Dark Matter Heating and Early Core Formation in Dwarf Galaxies
  We present more results from a fully cosmological LCDM simulation of a group
of isolated dwarf galaxies that has been shown to reproduce the observed
stellar mass and cold gas content, resolved star formation histories, and
metallicities of dwarfs in the Local Volume. Here we investigate the energetics
and timetable of the cusp-core transformation. As suggested by previous work,
supernova-driven gas outflows remove dark matter (DM) cusps and create kpc-size
cores in all systems having a stellar mass above 1e6 Msun. The "DM core mass
removal efficiency" -- dark mass ejected per unit stellar mass -- ranges today
from a few to a dozen, and increases with decreasing host mass. Because dwarfs
form the bulk of their stars prior to redshift 1 and the amount of work
required for DM heating and core formation scales approximately as Mvir^{5/3},
the unbinding of the DM cusp starts early and the formation of cored profiles
is not as energetically onerous as previously claimed. DM particles in the cusp
typically migrate to 2-3 core radii after absorbing a few percent of the energy
released by supernovae. The present-day slopes of the inner dark matter mass
profiles, Gamma=d log M/dlog R=2.5-3, of the simulated "Bashful" and "Doc"
dwarfs are similar to those measured in the luminous Fornax and Sculptor dwarf
spheroidals. None of the simulated galaxies has a circular velocity profile
exceeding 20 km/s in the inner 1 kpc, implying that supernova feedback is key
to solve the "too-big-to-fail" problem for Milky Way subhalos.
