Effects of baryon removal on the structure of dwarf spheroidal galaxies
  Dwarf spheroidal galaxies (dSphs) are extremely gas-poor, dark
matter-dominated galaxies, which make them ideal to test the predictions of the
cold dark matter (CDM) model. We argue that the removal of the baryonic
component from gas-rich dwarf irregular galaxies, the progenitors of dSphs, can
substantially reduce their central density. Thus, it may play an important role
in alleviating one of the problems of the CDM model related to the structure of
relatively massive satellite galaxies of the Milky Way (MW). Traditionally,
collisionless cosmological N-body simulations are used when confronting
theoretical predictions with observations. However, these simulations assume
that the baryon fraction everywhere in the Universe is equal to the cosmic
mean, which can be incorrect for dSphs. We find that the combination of (i) the
lower baryon fraction in dSphs compared to the cosmic mean and (ii) the
concentration of baryons in the inner part of the MW halo can go a long way
towards explaining the observed circular velocity profiles of dSphs. We find
that the blowing away of baryons by ram pressure, when the dwarfs fall into
larger galaxies, decreases the circular velocity profile of the satellite and
reduces the density in the central ~200-500 pc by a factor of (1 - f_b)^4 ~
0.5, where f_b is the cosmological fraction of baryons. Additionally, the
enhanced baryonic mass in the central regions of the parent galaxy generates
tidal forces, which are larger than those experienced by subhaloes in
traditional N-body simulations. Increased tidal forces substantially alter
circular velocity profiles for satellites with pericentres less than 50 kpc. We
show that these two effects are strong enough to bring the predictions of
subhaloes from CDM simulations into agreement with the observed structure of MW
dSphs, regardless of the details of the baryonic processes.
