PAndAS' cubs: discovery of two new dwarf galaxies in the surroundings of
  the Andromeda and Triangulum galaxies
  We present the discovery of two new dwarf galaxies, Andromeda XXI and
Andromeda XXII, located in the surroundings of the Andromeda and Triangulum
galaxies (M31 and M33). These discoveries stem from the first year data of the
Pan-Andromeda Archaeological Survey (PAndAS), a photometric survey of the
M31/M33 group conducted with the Megaprime/MegaCam wide-field camera mounted on
the Canada-France-Hawaii Telescope. Both satellites appear as spatial
overdensities of stars which, when plotted in a color-magnitude diagram, follow
metal-poor, [Fe/H]=-1.8, red giant branches at the distance of M31/M33.
Andromeda XXI is a moderately bright dwarf galaxy (M_V=-9.9+/-0.6), albeit with
low surface brightness, emphasizing again that many relatively luminous M31
satellites still remain to be discovered. It is also a large satellite, with a
half-light radius close to 1 kpc, making it the fourth largest Local Group
dwarf spheroidal galaxy after the recently discovered Andromeda XIX, Andromeda
II and Sagittarius around the Milky Way, and supports the trend that M31
satellites are larger than their Milky Way counterparts. Andromeda XXII is much
fainter (M_V=-6.5+/-0.8) and lies a lot closer in projection to M33 than it
does to M31 (42 vs. 224 kpc), suggesting that it could be the first Triangulum
satellite to be discovered. Although this is a very exciting possibility in the
context of a past interaction of M33 with M31 and the fate of its satellite
system, a confirmation will have to await a good distance estimate to confirm
its physical proximity to M33. Along with the dwarf galaxies found in previous
surveys of the M31 surroundings, these two new satellites bring the number of
dwarf spheroidal galaxies in this region to 20.
