Mechanisms of Baryon Loss for Dark Satellites in Cosmological SPH
  Simulations
  We present a study of satellites in orbit around a high-resolution, smoothed
particle hydrodynamics (SPH) galaxy simulated in a cosmological context. The
simulated galaxy is approximately the same mass as the Milky Way. The
cumulative number of luminous satellites at z = 0 is similar to the observed
system of satellites orbiting the Milky Way although an analysis of the
satellite mass function reveals an order of magnitude more dark satellites than
luminous. Some of the dark subhalos are more massive than some of the luminous
subhalos at z = 0. What separates luminous and dark subhalos is not their mass
at z = 0, but the maximum mass the subhalos ever achieve. We study the effect
of four mass loss mechanisms on the subhalos: ultraviolet (UV) ionising
radiation, ram pressure stripping, tidal stripping, and stellar feedback, and
compare the impact of each of these four mechanisms on the satellites. In the
lowest mass subhalos, UV is responsible for the majority of the baryonic mass
loss. Ram pressure stripping removes whatever mass remains from the low mass
satellites. More massive subhalos have deeper potential wells and retain more
mass during reionisation. However, as satellites pass near the centre of the
main halo, tidal forces cause significant mass loss from satellites of all
masses. Satellites that are tidally stripped from the outside can account for
the luminous satellites that are lower mass than some of the dark satellites.
Stellar feedback has the greatest impact on medium mass satellites that had
formed stars, but lost all their gas by z = 0. Our results demonstrate that the
missing satellite problem is not an intractable issue with the cold dark matter
cosmology, but is rather a manifestation of baryonic processes.
