bed for theories of structure formation and
evolution on small scales. Deep Subaru and Hubble Space Telescope photometry
demonstrates that their stellar populations are old, and that the star
formation activity did not last longer than 2 Gyr in these systems. A few
mechanisms that may lead to such a rapid quenching have been investigated by
means of hydrodynamic simulations, without providing any final assessment so
far. This is the first in a series of papers aimed at analysing the roles of
stellar feedback, ram pressure stripping, host-satellite tidal interactions and
reionization in cleaning the lowest-mass Milky Way companions of their cold
gas, by using high-resolution, three-dimensional hydrodynamic simulations. We
simulate an isolated ultrafaint dwarf galaxy loosely modeled after Bootes I,
and examine whether or not stellar feedback alone could drive a substantial
fraction of the ambient gas out from the shallow potential well. In contrast to
simple analytical estimates, but in agreement with previous hydrodynamical
studies, we find that most of the cold gas reservoir is retained. Conversely, a
significant fraction of the metal-enriched stellar ejecta crosses the
boundaries of the computational box with velocities exceeding the local escape
velocity and is, thus, likely lost from the system. Although the total energy
output from multiple supernova explosions exceeds the binding energy of the
gas, no galactic-scale outflow develops in our simulations and as such, most of
the ambient medium remains trapped within the weak potential well of the model
galaxy. It seems thus unavoidable that, in order to explain the dearth of gas
in ultrafaint dwarf galaxies, we will have to resort to environmental effects.
This will be the subject of a forthcoming paper.
