Simulations of isolated dwarf galaxies formed in dark matter halos with
  different mass assembly histories
  We present high-resolution N-body/hydrodynamics simulations of dwarf galaxies
formed in isolated CDM halos with the same virial mass, Mv~2.5x10^10 Msun at
z=0, in order to (1) study the mass assembly histories (MAHs) of the halo,
stars, and gas components, and (2) explore the effects of the halo MAHs on the
stellar/baryonic assembly of the simulated dwarfs and on their z~0 properties.
Overall, the simulated dwarfs are roughly consistent with observations. Our
main results are: a) The stellar-to-halo mass ratio is ~0.01 and remains
roughly constant since z~1 (the stellar MAHs follow closely the halo MAHs),
with a smaller value at higher z's for those halos that assemble their mass
later. b) The evolution of the galaxy gas fraction, fg, is episodic and higher,
most of the time, than the stellar fraction. When fg decreases (increases), the
gas fraction in the halo typically increases (decreases), showing that the SN
driven outflows play an important role in regulating the gas fractions -and
hence the SFR- of the dwarfs. However, in most cases, an important fraction of
the gas escapes the virial radius, Rv; at z=4 the total baryon fraction inside
Rv is 1.5-2 times smaller than the universal one, while at z=0 is 2-6 times
smaller, with the earlier assembled halos ejecting more gas. c) The SF
histories are episodic with changes in the SFRs of factors 2-10 on average. d)
Although the dwarfs formed in late assembled halos show more extended SF
histories, their z~0 SFRs are still below the ones measured for local isolated
dwarfs. e) The effects of baryons on Mv are such that at almost any time Mv is
10-20% smaller than the corresponding Mv obtained in pure N-body simulations.
Our results suggest that rather than increasing the strength of the SN-driven
outflows, processes that reduce the SF efficiency even more will help to solve
the potential issues faced by the CDM-based simulations of dwarfs.
